InCl3/CyNH2 Cocatalyzed Carbocyclization Reaction: An Entry to α-Disubstituted exo-Methylene Cyclopentanes

An efficient and cheap synthetic approach to functionalized exo-methylene cyclopentanes has been developed from alpha-disubstituted formyl-alkynes by merging amine catalysis with the indium activation of alkynes. We uncovered the crucial role of the amine cocatalyst and the development of a new cooperative catalytic system allowed the cyclization of a broad range of substrates. A mechanistic study was realized in order to rationalize the determining influence of the amine cocatalyst.