Intramolecular Rearrangements of Labda-8(17),14-dien-13-ol (Manool) Derivatives

The products of epoxidation of the enol ether 8,13-epoxy-17-norlabd-8-ene (2) arise from the acid-labile acetal nature of the expected epoxide. Acid-promoted 1,2-nucleophilic rearrangements of subsequently formed epoxides give rise to the isolated products, including the novel spiro hydroxy ketone 8β,13-epoxy-7β-hydroxy-10(9→8)abeo-17-norlabdan-9-one (8), the structure of which was determined by X-ray analysis of the acetate derivative. The structure of the major product, 8,13- epoxy-17-norlabd-8-en-7-one (5), was confirmed by synthesis.