Cyclization Reactions of Oxyallyl Cation. A Method for Cyclopentane Ring Formation

Unsaturated oxyallyl cations with a suitably positioned alkene bond undergo 5-exo-cyclization with the formation of vinylcyclopentane derivatives. Alkyne analogues provide allenes. The reaction proceeds with a moderate to excellent level of stereoselectivity and allows for asymmetric induction in the reaction with chiral substrate.