摘要:

Treatment of 1-methyl-2-nitroimidazole with bromine in water resulted in rapid dibromination to give 4,5-dibromo-1-methyl-2-nitroimidazole. In dioxane, the bromination was slower, and could be controlled to give 4-bromo-1-methyl-2-nitroimidazole5and 5-bromo-1-methyl-2-nitroimidazole6in a 4:1 ratio. In an attempt to displace the bromine, the monobromo compounds were treated with cysteamine hydrochloride. In each case the nitro group was displaced instead, the 4-bromo5resulting in 2-[(2-aminoethyl)thio]-4-bromo-1-methylimidazole9as sole product, and the 5-bromo6giving two products identified as the monosubstituted 2-[(2-aminoethyl)thio]-5-bromo-1-methylimidazole13and the disubstituted 2,5-bis[2-(aminoethyl)thio]-1-methylimidazole12. The latter product forms by further reaction of the former and was the sole material observed at long reaction times. A fraction of12may also originate from an initial displacement of bromine giving 5-[(2-aminoethyl)thio]-1-methyl-2-nitroimidazole14, although this cannot be observed due to a rapid further displacement of its nitro group. The bromonitroimidazoles5and6were reduced to 4-bromo-2-amino-1-methylimidazole25and 5-bromo-2-amino-1-methylimidazole26with Zn/HCl. On reflux in water, in the presence or absence of cysteamine hydrochloride, these undergo a protodebromination resulting in the same product, 2-amino-1-methylimidazole17. In D2O the 4-bromo isomer was demonstrated to react specifically to give 2-amino-4-deuterio-1-methylimidazole27. Attempted preparation of the bromoaminoimidazoles25and26by bromination of 2-amino-1-methylimidazole in water resulted in the clean formation ofcisandtrans2-amino-4,5-dihydro-4,5-di-hydroxyimidazolium ions18.

ISSN:0008-4042    

DOI:10.1139/v93-063

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

FeCl2or FeCl3react with cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) in an acidic medium (4 M HCl) to afford dark orange-red plates of [H4(cyclam)][FeCl5(OH2)](Cl)2(1).1crystallizes in a polar space group (orthorhombic,Pc21b) witha = 10.7730(6),b = 13.3418(10),c = 14.4564(10) Å,V = 2077.84(24) Å3, andDcalc = 1.68 g cm−3forZ = 4. Final values ofR = 0.031 andRw = 0.034 were obtained for 1950 independent observed (I > 3σ(I)) reflections. Cyclam reacts with neat trifluoroacetic acid to afford a colourless salt, [H4(cyclam)][CF3COO]4(2).2crystallizes in a centric space group (monoclinic,P21/c), witha = 8.7442(11),b = 10.5121(11),c = 15.2469(20) Å, β = 102.526(15)°,V = 1368.1(3) Å3, andDcalc = 1.593 g cm−3forZ = 2. Final values ofR = 0.059 andRw = 0.067 were obtained for 1336 independent observed (I > 3σ(I)) reflections. Extensive interionic hydrogen bonding between the cyclam cations, which adopt exodentate conformations, and anions results in network polymeric hydrogen bonding (1-D for1, 2-D for2). The networking in1is intrinsically polar because one chloride anion and the [FeCl5(OH2)]2−complex anion are involved in networking between the H4(cyclam)4+cations. The implications of the crystal structures are discussed from the perspective of rational design of polar solids.

ISSN:0008-4042    

DOI:10.1139/v93-064

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The various preparative procedures described in the literature for ReOCl3(PPh3)2were repeated. The standard methods were found to yield a yellow triclinic material (a = 11.793,b = 14.300,c = 16.422 Å, α = 64.04°, β = 84.31°, γ = 87.32°,R = 0.064). The unit cell contains three discrete monomeric molecules with thetrans-bis(phosphine) configuration, one of which has its Cl-Re=O unit disordered over two opposite directions. Recrystallization in CH2Cl2yielded crystals of the bright green monoclinic polymorph (C2/c,a = 24.347,b = 9.604,c = 15.666 Å, β = 116.77°,R = 0.025) containing the same monomeric molecule, but with a different conformation of the PPh3ligands and a different packing pattern. These two polymorphs actually correspond to "isomers" 1 and 2 described by Johnson, Lock, and Wilkinson in 1964. Attempts to prepare their third "isomer" yielded powders containing ReOCl3(PPh3)2(green polymorph) and ReNCl2(PPh3)2. The IR and31P NMR spectra of these samples are discussed.

ISSN:0008-4042    

DOI:10.1139/v93-065

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Dicyanobenzene-1,4 (1) and -1,2 are known to undergo substitution upon irradiation, in the presence of an olefin, in acetonitrile–methanol (3:1) solution. The products are 1:1:1 (methanol:olefin:aromatic) adducts, substituted on the aromatic ring with loss of a cyano group. This reaction, referred to as the photo-NOCAS (nucleophile–olefin combination, aromatic substitution) reaction, has been shown to be fairly general with regard to the olefin and the nucleophile that can be incorporated. Less is known about the scope of the reaction incorporating other electron-withdrawing substituted aromatic molecules. The purpose of this study was to determine if methyl 4-cyanobenzoate (10) would also take part in this reaction, to form 4-substituted aromatic esters. Irradiation of acetonitrile–methanol solutions of10and olefins 2,3-dimethyl-2-butene (2) and 1-methylcyclohexene (5) gave cyclic imine esters,11and13, respectively, instead of photo-NOCAS products. The photo-NOCAS products were obtained when the codonor biphenyl (4) was added to the irradiation mixture. Formation of the cyclic imine ester is attributed to excitation of the charge-transfer complex formed between10and the olefin. The addition of biphenyl (4) serves to generate the contact radical ion pair (CRIP) upon irradiation of the charge-transfer complex between10and4. This CRIP can dissociate to the solvent-separated radical ions, the radical cation of4can accept an electron from the olefin, and the olefin radical cation can go on to give the photo-NOCAS products. Irradiation of a solution of10and2in nonpolar solvent (benzene) gave the oxetane, believed to arise from the exciplex. In addition to photo-NOCAS products from10, 4-cyanophenylketones17and23are also formed by attack of the β-alkoxyalkyl radical at the carboxyl carbonyl. The differences in behaviour between 1,4-dicyanobenzene (1) and methyl 4-cyanobenzoate (10) under these reaction conditions are described and explained.

ISSN:0008-4042    

DOI:10.1139/v93-066

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Second-order rate constants for the demethylation of methyl di(3-nitrophenyl)phosphinate by iodide in acetone-d6at 25 °C have been measured. For a series of iodide salts the rate increased in the order: NBu4I < KI ≤ NaI < LiI. The addition of crown ethers or D2O has a retarding effect on the reaction rate. The results are discussed in terms of the increase of the nucleofugality of the phosphinate group via the complexation of metal ions with the phosphoryl function.

ISSN:0008-4042    

DOI:10.1139/v93-067

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

New preparative routes to the title compounds are reported in which the yields are substantially improved over previous methods. In one method, reaction of O2with a mixture of XC6H4CN2S2+Cl−and Ph3Sb leads to the products in 40–60% yield. In another, the reaction of the same salts with silylated amidines XC6H4C{NSiMe3}N(SiMe3)2in a 1:1 mol ratio leads to the same compounds in 18–65% yield. The syntheses of 3,7-(XC6H4)2{CN2S2N2C}, X = H, 4-CH3, 4-CH3O, 4-Cl, 4-CF3, and 3-CF3, are reported. Mixed derivatives were also prepared, but not isolated as pure compounds. The crystal structure of the 4-CF3compound has been determined by X-ray diffraction; triclinic,withZ = 1; cell dimensions:a = 6.835(2),b = 9.936(3),c = 6.320(2) Å, α = 96.44(3)°, β = 102.88(3)°, γ = 88.42(3)°.R = 3.4%,Rw = 3.5% for 1100 data. The eight-membered ring is flat with equivalent bond lengths between any two types of atoms, indicative of a delocalized electron distribution. The 10π central aromatic rings have been oxidized and reduced in CH2Cl2using voltammetric methods. The reversible one-electron reduction step gives stable 11π species. The resistance to oxidation of the title compounds is contrasted to the ease of oxidizing 3,7-[(CH3)2N]2{CN2S2N2C}, in accordance with earlier chemical studies.

ISSN:0008-4042    

DOI:10.1139/v93-068

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The secondary metabolites produced by the fungusStachybotryscylindrospora, which is known to be strongly antagonistic to the blue-stain fungusCeratocystiopsiscrassivaginata, have been examined. The compounds responsible for the antifungal activity are trichodermin (5) and trichodermol (6), two previously known mycotoxins belonging to the trichothecene family. The other metabolites, stachybotrydial (1), stachybotramide (8), and 6,8-dihydroxy-3,5,7-trimethylisochroman (7), although not active againstC.crassivaginata, are new natural products. The structures of the new compounds were established by spectroscopic techniques.

ISSN:0008-4042    

DOI:10.1139/v93-069

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A new approach to 1-(p-dimethylaminophenyl)-2-hydroxycyclobutene-3,4-dione (4), a precursor for the synthesis of symmetrical and unsymmetrical photoconductive squaraines, is described.Insitugeneration ofp-nitrophenyl ketene, by the reaction ofp-nitrophenylacetyl chloride and triethylamine in the presence of tetraethoxyethylene in anhydrous ether, results in a (2 + 2) cycloaddition between the ketene and the electron-rich olefin. The cycloadduct generated,6, was hydrolyzed to give 1-(p-nitrophenyl)-2-hydroxycyclobutene-3,4-dione (5) in 51% yield. Reductive alkylation of5by hydrogen in the presence of formaldehyde in DMF at 50–60 °C affords4in 81% yield. The overall yield of4is 41% from tetraethoxyethylene and is significantly better than other preparative procedures of4based on a partial Friedel–Crafts reaction or an arylation reaction of a squaric acid derivative with an aniline, where yields ranging from 8.5% to 24% were reported. Condensations of4with2equivalents ofN,N-dimethylaniline and its derivatives in refluxing 2-propanol in the presence of 6 equivalents of tributyl orthoformate yield symmetrical squaraine1aand unsymmetrical squaraines1b–1e. The synthesis is accomplished by a (2 + 2) cycloaddition – reductive alkylation – condensation reaction sequence and represents a new, cost-effective synthesis for photoconductive squaraines where the expensive squaric acid reactant is bypassed. The spectroscopic and the solid state properties of1a–1ehave been studied. Results show that the properties exhibited by1a–1eare essentially identical to those exhibited by other photoconductive, symmetrical squaraines that are synthesized by other known processes. From the resemblance in solid state properties,1a–1eare expected to be photoconductive. This has indeed been observed in preliminary experiments.

ISSN:0008-4042    

DOI:10.1139/v93-070

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

In view of the important biological functions of oxidized glutathione (GSSG), we investigated the correlation between dynamic and conformational properties and biological activity. Anisotropic molecular motion characterizes different GSSG molecular districts. This information, obtained by NMR carbon relaxation investigations, suggests that the peptide does not independently assume any stable structure in solution. Analysis of the effects of the addition of a stable spin label to the solution confirmed the absence of conformation of GSSG in D2O. Moreover, the paramagnetic effects observed on proton and carbon nuclei of oxidized glutathione suggest that the dipolar term is the main source of paramagnetic relaxation.

ISSN:0008-4042    

DOI:10.1139/v93-071

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The mechanism of the reaction CH(X2π) + CH4has been investigated byabinitiomolecular orbital calculations. Addition, insertion, and abstraction–addition reaction paths have been examined by, in total, five methods of approach. The addition reaction path has a rather high energy barrier. Our calculations have implied that the assumed insertion reaction path does not seem to exist for the reaction CH + CH4, and a two-step mechanism (abstraction–addition reaction path) was then proposed. For the abstraction–addition reaction, the reactants, transition state, intermediates, and products were optimized at the HF/3-21G and HF/6-31G* levels, and vibrational frequencies were calculated at the HF/3-21G level. Electronic correlation energy was estimated by means of the Møller–Plesset perturbation theory and configuration interaction method. The excited-state abstraction reaction was also studied in some detail.

ISSN:0008-4042    

DOI:10.1139/v93-072

出版商:NRC Research Press    

年代:1993

数据来源: NRC