Enantioselective epoxidation with chiral Mn-III(salen) catalysts: Kinetic resolution of aryl-substituted allylic alcohols

A set of aryl-substituted allylic alcohols rac-2 has been epoxidized by chi ral Mn(salen*) complexes 1 as the catalyst and iodosyl benzene (PhIO) as th e oxygen source. Whereas one enantiomer of the allylic alcohol 2 is prefere ntially epoxidized to give the threo- or cis-epoxy alcohol 3 (up to 80% ee) as the main product (dr up to - 95:5), the other enantiomer of 2 is enrich ed (up to 53% ee). In the case of 1,1-dimethyl-1,2-dihydronaphthalen-2-ol ( 2c), the CH oxidation to the enone 4c proceeds enantioselectively and compe tes with the epoxidation. The absolute configurations of the allylic alcoho ls 2 and their epoxides 3 have been determined by chemical correlation or,C D spectroscopy. The observed diastereo- and enantioselectivities in the epo xidation reactions are rationalized in terms of a beneficial interplay betw een the hydroxy-directing effect and the attack along the Katsuki trajector y.