A new strategy for synthesis of attached rings

The first investigation of the use of pinacol-terminated Prins cyclizations to form attached rings is reported. Treatment of triisopropylsilyl ethers of (Z)- or (E)-[2-(6,6-dimethoxyhexylidene)cyclohexanol with SnCl4 provides bicyclic products having attached rings. The approach is synthetically useful in the Z alkylidenecyclohexane series, proceeding selectively by a pathway involving carbon migration in the pinacol rearrangement step, to provide methoxy epimers of 1-(2-methoxycyclohexyl)cyclopentylcarboxaldehyde. Reaction of the corresponding E stereoisomer is more complex and yields a mixture of products resulting from both hydride and carbon migration in the pinacol rearrangement step.