Intramolecular ene reaction of epoxyallylsilanes: synthesis of allyl- and vinylsilane-functionalized cyclohexanols.

[reaction: see text] Epoxyallylsilanes bearing the bulky tert-butyldiphenylsilyl group undergo an uncommon tandem rearrangement-cyclization process upon treatment with Lewis acids. Two pathways for the carbonyl ene reaction are observed: one leading to allylsilane-cyclohexanols when the epoxyallylsilane (28-31) is nonsubstituted, 2-, or 4-monosubstituted and other leading to vinylsilane-cyclohexanols when the epoxyallylsilane (24-27) is 2,4-disubstituted or trisubstituted. An explanation for the observed regio- and stereoselectivity is advanced and a reliable mechanism proposed.