One-Pot Synthesis of Benzofuropyridines and Benzofuroquinolines via Tandem Cycloaddition-Cyclization of Halopyridine- and Haloquinoline N- Oxides with Arynes

A transition-metal-free approach for the one-pot synthesis of benzofuro[3,2-c]pyridines, benzofuro[3,2-b]pyridines, and benzofuro[3,2-c]quinolines has been developed by the reaction of suitably chlorinated pyridine N-oxides and quinoline N-oxides with arynes. A tandem three-step protocol involving the cycloaddition-rearrangement-SNAr cyclization by the reaction of 4-chloropyridine N-oxides with in situ generated aryne intermediates provided benzofuro[3,2-c]pyridines. The Cl substitution at the C-3 position of pyridine N-oxides afforded benzofuro[3,2-b]pyridines. The methodology worked successfully with 2-aryl-4-chloroquinoline N-oxides, affording 2-arylbenzofuro[3,2-c]quinolines. The transition-metal-free strategy comprising a multistep cascade is amenable to a modular synthesis of diversely fused benzofuropyridines and benzofuroquinolines.