KF/alumina catalyzed regioselective benzylation and benzoylation using solvent-free grind-stone chemistry

Abstract

Potassium fluoride-impregnated on alumina catalyzes solvent-free regioselective O-benzylation, benzoylation and cinnamylation of phenols. Reaction proceeds simply by triturating together equivalent amounts of phenol and corresponding halide in the presence of 5 mol% of KF/alumina for 5–20 min with a mortar and pestle, without need for any additive such as phase-transfer catalyst or solvent. Key features of the protocol include its efficiency also for solid–solid precursors and regioselectivity for phenolic hydroxyls versus alcoholic hydroxyls. Utility of the protocol for N- and S-benzylation has also been explored. Products were obtained in excellent yields and the catalyst can be easily recycled several times without significant loss of activity.