Highly Active and Enantioselective Rhodium-Catalyzed Asymmetric 1,4-Addition of Arylboronic Acid to α,β-Unsaturated Ketone by using Electron-Poor MeO-F12-BIPHEP

The asymmetric 1,4-addition of phenylboronic acid to cyclohexenone were performed by using a low amount of rhodium/(R)-(6,6'-dimethoxy-biphenyl- 2,2'-diyl)bis[bis(3,4,5-trifluorophenyl)phosphine] (MeO-F-12-BIPHEP) catalyst. Because the catalyst shows thermal resistance at 100 degrees C, up to 0.00025 mol% Rh catalyst showed good catalytic activity. The highest turnover frequency (TOF) and turnover number (TON) observed were 53,000 h(-1) and 320,000, respectively. The enantioselectivities of the products were maintained at a high level of 98% ee in these reactions. The Eyring plots gave the following kinetic parameters (Delta Delta H-not equal = -4.0 +/- 0.1 kcalmol(-1) and Delta Delta S-not equal = -1.3 +/- 0.3 cal mol(-1)K(-1)), indicating that the entropy contribution is relatively small. Both the result and consideration of the transition state in the insertion step at the B3LYP/6-31(d) [LANL2DZ for rhodium] levels indicated that the less sigma-donating electron-poor (R)-MeO-F-12-BIPHEP could be creating a rigid chiral environment around the rhodium catalyst even at high temperature.