Regioselective Synthesis of Benzofuran‐Annulated Six‐Membered Sulfur Heterocycles by Aryl Radical Cyclization

Abstract

The tin hydride–mediated cyclization of a number of sulfides and sulfones under mild and neutral conditions has been investigated. The sulfides were in turn derived from 3(2H) benzothiofuranone and 2‐bromobenzyl bromides by phase‐transfer‐catalyzed reaction, and the corresponding sulfones were prepared by treatment of the corresponding sulfides with m‐CPBA at room temperature. The sulfides and sulfones were then reacted with ⁿ Bu₃SnH‐AIBN to afford regioselectively benzofuran‐annulated six‐membered sulfur heterocycles.

Keywords:

• 6‐endo trig
• radical cyclization
• regioselective
• sulfur heterocycles
• tri‐n‐butyltin hydride

Acknowledgment

We thank the CSIR (New Delhi) for financial assistance, and one of us (B. Chattopadhyay) is thankful to the CSIR (New Delhi) for a junior research fellowship. We also thank the Department of Science and Technology (DST) (New Delhi) for providing UV‐VIS and FT‐IR spectrometers under the DST‐FIST program.