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 the 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 the further elaboration.