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-vinylcopper intermediate which upon treatment with alpha,beta-unsaturated ketones leads to allylsilane containing ketones resulting from conjugate addition. These oxoallylsilanes bearing the bulky tert-butyldiphenylsilyl group undergo highly selective intramolecular cyclizations when treated with Lewis acid affording unsaturated cyclopentanols. Two reactivity patterns are observed: 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 cyclopentenones.
Barbero
A
A
Departamento de Química Orgánica, Universidad de Valladolid, Valladolid 47011, Spain.
Castreño
P
P
García
C
C
Pulido
F J
FJ