Zinc- and Indium-Promoted Conjugate Addition−Cyclization Reactions of Ethenetricarboxylates with Propargylamines and Alcohol:  Novel Methylenepyrrolidine and Methylenetetrahydrofuran Syntheses

A new zinc- and indium-promoted conjugate addition−cyclization reaction to afford nitrogen- and oxygen-containing five-membered heterocycles has been developed. Reaction of ethenetricarboxylates with propargylamines (1 equiv) in the presence of ZnBr₂ or InBr₃ afforded methylenepyrrolidines in high yields. The stoichiometric use of ZnBr₂ or InBr₃ at room temperature and the catalytic use of InBr₃−Et₃N at 80 °C were effective. Reaction of ethenetricarboxylates with propargyl alcohol in the presence of ZnBr₂ or InBr₃ afforded methylenetetrahydrofurans.