STUDIES IN ORGANOSULFUR CHEMISTRY. I. NUCLEAR MAGNETIC RESONANCE (PROTON, CARBON-13, OXYGEN-17 (1) J(C-H)) INVESTIGATIONS OF ORGANOSULFUR COMPOUNDS. II. MECHANISTIC STUDY OF PHASE TRANSFER CATALYZED REACTIONS OF DICHLOROCARBENE WITH SULFIDES AND SULFOXIDES. III. STUDIES DIRECTED TOWARD ASYMMETRIC SYNTHESIS USING CHIRAL PHASE TRANSFER CATALYSTS.

摘要

In Chapter I, an extensive study of the ('13)C and ('17)O nuclear magnetic resonance (NMR) chemical shifts and ('13)C-H coupling constants of unsaturated acyclic and saturated cyclic sulfides, sulfoxides, sulfones, and methyl sulfonium salts is reported. The ('13)C NMR substituent effects on doubly bonded carbon atoms which are separated from the sulfur moiety by n methylene groups (where n = 0, 1, 2, or 3) are caused primarily by large electric field effects originating on the sulfur atom. These field effects polarize the electron density of the double bond from the terminal carbon atom towards its neighbor. For those examples where n = 0 or 1, further evidence for conjugation and homoconjugation, respectively, was obtained. ('13)C-H coupling constants were measured in order to assess the extent of rehybridization of the carbon-hydrogen bonds due to these influences. The unusual (beta) effects in both saturated and unsaturated sulfur compounds may be explained qualitatively on the basis of electric field contributions to the chemical shift differences. Thietane 1-oxide and thietane 1,1-dioxide have unusually large (beta) and (gamma) substituent effects which appear to be due to a combination of bond angle deformations and hyperconjugative effects. Sulfoxides and sulfones having bulky alkyl substituents also have unusual ('13)C NMR substituent effects which also appear to reflect the influences of bond angle changes which relieve steric interactions.;We also report the ('13)C-H coupling constants for several cyclic sulfoxides and sulfones. The values for the former increase substantially when the sulfinyl S=O bond is in an axial orientation. This may result from a hyperconjugative interaction between the lone pair of electrons and the C(,(beta))-C(,(gamma)) bond.;Chapter II details the results of a mechanistic study of the deoxygenation of sulfoxides with dichlorocarbene generated by phase transfer catalysis. The reaction proceeds through a 1,3-zwitterionic intermediate and affords the corresponding sulfides in good yields. Under similar conditions, dichlorocarbene adds to sulfides to give sulfonium bis(chloro)methylides which are attacked by hydroxide anion to give sulfoxides in low yields. Treatment of (alpha), (alpha)-dichloromethyl-dimethyl sulfonium tetrafluoroborate with aqueous base gave a 63:37 ratio of dimethyl sulfide and dimethyl sulfoxide/dichloromethane. The data are suggestive of an equilibrium between the sulfonium ylide and the free sulfide and carbene where K(,eg) is large. Oxidation of trans-thiadecalin by this method afforded a 94:6 ration of the axial:equatorial sulfoxides in 20% overall yield.;In Chapter III, the attempted enantioselective oxidations of prochiral sulfides using chiral phase transfer catalysts are described. The oxidations using metaperiodate afforded moderate yields of racemic sulfoxides; a reduction of acetophenone with borohydride gave a good yield of 1-phenylethanol but only 1.2% ee when a chiral catalyst was used.;The ('17)O NMR chemical shifts for numerous alkyl, aryl, cyclic, and acyclic sulfoxides and sulfones are reported. A (gamma)-upfield substituent effect similar to the one often encountered in ('13)C NMR is noted. Large downfield shifts occur in divinyl and diallyl sulfoxides (relative to their saturated analogues) but not for the sulfones. This may arise from the effects of orbital mixing between the sulfur 3d and the carbon 2p orbitals on the average electronic excitation energies of the lone pair of electrons on sulfinyl sulfur.