Atroposelective Synthesis of N–N Axially Chiral Indoles and Pyrroles via NHC-Catalyzed Diastereoselective (3 + 3) Annulation Strategy
Sowmya Shree Ranganathappa, Bhabani Sankar Dehury, Gautam Kumar Singh, Sayan Shee, Akkattu T. Biju
Abstract
The synthesis of N–N axially chiral molecules in the enantiopure form has emerged as an interesting research topic primarily due to the significance and intricacy in synthesizing these molecules, especially bearing heterocyclic motifs. Herein, we disclose a method for the introduction of N–N axial chirality along with a point chiral center via the N-heterocyclic carbene (NHC)-catalyzed atroposelective synthesis of dihydropyridinone-containing indoles and pyrroles. The reaction follows a (3 + 3) annulation approach by the interception of indole/pyrrole-derived enamines with α,β-unsaturated aldehydes under oxidative NHC catalysis proceeding via the α,β-unsaturated acylazoliums. The N–N axially chiral indoles/pyrroles were formed under mild conditions in broad scope with high selectivity. In addition, preliminary DFT studies of the N–N rotational barrier of the axially chiral products were performed.