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.