Gold catalysis: Deuterated substrates as the key for an experimental insight into the mechanism and selectivity of the phenol synthesis

The second phase of the gold-catalyzed phenol synthesis, the ring opening of the intermediate arene oxide, follows general acid catalysis. The product selectivity is determined by the substrate only and can be explained by the stability of the intermediate arenium ions. Thus, even remote substitutents can be used to control the chemoselectivity of the overall reaction by electronic influences and their influence is stronger than the steric influence of neighboring substituents. This is supported by quantum chemical calculations of the intermediates. The lack of exchange of deuterium labels excludes even equilibria with acetylide or vinylidene intermediates and the observed deuterium distribution in the final products is in accord with the NIH-shift reaction. In addition, these findings now explain previously obtained results.