Stereoselective synthesis of carbocyclic ring systems by pinacol-terminated Prins cyclizations

Studies that expand the scope of the Prins-pinacol synthesis of carbocyclic ring systems are described. The construction of cyclopentacyclooctanones by ring-enlarging cyclopentane annulations of cycloheptanone precursors is broadly examined as is the synthesis of related bicyclic ketones containing larger rings. Prins-pinacol reactions of acyclic alkenyl acetals were examined to gain insight into intrinsic stereochemical control elements in ring-enlarging cyclopentane annulations. The outcome of the carbocyclic constructions described in this report are rationalized by the mechanistic analysis we developed recently to describe Prins-pinacol constructions of tetrahydrofurans.