A Nucleophilic Activation of Carboxylic Acids by Proline: Oxa-Michael Addition to Methyl Vinyl Ketone under Solvent-Free Conditions

Abstract

A serendipitous nucleophilic activation of carboxylic acids by proline helped to achieve a direct hydrocarboxylation of methyl vinyl ketone at 60 °C under solvent-free conditions. A variety of carboxylic acids were used successfully in this oxa-Michael addition, affording useful 4-acyloxy-2-butanones in moderate yields. The reactions are carried out under solvent-free conditions, and the products are isolated in high purity by a simple work-up procedure without any need for column chromatographic purification, imparting a green quotient to the protocol. A heterodimeric non-covalent interaction between the amino acid and the carboxylic acid appears to be the most plausible mechanistic interpretation for the nucleophilic activation; additionally, the possible activation of the Michael acceptor by iminium ion formation presents an interesting case of proline acting as a bifunctional catalyst.

Key words

carboxylic acids - proline - heterodimeric association - bifunctional catalysis - enones - oxa-Michael addition - solvent-free - hydrocarboxylation

• References and Notes

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