Regioselective oxidative cation-olefin cyclization of poly-enes:: catalyst turnover via hydride abstraction

Electrophilic P2Pt2+ complexes are shown to catalyze the regio- and diastereoselective oxidative cascade cyclization of poly-enes. The reactions are stereospecific with respect to the initiating alkenes geometry and suggest an all-chair, semiconcerted transition structure. Catalyst turnover after cyclization apparently occurs via beta-hydride elimination and subsequent hydride abstraction (from P2Pt-H+) by added Trityl cation (in the form of trityl methyl ether or a resin version thereof) to regenerate the active P(2)pt(2+) state. One intriguing possibility is that the high regioselectivity observed in the beta-H elimination is due to a regio-defining beta-agostic resting state.