Stereoselective a-Oxyfunctionalisation of Benzo(hetera)cyclanones by Dimethyldioxirane.

a-Hydroxy ketones including their cyclic derivatives are important synthetic building blocks. Chiral, non-racemic a-hydroxy ketones (and esters) are widespread in natural products. Therefore, there is a high demand to develop efficient methods for the construction of their enantiopure or at least enantiomerically enriched representatives and a number of procedures have been published in the last decades [1,2]. Our interest in the synthesis of a-hydroxy benzo(hetera)cyclanones, particularly 3-hydroxychromanones, prompted us to investigate the synthetic utility of the recently developed electrophilic chiral oxidizing system, namely dimethyldioxirane (DMD)/Jacobsen's catalyst [3] in the oxyfunctionalization of enol derivatives. Enol acetates were choosen as prochiral substrates because their higher stability as compared to silyl enol ethers and their high reactivity toward DMD