Palladium-Catalyzed Stereospecific Oxidative Cascade Reaction of Allenes for the Construction of Pyrrole Rings: Control of Reactivity and Selectivity

A palladium-catalyzed oxidative cascade reaction of alpha-tosylamide allenes has been developed. The reactivity of the allenes is controlled by the tosylamide group. In the presence of terminal alkynes the reaction proceeds via a pathway leading to a one-pot construction of pyrrole rings. Moreover, a solvent-controlled chemoselectivity of the cascade reaction was realized, leading to a stereospecific and divergent synthesis of (Z)-tetrasubstituted olefins, 2,5-dihydropyrroles, and pyrroles. Enantioenriched (Z)-tetrasubstituted olefins and 2,5-dihydropyrroles are readily synthesized by chirality transfer using this approach.