DFT study on the “Silver effect” in gold-catalyzed hydroamination of terminal alkynyl sulfamides

The mechanism and “silver effect” in regiodivergent gold-catalyzed hydroamination of terminal alkynyl sulfamides have been explored by the density functional theory (DFT) in the model systems composed of [AuCl(Ph3P)]/AgOTf (series A), AuCl(Ph3P)]/K2CO3 (series B) and [AuCl(Ph3P)]/Ag2CO3 (series C). Our results clearly showed that the regioselectivity of the terminal alkynyl sulfamides is mainly controlled by true involvement of Ag in the catalysis when using different silver salts as a component of gold-based catalytic system, rather than the steric effect. In the [AuCl(Ph3P)]/AgOTf and [AuCl(Ph3P)]/Ag2CO3 catalytic systems, the formation of π-activation or σ-gold-π-silver intermediates turns more favorable the 6-endo-dig cyclization in comparison with the 5-exo-dig pathway. On the other hand, the 5-exo-dig cyclization involving a three-membered Au-C-Au ring activated alkyne intermediate is likely the major pathway for the [AuCl(Ph3P)]/K2CO3 catalytic system. Furthermore, the regioselectivity and its origin as well as the rationalization of “silver effect” are also examined and discussed in detail. © 2020 Elsevier B.V.