Palladium-catalyzed heteroannulation of 1,3-dienes to form alpha-alkylidene-gamma-butyrolactones

alpha-Alkylidene-gamma-butyrolactones are readily prepared by the palladium -catalyzed heteroannulation of a variety of 1,3-dienes by alpha-iodo and al pha-bromo acrylic acids. The best results are obtained by employing a catal ytic amount of the sterically hindered chelating alkyl phosphine D-t-BPF [( di-tert-butylphosphino)ferrocene]. In most cases, this process is highly re gioselective. The reaction is believed to proceed via (1) oxidative additio n of the vinylic halide to Pd(0), (2) organopalladium addition to the less hindered end of the 1,3-diene to form a pi-allylpalladium intermediate, and (3) nucleophilic displacement of the palladium by the carboxylate ion.