Preparation of C2-symmetric bicyclo[2.2.2]octa-2,5-diene ligands and their use for rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids

[reaction: see text] C2-symmetric bicyclo[2.2.2]octa-2,5-dienes containing benzyl, phenyl, and substituted phenyl groups at 2 and 5 positions were prepared enantiomerically pure by way of bicyclo[2.2.2]octane-2,5-dione as a key intermediate. These chiral diene ligands were successfully applied to rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to alpha,beta-unsaturated ketones. High enantioselectivity (up to 99% ee) as well as high catalytic activity was observed in the addition to both cyclic and linear substrates.