A Novel Prins Cyclization through Benzylic/Allylic C−H Activation

A step-economic method to construct the tetrahydropyran ring, involving sequential benzylic/allylic C−H bond activation via DDQ oxidation and nucleophilic attack of an unactivated olefin, is described. The equatorial-trisubstituted Prins products are obtained from benzyl and allyl homoallylic ethers with high yield and stereochemical fidelity.