Synthesis of highly polysubstituted cyclopentadienes through an oxypalladation initiated domino Heck reaction of internal alkynes

Abstract

We describe a facile approach to prepare a variety of densely polysubstituted cyclopentadiene derivatives in good yields (52%–75%) through a palladium(II)-catalyzed oxypalladation initiated domino Heck reaction of internal alkynes with diverse carboxylic acids and phthalimide in the presence of glycine as the ligand. Control experiments revealed that the free NH₂ and COOH groups of glycine played an important role in accelerating the reaction. The reaction showed a broad substrate scope for carboxylic acids and was easily performed on a gram scale. The present method features high regioselectivity toward internal alkynes, enables the formation of four C–O/C–C bonds in a one-pot reaction, and is the first example of accessing cyclopentadiene scaffolds via an oxypalladation reaction.