α-Benzylation of ketones by reaction with benzylamine. Regioselective reduction of C–C double bonds in conjugated enones

Abstract

Prolonged reaction of some ketones with benzylamine at reflux converts them into α-benzyl derivatives by a route involving Aldol condensation of the related ketimine with benzaldimine followed by exclusive reduction of the resultant C–C double bond. Reduction does not occur when pure benzylamine is used under oxygen-free nitrogen, however the inclusion of a trace of benzaldehyde restores the efficiency of the reaction. Treatment of several ketones in this manner established the scope of the process. When the reaction was extended to the reduction of α,β-unsaturated enones again using benzylamine, reaction times were shorter and the product yield greater. The possibility that the reductive step was an intramolecular 1,5-hydrogen transfer was studied.