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 lnBr(3)(-) Et3N at 80 degrees C were effective. Reaction of ethenetricarboxylates with propargyl alcohol in the presence of ZnBr2, or InBr3 afforded methylenetetrahydrofurans.