Unusual N[sbnd]H/O[sbnd]H Activation Mechanism for Au-Catalyzed N,O-Functionalization of 1,4-diyn-3-ols with N-hydroxyanilines

Au-catalyzed N,O-functionalization of 1,4-diyn-3-ols with N-hydroxyanilines provides a short and efficient approach to construct versatile pyrrole frameworks. Using DFT calculations, we systematically investigated the detailed mechanisms involved in this reaction. It was found that, the commonly asserted N[sbnd]H/O[sbnd]H activation mechanism was unfavoured due to a high energy barrier. The main reason was believed to be associated with the inversion of configuration on the sp³-hybrid C atom (generated after the H(N)-shift) which results in significant energy consumption for the subsequent H(O)-shift. Therefore, here we present a unique “1,4-elimination/1,4-syn-protodeauration” catalytic mechanism, in which (i) the charge delocalization on the carbon cation is conductive to the stability of the 1,4-elimination TS; (ii) the high exergonicity of the 1,4-elimination decreases the potential energy surface of the subsequent reaction; and (iii) the sp²-C site ensures energy-efficient retention of configuration during the 1,4-syn-protodeauration, in contrast to the energy-consuming inversion of configuration during the classical anti-protodeauration.