Simple Preparation ofTrans-Epoxides via Ylide Intermediates

A practical route to epoxides with control of the relative and absolute stereochemistry has been developed, allowing epoxides to be readily prepared on a 20 mmol scale by generating the reactive intermediate (the diazo compound) in situ from benzaldehyde tosylhydrazone sodium salt. In this paper, we describe the optimum conditions for three procedures to obtain the desired racemic and enantiomerically enriched epoxides (Scheme [1] ). High diastereoselectivities (98-100%) and very high yields of epoxide were obtained. Asymmetric epoxidation was carried out using the chiral camphor-derived [2.2.1] bicyclic sulfide 4 and the desired epoxide was obtained with excellent enantioselectivity (94%).