Stereoselective Addition of α-Methylsulfenyl Benzyl Carbanions to N-Sulfinylketimines: Asymmetric Synthesis of α,α-Dibranched β-Sulfanyl Amines

(R)- and (S)-N-sulfinylketimines react with the ortho-sulfinyl benzyl carbanion derived from (S)-1 affording epimeric mixtures at the benzylic carbon of alpha,alpha-dibranched beta-sulfanyl amines. The N-sulfinyl group completely controls the configuration at the quaternary carbon bonded to the nitrogen, whereas the C-sulfinyl group is responsible for the level of asymmetric induction. High stereoselectivity can be achieved when the configuration at the sulfur atoms of the reagents are opposite (matched pair). After a two-step desulfinylation process, this reaction provides a procedure for synthesizing diastereomerically pure syn-1,2-sulfanyl amines containing a chiral quaternary carbon adjacent to nitrogen.