REACTION DES ENOLATES MASQUES DE SILICIUM ISSUS WESTERS DE TRIMETHYLSILYLE AVEC LES DERIVES CARBONYLES α,β-INSATURES

Abstract

Bis(trimethylsilyl) ketene acetals RCH[dbnd]C[OSi(CH₃)₃]₂ 1 add to PhCH[dbnd]CH[sbnd]COR¹ 2 in the presence of catalytic amounts (10%) of TiCl₄ leading, in good to excellent yields to the corresponding β-hydroxy or δ-ketoacids. Under kinetic control, the regioselectivity of the reaction markedly depends on the nature of R and R¹. Mixtures of 1,2 and 1,4 products are formed in some of the cases; in others, solely Michael or aldol adducts are obtained. On the contrary, the stereoselectivity, which ranges from zero to moderate, is slightly influenced by R and R¹.

It is also shown that trimethylsilyl ester of α-trimethylacetic acid (CH₃)₃SiCH₂CO₂Si(CH₃)₃ 5 add to 2 in the presence of TBAF (10%) in THF.

Key Words:

• Silyl ketene acetals
• α,β-unsaturated carbonyl compounds
• aldol reaction
• Michael addition
• Regioselectivity
• β-hydroxyacids
• δ-ketoacids.