Asymmetric methylene transfer reactions II: Asymmetric synthesis of oxiranes from carbonyl compounds by methylene transfer reaction using chiral S-neomenthyl and S-exo-2-bornyl sulfoximines

Abstract

Abstract Three chiral sulfoximines, viz. , (1R,Ss)-(−)-S-methyl-S- exo -2-bornyl-N-tosyl sulfoximine, 9a , its epimer at sulfur, (1R,Rs)-(+)- 9b , and (1R,3S,4S,1′S,Rs)-(+)-S-methyl-S-neomenthyl-N-(camphor-10-sulfonyl) sulfoximine, 19 , were used as methylene transfer reagents in the preparation of nonracemic oxiranes (enantiomeric excess, 19–86%) from prochiral carbonyl compounds. Sulfoximines 9a and 9b were found to be less effective (ee, 19–68%) than the corresponding S-neomenthyl sulfoximines 2a and 2b (ee, 56–86%), and, sulfoximine 19 , despite having a chiral auxiliary on nitrogen in place of the tosyl group, was found to be only as effective as the corresponding N-tosyl sulfoximine 2b in influencing the steric course of these reactions. The absolute configuration at sulfur of all the synthesised sulfoxides and sulfoximines has been established by X-ray studies.