Intramolecular cyclization of tert-butyldiphenylallylsilane units and carbonyl groups: Allylsilane terminated cyclization versus the ene reaction

tert-Butyldiphenylsilylcopper reacts with allene to give an allylsilane-vin ylcopper intermediate which upon treatment with alpha,beta -unsaturated ket ones leads to allylsilane containing ketones resulting from conjugate addit ion. These oxoallylsilanes bearing the bulky tert-butyldiphenylsilyl group undergo highly selective intramolecular cyclizations when treated with Lewi s acid affording unsaturated cyclopentanols. Two reactivity patterns are ob served: allylsilane terminated cyclization involving elimination of silicon or an ene reaction without losing the silyl group. The pathway depends on the ability of a hydrogen beta to the carbonyl to be removed in an ene-type process. alpha,beta -Unsaturated acid chlorides lead to silylated cyclopen tenones.