Polyfunctional beta-Dicarbonyl Compounds by Michael Addition Reactions of Ester Enolates to alpha-Benzylidene and alpha-Alkylidene-beta-dicarbonyl Compounds
Abstrakt
The scope and stereoselectivity of the Michael addition of ester enolates to a-benzylidene and a-alkylidene beta-dicarbonyl compounds was studied. Most substrates reacted in good to excellent yields.
Michael acceptors bearing carboxylic functionalities reacted directly in the beta-position, whereas aldol and Michael addition competed with unsaturated ketones. The diastereoselectivity of the process is dependent on the substitution pattern of the Michael acceptor and the geometry of the enolate. (Z)-Enolates add to unsaturated malonates or dibenzoylmethane derivatives with good anti-selectivity, whereas (E)-enolates afforded the syn-diastereomers predominately.
Unsaturated nitriles and Meldrum's acid derivatives reacted with low diastereoselectivity. A stereochemical model is proposed that accounts for all experimental results and allows the stereochemical outcome to be predicted.