摘要:

The title spirocyclic ketones, possessing possible substitution patterns 1,4-dithiaspiro[4.5]decan-6-one (1a), -7-one (3a), and -8-one (5a), and 1,5-dithiaspiro[5.5]undecan-7-one (2a), -8-one (4a), and -9-one (6a), have been reduced with new strains of yeast (Saccharomycescerevisiae, JCM 1819 and JCM 2214). Reductions of the prochiral ketones1a–4aoccur with high enantiofacial selectivity on the preparative scale (up to 99% ee). The product alcohols (1,4-dithiaspiro[4.5]decan-6-ol (1b) and -7-ol (3b) and 1,5-dithiaspiro[5.5]undecan-7-ol (2b) and -8-ol (4b)) have theSconfiguration, as confirmed by 2D COSY experiments of the (S)-MTPA esters of1b–4busing the configuration correlation model of Mosher.Keywords: microbial reduction,Saccharomycescerevisiae, dithiaspiro ketones, substrate- and stereoselectivity, H,H-COSY spectra.

ISSN:0008-4042    

DOI:10.1139/v90-080

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The proton and13C NMR of azulene and dialkylaminohydroxyphenyl squaraines have been investigated. The four-membered ring carbon resonances occur in the 180–190 ppm range and are attributed to the cyclobutenediylium character of this structure. Some charge delocalization from the central ring to the pendent aromatic substituents was also observed, indicative of a substituent effect of the squaraine moiety on aminoaromatic systems equivalent to that of a formyl or acetyl group. Hydroxy squaraines10and11show the presence of two isomeric squaraine species in the proton NMR in deuterochloroform. Saturation transfer experiments confirm that these species are readily interconverted, andcis/transisomerismis consistent with these observations. The free energy difference between the two isomers at 318 K is calculated to be 3.0 and 3.2 kJ/mol for hydroxysquaraines10and11respectively.Keywords: squaraines, saturation transfer, NMR.

ISSN:0008-4042    

DOI:10.1139/v90-081

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The pH-dependences of the apparent second-order rate constantsfor the reduction of 2,4,6-cycloheptatrien-1-ol and 9-xanthydrol by each of 1-benzyl-1,4-dihydronicotinamide (BNH) and 10-methyl-9,10-dihydroacridine (MAH) have been measured in 20% acetonitrile – 80% water, at 25 °C and ionic strength 1.0. For each of these reactions, the pH-dependence ofis only consistent with reduction occurring via the aromatic cation (either tropylium or xanthylium) that is present in equilibrium with these alcoholic species. The relative second-order rate constantsfor reductions by these two reducing agents (1700 for tropylium and 770 for xanthylium) are similar for these two cations. These ratios are also similar to those observed for a variety of nitrogen heteroaromatic hydride acceptors, even though the absolute magnitudes of these rate constants vary by 1010-fold. The second-order rate constants for the reductions of the tropylium and xanthylium cations are predicted reasonably well by theirvalues, with the latter cation being (7 × 105)-fold more reactive than its π-isoelectronicN-methyl acridinium cation. The xanthylium cation has the greatestratio yet observed for any heteroaromatic cation, and this value further extends the known range of this ratio as a function of reactivity.Keywords: hydride transfer, kinetics of reduction, 1,4-dihydropyridine derivatives, tropylium cation, xanthylium cation.

ISSN:0008-4042    

DOI:10.1139/v90-082

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Dynamic NMR methods are used to study 3-substituted benzocycloheptene derivatives, useful models for investigating the conformational effect of the stereoelectronic π–σ* orbital interaction. The 11 compounds studied are divided in two subgroups, the first one containing mainly halogenated derivatives (F, Cl, Br, and OCH3) and the second consisting of oxy derivatives (OCH3, OCH2CH3, OCH=CH2, OAc,p-OPh-R, where R = H, OCH3, and NO2). The results for the first series show the presence of two chair conformations (CaandCe) characterized by a decreasingCapopulation with increasing electronegativity of the substituent. This trend suggests the presence of a dominant π–σ* interaction for Cl and Br stabilizing theCaform. The largerCepopulation observed for F suggests that a strong attractive interaction with the aromaticperihydrogen is present in this compound. Finally, in the oxy-substituent series, the populations trend does not correspond to that predicted from the π–σ* orbital interaction, but the individual population perturbations appear to be caused primarily by electrostatic interactions involving the nonsymmetrical polar substituents.Keywords: low temperature NMR, conformational analysis, seven-membered rings, orbital interactions, benzocycloheptene derivatives.

ISSN:0008-4042    

DOI:10.1139/v90-083

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

On the basis of data found in the literature, it is shown that a correlation exists between the molar extinction coefficient at the maximum optical absorption of the solvated electron (ϵmax), its width at half height (W1/2), and the energy corresponding to that maximum (EAmax)Keywords: solvated electrons, polar solvants, optical absorption spectra. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v90-084

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The new bis(dithiolate) complexes Mo(1,2-S2-4-R-C6H3)2(PMePh2)2, R = H, Me, are readily synthesized from three different types of starting materials:trans-Mo(N2)2(PMePh2)4, MoCl4(PMePh2)2, and MoOCl2(PMePh2)3. The31P NMR spectra of the dithiolate complexes at low temperature are consistent with acisstereochemistry of the PMePh2ligands and isomerism with respect to inversion at sulfur and relative positioning of the methyl groups on the chelating 1,2-S2-4-Me-C6H3ligands. The singlet in the31P NMR spectrum at room temperature arises from rapid interconversion of these isomers. Substitution of one or two of the PMePh2ligands in the dithiolate complexes proceeds under mild conditions to give the complexes Mo(S2C6H4)2(CO)(PMePh2), Mo(S2C6H4)2(CN-t-Bu)(PMePh2), Mo(S2C6H3Me)2(dppe), Mo(S2C6H4)2(depe), Mo(S2C6H4)2(PMePh2)(PMe3), Mo(S2C6H4)2(PMePh2)(P(OMe)3), and Mo(S2C6H4)2(P(OMe)3)2. The31P and13C NMR spectroscopy of these bis(dithiolate) complexes suggest that they have monodentate ligandscisdisposed.A reversible equilibrium exists between Mo(S2C6H4)2(PMePh2)2and Mo(S2C6H4)2(CO)(PMePh2) in the presence of carbon monoxide in solution. Isolation of Mo(S2C6H4)2(CO)(PMePh2) is facilitated by use of CH3I as a "phosphine sponge" reagent. If the sulfur ligands are viewed as dianions, then this is the first thermally stable carbonyl complex of molybdenum(IV).Keywords: molybdenum, dithiolate, diphenylmethylphosphine, carbonyl, NMR.

ISSN:0008-4042    

DOI:10.1139/v90-085

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Reactions of Ti(III) and Ti(IV) thiolates with Rh complexes have been investigated. In the reaction of Cp2Ti(SMe)2and [(COD)2Rh]BF4or [(COD)Rh(sol)2]PF6, thiolate abstraction yields ((COD)Rh(μ-SMe))2,1. Reaction of (Cp2Ti(μ-SMe))2with ((COD)Rh(μ-Cl))2results in ligand exchange affording (Cp2Ti(μ-Cl))2and1. The complex1crystallizes in the monoclinic space groupP21/n, witha = 8.551(2) Å,b = 10.058(3) Å,c = 22.187(4) Å, β = 92.54(1)°,Z = 4, andV = 1906(1) Å3. The structural data show a relatively short approach between the Rh centres (2.948 Å) and between the bridging sulfur atoms (2.888 Å). The implications of these structural features in terms of metal–metal and sulphur–sulfur bonding are discussed. In addition, the implications of these results with respect to the formation of thiolato-bridged, early–late heterobimetallics is considered.Keywords: thiolate abstraction, rhodium thiolate bridged dimer.

ISSN:0008-4042    

DOI:10.1139/v90-086

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Ion/molecule reactions of protonated alkylamine ion species, RNH3+, were studied in mixtures of methylamine with ethylamine, propylamine, or butylamine by ICR mass spectrometry at 10−5Torr. The occurrence of methyl group transfer from methylamine to higher protonated alkylamine ion species was observed. The rate constants of some bimolecular reactions occurring in these systems were estimated by numerical simulation.Keywords: ion/molecule reactions, methylamine, ethylamine, propylamine, butylamine, ICR mass spectrometry.

ISSN:0008-4042    

DOI:10.1139/v90-087

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Five 1-alkyl-3-methylindazoles were prepared by treatment of 1-(2-bromophenyl)-1-methoxy-1-(2-alkylazo)ethanes with tri-n-butyl stannane and AIBN at 80 °C in benzene. Yields in the radical cyclization step ranged from 39 to 92%. 1-Phenyl-3-methylindazole was prepared by an analogous route but in very poor yield (<5%). Rate constants for the 5-endoradical closures, estimated by the radical clock method, were 5.2 × 109 s−1and 9.2 × 108 s−1for two of the alkyl systems. Rate constants for analogous 5-endocyclizations of aryl radicals onto C—C double bonds are much smaller than those for cyclizations to the azo functional group.Keywords: cyclization, radical; azo group, radical closure to; indazoles, radical synthesis of.

ISSN:0008-4042    

DOI:10.1139/v90-088

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The twofold barrier to rotation about thebond in benzyl fluoride is deduced from the long-range1H,1H;1H,19F; and13C,19F nuclear spin–spin coupling constants in solution. The barrier changes from 3.2(2) kJ/mol in the polar solvent, acetonitrile-d3, to 0.7(2) kJ/mol in the nonpolar environment provided by cyclohexane-d12. In all solutions the conformer of greatest stability has the C—F bond in a plane perpendicular to that of the phenyl group. Extrapolation of the barrier to the vapor phase, using a simple reaction field model, indicates that the most stable conformer for the free (unclustered) molecule is now that with the C—F bond in the phenyl plane and that the barrier to internal rotation is 1.1(7) kJ/mol. Molecular orbital calculations with the basis sets STO-3G, 4-21G, 4-31G, 6-31G, and 6-31G* all predict the latter conformer as that of lowest energy. However, they disagree significantly among themselves as to the height of the internal barrier. The complete geometries are given for both conformers, as computed with the 6-31G basis, and the side-chain geometries are tabulated for the planar and perpendicular conformers, as given by all the bases.Keywords: benzyl fluoride, internal rotational potential;13C,19F spin–spin coupling constants in benzyl fluoride; benzyl fluoride, molecular orbital computations.

ISSN:0008-4042    

DOI:10.1139/v90-089

出版商:NRC Research Press    

年代:1990

数据来源: NRC