Conformational Variations in Vinylsulfoximines

In a series of vinylsulfoximines {S-ethenyl-S-phenyl-N-(p-tolylsulfonyl)sulfoximide [(1c); C₁₅H₁₅NO₃S₂], (E)-S-phenyl-S-(prop-1-enyl)-N-(p-tolylsulfonyl)sulfoximide [(1d); C₁₆H₁₇NO₃S₂], (E)-S-(2-cyclohexylethenyl)-S-phenyl-N-(p-tolylsulfonyl)sulfoximide [(1e); C₂₁H₂₅NO₃S₂], (E)-S-phenyl-S-(4-phenylbut-1-enyl)-N-(p-tolylsulfonyl)sulfoximide [(1f); C₂₃H₂₃NO₃S₂], (E)-S-(3-methyl-1-trimethylsilylbut-1-enyl)-N-(p-tolylsulfonyl)-S-(2-trimethylsilylphenyl)sulfoximide [(2a); C₂₄H₃₇NO₃S₂Si₂], (E)-S-(2-phenyl-1-trimethylsilylethenyl)-N-(p-tolylsulfonyl)-S-(2-trimethylsilylphenyl)sulfoximide [(2b); C₂₇H₃₅NO₃S₂Si₂], (E)-S-phenyl-N-(p-tolylsulfonyl)-S-(1-trimethylsilylprop-1-enyl)sulfoximide [(2d); C₁₉H₂₅NO₃S₂Si]} and in phenyl vinyl sulfone [(3); C₈H₈O₂S], the vinyl double bond is found to be approximately syn-coplanar with either the S=O or the S=N bond, the preference between these two being correlated in most cases with the size of the terminal vinyl substituent. Addition of trimethylsilyl groups at the α position of the vinyl group, and in the ortho position of the phenyl substituent on S, introduces further steric constraints, so that the substituted phenyl group becomes syn-coplanar with the vinyl double bond. The observed conformations may also be preferred in solution, as they are consistent with the observed diastereoselectivity of addition reactions of vinylsulfoximides.

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