Catalytic hydrogen transfer over magnesia. Part XXV. Liquid and vapor phase reduction of ketoesters

Abstract

The reactivity of two series of compounds: alkyl x-oxoalkanoates (x = 2, 3, 4 and 6), and alkyl ω-phenyl-y-oxoalkanoates (y = 2 and 4) has been studied in the catalytic transfer hydrogenation (CTH) over magnesium oxide as the catalyst. The catalytic tests have been performed either in liquid or vapor phase with secondary alcohols (2-propanol to 2-octanol) as hydrogen donors. A strong diminution of reactivity of the ketoesters in CTH has been observed, in contrast to simple aliphatic or aralkyl ketones. The occurrence of transalcoholysis between ketoesters and alcohols used as hydrogen donors resulted in the formation of new ketoesters as side products. The hydroxoesters, i.e. the products of the CTH reaction, have been obtained with only moderate to good yields (up to 50 %). It has been found that in the CTH of ketoesters with the carbonyl group in a γ position, such as alkyl levulinates and benzoylpropionates, the appropriate lactones (γ-valerolactone and 5-phenyl-γ-valerolactone) have been formed.