Abstract
The cyclization of N-propargyl benzamide with gold catalysts has become a popular benchmark reaction over the past two decades. The prevailing consensus denotes protodeauration as rate-limiting. Cyclization with [L1Au(NCCH(3))]SbF(6) and L1AuOTs (L1 = t-Bu(2)(o-biphenyl)P, also known as Johnphos) in dichloromethane and methanol in conjunction with deuterium labeling studies reveals a solvent-dependent switch to π-activation for the rate-limiting step. Computational calculations support this change of the rate-determining step.