Regioselective Synthesis of Heterocycles from 3-Cyclohex-2-enyl-4-hydroxy-1-methylquinolin-2-(1H)-one

Abstract

3-Cyclohex-2-enyl-4-hydroxy-1-methylquinolin-2(1H)-one (5) reacts with pyridine hydrotribromide in CH₂Cl₂ at 0–5°C for 0.75h to give a furo fused heterocycle 6 in 96% yield. Product 6 on treatment with KOH-EtOH eliminates HBr to give compound 8 which on treatement with Pd-C in refluxing diphenyl ether for 0.5h furnishes benzofuro[3,2-c]quinolone 9 in 90% yield. Substrate 5 on sequential treatment with Ac₂O-AcONa and Br₂/AcOH followed by KOH-EtOH, however produces bicyclic product 7 in excllent overall yield. Substrate 5 reacts with 1 equivalent of m-chloroperbenzoic acid in refluxing benzene to furnish bicyclic heterocycle 12 in 80% yield and with cold conc. H₂SO₄ at 0–5°C for 2h generates the bicyclic heterocycle 14 in 90% yield.