Asymmetric Synthesis of Axially Chiral Naphthyl-C3-indoles via a Palladium-Catalyzed Cacchi Reaction

Atropoisomeric biaryl motifs are widely found in natural products and bioactive compounds as well as chiral catalysts and ligands. Various efficient approaches have been disclosed for the construction of chiral six-six biaryl skeletons. In contrast, the enantioselective synthesis of axially chiral arylindoles through the strategy of de novo construction, other than the asymmetric functionalization of indoles, remain a challenging task. Herein we report an efficient Pd(0)/(S)-Segphos-catalyzed atroposelective Cacchi reaction of 2-alkynylanilines with sterically congested naphthyl halides, which afforded an array of naphthyl-C3-indoles in high yields with good to excellent atroposelectivities. The addition of water and the modulation of the manipulation procedure by premixing the palladium complex and the naphthyl halide were the keys to success. The conformational stability of the obtained axially chiral naphthyl-C3-indole containing a synthetically more-valuable free NH moiety is revealed through kinetic experiments.

Automated summary

Atropoisomeric biaryl motifs are widely utilized in natural products and chiral catalysts. This study presents an efficient Pd(0)/(S)-Segphos-catalyzed atroposelective Cacchi reaction to construct a variety of naphthyl-C3-indoles with high yields and good to excellent atroposelectivities. The conformational stability of the obtained axially chiral naphthyl-C3-indole containing a synthetically more-valuable free NH moiety was revealed through kinetic experiments, highlighting the importance of water addition and manipulation procedure modulation for success.