Rhodium Catalysts Based on Phenyl Substituted Cp Ligands for Indole Synthesis via Oxidative Coupling of Acetanilides and Alkynes
Vladimir B. Kharitonov, Dmitry V. Muratov, А. N. Rodionov, Yulia V. Nelyubina, Mger A. Navasardyan, Mikhail S. Nechaev, Dmitry A. Loginov
Abstract
Abstract Rhodium‐catalyzed oxidative coupling of acetanilides and alkynes via C−H activation is the most powerful synthetic tool for producing the indole motif from commercially available precursors. However, this reaction usually requires large catalyst loadings (5 mol% of rhodium). In this study, a 1,2‐diphenylcyclopentadienyl ligand‐based catalyst was developed that works well at 1 mol% loading of rhodium. DFT calculations of the C−H activation step provided insight into its high catalytic activity. The catalyst efficiency was also demonstrated in the synthesis of naturally occurring isocoumarins, such as polygonolide, tubakialactone B and penicimarine F. The developed catalytic protocols tolerate a wide range of functional groups, for example, halide, nitro, hydroxy, and alkoxy.