Electrostatic control of regioselectivity via ion pairing in a Au(i)-catalyzed rearrangement

Abstract

The rearrangement of 3-substituted aryl alkynyl sulfoxides catalyzed by cationic Au(I) complexes was studied with different counterions in solvents spanning a range of dielectric constants (ε). Pulsed-gradient diffusion NMR experiments demonstrated strong ion pairing in low-ε solvents. The regioselectivity of the reaction was insensitive to ε when ion pairing was weak but increased monotonically as ε was decreased in the regime of strong ion pairing. DFT calculations of putative product-determining transition states indicated that the product resulting from the more polar transition state is favored due to electrostatic stabilization in the presence of strong ion pairing.