Solvent-Dependent Change in the Rate-Determining Step of Au(I)-Catalyzed N‑Propargyl Benzamide Cyclization

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(NCCH3)]­SbF6 and L1AuOTs (L1 = t-Bu2(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.