Additions of Enantiopure α-Sulfinyl Carbanions to (S)-N-Sulfinimines: Asymmetric Synthesis of β-Amino Sulfoxides and β-Αmino Alcohols

The addition of the lithium anions derived from (R)- and (S)-methyl and -ethyl p-tolyl sulfoxides to (S)-N-benzylidene-p-toluenesulfinamide provides an easy access route to enantiomerically pure β-(N-sulfinyl)amino sulfoxides. Stereoselectivity can be achieved when the configurations at the sulfur atoms of the two reagents are opposite (matched pair), thus resulting in only one diastereoisomer, even for the case in which two new chiral centers are created. The N-sulfinyl group primarily controls the configuration of the carbon bonded to the nitrogen, whereas the configuration of the α-sulfinyl carbanion seems to be responsible for the level of asymmetric induction, as well as for the configuration of the new stereogenic C−SO carbon in the reactions with ethyl p-tolyl sulfoxides. An efficient method for transforming the obtained β-(N-sulfinyl)amino sulfoxides into optically pure β-amino alcohols, based on the stereoselective non-oxidative Pummerer reaction, is also reported.