THEORETICAL AND EXPERIMENTAL ANALYSES OF THE DEPROTONATION OF THIIRANE S-OXIDES - THE STEREOSELECTIVE FORMATION OF TRANS-ALKYLSULFENATE ANDGEM-SILYLETHENESULFENATE ANIONS

Experimental and theoretical studies of the regioselective deprotonati on of thiirane S-oxides are reported. Experimentally under the reactio n conditions of LiHMDS/THF/-78 degrees C with anti-alkylthiirane S-oxi des or anti-silylthiirane S-oxides as starting materials, the products of ring-opening are (E)-2-alkylethenesulfenate and 1-silylethenesulfe nate anions, respectively. Experiments involving deuterium labeling cl early indicate that a regioselective deprotonation reaction was follow ed by a stereoselective ring-opening. Ab initio methods at both the Ha rtree-Fock and Moller-Plesset perturbation theory levels with the 6-31 +G(d) basis set were used to examine both lithiated methyl- and silylt hiirane S-oxides. Of the possible anti-substituted species, the coordi nation of the lithium anti to the methyl and gem to the silyl is predi cted to be the most stable. These stable intermediates with the lithiu m syn to the sulfoxide could ring-open to yield the experimentally obs erved products.