A new class of highly acidic confined iminoimidodiphosphate (iIDP) Bronsted acids catalyze the asymmetric Prins cyclization of both aliphatic and aromatic aldehydes. Diverse functionalized 4-methylenetetrahydropyrans are obtained in good to excellent yields and with good to excellent regio- and enantioselectivities. Our iIDP catalysts provide an efficient and scalable enantioselective approach to various fragrances, including rose oxide and doremox.