Determination of the absolute configuration of optically active 2,2-dimethyl-3,4-epoxychromans prepared by the catalytic enantioselective epoxidation with the dimethyldioxirane/Jacobsen Mn(III)salen system

Enantioselective epoxidation of 2,2-dimethyl-2H-chromenes 1a-d by using Mn(III)salen complexes (R,R)-3 and (S,S)-3 as catalysts and dimethyldioxirane (DMD) as oxygen donor afforded optically active 2,2-dimethyl-3,4-epoxychromans 2a-d in good yields and high enantioselectivities (up to 93% e.e.). The absolute configuration of the (3S,4S)-6,7-bis(tosyloxy)-2,2-dimethyl-3 (3S,4S)-2d has been determined by X-ray diffraction. The absolute configurations of the other nonracemic epoxychromans were assigned by circular dichroism (CD) measurements relative to the (3S,4S)-2d epoxide as reference compound. Copyright (C) 1996 Elsevier Science Ltd