The synthesis of benzofuroquinolines. I. Some benzofuro[2,3‐<i>b</i>]quinoline and benzofuro[3,2‐<i>c</i>]quinoline derivatives

Abstract

Abstract Benzofuro[2,3‐ b ]quinoline ( Ia ) and its 11‐methyl derivative ( Ib ) were synthesized by demethylcyclization of 3‐( o ‐methoxyphenyl)‐1,2‐dihydroquinolin‐2‐ones (VIa,b). Benzofuro[2,3‐ b ]quinoline‐11‐carboxylic acid (Id) was synthesized by chlorination followed by the action of potassium hydroxide of a lactone (IX) prepared by demethyl‐cyclization of 3‐( o ‐methoxyphenyl)‐2‐oxo‐1,2‐dihydroquinoline‐4‐carboxylic acid (VIII). Isomeric benzofuro[3,2‐c]quinoline (Ha) and its 6‐methyl derivative (IIb) were synthesized by demethyl‐cyclization of 3‐( o ‐methoxyphenyl)‐1,4‐dihydroquinolin‐4‐ones (XIa,b). Both the methyl derivatives (Ib and IIb) were converted to the carboxylic acids (Id and IId) through condensation with benzaldehyde followed by oxidation. The benzofuroquinolines (Ia,b,d and IIa,b) thus obtained were oxidized to the corresponding N ‐oxides (IIIa,b,d and IVa,b).