Lewis base-catalyzed Michael reactions between trimethylsilyl enolate and α,β-unsaturated carbonyl compounds

Michael reactions between trimethylsilyl enolates and alpha,beta-unsaturated carbonyl compounds by using a Lewis base catalyst such as lithium benzamide 4 or lithium succinimide 5 in DMF proceeded smoothly to afford the corresponding Michael-adducts in good to high yields (Tables 1-3). In order to extend the scope, Michael reactions catalyzed by lithium acetate (AcOLi), a weak and readily available Lewis base, were studied in detail. AcOLi behaved as an effective Lewis base catalyst in Michael reactions between trimethylsilyl enolates and alpha,beta-unsaturated carbonyl compounds at 0 degreesC or at room temperature (Tables 4-6). Hindered alpha,beta-unsaturated ketones behaved as excellent Michael-acceptors in the above reaction at room temperature (Table 5). This catalytic Michael reaction also proceeds smoothly in the presence of other lithium carboxylates that are easily prepared in situ by treating carboxylic acids with lithium carbonate (Li2CO3) (Scheme 2). This is the first example of Lewis base-catalyzed Michael reactions between alpha,beta-unsaturated carbonyl compounds and trimethylsilyl enolates.