Palladium-Catalyzed Regioselective 5-exo-O-Cyclization/Oxidative Heck Cascades from o-Alkynylbenzamides and Electron-Deficient Alkenes

A Pd-catalyzed 5-exo-selective oxycyclization/oxidative Heck coupling cascade is described, starting from readily available ortho-alkynylbenzamides and functionalized olefins. The key to a high regioselectivity in the cyclization step is the choice of catalyst and/or additives. Thus, Pd(OAc)(2) provides the desired 5-exo products predominantly, whereas with PdCl2 or Pd(TFA)(2), the corresponding 6-endo products prevail. The subsequent oxidative Heck-type coupling takes place stereoselectively with the very predominant formation of E isomers, leading to an effective preparation of structurally diverse carbonyl-substituted allylideneisobenzofuranimines.