The monobenzoylation of 1-phenyl-1,2-ethanediol in the presence of different tin reagent has been studied. The stannylene ketal of 1-phenyl-1,2-ethanediol has been prepared and used as a catalyst or generated in situ by exchange with other mixed tin ketals. In either case, the acylation occurs rapidly with 2 mol% of the catalyst with the known selectivity. These experiments clearly establish the catalytic nature of the acylation reaction. (c) 2005 Elsevier B.V. All rights reserved.