CONJUGATE ADDITIONS OF ORGANOCUPRATES TO CYCLOALKENONE COMPLEXES OF THE CHIRAL RHENIUM LEWIS-ACID [(ETA(5)-C5H5)RE(NO)(PPH(3))](+) - ENANTIOSELECTIVE SYNTHESES OF 3-SUBSTITUTED CYCLOALKANONES
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abstract
Reactions of organocuprates R2CuLi and cycloalkenone complexes (+)-(R)-[(5-C5H5)Re(NO)(PPh3) (1-0=CCH=CHCH2(CH)n)]+ BF4- (n = 2, 1) are conducted in THF or CH2C12 between -15 C and -116 C. Workups with aqueous HI give the corresponding 3-substituted cycloalkanones and iodide complex (5-C5H5)Re(NO)(PPh3) (I). Under optimized conditions, 3-substituted cyclohexanones are obtained in 3983% yields and 6485% ee (R = Me, R; n-Bu, R; t-Bu, S; Ph, S or R), and 3-substituted cyclopentanones are obtained in 50-73% yields and 79-93% ee (R = Me, R; Ph, S). Evidence for intermediate enolate complexes is presented, protocols for recycling the chiral rhenium auxiliary are described, and possible mechanisms of 1,4-asymmetric induction are discussed. 1995, American Chemical Society. All rights reserved.
