Tuning the Conformational Flexibility of Catalysts

Significance

A new type of phase-transfer ­catalysts (PTC, like A and B) is designed and employed in the conjugate addition of sterically demanding nitroalkanes to bulky β-aryl-substituted enones, and high efficiency and enantioselectivity were achieved. With catalyst A or B, derived from the same chiral binaphthyl ammonium motif, both enantiomers of the adduct can be obtained, only by changing the length of the linker. A synergistic stabilization and/or activation of both the nucleophile and the electrophile by the dicationic catalysts was proposed, thus the different relative ­orientation of the chiral binaphthyl units in the structure A and B may be the reason for the reversal of enantioselectivity.