ORGN 984

Our findings with acetophenone derivatives are that the introduction of substituents para- to the tether position has little effect on the enantioselectivity (93% for acetophenone), suggesting that the CH-pi stereocontrol effect continues to work effectively in this system (Figure 1). However, the introduction of meta-substituents (as in 5) results in significant reduction of the reaction but at only a low cost to the e.e. This provides evidence for the extension of the CH-pi stabilisation through a methyl group.

The placement of meta-substituents on the catalysts (as in 5) increases the bulk around the arene ring and enforcing a higher level of steric control (Figure 2). With this modification, reduction of acetyl cyclohexanone can be achieved in up to 89% e.e. with in contrast to only 69% for 1.