beta-Siloxy unsaturated nitriles: stereoselective cyclizations to cis- and trans-decalins.

[formula: see text] beta-Siloxy unsaturated nitriles are excellent precursors to enolate and nitrile anions that cyclize to cis- and trans-decalins, respectively. The stereoelectronic requirements of endocyclic enolates and exocyclic nitrile anions are complementary, providing cis- and trans-decalins from a common intermediate. This cyclization allows the synthesis of diastereomeric cis- and trans-decalins containing a contiguous array of quaternary-tertiary-quaternary stereocenters.