Synthesis of electrophilic N-heterocyclic carbenes based on azahelicene

Helical-chiral analogues of imidazopyridine-2-yilidene were synthesized from 2-aza[6]helicene. The energies of their frontier orbitals were analyzed by the density functional theory calculations. The exceedingly large extension of NHC's pi system by helicene annelation significantly enhanced the pi electron-accepting properties of the carbene center while the strong sigma electron-donating properties of imidazopyridine-2-yilidenes were retained. (C) 2020 Elsevier Ltd. All rights reserved.