Palladium catalyzed carboannulation of nitrostyrenes with internal alkynes: a new synthetic strategy for cross coupling/C–H annulation and facile access to indenones

Abstract

Palladium(II) catalyzed carboannulation reaction of internal alkynes with nitrostyrenes to afford 2,3-disubstituted indenones is reported. The annulation reaction proceeds through transmetalation of Pd(II) with aldehydes generated from the nitrostyrene (C–H activation) and insertion of the alkynes, followed by cyclization via intramolecular nucleophilic addition of intermediate organopalladium(II) species. This reaction proceeded in moderate to good yields and with high regioselectivity. Electron-rich nitrostyrenes were transformed to the corresponding aldehydes in high yields without addition of any peroxide reagent.