We sought to determine the mechanistic basis for the generality displayed by 1a across such a wide set of substrate structures and reaction manifolds. Catalysts possessing less polarizable aryl substituents (1b-g) induced lower levels of enantioselectivity (Figure ), as was observed in oxetane-opening reactions and has been observed more broadly in a wide variety of reactions promoted by this family of catalysts. 4e In particular, the fact that enantioselectivity systematically decreases with increased fluorine substitution on the ring (1d-g) is consistent with the participation of cation-p interactions playing a key role in enantioinduction, and would appear to preclude a significant role for the steric properties of the arene. The fact that enantioselectivity was observed to correlate positively with reaction rate provides further definitive evidence for the critical role of stabilizing noncovalent interactions rather than destabilizing steric effects in these reactions (Figure ).