Palladium-catalyzed hydroamination of vinylidenecyclopropane-diester with pyrroles and indoles: an approach to azaaromatic vinylcyclopropanes.

A new method for the synthesis of azaaromatic vinylcyclopropanes (VCPs) has been disclosed in this paper by using pyrrole or indole derivatives as nucleophilic reagents to react with vinylidenecyclopropane-diesters (VDCP-diesters) in the presence of a Pd catalyst, a phosphine ligand and a base under mild conditions in up to 98% yield with a reasonable substrate scope. This reaction is one of the few examples of hydroamination at electron-rich allene's β-position. A plausible reaction mechanism has also been proposed through a zwitterionic π-propargyl -palladium species according to the previous work and the obtained deuterium labeling experimental result.