Preparation of Acyloins by Cerium‐Catalyzed, Direct Hydroxylation of β‐Dicarbonyl Compounds with Molecular Oxygen

Abstract

Abstract We report the metal‐catalyzed α‐hydroxylation of a variety of cyclic and acyclic β‐dicarbonyl compounds by molecular oxygen. The decisive advantage of this new method is the use of catalytic amounts of the nontoxic cerium salt CeCl 3 ·7H 2 O in 2‐propanol at ambient temperature. Most of the cyclic substrates 4a − 4i give high yields of analytically pure products 5a − 5i , and the workup procedure is simple filtration through silica gel. The oxidation of acyclic dicarbonyl compounds 4j − 4p , however, is accompanied by side reactions and decomposition, reducing the yields of products 5j − 5p significantly. A proposed mechanism is in agreement with experimental results, in particular the observed oxygen uptake. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)