One-pot allyl-/crotylboration-Prins cyclization of aldehydes

Multi-substituted tetrahydropyrans (THPs) have been prepared via a one-pot, In(OTf)3-catalyzed, sequential allyl-/crotylboration-Prins cyclization. The homoallylic borate intermediate formed during the allyl- and crotylboration was converted in situ to an oxocarbenium ion and trapped with a nucleophile. The reaction has been extended to include a one-pot allylboration–cross Prins cyclization as well.