Enantioselective synthesis of chiral α-alkynylated thiazolidones by tandem S-addition/acetalization of alkynyl imines.

A SPINOL-derived chiral phosphoric acid catalyzed asymmetric formal [2 + 3]-annulation of in situ generated alkynyl imines and 1,4-dithiane-2,5-diol has been developed to afford enantiopure α-alkynylated thiazolidones with up to 72% yield and 98.5 : 1.5 er. This tandem annulation involved a tandem S-addition of alkynyl imines/intramolecular acetalization, followed by PDC-mediated oxidation. The α-alkynylated thiazolidones could facilely afford the corresponding chiral α-alkynylated or α-alkenylated cyclic sulfoxides via further elaboration.