Palladium-catalyzed cross-coupling reaction of anilinium hypophosphite with alkenyl bromides and triflates: application to the synthesis of GABA analogs

Alkenyl bromides and triflates undergo palladium-catalyzed cross-coupling with anilinium hypophosphite to afford monosubstituted phosphinates (salts of alkenylphosphonous acids). The reaction is an extension of our previously reported methodology for the synthesis of aryl- and benzyl-phosphonous acids. Our preliminary results show that the best reaction conditions are observed with Pd(OAc)2/dppp as a catalyst, in refluxing benzene or tetrahydrofuran. This novel PC bond forming reaction is applied to the synthesis of (1,2,3,6-tetrahydropyridin-4-yl)-methylphosphinic acid (TPMPA), a selective competitive antagonist for GABAC receptors. The divergent synthesis proceeds through protected (1,2,3,6-tetrahydropyridin-4-yl)-phosphinic acid, a previously unknown isoguvacine-like GABA analog. This synthetic intermediate is also an ideal precursor to other biologically interesting GABA analogs.