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 α-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.