Limitations, mechanism and understanding of the origins of stereocontrol in (S)-dimethylsulfonium-(p-tolylsulfinyl)methylide-mediated epoxidation reactions

The reaction of the (S)-dimethylsulfonium-(p-tolylsulfinyl)methylide with aldehydes gave α,β-epoxy sulfoxides with high enantioselectivity and diastereoselectivity dependent on the aldehyde. The mechanism of the ‘model’ reactions [ylide substituted with Me S(O) or Ph S(O) with MeCHO or PhCHO] has been studied in detail using density functional theory.

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(2S,3S,SS)-(p-Bromophenyl-2-(p-tolylsulfinyl)-oxiraneC15H13BrO2SEe >98%[α]D = +52.1 (c 0.6, acetone)Source of chirality: (−) – (1R, 2S, 5R)-mentholAbsolute configuration: (2S,3S,SS)

(2S,3S,SS)-3-o-Chlorophenyl-2-(p-tolylsulfinyl)-oxiraneC15H13ClO2SEe >98%[α]D = +38.9 (c 0.75, acetone)Source of chirality: (−) – (1R, 2S, 5R)-mentholAbsolute configuration: (2S,3S,SS)

(2S,3S,SS)-3-(m-Nitrophenyl2-(p-tolylsulfinyl)-oxiraneC15H13NO4SEe >98%[α]D = +55.4 (c 0.6, acetone)Source of chirality: (−) – (1R, 2S, 5R)-mentholAbsolute configuration: (2S,3S,SS)

(2S,3R,SS)-3-α-Naphthyl-2-(p-tolylsulfinyl)-oxiraneC19H16O2SEe >98%[α]D = −211.2 (c 0.4, acetone)Source of chirality: (−) – (1R, 2S, 5R)-mentholAbsolute configuration: (2S,3R,SS)

(2S,3S,SS)-3-Pentyl-2-(p-tolylsulfinyl)-oxiraneC14H20O2SEe >98%[α]D = +52.1 (c 0.6, acetone)Source of chirality: (−) – (1R, 2S, 5R)-mentholAbsolute configuration: (2S,3S,SS)