Ag(I)-Promoted Cascade Cyclization of 1-Isocyano-2-((2-alkoxyphenyl)ethynyl)benzenes to Access Benzofuro[2,3-b]quinolines.

This work discloses an alternative synthetic route to access benzofuro[2,3-b]quinolines. The reaction proceeds via Ag(I)-assisted cascade cyclization of 1-isocyano-2-((2-alkoxyphenyl)ethynyl)benzenes, derived from the corresponding N-(2-((2-alkoxyphenyl)ethynyl)phenyl)formamide derivatives, allowing a one-pot, two-step assembly of the benzofuroquinoline scaffolds with four fused rings. The salient features of the synthetic method are broad substrate scopes, good to excellent yields, and ease of experimental procedure. A gram-scale synthesis demonstrated the scalability and practical applicability of the present transformation. Mechanistic pathway of the current transformation was proposed based on control experiments and density functional calculations on the electronic structures. The photophysical properties and frontier molecular orbitals of some selected benzofuro[2,3-b]quinolines were evaluated using UV-vis absorption and fluorescence spectroscopy and time-dependent density functional theory (TD-DFT) calculations.