Rhodium(â…¢)-Catalyzed Oxidative Coupling Between N-phenoxyacetamides And Alkenes

Synthetic access to ortho-alkenyl phenols continues to be of central importance because of their prevalence in natural products and biologically active molecules. Traditional methods, usually require prefunctionalization of the substrates, are of low efficiency. Contrast to the traditional methods, transition metal-catalyzed direct functionalization of C-H bonds pathway represents an efficient and atom-economic strategy.Rhodium catalysts are well known for their active role in the C-X(X=C, N, O) coupling reactions that proceed via C-H activation. In the first part of this article, a review of rhodium(Ⅲ) catalyzed C-H activation reactions has been shown to introduce the background of oxidative coupling between arenes and alkenes, trying to give the reader a basic understanding of the catalyst.In the second part of this article, by introducing the concept of internal oxidant, the authors designed the synthetic route that select N-phenoxyacetamide and alkene as the starting materials. Combined with the existing literature reports involved in [Cp*RhCl2]2 catalyzed olefination, the reaction condition was systematically screened to obtain the optimal condition.Under the optimal condition, a wide range of substrates participate in the reaction, obtaining the corresponding ortho-alkenyl phenols in moderate to high yields. What’s more, the reaction system is conducted at room temperature and completed in 2 hours without the addition of external oxidant, which made great progress compared with the prior ortho-alkenyl phenol synthesis systems.We propose a mechanism in which the cyclometalation of the substrate first affords a five-membered rhodacycle, which undergoes regioselective alkene insertion to generate a seven-membered metallacycle. Subsequently, P-hydrogen-atom elimination happened in the seven-membered metallacycle, generating ortho-alkenyl immediate which coordinate the Rh(Ⅰ) species. Subsequently, a fast oxidative addition of Rh(I) to the O-N bond was happened to give the Rh(Ⅲ) species, which was finally protonated by acetic acid to release the final product.