Palladium-Catalyzed Tandem Dearomative Heck Reaction of N-Propiolyl Indoles or Pyrroles with Aryl Bromides.

Abstract

An efficient Pd-catalyzed tandem dearomative Heck reaction of N-propiolylindoles or pyrroles with aryl bromides has been developed. The protocol provides access to a series of benzopyrrolizinone and pyrrolizinone derivatives bearing a quaternary stereocenter and a tetrasubstituted olefin moiety in moderate to high yields by employing Pd(PtBu3)2 as the catalyst. We propose that the reaction might proceed through a cascade sequence involving alkyne syn-arylpalladation and E-to-Z isomerization of vinyl-Pd(II) species, followed by dearomative Heck cyclization. Several synthetic transformations of the product were conducted to demonstrate its practical utility.