Role of 2-oxonia Cope rearrangements in Prins cyclization reactions.

[reaction--see text] The 2-oxonia Cope rearrangement is undetectable in typical Prins cyclization reactions. We have investigated the Cope rearrangement in a Prins cyclization reaction using a competitive reduction of the oxocarbenium ion intermediate, and a racemization reaction mediated by the rearrangement. In our unactivated substrate, the 2-oxonia Cope rearrangement was much faster than Prins cyclization. An enantioselective allyl transfer reaction also was developed using a 2-oxonia Cope rearrangement.