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 chiral Mn(salen*) complexes 1 as the catalyst and iodosyl benzene (PhIO) as the oxygen source. Whereas one enantiomer of the allylic alcohol 2 is preferentially 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 enriched (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 competes with the epoxidation. The absolute configurations of the allylic alcohols 2 and their epoxides 3 have been determined by chemical correlation or CD spectroscopy. The observed diastereo- and enantioselectivities in the epoxidation reactions are rationalized in terms of a beneficial interplay between the hydroxy-directing effect and the attack along the Katsuki trajectory.
Adam
W
W
Institute of Organic Chemistry and Department of Food Chemistry, University of Würzburg, Am Hubland, 97074 Würzburg, Germany. adam@chemie.uni-wuerzburg.de
Humpf
H U
HU
Roschmann
K J
KJ
Saha-Möller
C R
CR
D004852:Epoxy Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D007700:Kinetics; D008345:Manganese / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D020005:Propanols / Q000737:chemistry* / Q000302:isolation & purification; D013237:Stereoisomerism; D013379:Substrate Specificity
D004852:Epoxy Compounds; D009942:Organometallic Compounds; D020005:Propanols; C006463:allyl alcohol; D008345:Manganese