Stereoselective Electrophilic α-Alkynylation of α,α-Disubstituted N - tert -Butanesulfinyl Ketimines for Construction of Less Accessible Acyclic Quaternary Stereocenters.

In order to construct less accessible acyclic quaternary stereocenters, a protocol was developed to α-alkynylate α,α-disubstituted N - tert -butanesulfinyl ketimines stereoselectively using 1-(2-trimethylsilylethynyl)-1,2-benziodoxol-3(1 H )-one in the presence of fluoride. Despite the steric and electrical similarity between the two α-substituents, the entire reaction proceeded in a strongly stereoselective manner: t BuOK promoted α-deprotonation of the acyclic ketimine to generate stereodefined fully substituted aza-enolates, which stereoselectively formed C-C bonds with electrophilic alkynylation reagents, affording α-alkynylation products with excellent stereocontrol.