摘要:

J. CHEM. RESEARCH (S), 1997 225 J. Chem. Research (S), 1997, 225 J. Chem. Research (M), 1997, 1601–1614 Kinetics of Bromination of Some Aromatic Oxocarboxylic Acids M. Krishna Pillay*a and K. Banumathib aDepartment of Chemistry, Bharathidasan University, Tiruchirapalli 620 024, India bDepartment of Chemistry, Seethalakshmi Ramaswami College, Tiruchirapalli 620 002, India Rates of enolization, monitored by bromine scavenging, are determined for some aromatic carboxylic acids, ArCO[CH2]nCO2H.It was first suggested by Lapworth1 that ketones undergo a-halogenation only through their enol form. This was followed by extensive investigation into the halogenation of dialkyl and alkyl aryl ketones by Dawson and co-workers,2–4 Nathan and Watson,5 and Zucker and Hammett.6 Bell and co-workers studied the a-halogenation of alicyclic mono- and di-ketones,7 and oxo esters,8 etc. So far a systematic kinetic study on the bromination of aromatic oxocarboxylic acids has not been carried out.This prompted us to undertake the title investigation to understand the steric and electronic effects of substituents on the rate of bromination of aryloxocarboxylic acids. A kinetic study on the acid-catalysed bromination of ArCO[CH2]nCO2H (1) reveals that the order with respect to [Br2] is zero and that with respect to [1] and [H+] is one. Thus the rate of disappearance of bromine is determined solely by the rate at which the oxocarboxylic acid is transformed into the enolic form.The rates of the tautomeric change of ArCO[CH2]nCO2H are presented in Table 4. Kinetic data reveal that electronreleasing substituents in the benzene ring accelerate the rate while electron-withdrawing groups retard it. Hammett correlation of this substituent effect is obtained with s values and the reaction constant is found to be µ0.78 at 303 K. 3p-Nitro- 4p-methoxy- and 3p-bromo-4p-methoxy-substituted oxoacids deviate considerably from the linear Hammett plot obtained with other substituents.The reduced reactivity of these two compounds may not be due to steric effects17 but may be ascribed to hydrogen bonding interactions between OMe and H3O+ or other acidic solvent species.18 The rate of enolization is found to be enhanced to a greater extent by the introduction of a methyl group ortho to the carbonyl moiety. The enhanced reactivity is explained by considering their preferred conformations. 1H and 13C NMR spectral data of these compounds reveal that the carbonyl moiety is twisted out of the benzene ring plane.These compounds which are in a higher energy level in the ground state due to reduced conjugative interaction pass through the energy barrier in a facile manner. The reactivity of 1p-naphthyloxobutanoic acid is very high compared to the 2p-naphthyl analogue. This may be ascribed to the conformation-dependent conjugation effect as in ortho-substituted compounds. Lengthening of the alkyl chain leads to an increase in the reaction rate.This suggests that the opposing effect caused by coordination of H3O+ with carbonyl oxygen by CO2H decreases as it is far removed from the reaction centre. Enolization rate constants of 4p-OMe and 2p,4p,6p-Me3 substituted oxoacids could not be measured owing to ring bromination. Techniques used: 1H and 13C NMR, IR References: 28 Tables 1–3: Kinetic data Table 5: 1H and 13C NMR data Received, 29th January 1997; Accepted, 26th March 1997 Paper E/7/00665I References cited in this synopsis 1 A.Lapworth, J. Chem. Soc., 1904, 30. 2 H. M. Dawson and H. Ark, J. Chem. Soc., 1911, 1740. 3 H. M. Dawson and F. Powis, J. Chem. Soc., 1913, 2135. 4 H. M. Dawson, C. R. Hoskins and J. E. Smith, J. Chem. Soc., 1929, 1884. 5 W. S. Nathan and H. B. Watson, J. Chem. Soc., 1933, 217. 6 L. Zucker and L. P. Hammett, J. Am. Chem. Soc., 1939, 61, 2779. 7 R. P. Bell and O. M. Lidwell, Proc. R. Soc. London, A, Math.Phys. Sci., 1940, 176, 88. 8 R. P. Bell and H. F. F. Ridgewell, Proc. R. Soc. London, A, Math. Phys. Sci., 1967, 298, 178. 17 M. Krishna Pillay and S. Palanivelu, J. Indian Chem. Soc., 1986, 63, 1055. 18 R. G. Coombes, J. G. Golding and P. Hadjigeorgiou, J. Chem. Soc., Perkin Trans. 2, 1979, 1451. *To receive any correspondence. Table 4 Enolization rate constants of 4-oxo 4-substituted phenylbutanoic acids at 303 Ka Entry Substituent 106 k2/dm3 molµ1 sµ1 123456789 10 11 12 13 14 15 16 17 18 19 20 H4 p-Me 4p-Et 4p-Ph 4p-Cl 4p-Br 4p-I 3p-NO2 3p,4p-Me2 3p-Me-4p-Cl 3p-NO2-4p-Me 3p-NO2-4p-OMe 3p-Br-4p-OMe 2p,4p-Me2 2p-Me-4p-Cl 3p-Br-2p,4p,6p-Me3 3-Oxo-4-(1p-naphthyl)butanoic acid 4-Oxo-4-(2p-naphthyl)butanoic acid 5-Oxo-5-phenylpentanoic acid 6-Oxo-6-phenylhexanoic acid 6.89�0.15 9.49�0.26 8.44�0.22 7.48�0.14 4.56�0.11 4.60�0.12 5.73�0.23 1.94�0.06 10.2�0.24 5.32�0.12 2.38�0.06 2.17�0.04 4.56�0.11 21.9�0.58 13.3�0.23 22.1�0.39 18.0�0.31 5.51�0.07 21.4�1.4 29.7�0.67 a[Substrate] =1.2Å10µ2 mol dmµ3, [Br2] =1.0Å10µ3 mol dmµ3, [HClO4] =1.0 mol dmµ3, [NaBr] =0.2 mol dmµ3, m=1.2

ISSN:0308-2342    

DOI:10.1039/a700665i

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

N X+ R3 Y Z N N2 – N X R3 N Z– Y N2 + 3 4 (X = NPh, O, S) N S R3 R4 N3 a R3 = Me, R4 = H b R3 = Me, R4 = CN c R3 = Me, R4 = CHO d R3 = Me, R4 = NO2 e R3 = Ph, R4 = CN f R3 = MeS, R4 = CN g R3 = MeSO2, R4 = CN 5 N S N O Me 6 N S N O N+ Me 7 O– N S Me N N N 8 Me N S C N 9 226 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 226 J. Chem. Research (M), 1997, 1631–1650 Rates and Products of the Thermal Decomposition of 5-Azidoisothiazoles (The late) Gerrit L’abb�e, Leonard K.Dyall, Kathleen Meersman and Wim Dehaen* Department of Chemistry, University of Leuven, Celestijnenlaan 200F, 3001 Leuven (Heverlee), Belgium 5-Azidoisothiazoles have been thermolysed in p-xylene solutions to yield bicyclic products; there are appreciable neighbouring group effects on the reaction rates. Both azidobenzenes and the a-azides of five-membered heteroaromatics thermolyse when heated in solution, but there are important differences in both reaction products and rates.Whereas simple azidobenzenes thermolyse slowly,1 the heterocyclic a-azides normally undergo ring opening.3,4 A further important difference between azidobenzenes and these heterocyclic a-azides relates to neighbouring group effects from such ortho substituents as nitro and formyl. In the azidobenzenes, an ortho nitro group is known to increase the thermolysis rate by 1060-fold, and an ortho formyl one by 29-fold.11 In both cases, a cyclic product results.1 The stabilization provided by the ring hetero-atom (represented by 3) places a high negative charge on the inner azido nitrogen atom, which must inhibit the formation of the bridging bond represented in the transition state 4.In this paper we explore the possibility that suitable 4-substituents in 5-azidoisothiazoles might exert large neighbouring group effects. We have synthesized the azides 5a–g, which were fully characterized by 1H and 13C NMR and IR spectroscopy, as well as by mass spectroscopy.The decay of the azido band in the IR spectrum was monitored, and all the decompositions were smoothly first-order. Rate constants are presented in Table 1, and the activation parameters for 5a in Table 2 (for both Tables see full text). The four 5-azido-4-cyano compounds 5b, 5e, 5f and 5g were chosen in order to see what effect substituents at position 3 in the ring might exert on the rate. The methyl, phenyl and methylsulfanyl groups had virtually no effect, whereas the strongly electron-withdrawing methylsulfonyl group reduced the rate by about 30%. An interesting feature of the reaction rates is the seven-fold increase when a 4-cyano group is introduced into 5-azido-3-methylisothiazole.In our studies of other a-azido heterocycles the cyano group has generally had the opposite effect on rates.5,11,12,14 With the 5-azidoisothiazoles, we must assume that 4-substituents such as formyl and nitro, which have similar inductive and resonance properties to cyano, will cause a rate increase of similar magnitude.In fact, these two groups do cause moderately large rate enhancements. These two neighbouring group effects are larger than those observed with 5-azidoisoxazoles, 12 but substantially smaller than those measured for azidobenzenes.11 As expected, 5c furnished 4-methylisothiazolo[5,4-c]- isoxazole 6 and 5d yielded 6-methylisothiazolo[4,5-c]-1,2,5- oxadiazole 1-oxide 7 upon thermolysis. Thermolysis of 5-azido-3-methylisothiazole 5a in 2,3-dimethylbutadiene as solvent yielded the triazoline 8; we did not obtain any derivative of the expected ring-opened cyano thione 9.Thermolyses of the azides 5f and 5g in the diene did not lead to isolation of triazolines, but moderately good yields of the corresponding primary amine were identified. This result appeared to demonstrate that a nitrene intermediate had been formed in the unimolecular decomposition of the azide. Techniques used: IR, 1H and 13C NMR, low- and high-resolution mass spectrometry References: 21 Schemes: 2 Table 1: First-order rate constants for thermal decomposition of 5-azidoisothiazoles in p-xylene solution Table 2: Arrhenius data for thermolysis of 5a in p-xylene solution Received, 17th March 1997; Accepted, 7th April 1997 Paper E/7/01866E References cited in this synopsis 1 L.K. Dyall, in The Chemistry of Functional Groups, ed. S. Patai and Z. Rappoport, Wiley, Chichester, 1983, Supplement D, p. 287. 3 M. Funicello, P. Spagnolo and P. Zanirato, Acta Chem. Scand., 1993, 47, 231. 4 W. Dehaen and J. Becher, Acta Chem. Scand., 1993, 47, 244. 5 G. L’abb�e, L. Dyall, K. Meersman and W. Dehaen, J. Chem. Soc., Perkin Trans. 2, 1994, 2401. 11 L. K. Dyall and P. A. S. Smith, Aust. J. Chem., 1990, 43, 997. 12 G. L’abb�e, L. Dyall, K. Meersman and W. Dehaen, J. Chem. Soc., Perkin Trans. 2, 1996. 14 L. K. Dyall, P. M. Suffolk, W. Dehaen and G. L’abb�e, J. Chem. Soc., Perkin Trans. 2, 1994, 2215. *To receive any correspondence (e-mail: wim.dehaen@chem. kuleuven

ISSN:0308-2342    

DOI:10.1039/a701866e

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Ni N N N N 11 1 8 4 J. CHEM. RESEARCH (S), 1997 227 J. Chem. Research (S), 1997, 227 J. Chem. Research (M), 1997, 1651–1662 Synthesis, Characterisation and Kinetic Studies of Acidpromoted Dissociation Reactions of the Nickel(II) Complex of a [Me4(14)-tetraene-N4] Macrocyclic Ligand Ashok K. Singh,* G. Bhattacharjee and Sudeshna Chandra Department of Chemistry, University of Roorkee, Roorkee-247 667, UP India The kinetics of acid-promoted dissociation reactions of NiII complex cations of an Me4-tetraene macrocyclic ligand follow good first-order reactions with acids in various solvents with the rate of reaction proceeding faster in media of higher dielectric constant.The chemistry of metal complexes of tetraaza macrocyclic ligands is of general interest because such compounds have been used as dyes and pigments1 as well as having been advanced as models for more complex biological systems.2 Much work has been carried out on 14-membered tetraaza macrocycles of transition metals (Ni, Cu, Cd)3–5 but not many detailed kinetic studies on acid-promoted dissociations of these complexes have been reported.6 A common feature of template reactions is the isolation of the macrocyclic ligand as a complex of the metal template ion, and such reactions are frequently the synthetic method of choice for the preparation of macrocyclic complexes.Here we report the synthesis, characterisation and acid-promoted dissociation of the NiII complex of a tetradentate tetraaza cyclotetradecane macrocyclic ligand.Ethylenediamine and acetylacetone react in the presence of divalent nickel to form a 14-membered N4-tetradentate macrocyclic complex. This complex, synthesised via a metal template method, is of the type [M[Me4(14)-tetraene-N4]] where the coordination takes place through the imine nitrogen atoms which are bridged by acetylacetone moieties. The complex was characterised by UV–VIS, IR, NMR and CHN analysis. The kinetics of acid-promoted dissociation reactions of complex cations of NiII were studied spectrophotometrically in HCl, HNO3 and H3PO4 at 25.0�0.1 °C in various organic solvents such as methanol, N,N-dimethylformamide, acetonitrile and 1,4-dioxane under pseudo-first-order conditions.Good first-order kinetics were observed in all cases. The rate-constant values show that the reaction proceeds faster in media of higher dielectric constant. The rate of reaction decreases with a decrease in the acid strength (H3PO4sHNO3sHCl).The general mechanism proposed for the acid-promoted dissociation of polyamine complexes6 may be adopted for this complex, as shown below: [M(L)]2+h[M(L)*]2+ [M(L)*]2++H+hproducts As shown above, a mechanism with the acid-dependent reaction of the ‘activated’ species [M(L)*]2+ has been proposed. Product analysis, done on the basis of a comparison of physical data such as boiling points, Rf values and spectral characteristics with those of the ligand, demonstrated that the product is the protonated ligand. Techniques used: UV–VIS, IR, 1H NMR, CHN analysis, TLC References: 14 Figs. 1–3: First-order rate coefficients for acid-promoted dissociation reactions of [Me4(14)-tetraene]Ni with HNO3, HCl and H3PO4 at 25 °C in various solvents Fig. 4: Arrhenius plots for the reactions of [Me4(14)-tetraene]Ni complex with HNO3 in 1,4-dioxane and DMF Figs. 5 and 6: Proposed stepwise mechanisms for the acid-promoted dissociations of [Me4(14)-tetraene]Ni with H3PO4, HCl and HNO3 Fig. 7: UV–VIS scan of the complex, ligand and product Tables 1–3: First- and second-order rate coefficients for acidpromoted dissociation reactions of [Me4(14)-tetraene]Ni with HNO3, HCl and H3PO4 at 25 °C in various solvents Table 4: Solvent parameter values for the solvents employed Table 5: Activation parameters for the reactions of [Me4(14)-tetraene]Ni with HNO3 in 1,4-dioxane and DMF Received, 27th November 1996; Accepted, 8th April 1997 Paper E/6/08028F References cited in this synopsis 1 R. Price, in The Chemistry of Synthetic Dyes, Academic Press, New York, 1970, p. 3. 2 D. H. Busch, Rec. Chem. Prog., 1964, 25, 107. 3 K. Hideg and O. H. Hankovsky, J. Inorg. Nucl. Chem., 1978, 40, 699. 4 R. Bembi, T. G. Roy, A. K. Jhanji and A. Maheshwari, J. Chem. Soc., Dalton Trans., 1990, 3531. 5 R. Bembi, Proc. Indian Natl. Sci. Acad., Part A., 1986, 52, 776. 6 N. F. Curtis and S. R. Osvath, Inorg. Chem., 1988, 27, 305. *To receive any correspondence (e-mail: chemt@rurkiu.ernet.in

ISSN:0308-2342    

DOI:10.1039/a608028f

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

O O O O 3 O 1 O RO2C CO2H 2 R = H 4 R = Me O O O O 3 NH O CO2H O R 1¢ 2¢ 3¢ 4¢ 5¢ 6¢ N O O O 1¢ 2¢ 3¢ 4¢ 5¢ 6¢ R 6 5 a R = 4¢-OMe b R = 4¢-Br c R = H d R = 4¢-Cl e R = 3¢-Cl f R = 2¢-Cl g R = 4¢-F i ii O MeO2C CO2H O MeO2C NH O OMe 1¢ 2¢ 3¢ 4¢ 5¢ 6¢ i N O O O 6a OMe ii 7 HO2C O CO2H O O CO2H O 1¢ 2¢ 3¢ 4¢ 5¢ 6¢ 8 O O O 1¢ 2¢ 3¢ 4¢ 5¢ 6¢ a R = 4¢¢-OMe b R = 4¢¢-Br c R = H d R = 4¢¢-Cl e R = 3¢¢-Cl f R = 2¢¢-Cl g R = 4¢¢-F NH O R 1¢¢ 2¢¢ 3¢¢ 4¢¢ 5¢¢ 6¢¢ 9 ii or iii N O O O R 1¢¢ 2¢¢ 3¢¢ 4¢¢ 5¢¢ 6¢¢ a R = 4¢-OMe b R = 4¢-Br c R = H d R = 4¢-Cl e R = 3¢-Cl f R = 2¢-Cl g R = 4¢-F 6 iv i 2 228 J.CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 228–229 J. Chem. Research (M), 1997, 1516–1536 Chemical Transformation of 1,8-Cineole. Synthesis of N-Phenylimides from Cineolic Acid Armando J. D. Silvestre,a Jos�e A. S. Cavaleiro,*a Artur M. S. Silva,a Bernard Delmondb and Claude Filliatreb aDepartment of Chemistry, University of Aveiro, 3810 Aveiro, Portugal bInstitut du Pin, Universit�e de Bordeaux I, 351 Cours de La Lib�eration, 33405 Talence, France Chemical transformations of 1,8-cineole into cineolic acid derivatives, including N-phenylimides 6, are reported; based on spectroscopic data the regioselectivity of some of the reactions and the heterocyclic ring conformation for each group of compounds have been established. 1,8-Cineole 1 is a very abundant component of the Eucalyptus globulus Labill. essential oil. It is a compound of very small economic significance and therefore any new application for it might contribute towards increasing its value.Following previous work on the chemical modification of cineole16,19 and on the synthesis of N-phenylimides20 and taking into account that such compounds can be used as precursors in the synthesis of biologically active sulfonated imides,21 studies on the synthesis of N-phenylimides from cineolic acid 2, which can be obtained from 1,8-cineole, have now been undertaken.Cineolic acid 2 and the corresponding anhydride 3 and monomethyl ester 4 were prepared as described by Rae et al.15 The synthetic route to the imides 6 was planned to follow the classical procedure shown in Scheme 2. 2,2,6-Trimethyl- 6-phenylcarbamoyltetrahydro-2H-pyran-3-carboxylic acids 5 were regioselectively obtained in high yields, but their attempted cyclizations by refluxing in acetic anhydride were not successful and the carboxanilides 5 were quantitatively recovered after 24 h.Enhancement of the nucleophilic character of the carboxanilide nitrogen, by abstraction of its proton, using sodium hydride, was expected to promote the cyclization. To proceed in such way, protection of the free carboxylic group was necessary. It was decided to use compound 4 with the 6-carboxylic group functionalized as an ester, and then to functionalize the 3-carboxylic group as a carboxanilide using a known procedure.22 The desired imide 6a was obtained, in very low yields, by refluxing 7 in dry tetrahydrofuran (THF), in the presence of sodium hydride (Scheme 3).To improve the yield of this reaction, protection of the 6-carboxylic group as a phenyl ester was considered. The phenyl ester 8 was synthesized regioselectively. This compound was then converted into the anilides 9 using two different procedures22,23 as shown in Scheme 4; however, procedure iii gave better yields. Subsequently, the desired imides 6 were obtained in fairly good yields by refluxing 9 in dry THF in the presence of NaH.The imides 6 were unstable: they completely hydrolysed on standing in solution in contact with moisture during 3 days, as was demonstrated with a test carried out with imide 6a. Mass spectrometric studies on compound 10 showed that the hydrolysis was also regioselective (Scheme 5). *To receive any correspondence (e-mail: jcavaleiro@dq.ua.pt). Scheme 2 Reagents and conditions: i, adequate aniline, Et2O, room temp.; ii, Ac2O, reflux Scheme 3 Reagents and conditions: i, p-anisidine, DCC, PPy, CH2Cl2, room temp.; ii, NaH, THF, reflux Scheme 4 Reagents and conditions: i, phenol, DDC, PPy, THF, room temp.; ii, adequate aniline, DCC, PPy, CH2Cl2, room temp.; iii, adequate aniline, cyanuric chloride, triethylamine, acetone, room temp.; iv, NaH, THF, refluxN O O O 6a OMe O NH OMe HO O 10 i O J.CHEM. RESEARCH (S), 1997 229 The structures of all the products were unambiguously established by using several 1D and 2D NMR techniques and also by mass spectrometry.The regioselectivity observed15,16 in the functionalization of 2 and 3 was further confirmed through NOESY experiments with compound 7. The conformation of the tetrahydropyran ring of compounds 2, 4, 5 and 7–10 was established on the basis of NMR data. Proton-coupled 13C NMR of 6-CO and the multiplicity of the resonance of 3-H suggest that the tetrahydropyran ring is in a chair conformation. However, NOESY experiments carried out with compound 7, as well as the one-dimensional selective INEPT spectrum of compound 8, strongly suggest that in these compounds the tetrahydropyran ring is present in a distorted chair conformation.Analysis of the mass spectra of compounds 2, 4, 5, 7, 8 and 9 revealed the possibility of determining the substitution pattern of the carboxylic acid groups and therefore of confirming the regioselectivity of some of the reactions previously described. Two important fragmentations were observed.The first one corresponds to the loss of 6-COR1. The second fragmentation corresponds to the loss of R2H from the 3-carboxylic acid group or derivatives, leading in all cases to the formation of an intense peak at m/z 153. The identity of the group R1 can be determined based on the difference between the mass of the molecular ion and the mass of the first fragment; based on the difference between the masses of the first and the second fragment the group R2 can be identified.Techniques used; NMR [1H, 13C, HETCOR (1H/13C), COSY (1H/1H), selective INEPT, NOESY and HMBC], mass spectrometry (low- and high-resolution), elemental analysis References: 25 Schemes: 5 Table 1: Connectivities found in the HMBC spectrum of 2 Figures: 2 Received, 7th February 1997; Accepted, 17th March 1997 Paper E/7/00887B References cited in this synopsis 15 I. D. Rae and A. M. Rewood, Aust. J. Chem., 1974, 1143. 16 A. J.D. Silvestre, J. A. S. Cavaleiro, A. M. S. Silva, B. Delmond and C. Filliatre, Heterocycl. Commun., 1996, 2, 371. 17 A. J. D. Silvestre, J. A. S. Cavaleiro, B. Delmond, C. Filliatre and G. Bourgeois, Flavour Fragrance J., 1994, 9, 51. 18 A. J. D. Silvestre, J. A. S. Cavaleiro, B. Delmond, C. Filliatre and G. Bourgeois, Industrial Crops and Products, 1997, 6, 27. 19 J. A. S. Cavaleiro, G. M. S. F. C. Nascimento, M. G. M. S. Neves, M. T. Pinto, A. J. D. Silvetre and M. G. H. Vicente, Tetrahedron Lett., 1996, 37, 1893. 20 A. C. Tom�e. J. A. S. Cavaleiro, F. M. J. Domingues and R. J. Cremlyn, Phosphorus Sulphur Silicon Relat. Elem., 1993, 79, 187. 21 M. Hargreaves, J. Pritchard and H. Dave, Chem. Rev., 1970, 70, 439. 22 D. Tanner and P. Somfai, Tetrahedron, 1988, 44, 613, 619. 23 K. Venkataraman and D. R. Wagle, Tetrahedron Lett., 1979, 32, 3037. Scheme 5 Reagents and conditions: CHCl3, room temp., 3 days Table 2 Most important fragmentations of compounds 2–10 Compound 1st frag. (loss of) 2nd frag. (loss of) 23456789 10 .CO2H CO .CO2Me .CONHC6H4R CO .CO2Me .CO2Ph .CO2Ph .CO2H H2O H2O H2O H2O .(RC6H4NH) MeOC6H4NH2 H2O R-C6H4NH2 Me

ISSN:0308-2342    

DOI:10.1039/a700887b

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

HFe(CN)6 3– Fe(CN)6 4– + H+ HL L– Ka Cr(H2O)6 3+ Cr(H2O)5OH2+ + H+ KM1 Cr(H2O)6 3+ + L– OS1 KOS1 Cr(H2O)5OH2+ + L KOS2 Cr(H2O)5L Cr(H2O)6 3+ –H2O k1 –H2O k2 Cr(H2O)4OHL Cr(H2O)5OH2+ OS2 fast fast Product 230 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 230–231 J. Chem. Research (M), 1997, 1545–1559 Kinetics and Mechanism of the Anation and Complexation between Hydroxopentaaquochromium(III) Ions and the Hexacyanoferrate(II) Ion S. I. Ali,* Zaheer Khan and Seema Sharma Department of Chemistry, Jamia Millia Islamia, Jamia Nagar, New Delhi - 110 025, India The kinetics of the anation of the chromium(III) species, Cr(H2O)6 3 + and Cr(H2O)5OH2+, by hexacyanoferrate(II) ions in the pH range 4.5–5.4 are reported.The recognition of the formation and of the interconversion of hydrolytic chromium(III) oligomers, as well as the reactivity of the conjugate base pairs of the starting material, has resulted in tetravalent chromium attracting the attention of many workers.2,3 Here we report our mechanistic studies on the anation of chromium(III) by hexacyanoferrate(II) in the pH range 4.5-5.4.It was observed that the reaction followed a first-order rate law with respect to [CrIII]T under pseudo-first-order conditions [an excess of Fe(CN)6 4 µ]. Under the kinetic conditions, the stoichiometry conforms to: 2Cr(H2O)5OH2++Fe(CN)6 4 µ h[Cr(H2O)4OH]2Fe(CN)6+2H2O (1) The present kinetic studies were carried out in the pH range 4.5–5.4.It is noted that, at constant Fe(CN)6 4µ concentration, as the pH increased, kobs increased (Table 1). The plot of log kobs vs. log [H+] (pH=5.0–5.4) shows a fractional order in [H+]. It was observed that the reaction rate increases with increasing ionic-strength, indicating the easy removal8,17,29 of coordinated water molecules and the formation of outer-sphere complexes. Under our experimental conditions (pH=4.5–5.4), Cr(H2O)6 3 + and Cr(H2O)5OH2+ were the main reactive species.The hexacyanoferrate(II) ion also participated in the acid–base equilibria. Scheme 1 explains all the observations. Consistent with the proposed mechanism, the following rate equation was derived: 1/kobs=A/C+B/C[Fe(CN)6 4µ]T (11) where A=KaKOS1[H+]+KaKM1KOS2, B=[H+]2+[H+]Ka+ KM1[H+]+KM1Ka and C=k1KOS1Ka[H+]+k2KOS2KaKM1. The double reciprocal plots {i.e. 1/kobs vs. 1/[Fe(CN)6 4µ]T, Fig. 1} are linear with positive intercepts and therefore confirmed the proposed mechanism.In the pH range 5.0–5.4, k1KOS1Ka[H+] and KaKOS1[H+] can be neglected in comparison with k2KOS2KaKM1 and KaKM1KOS2, respectively, and [H+]Ka and [H+]2ka can also be neglected. Therefore, eqn. (11) can be written as eqn. (12). Double *To receive any correspondence. Table 1 Rate constants at various pH, ionic strength and temperature for the anation of Cr(H2O)5OH2+ with hexacyanoferrate(II) ions Ionic strength/ Temp. 104 [Cr(H2O)5OH2+]T/ 103[Fe(CN)6 4 µ]T/ 104kobs/ pH mol dmµ3 T/K mol dmµ3 mol dmµ3 sµ1 5.0 0.04 313 2.7 2.67 3.20 3.73 4.27 4.80 5.32 3.0�0.4 3.6�0.4 4.0�0.5 4.5�0.6 5.0�0.2 5.7�0.4 5.0 0.05 0.10 0.20 0.30 0.40 0.50 313 2.7 2.67 2.5�0.3 3.0�0.4 4.0�0.5 5.0�0.5 6.3�0.6 7.5�0.4 4.5 5.0 5.2 5.4 0.10 313 2.7 2.67 1.5�0.3 3.0�0.5 5.0�0.2 7.2�0.5 5.0 0.04 313 2.7 3.1 4.3 4.8 5.3 2.67 2.0�0.6 2.4�0.3 2.7�0.3 3.3�0.5 3.5�0.2 5.0 0.10 303 308 318 323 2.7 2.67 1.2�0.2 1.8�0.3 4.4�0.4 4.6�0.3 Scheme 1J.CHEM. RESEARCH (S), 1997 231 reciprocal plots between kobs µ1 and [hexacyanoferrate(II)]T µ1 at constant pH (which are linear) confirmed the proposed mechanism.Plots according to eqn. (12) were used to evaluate k2 and KOS2 at different temperatures, the values for which are given in Table 2. To confirm the validity of rate law (12), the rate constants were calculated (kcal) in various kinetic runs by substituting the values of k2 and KOS2 in eqn. (12) and comparing with the kobs values. The close agreement between the kobs and kcal values provides supporting evidence for the proposed mechanism (Scheme 1). 1/kobs=1/k2{1+([H+]+Ka)/KOS2Ka[Fe(CN)6 4µ]} (12) Techniques used: Spectrophotometry References: 31 Tables: 2 Figures: 1 Equations: 12 Schemes: 1 Received, 24th April 1996; Accepted, 19th March 1996 Paper E/6/02878K References cited in this synopsis 1 L. Spiccia, H. S. Evans, W. Marty and R. Giovanoli, Inorg. Chem., 1987, 26, 474. 2 L. Spiccia and W. Marty, Inorg. Chem., 1985, 25, 266. 3 F. P. Rotzinger, H. Stunzi and W. Marty, Inorg. Chem., 1986, 25, 489. 8 J. N. Mandal and G. S. De, Indian J. Chem., 1980, 19A, 25. 17 B. K. Niogy and G. S. De, Proc. Indian Acad. Sci., 1983, 92, 153. 29 R. E. Hamm, R. L. Johnson, R. H. Perkins and R. E. Davis, J. Am. Chem. Soc., 1958, 80, 4469. Fig. 1 The dependence of kobs µ1 vs. [Fe(CN)6 4 µ]µ1 at various temperatures. (A) 30, (B) 35, (C) 40, (D) 45 and (E) 50 °C, pH=5.0, [Cr(H2O)5OH2+] =2.6Å10µ4 mol dmµ3 and ionic strength=0.1 mol dmµ3 Table 2 Values of anation rate constant (k2), outer-sphere complexation constant (KOS2), activation and thermodynamic parameters for the anation of Cr(H2O)5OH2+ by hexacyanoferrate(II); [Cr(H2O)5OH2+] =2.6Å10µ4 mol dmµ3, [Fe(CN)6 4 µ] =2.6Å10µ3 mol dmµ3, pH=5.0, ionic strength=0.1 mol dmµ3 104 k2/ KOS2/ 104 k2 (cal)/ KOS2 (cal)/ kT/h T/K sµ1 dm3 molµ1 sµ1 dm3 molµ1 10µ12 303.2 308.2 313.2 318.2 323.2 5.5 8.4 14.7 17.7 23.9 115.7 110.2 90.9 89.0 83.3 5.8 6.6 12.5 18.0 25.5 115.7 110.2 90.9 89.0 83.3 6.32 6.42 6.52 6.63 6.73 DH‡/ DS‡/ DH0/ DS0/ DG0/ kJ molµ1 J Kµ1molµ1 kJ molµ1 J K molµ1 kJ molµ1 57.

ISSN:0308-2342    

DOI:10.1039/a602878k

出版商:RSC    

年代:1997

数据来源: RSC

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COMe Ph Ph Me O Ph Ph Ph Ph + TCS room temp. EtOH 7 + 8 (1) Me O 11,12 NO2 NO2 NO2 COMe + TCS EtOH room temp. (2) O2N O H Me NO2 O2N O H Me NO2 ( E)-12a ( Z)-12b R Me R O R R R 1 R = H 3 R = 4-Cl 5 R = 4-Br 9 R = 4-OMe 2 R = H 4 R = 4-Cl 6 R = 4-Br 10 R = 4-OMe 232 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 232–233 J. Chem. Research (M), 1997, 1537–1544 A New Approach to the Stereoselective Synthesis of b-Methylchalcones Saad S. Elmorsy,* Abdel Galel M. Khalil, Margret M.Girges and Tarek A. Salama Chemistry Department, Faculty of Science, Mansoura University, 35516, Mansoura, Egypt Many b-methylchalcone derivatives are prepared via the self condensation of aralkyl ketones mediated by tetrachlorosilane–ethanol under mild conditions. The present study is concerned with the elaboration of a highly efficient and stereodefined synthesis of b-methylchalcones. Unlike titanium tetrachloride, the reaction of aryl methyl ketone with an equimolar amount of tetrachlorosilane (TCS) in the presence of absolute ethanol and in the absence of catalyst afforded a b-methylchalcone along with a smaller amount of 1,3,5-triarylbenzene, with no polymeric compound being detected18 (Table 1, entries 1–5).The reaction time required for optimum yields was ca. 3 h in most cases. With the variation in yields given in Table 1, it can be seen that there are important differences in the behaviour of the TCS–EtOH reagent towards aryl methyl ketones.Substituents such as methoxy and phenyl, which increase the negativity of the acetyl group by resonance or inductive effects, retard the yield of b-methylchalcone as shown in entries 4 and 5 [eqn. (1)]. On the other hand, substituted acetophenones having strongly electron withdrawing groups such as nitro groups gave only b-methylchalcones. Thus 3p- or 4p-nitroacetophenone in entries 6 or 7 was treated with a slight excess of tetrachlorosilane in ethanol to afford the b-methylchalcone 11 or 12 respectively in very good yield.Thus the formation of *To receive any correspondence. Table 1 Reaction of aryl methyl ketones with TCS–EtOH Yield Entry Substrate t/h Product (%)a 1 Acetophenone 2 1,3-diphenylbut-2-en-1-one 1 +1,3,5-triphenylbenzene 2 62 34 2 4p-Chloroacetophenone 3 1,3-Bis(4-chlorophenyl)but-2-en-1-one 3 +1,3,5-tris(4-chlorophenyl)benzene 4 64 28 3 4p-Bromoacetophenone 4 1,3-Bis(4-bromophenyl)but-2-en-1-one 5 65 +1,3,5-tris(4-bromophenyl)benzene 6 23 4 4-Acetylbiphenyl 2 1,3-Bis(biphenyl-4-yl)but-2-en-1-one 7 +1,3,5-tris(biphenyl-4-yl)benzene 8 59 32 5 4p-Methoxyacetophenone 2 1,3-Bis(4-methoxyphenyl)but-2-en-1-one 9 +1,3,5-tris(4-methoxyphenyl)benzene 10 58 37 6 3p-Nitroacetophenone 10 1,3-Bis(3-nitrophenyl)but-2-en-1-one 11 77 7 4p-Nitroacetophenone 8 1,3-Bis(4-nitrophenyl)but-2-en-1-one 12 74 aIsolated yields after column chromatography.J.CHEM. RESEARCH (S), 1997 233 a triarylbenzene can be inhibited by slowing the rate of the second aldol condensation with a substituted acetophenone having a strongly electron withdrawing group.Moreover, the reaction in a slight excess of absolute ethanol as solvent ultimately leads to a decrease in the yield of the 1,3,5-triarylbenzene derivatives [eqn. (2)]. The products of the double condensation were obtained either as mixtures of E- and Z-isomers of the b-methylchalcone (entries 1,2,3 and 7) or exclusively as E-isomers (entries 4, 5 and 6).The structural analysis for the cis-and transisomers was carried out by UV absorption and 1H NMR spectral methods. The E- and Z-isomers exhibit remarkable spectroscopic differences which allow the reported structure assignments. The reaction rate and stereochemical course of the double condensation of aralkyl ketones were influenced by such factors as the kind of substituent at the aromatic ring and the molar ratio of the reactants. The mild conditions and simplicity of the operation offer distinct advantages over the reported methods. In principle, it is found that b-methylchalcone derivatives can be easily prepared from readily accessible and cheap TCS in the presence of absolute ethanol at room temperature. Techniques used: IR, UV, GCMS and 1H NMR References: 24 Table 1: Reaction of aryl methyl ketones with TCS–EtOH Table 2: Spectral data of the b-methylchalcones Received, 8th November 1996; Accepted, 20th March 1997 Paper E/6/07611D Reference cited in this synopsis 18 L. J. Mazza and A. Guarna, Synthesis, 1980, 1, 41.

ISSN:0308-2342    

DOI:10.1039/a607611d

出版商:RSC    

年代:1997

数据来源: RSC

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N NH Me O 1 N NH CH2Cl O 3 NCS 2 N N CH2 O 4 N N O N Ar O O TEA N O O Ar 5a–e 8a–e N N O N Ar O O 9a–c PhNO2 a b c d e Ar = Ph Ar = C6H4Me- p Ar = C6H4Cl- p Ar = C6H4OMe- p Ar = C6H4NO2- p – + 234 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 234–235 J. Chem. Research (M), 1997, 1560–1575 Dipolar Cycloaddition Reactions with Quinazolinones: a New Synthesis of Azoloquinazolinone Derivatives Sami S. Ghabrial* and Mayssoune Y. Zaki National Organization for Drug Control and Research (NODCAR), P.O.Box 29, Cairo, A.R. Egypt Several new pyrroloquinazolinone derivatives are synthesised via a novel route involving the action of dipolarophiles on the diionic species generated in situ from the reaction of N-chlorosuccinimide with 2-methylquinazolin-4-one and subsequent treatment with triethylamine. Quinazolin-4-one (1) and its annelated azolo derivatives have been found to exhibit antibacterial activity against a variety of organisms, e.g. tuberculostatic activity.1,2 Moreover, the pyrrole moiety is also reported to be an active and essential component in a number of drugs and pharmaceutical preparations controlling infections of bacteria, protozoa and viruses, besides being analgesic and hypnotic.3-10 The incorporation of the two moieties increases the biological activity of both and thus it was of value to synthesise a number of new heterocyclic derivatives having both these moieties in the same molecules.A novel synthesis was developed which involved the use of N-chlorosuccinimide (NCS; 2) as chlorinating agent.In continuation our efforts towards the synthesis of biologically active fused heterocycles,1,2,3 we found that4,5 2-methyl quinazoline (1) reacted with N-chlorosuccinimide (2) to yield 2-chloromethylquinazoline (3) in situ which was separated and the structure confirmed on the basis of its analytical and spectral data [1H NMR 4.56 (s, 2 H, CH2Cl), 7.53–8.15 (m, 4 H, ArH’s) and 12.02 (brs, 1 H, NH)]. Compound 3 was then treated with triethylamine (TEA) to afford the zwitterionic 4 created by the loss of HCl.This zwitterionic species 4 was used as the starting material for the present study and its reactions with some N-arylmaleimides 5, 3-aryl- 2-cyanothioacrylamides 6 and w-nitrostyrenes 7 resulted in the formation of several new azoloquinazolinones required for medicinal studies. A mixture of 1, N-phenylmoleimide (5a) and the equivalent amount of TEA in dry chloroform was stirred for 1 h afforded a product of molecular formula C19H13N3O3 which corresponded to the addition of one molecule of 1 to one molecule of 5a followed by HCl elimination.The IR spectrum of this reaction product showed the presence of sat. CH2 and CH (2980 cmµ1), CO (1680) and C�N (1630) in addition to the (·CO·NAr·CO·) group as two widely separated bands at 1790 and 1710 cmµ1. The 1H NMR spectrum revealed signals for pyrrolidine-CH2, pyrrolidine H-3 and pyrrolidine H-4 in addition to aromatic protons in their expected positions (cf.Experimental, see full text). Based on the above data, this reaction product was formulated as the 3a,11a-dihydro-11H-pyrrolo[3p,4p:4,5]pyrrolo[ 2,1-b]quinazoline-1,3,5-trione derivative 8a. The formation of 8a in this reaction was assumed to proceed via the initial reaction of 1 with 2 to yield in situ the non-isolable 2-chloromethylquinazolinone 3. This reacts with TEA to yield the zwitterionic species 4 which then reacts with 5a via a dipolar cycloaddition reaction to yield isolable 8a.This reaction constitutes a simple and easy one pot reaction leading to a fused heterocyclic derivative which is otherwise difficult to obtain. Similarly, compound 4 reacted with each of the N-arylmaleimides 5b–e to give the corresponding pyrrolo-pyrroloquinazolinone derivatives 8b–e respectively. The structures of 8b–e were also established on the basis of correct elemental analysis and spectral data which were found to be in good agreement with the assigned structures.On the other hand, dehydrogenation of 8a–c using either chloranil or nitrobenzene resulted in the formation of the corresponding 11H-pyrrolo[3p,4p:4,5]pyrrolo[2,1-b]quinazoline- 1,3,5-trione derivatives 9a–c respectively. The structure *To receive any correspondence. Scheme 1 Scheme 2J. CHEM. RESEARCH (S), 1997 235 of 9a–c was confirmed by elemental analysis and spectral data.The IR spectra of compounds 9a–c showed the presence of CO (1890) and the (·CO·NAr·CO·) group (1780, 1710) in addition to sat. CH2 (2980) and C�N (1630 cmµ1). The 1H NMR spectra of compounds 9a,c revealed only signals for pyrroline-CH2 (d, 4.8) and aromatic protons (m, 7.2–8.0). No pyrrolidine H-3 or H-4 signals were detected in these spectra in accordance with the dehydrogenation reaction. The behaviour of 4 towards a variety of 3-aryl-2-cyanothioacrylamide derivatives 6a–e was also investigated. Thus, it was found that 1 and 4 reacted with 3-pmethoxyphenyl- 2-cyanothioacrylamide (6a) in the presence of TEA to yield a product with molecular formula C20H16N4SO2 which had an absorption band corresponding to the nitrile function in the IR spectrum.Moreover, pyrrolidine- CH and CH2 protons were detected by 1H NMR. Based on the above spectral data, the reaction product was formulated as the thiocarboxamido-3H-pyrrolo[2,1-b]quinazolin- 9-one derivative 10a.The reaction is assumed to proceed via the initial formation of 4 followed by cycloaddition to 6a to yield the product 10a. In a similar manner, each of 6b–e reacted with 1 and NCS in the presence of TEA to yield the corresponding 2,3-dihydropyrrolo[ 2,1-b]quinazolin-9(1H)-one derivatives 10b–e, respectively. The structures of 10b–e were also confirmed by elemental analysis and spectral data as for 10a. Evidence for the structures of 10a–e was provided by the action of sodium ethoxide.Thus, each of 10a–e reacted with boiling sodium ethoxide to give, after acidification, products corresponding to the loss of one molecule of HCN in each case. The IR spectra of these reaction products showed that the bands of the nitrile function were entirely absent. Accordingly, these reaction products were formulated as the thiocarboxamido- 3H-pyrrolo[2,1-b]quinazolin-9-one derivatives 11a–c, respectively. Moreover, the 1H NMR revealed pyrroline- CH2, aromatic and NH2 protons only.Furthermore, compound 1 and NCS in chloroform and TEA (i.e. 4) reacted with a variety of w-nitrostyrenes 7a–e. Thus 4 reacted with w-nitrostyrene 7a to yield the cycloadduct 12a. IR and 1H NMR spectra showed the structure to be the 2-nitro-2,3-dihydropyrrolo[2,1-b]quinazolin-9(1H)- one derivative 12a. Analogously, each of 7b–e reacted with 4 to afford the 2-nitro-2,3-dihydropyrrolo[2,1-b]quinazolin- 9(1H)-ones 12b–e, respectively. Moreover, compounds 12a–c could also be dehydrogenated by the action of chloranil to give the corresponding 2-nitro-4H-pyrrolo[2,1-b]quinazolin-9-one derivatives 13a–c, respectively. 1H NMR revealed signals for pyrroline-CH2 and aromatic protons only. Techniques used: 1H NMR, FTIR, elemental analysis References: 14 Tables 1 and 2: Data for compounds 3, 8, 9, 10, 11, 12 and 13 Received, 19th March 1997; Accepted, 21st March 1997 Paper E/7/01931I References 1 A. O. Abdelhamid, F. A. Khalifa and S. S. Ghabrial, Phosphorus Sulfur Relat. Elem., 1988, 40, 41. 2 S. S. Ghabrial, Phosphorus Sulfur Silicon Relat. Elem., 1993, 84, 17. 3 S. S. Ghabrial and M. Y. Zaki, Indian J. Chem., 1994, 33, 855. 4 S. S. Ghabrial, I. Thomson and K. B. G. Torssell, Acta Chem. Scand., Ser. B, 1987, 41, 426. 5 S. S. Ghabrial and A. O. Abdelhamid, Arch Pharm., 1985, 320, 1281. 6 K. Hermann, Naturwissenschaften, 1959, 43, 185. 7 K. Hermann, Arch. Pharm., 1958, 291, 238. 8 H. Yale and J. Bemstin, US Pat. 2 727 896, 1955 (Chem. Abstr., 1956, 50, 12 115a). 9 H. Gilman, L. Rowe and J. Dickey, Recl. Trav. Chim. Pays-Bas, 1933, 52, 395. 10 F. Mann and B. Saunders, Practical Organic Chemistry, Longman, London, 4th edn., 1975, p. 293. 11 D. Papa and M. T. Bogert, J. Ahem. Soc., 1936, 58, 1701. 12 J. S. A. Brunskill, A. De and D. F. Ewing, J. Chem. Soc., Perkin Trans. 1, 1978, G29. 13 E. I. Du Pont de Nemours, US Pat. 2 444 536, 1948 (Chem. Abstr., 1948, 43, 7340c). 14 A. I. Vogel, A Text Book of Practical Organic Chemistry, Longman, London, 4th edn., 1980, pp. 673, 796.

ISSN:0308-2342    

DOI:10.1039/a701931i

出版商:RSC    

年代:1997

数据来源: RSC

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N N O 1 N N O 2 Me N N O 3 Me Ph N O 4 Br N N NMe2 O 5 N O 1 2 3 4 5 6 7 N O– + N N Me O N N Me O N N Me O N N Me O Ph Ph N O N O Br Br N N Ar O N N Ar O 130.2 146.9 106.9 106.1 106.8 111.5 109.0 106.2 110.4 111.1 103.4 142.0 124.3 132.3 121.0 108.7 1.485 1.409 1.351 1.459 1.325 1.467 1.199 1.431 1.367 1.295 1.373 130.0 145.7 106.6 107.0 107.0 110.3 108.1 107.6 109.6 109.7 104.9 142.9 125.2 129.9 120.9 109.1 1.477 1.392 1.365 1.445 1.358 1.451 1.208 1.428 1.387 1.311 1.376 2 2 3 3 1.467 123.0 126.6 144.3 108.8 110.2 110.5 106.0 108.4 106.8 110.0 111.1 103.7 138.4 125.1 131.2 104.5 1.446 1.367 1.456 1.340 1.475 1.198 1.419 1.370 1.353 1.376 4 4 1.373 1.379 1.336 1.373 1.427 1.433 1.213 1.341 1.295 129.2 125.0 117.3 116.6 126.1 104.9 112.2 110.0 105.8 106.3 5 5 238 J. CHEM.RESEARCH (S), 1997 J. Chem. Research (S), 1997, 238–239 J. Chem. Research (M), 1997, 1615–1630 Crystal and Molecular Structures of Two Pyrrolo[1,2-c]imidazol-5-ones Alexander J. Blake,*,† Hamish McNab* and (the late) Craig Thornley Department of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, UK The crystal structures of the pyrrolo[1,2-c]imidazol-5-ones 2 and 3 are reported; the results show that the system behaves structurally as a simple cyclic N-acylimidazole, with no special cyclic delocalisation.Some years ago, one of us (H. M.) reported the first synthesis of the parent compound of the pyrrolo[1,2-c]imidazol-5-one system 1,1 and more recently we have shown how this can be improved and extended to provide a versatile and convenient route to substituted members of this and related series.2,3 Since these compounds are now readily available, we have embarked on a systematic study of their properties and report here the results of an X-ray crystallographic investigation of the pyrrolo[1,2-c]imidazol-5-ones 2 and 3.2 Previous structural studies of the fully unsaturated pyrrolizin-3-one system4 are confined to our earlier results on the 6-bromo derivative 4,5 and no work on azapyrrolizinones has been reported.Pyrrolizinones possess an unusual conjugated system, in which ‘normal’ amide resonance creates a formally antiaromatic canonical form which is reflected in an unusually long C(3)–N(4) bond (Scheme 1). The effect, if any, of the replacement of a CH with an N on this delocalisation was a major focus for the present study. The principal dimensions of 2 and 3 are summarised in Fig. 1, together with those of the model pyrrolizinone 4. In addition, pyrrolo[1,2-c]imidazoles may be regarded as cyclic N-acylimidazoles, so the dimensions of the model N-cinnamoylimidazole 56 are also included in Fig. 1. Views of 2 and 3 showing the crystallographic numbering schemes are shown in Fig. 2. In the full text version of this paper, we present a detailed analysis of the data presented in Fig. 1, and the major conclusions are as follows: (i) The bond lengths in the amide region [N(4)·C(5)·O(5)] are not significantly different in 2, 3 or the model compounds 4 and (especially) 5, confirming that the pyrrolo[1,2-c]imidazoles may be regarded structurally as N-acylazoles, with no special contribution due to cyclic delocalisation of electrons.However, it should be emphasised that the N(4)·C(5) bonds in particular are almost 0.1 Å longer than is typical for a cyclic tertiary g-lactam7 [1.335(9) Å], presumably owing to competitive delocalisation of the nitrogen atom lone pair into the imidazole ring as well as into the carbonyl group.(ii) The formal double and single bonds are consistently longer and shorter respectively in 3 than in 2 for the conjugating pathway C(3)·N(2)·C(1)·C(8)· C(7)·C(6)·C(5) linking the 3-phenyl substituent with the carbonyl group. This confirms earlier spectroscopic studies2 which suggest that the phenyl group in 3 behaves as a net electron donating group. (iii) The individual 5-membered rings of the two pyrrolo[1,2-c]imidazoles are both essentially flat, but the systems as a whole are not perfectly planar, with the angles between the two 5-membered rings in 2 and 3 being 2.5 and 4.2° respectively.(iv) Both compounds 2 and 3 display very large exocyclic bond angles (142.0–146.9°) at the ring junctions which is a characteristic feature of the geometry of such fused 5-membered rings.5 (iv) Crystal packing *To receive any correspondence. †Present address: Department of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK.Scheme 1 Fig. 1 Principal molecular dimensions of 2, 3, 4 and 5. Typical ESDs of the bond lengths are 0.004, 0.005, 0.10 and 0.002 Å respectively and those of the bond angles are 0.3, 0.4, 0.7 and 0.2° respectivelyJ. CHEM. RESEARCH (S), 1997 239 in 2 involves N(2)...H·C(3) contacts which lead to helices of molecules in the a crystallographic direction. Crystal Data for 2.·C7H6N2O, M=134.14, orthorhombic, a=4.3013(4), b=11.3334(7), c=13.4102(7) Å, V=653.73(8) Å3 [from 2y values of 26 reflections measured at �w (28R2yR30°, l=0.71073 Å, T=280 K)], space group P212121 (No. 19), Z=4, Dx=1.363 g cmµ3, yellow equant crystal, 0.46Å0.39Å0.39 mm, m(Mo-Ka)=0.095 mmµ1. Data collection and processing. Stoe Stadi-4 four-circle diffractometer, w/2y scans, graphite-monochromated Mo-Ka X-radiation; 940 reflections measured (5R2yR45°, �h, k, l), 857 unique [merging R=0.038], giving 704 with FE4s(F) and 857 which were retained in all calculations.No crystal decay was observed and no corrections were applied for absorption. Structure solution and refinement. Automatic methods8 (all non-H atoms). Full-matrix least-squares refinement9 with all non-H atoms anisotropic. Methyl hydrogen atoms were located from a DF synthesis and others were introduced at geometrically calculated positions: subsequent refinement allowed rotation of the rigid methyl group hydrogens while a riding model was adopted for the others [Uiso(H)= xUeq(C); x=1.5 for methyl hydrogens and 1.2 for others].The weighting scheme wµ1=[s2(Fo 2 )+(0.0964P)2], P= 13 [MAX(Fo 2 ,0)+2Fc 2], gave satisfactory agreement analyses. Final R1 [FE4s(F)] =0.0529, wR2 [all data] =0.1330, S[F2] =1.09 for 93 refined parameters. An extinction correction9 refined to 0.015(10) and the final DF synthesis showed no peaks out of the range 0.25 to µ0.18 eŵ3. Crystal Data for 3.·C13H10N2O, M=210.23, monoclinic, a=7.227(3), b=20.063(9), c=7.107(4) Å, b=97.18(6)°, V=1022.4(8) Å3 [from 2y values of 25 reflections measured at �w (28R2yR30°, l=0.71073 Å, T=150 K)], space group Cc (No. 9), Z=4, Dx=1.366 g cmµ3, red columnar crystal, 0.74Å0.16Å0.08 mm, m(Mo-Ka)=0.089 mmµ1. Data collection and processing. Data collection as for 2 above; 1051 reflections measured (5R2yR45°, �h, �k, l), 679 unique [merging R=0.099], giving 610 with FE4s(F) and 679 which were retained in all calculations.No crystal decay was observed and no corrections were applied for absorption. Structure solution and refinement. The structure was solved and refined as for 2 above. The weighting scheme wµ1=[s2(Fo 2 )+(0.076P)2+0.21P], P=13 [MAX(Fo 2 ,0)+2Fc 2], gave satisfactory agreement analyses. Final R1[FE 4s(F)] =0.0343, wR2 [all data] =0.1032, S[F2] =1.12 for 145 refined parameters. An extinction correction9 refined to 0.009(4) and the final DF synthesis showed no peaks out of the range 0.16 to µ0.19 eŵ3.Technique used: X-ray diffraction References: 9 Fig. 3: Packing diagram for 2 Fig. 4: Packing diagram for 3 Tables 1–8: Lists of refined parameters and molecular geometry descriptors for both structures We are grateful to The University of Edinburgh for a Research Studentship (to C. T.) and to the EPSRC (formerly the SERC) for the provision of a four-circle diffractometer. Received, 12th March 1997; Accepted, 3rd April 1997 Paper E/7/01729D References cited in this synopsis 1 H. McNab, J. Chem. Soc., Perkin Trans. 1, 1987, 653. 2 H. McNab and C. Thornley, J. Chem. Soc., Perkin Trans. 1, is. 3 S. E. Campbell, M. C. Comer, P. A. Derbyshire, X. L. M. Despinoy, H. McNab, R. Morrison, C. C. Sommerville and C. Thornley, J. Chem. Soc., Perkin Trans. 1, in the press. 4 H. McNab and C. Thornley, Heterocycles, 1994, 37, 1977. 5 A. J. Blake, H. McNab and R. Morrison, J. Chem. Soc., Perkin Trans. 1, 1988, 2145. 6 C. P. Huber, Acta Crystallogr., Sect. C, 1985, 41, 1076. 7 P. Chakrabarti and J. D. Dunitz, Helv. Chim. Acta, 1982, 65, 1555. 8 SHELXS86, G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467. 9 SHELXL96, G. M. Sheldrick, University of G�ottingen, Germany, 1996. Fig. 2 Views of 2 and 3 showing the crystallographic numbering schemes. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radi

ISSN:0308-2342    

DOI:10.1039/a701729d

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

R1 CN ArNH SK NCCH(R1)CSNHAr 3 + ArNCS 10a,b 11 N S Ph R1 CN R2 S PhHN COR2 NH2 R1 R1 CN PhNH SK 10a S PhHN CN NH2 R1 16 15 ii iii N S Ph 12 17 S PhHN CO2Et NH2 R1 13 N S Ph 12 R1 CN i 14 R1 CN PhHN SMe 18 N NH R1 NH2 PhHN 19 iv v AcOH N S R1 = a Ar = Ph b Ar = 4-BrC6H4 10,11 15a R1 = Ph b R2 = 2-C4H3S c R2 = 2-C4H3O d R2 = Me O HN R1 CN 240 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 240–241 J. Chem. Research (M), 1997, 1681–1694 A Convenient Synthesis of Thiophene, 1,3-Thiazole, 2,3-Dihydro-1,3,4-thiadiazole and Pyrazole Derivatives Abdou O.Abdelhamid*a and Saad M. Al-Shehrib aDepartment of Chemistry, Faculty of Science, Cairo University, Giza, Egypt bDepartment of Science, King Khalid Military Academy, P.O. Box 22140, Riyadh 11495, Saudi Arabia 3-Aminothiophenes and 2,3-dihydro-1,3,4-thiadiazoles are synthesised via the reaction of 2-cyano-2-[4-(2-naphthyl)- 1,3-thiazol-2-yl]thioacetanilides with a-haloketones or hydrazonoyl halides.The interesting pharmacological properties of thiazole derivatives1 –4 in relation to the various changes in the structure of these compounds is worth studying in order to synthesise less toxic and more potent drugs. Therefore, the fusion of other heterocyclic moieties to the thiazole ring may lead to the fulfilment of this objective. The present investigation deals with the synthesis of some such compounds. In continuation of our interest in the chemistry of the thiazoles,5–8 the syntheses of several new thiazole and dihydrothiadiazole derivatives are described. 2-Bromoacetylnaphthalene (1) reacts with cyanothioacetamide (2) in ethanol to afford [4-(2-naphthyl)-1,3-thiazol- 2-yl]acetonitrile (3). Compound 3 reacted with benzaldehyde, p-tolualdehyde and salicylaldehyde to give the corresponding 3-aryl-2-[4-(2-naphthyl)-1,3-thiazol-2-yl]acrylonitriles 4a,b and 3-[4-(2-naphthyl)-1,3-thiazol-2-yl]coumarin (5). Coumarin 5 was also prepared by boiling coumarin- 3-carbothioamide (6)10 with 1 in ethanol (see Scheme 1).a-Substituted cinnamonitrile reacted with 3 in ethanol containing a catalytic amount of piperidine to give the same product 4a. Compound 4, a typical a,b-unsaturated nitrile, underwent fission at the exocyclic ethylenic double bond on heating with hydrazine or phenylhydrazine in ethanol to give 3 and the corresponding aldehyde hydrazone. Also, compound 3 reacted with benzenediazonium chloride in ethanolic sodium acetate solution to afford 2-cyanocarbonyl- 4-(2-naphthyl)-1,3-thiazole phenylhydrazone (9).Compound 3 reacted with aryl isothiocyanates in the presence of potassium ethoxide solution to give the potassium salts 10a,b which were converted into 2-cyano-2-[4-(2-naphthyl)- 1,3-thiazol-2-yl]thioacetanilides 11a,b by treatment with acetic acid. Treatment of 10a with each of ethyl chloroacetate, a-haloketones or chloroacetonitrile gave the 3-amino-2-substituted thiophenes 13, 15a–d and 16, respectively (see Scheme 2).The IR spectrum of 13 especially revealed bands at 3491, 3315 (NH2) and 1664 cmµ1 (CO) with no cyano absorption band.11 Similarly, 10a reacted with phenacyl bromide, 2- bromoacetylthiophene, 2-bromoacetylfuran, chloroacetone and chloroacetonitrile to give 3-amino-2-acylthiophenes 15a–d and 3-amino-2-cyanothiophene 16, respectively (see Scheme 2). The structures 14 and 17 were ruled out on the basis of spectral studies. The IR spectrum of 15 revealed bands at 3425, 3228, 3103 (NH and NH2), 1650 cmµ1 (CO) and no cyano group absorption band in the region 2100–2300.The IR spectrum of 16 revealed bands at 3402, 3321, 3220 (NH2 and NH), 2187 (CN) and 1630 cmµ1 *To receive any correspondence. Scheme 1 Scheme 2 Reagents: i, ClCH2CO2Et; ii, XCH2CO2R (a) R2=Ph; X=Br; (b) R2=2-C4H3S; X=Br; (c) R2=2-C4H3O; X=Br; (d) R2=Me; X=Cl; iii, ClCH2CN; iv, MeI; v, N2H4R1 CN ArNH SK + Ph NNHPh Cl N N S R1 CN Ar Ph 21 N N S R1 CN Ar Ph 22 10a,b 20 R1 CN ArNH SK R3CO NNHPh X N N S R1 CN COR3 Ar N S R1 CN N Ar O S R1 CN N N N S R1 CN COR3 R3 NPh R3 Ph NPh + 24 10a,b 23a-e 25 26 27 a R3 = Ph, X = Br b R3 = Me, X = Cl c R3 = OEt, X = Cl d R3 = NHPh, X = Cl e R3 = 2-C10H7, X = Br 23 RCOCH2Br + PhSO2Na RCOCH2SO2Ph N N R4 SO2Ph R Ph 29 28 a R4 = Ph b R4 = MeCO c R4 = PhCO d R4 = PhNHCO 29 e R4 = CO2Et f R4 = 2-C4H3OS g R4 = 2-C4H3O2 h R4 = 2-C10H7 29a-h R = 2-C10H7 1 + 20(23) N S RCO SO2Ph Ar R3 N NPh 31 N N S RCO SO2Ph Ar COR3 32 N N S RCO SO2Ph Ph COR3 33 RCO SO2Ph ArHN SK RCOCH2SO2Ph 23 + 28 ArNCS J.CHEM. RESEARCH (S), 1997 241 (C�N). Treatment of compound 10a with methyl iodide in ethanol gave the methylsulfanyl derivative 18. Structure 18 was con- firmed by the following: (a) the IR spectrum revealed bands 3350 (NH) and 2185 (CN) cmµ1; (b) the 1H NMR spectrum showed signals at d 2.14 (s, 3 H, CH3), 6.92 (s, 1 H, thiazole H-5) and 7.15–8.24 (m, 13 H, ArH’s); (c) it is converted into the aminopyrazole 19 upon refluxing with hydrazine hydrate, in ethanol.Treatment of 10a with N-phenylbenzohydrazonoyl chloride (20) gave a single product (TLC). The IR spectrum of the product showed a band at 2192 cmµ1 corresponding to a cyano group. Structure 22 was excluded on the result of the elemental analyses, spectral data and the reaction of 10b with 20, which gave the same product 21 which was obtained before (see Scheme 3). These results indicate that 21 is formed by the loss of aniline and 4-bromoaniline, respectively.The reaction of the a-oxohydrazonoyl halides 23 with 10a,b was also studied. Thus, treatment of 23a with 10a in ethanol gave only a single product 27 (TLC), the structure of which was deduced on the basis of elemental analyses and spectral data. The structure of 27a was further confirmed by the reaction of 10b with 23a which gave the same product 27 (see Scheme 4). According to the above results structures 24–26 were excluded.Similarly, 23b–e reacted with 10a or 10b to give the 2,3-dihydrothiadiazoles 27b–e, respectively. The b-oxo sulfone 28 reacted with the appropriate hydrazonoyl halide 20 or 23a–f to give the pyrazoles 29a–h, respectively (see Scheme 5). The IR spectrum of 29 revealed absorption bands at 1720–1660 cmµ1 due to CO and 1350, 1310 cmµ1 due to SO2 groups. Treatment of 28 with aryl isothiocyanates in the presence of N,N-dimethylformamide containing potassium hydroxide solution formed a non-isolable product, 30a,b, which reacted with hydrazonoyl chloride 23b to give a single product (TLC) of molecular formula C28H20N2O4S (see Scheme 6).The structure of the product was inferred from its spectral data to be 33. The structure was further confirmed by reaction of 30b with 23b under the same experimental conditions as before, which produced the same product 33b. The results indicate that 33b is formed by loss of aniline. Similarly, the reaction of 23a,c,d, with 30a or 30b gave the 2,3-dihydro- 1,3,4-thiadiazoles 33a,c,d, respectively (see Scheme 6).Especially, the IR spectra of 33 showed one absorption band due to a CO group in the region 1720–1660 cmµ1. The structures 31 and 32 were ruled out on the basis of spectral data. The foregoing results indicate that both aryl and aroyl groups have similar effects on the behaviour of hydrazonoyl halides. All new compounds were characterised by elemental analysis, IR, 1H and 13C NMR.Techniques used: IR, 1H and 13C NMR, elemental analysis, TLC References: 19 Tables 1 and 2: Characterisation and spectral data for the newly synthesised derivatives Received, 2nd January 1997; Accepted, 9th April 1997 Paper E/7/00067G References 1 M. K. Route, B. Padhi and N. K. Das, Nature, 1954, 173, 516. 2 A. Makie and A. L. Misra, J. Chem. Soc., 1954, 3919. 3 A. Mostafa, W. Asker, S. Khattab and K. Abou Elazayem, J. Am. Chem. Soc., 1960, 82, 2029. 4 Thiazole and its Derivatives, ed. J. V. Metzger, Wiley, New York, 1979, vol. 39. 5 A. O. Abdelhamid and M. A. Afifi, Sulfur Lett., 1987, 6, 125. 6 A. O. Abdelhamid and A. M. Afifi, Phosphorus Sulfur Relat. Elem., 1988, 36, 129. 7 B. E. Elanadouli, A. O. Abdelhamid and A. S. Shawali, J. Heterocycl. Chem., 1984, 21, 1087. 8 A. O. Abdelhamid and F. A. Attaby, J. Heterocycl. Ch., 1991, 28, 41. 10 J. S. Brunskill, A. De. Z. Elgabar, H. Jeffrey and D. F. Ewing, Synth. Commun., 1978, 8, 533. 11 D. L. Pavia, G. M. Lampman and G. S. Kriz Jr., in Introduction to Spectroscopy, Saunders, Philadelphia, 1979. Scheme 3 Scheme 4 Scheme 5 Scheme 6

ISSN:0308-2342    

DOI:10.1039/a700067g

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Cr y Cl O CH2OH–CH2OH + HOCH2 C H O Cr O Cl O– bpyH+ HOCH2 C H H O Cr OH O Cl O– bpyH+ HOCH2 C H H O Cr OH O Cl O– bpyH+ slow HOCH2–CHO + (OH)2CrClO– bpyH+ # 242 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 242–243 J. Chem. Research (M), 1997, 1663–1680 Kinetics and Mechanism of the Oxidation of Diols by 2,2p-Bipyridinium Chlorochromate Kavita Loonker, Pradeep K. Sharma and Kalyan K. Banerji* Department of Chemistry, J.N.V. University, Jodhpur 342 005, India The oxidation of diols by 2,2p-bipyridinium chlorochromate involves a hydride-ion transfer via a chromate ester intermediate.In continuation of earlier work2–5 on the oxidation by 2,2p-bipyridinium chlorochromate (BPCC), we report in this paper the kinetics of oxidation of some vicinal diols, nonvicinal diols and two of their monoethers by BPCC in dimethyl sulfoxide (DMSO). The mechanistic aspects are discussed. The reactions were followed under pseudo-first order conditions by keeping a large excess (Å15 or greater) of the diols over BPCC.The solvent was DMSO, unless specified otherwise. The reactions were followed by monitoring the decrease in the concentration of BPCC spectrophotometrically at 365 nm for up to 80% of the reaction. The pseudo-first-order rate constants, kobs, were evaluated from the linear (r 0.990–0.999) plots of log [BPCC] against time. The second-order rate constant, k2, was determined using the relation; k2=kobs/ [diol]. Since the reductants are monohydric and dihydric alcohols, a statistical factor of 2 was applied to the rates of oxidation of monohydric compounds, wherever a kinetic correlation of the rates of the two groups of compounds was attempted.The oxidation of the diols by BPCC resulted in the formation of the corresponding hydroxycarbonyl compounds. The overall reaction may therefore be written as eqn. (1). HOCH2—CH2OH+O2CrClOµ bpyH+ hHOCH2—CHO+H2O+OCrClOµ bpyH+ (1) BPCC undergoes a two-electron change.This is an accord with our earlier observations with both PFC6 and BPCC.2 There is no noticeable oxidation of pinacol by BPCC. The isolation of the hydroxycarbonyl compounds as the products and the resistance of the pinacol towards oxidation by BPCC indicate that the diols behave as monohydric alcohols towards BPCC. The reactions were found to be first-order with respect to BPCC and the diol. The reaction is catalysed by hydrogen ions, though the degree of catalysis is moderate. The hydrogen- ion dependence takes the form: kobs=c+d[H+].The oxidation of [1,1,2,2-2H4]ethane-1,2-diol showed the presence of a substantial primary kinetic isotope effect (kH/kD=6.35 at 303 K). This confirmed that an a-C·H bond is cleaved in the rate-determining step. The rate constants for the oxidation of the diols were obtained at different temperatures and the activation parameters were evaluated. The oxidation of diols by BPCC, in an atmosphere of nitrogen, failed to induce the polymerization of acrylonitrile.Furthermore, the addition of acrylonitrile had no effect on the rate. This indicates that a hydrogen-abstraction mechanism, giving rise to free radicals, is unlikely. The oxidation of ethane-1,2-diol was studied in nineteen different organic solvents. The kinetics were similar in all the solvents. The rate constants for the oxidation, k2, in eighteen solvents (CS2 was not considered, as the complete range of solvent parameters was not available) did not exhibit any significant correlation in terms of the linear solvation energy relationship of Kamlet et al.12 The data on the solvent effect were analysed also in terms of Swain’s equation14 of cation- and anion-solvating concept of the solvents [eqn.(5)]. log k2=aA+bB+C (5) The rates of oxidation of ethane-1,2-diol in the different solvents show an excellent correlation in Swain’s equation14 [eqn. (6)] with the cation-solvating power playing the major role.In fact, the cation solvation alone accounts for ca. 98% of the data. Here n is the number of data points and is Exner’s statistical parameter.13 log k2=0.27(�0.04)A+1.68(�0.03)Bµ5.64 (6) R2=0.9948; sd=0.03; n=19; c=0.05 The rate constants for the oxidation of the four vicinal diols showed an excellent correlation with Taft’s s* values15 with negative reaction constants. The negative polar reaction constant indicates an electron-deficient carbon centre in the transition state of the rate-determining step.The formation of a carbocationic transition state is supported by the greater role of the cation-solvating power of the solvents. Thus a mechanism involving a hydride transfer is likely for the reaction. The hydride-ion transfer may take place either by a single bimolecular step or via a chromate ester. Kwart and Nickle16 have shown that a study of the dependence of the kinetic isotope effect on temperature can be gainfully employed to resolve this problem. The data for protio- and deuterio-ethane-1,2-diols, fitted to the familiar expression kH/kD=AH/AD (exp(DEa/RT),16,17 show a direct correspondence with the properties of a symmetrical transition state in which the activation-energy difference (DEa) for kH/kD is equal to the zero-point energy difference for the respective C·H and C·D bonds (24.5 kJ molµ1) and the frequency factors and the entropies of activation of the respective reactions are nearly equal.It is thus evident that in the present studies the hydrogen transfer does not occur by an acyclic biomolecular process. The only truly symmetrical processes involving linear transfer of hydrogen are intrinsically concerted sigmatropic reactions characterized by transfer with cyclic state.19 Littler20 has also shown that a cyclic hydride transfer, in the oxidation of alcohols by CrVI, involves six electrons and, being a H�uckel-type system, is an allowed process. The mechanism shown in Scheme 1 accounts for all the observed data.*To receive any correspondence. Scheme 1J. CHEM. RESEARCH (S), 1997 243 Thanks are due to the University Grants Commission (India) for financial support. Techniques used: Spectrophotometry, correlation analysis References: 22 Equations: 8 Table 1: Analyses of products in the oxidation of diols by BPCC Table 2: Rate constants for the oxidation of ethane-1,2-diol by BPCC a 303 K Table 3: Dependence of the reaction rate on hydrogen-ion concentration Table 4: Rate constants and the activation parameters for the oxidation of diols by BPCC Table 5: Solvent effect in the oxidation of ethane-1,2-diol by BPCC at 303 K Received, 11th September 1996; Accepted, 9th April 1997 Paper E/6/06277F References cited in this synopsis 2 D.Mathur, P. K. Sharma and K. K. Banerji, Indian J. Chem., 1993, 32A, 961. 3 S. Rathore, P. K. Sharma and K. K. Banerji, J. Chem. Res. (S), 1994, 298. 4 S. Rathore, P. K. Sharma and K. K. Banerji, J. Chem. Res. (S), 1994, 446. 5 S. Rathore, P. K. Sharma and K. K. Banerji, Indian J. Chem., 1995, 34B, 702. 6 R. Khanchandani, P. K. Sharma and K. K. Banerji, J. Chem. Res., 1995, (S) 432; (M) 2622. 12 M. J. Kamlet, J. L. M. Abboud, M. H. Abraham and R. W. Taft, J. Org. Chem., 1983, 48, 2877 and references cited therein. 13 O. Exner, Collect. Czech. Chem. Commun., 1966, 31, 3222. 14 C. G. Swain, M. S. Swain, A. L. Powell and S. Alumni, J. Am. Chem. Soc., 1983, 105, 502. 15 K. B. Wiberg, Physical Organic Chemistry, Wiley, New York, 1963, p. 416. 16 H. Kwart and M. C. Latimer, J. Am. Chem. Soc., 1971, 93, 3770. 17 H. Kwart and J. H. Nickel, J. Am. Chem. Soc., 1973, 95, 3394. 19 R. W. Woodward and R. Hoffmann, Angew. Chem., Int. Ed. Engl., 1969, 8, 781. 20 J. S. Littler, Tetrahedron, 1971, 27

ISSN:0308-2342    

DOI:10.1039/a606277f

出版商:RSC    

年代:1997

数据来源: RSC