Reformatsky Reaction to Alkynyl N-tert-Butanesulfinyl Imines: Lewis Acid Controlled Stereodivergent Synthesis of β-Alkynyl-β-Amino Acids

A highly diastereoselective Refortmatsky reaction to N-tert-butanesulfinyl propargylaldimines and ketimines is presented. The reaction proceeded with excellent yields and diastereoselectivities provided by the sulfinyl group in the presence of Me3Al. The use of TBSOTf as a Lewis acid promoter switched the sense of the stereoinduction. Thus, this methodology allowed the stereodivergent asymmetric synthesis of β-alkynyl β-amino acid derivatives, from the same sulfinyl configuration, by simply changing the Lewis acid promoter.