Lewis Acid Induced Asymmetric Prins Reactions of Chiral Acetals with Alkenes

Me 2 AlCl induced reaction of acetal 1 with methylenecyclohexane at -78°C gives a 61% yield of 3 as a 7:3 mixture of diastereomers. MeAlCl 2 induced reaction of acetal 2 with methylenecyclohexane gives a 53% yield of 6 as a 7:3 mixture of isomers. Reaction of 1 with isoprene gives 7 as a mixture of all 4 possible isomers. Reaction of acetal 8 with methylenecyclohexane gives the conjugate addition product 9 in 70% yield as a 4:1 mixture of isomers.