Asymmetric Oxidative Cation/Olefin Cyclization of Polyenes: Evidence for Reversible Cascade Cyclization

Platinum and silver work together: Activation of [(xylyl-phanephos)PtCl2] by silver generates an electrophilic catalyst that can enantioselectively, diastereoselectively, and regioselectively promote the stereospecific oxidative cyclization of polyene-ols (see scheme; Tr=trityl). Mechanistic experiments indicate that the stereochemistry-determining step is not the initial cyclization step, but rather a subsequent step in the reaction.