Regioselective Synthesis of 2H‐Benzothiopyrano[3,2‐c]quinolin‐7(8H)‐ones by Tri‐n‐butyltinhydride–Mediated Radical Cyclization

Abstract

A number of hitherto unreported 2H‐benzothiopyrano[3,2‐c]quinolin‐7(8H)‐ones have been regioselectively synthesized in 90–96% yield by tri‐n‐butyltinhydride–AIBN–mediated radical cyclization from 4‐(2′‐bromothioarylmethyl)‐1‐methylquinolin‐2(1H)‐ones and their corresponding sulfones. 4‐(2′‐Bromothioarylmethyl)quinolin‐2(1H)‐ones were in turn prepared from 4‐bromomethylquinolin‐2(1H)‐one and o‐bromothiophenols by refluxing in acetone in the presence of anhydrous K₂CO₃. These were converted to the corresponding sulfones by oxidation with two equivalents of m‐CPBA in refluxing dichloromethane for 1 h.

Keywords:

• 4‐bromomethyl‐1‐methylquinolin‐2(1H)‐one
• 6‐endo‐trig
• organotin reagent, radical cyclization
• sulfur heterocycles

Acknowledgments

N. Kundu is thankful to Council of Scientific and Industrial Research (CSIR) (New Delhi) for a senior research fellowship. We also thank Department of Science and Technology (DST) (New Delhi) for providing a UV‐Vis spectrophotometer and FT‐IR spectrometer under the Department of Science and Technology‐Financial assistance for Infrastructural Development of Science and Technology (DST‐FIST) program.