Sn-Beta zeolite is employed as catalyst in the Baeyer-Villiger oxidation of aromatic aldehydes. Aldehydes involving alkoxy substituents are oxidized to the corresponding formate ester which are hydrolyzed to the corresponding phenols. Choosing the adequate reaction conditions the main product can be preselected. Dioxane solvent and a hydrogen peroxide deficit give predominantly the ester whereas ethanol solvent or aqueous acetonitrile favor the phenol product. Double bonds in alkyl side chains do not react and the corresponding unsaturated phenols are obtained with very high chemoselectivity. Bronsted sites are active for the Baeyer-Villiger oxidation of aromatic aldehydes with H2O2 provided that the molecule does not contain olefinic groups. In any case, the selectivity of Bronsted acid zeolites is lower than that of Sn-Beta. (C) 2003 Elsevier Inc. All rights reserved.