Mechanistic Insights into Oxazolone Synthesis by Bimetallic Au-Pd-Catalyzed Catalysis and Catalyst Design: DFT Investigations.

Abstract

Bimetallic synergistic catalysis is one of the most effective and powerful strategies for the synthesis of oxazolones, an important species in organic synthesis. In this work, the mechanism of AuCl(PMe3)/AgOTf-Pd(0) ([Au-Pd]) bimetallic catalyst-catalyzed oxazolone synthesis using N-alkynyl carbamates as precursors was studied in detail by DFT calculations and the catalytic performances of a series of bimetallic catalysts were evaluated. The results show that the reaction begins from the [Au]-catalyzed cycloisomerization of N-alkynyl carbamates. After the five-membered intermediate is formed, the [Pd(0)]-catalyzed cycle starts, which contains three steps: oxidation addition, transmetalation, and reductive elimination. The whole reaction belongs to a catalyzed catalysis, and the reductive elimination is the rate-determining step. In the transmetalation process, both the [Pd(0)] catalyst and the ionic bridge are necessary. For the [Au-Pd]-catalyzed process, it is Cl- as the bridge, not OTf-. The cheaper metal compound, AgCl(PMe3), can serve as the alternative of AuCl(PMe3) to co-catalyze with the [Pd(0)] catalyst for the title reaction.