Organocatalytic intramolecular (4+2) annulation of enals with ynamides: atroposelective synthesis of axially chiral 7-aryl indolines

Catalytic enantioselective transformation of alkynes has become a powerful tool for the synthesis of axially chiral molecules. Most of these atroposelective reactions of alkynes rely on transition-metal catalysis, and the organocatalytic approaches are largely limited to special alkynes which act as the precursors of Michael acceptors. Herein, we disclose an organocatalytic atroposelective intramolecular (4 + 2) annulation of enals with ynamides. This method allows the efficient and highly atom-economical preparation of various axially chiral 7-aryl indolines in generally moderate to good yields with good to excellent enantioselectivities. Computational studies were carried out to elucidate the origins of regioselectivity and enantioselectivity. Furthermore, a chiral phosphine ligand derived from the synthesized axially chiral 7-aryl indoline was proven to be potentially applicable to asymmetric catalysis.

Automated summary

Catalytic enantioselective transformation of alkynes is an important method for synthesizing axially chiral molecules. This study presents an organocatalytic approach for the atroposelective intramolecular (4 + 2) annulation of enals with ynamides. The method allows for the efficient and atom-economical preparation of various axially chiral 7-aryl indolines with good enantioselectivity. Computational studies were conducted to understand the regioselectivity and enantioselectivity, and a chiral phosphine ligand derived from the synthesized molecules showed potential for asymmetric catalysis.