Abstract
Enantioselective epoxidation of 2,2-dimethyl-2 H-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 (3 S,4 S)-6,7-bis(tosyloxy)-2,2-dimethyl-3,4-epoxychroman (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.
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