Asymmetric Synthesis of Oxazolidines, Thiazolidines, and Pyrrolidines

Significance

An efficient methodology for the asymmetric synthesis of oxazolidines, thiazolidines, pyrrolidines and octahydroindoles by a DPPP-catalyzed reaction of β -amino alcohols, β -amino thiols or γ-amino malonates with terminal acetylenes is reported. Of the phosphine catalysts tested (DPPP, DPPM, DPPE, DPPB, Ph₃P, Ph₂PEt, Me₃P), DPPP demonstrated the highest activity. A mechanism is proposed which proceeds with a double Michael addition to an electron-deficient acetylene to afford intermediate A which, upon intramolecular S_N2 cyclization, leads to the final product. The scope of the reaction was inadequately explored.