Studies on the Stereoselectivity of the Preparation of α,β-UNSATURATED ESTERS FROM α-Lithio-α-Silyl Esters

The reaction o f the lithium enolate o f a-trimethylsilyl esters with aldehydes and ketones has been shown to be an excellent entry into a, B-unsaturated esters as a result of the facile elimination o f the B-oxidosilane intermediate produced in the initial step of the reaction. (eq. 1) More recently it was shown that the bromomagnesium enolate o f trimethylsilyl acetates a1 lowed for the highly stereoselective preparation of (E) a, B-unsaturated esters via the isolable B-hydroxy-a-silyl ester, which was treated with BF₃0Et₂ to effect a trans elimination of the elements of trimethylsilanol⁵ (eq. 2) If this elimination were carried out with base, however, the stereoselectivity is much lower.