1,2-Silyl-Migrative Cyclization of Vinylsilanes Bearing a Hydroxy Group: Stereoselective Synthesis of Multisubstituted Tetrahydropyrans and Tetrahydrofurans<sup>1</sup>
trans-2-alkyl-3-silyltetrahydropyrans 2 exclusively (trans/cis = >99/1 to 97/3). The cyclization efficiency and rate strongly depended on the geometry of the C-C double bond and the silyl group. The use of (E)-vinylsilanes resulted in lower yields with poor cis-selectivity. In the cyclization of (Z)-1 (R = Bu), the silyl group used, the reaction time, and the yield of 2 were as follows: SiMe(2)Ph, 9.5 h, 75%;