The importance of vinylsilane stereochemistry and σ - π stabilization in iminium ion-vinylsilane cyclizations. A short total synthesis of the amaryllidaceae alkaloid (−) −epielwesine.

$\text{cis}$-3a-Aryl-2,3,3a,4,5,7a-hexahydro-1H-indoles 5 and 10 are formed in excellent yield from acid promoted cyclization of (Z)-vinylsilane imines 3 and 9. The failure of the corresponding (E)-vinylsilane isomer 4 to cyclize under similar conditions demonstrates that the β-silylcation intermediates formed in these reactions derive significant stabilization from σ - π delocalization.