Studies in Thio‐Claisen Rearrangement: Regioselective Synthesis of Thiopyrano[2,3‐b]pyran‐2‐ones and Thieno[2,3‐b]pyran‐2‐ones

Abstract

4‐Mercapto‐6‐methyl‐2‐pyrone was alkylated with different allylic and propargylic halides under phase transfer catalyzed condition in the presence of TBAB or BTEAC catalyst in chloroform–aqueous NaOH (1%) at room temperature. The S‐alkylated thiopyran‐2‐ones were then refluxed in quinoline or in chlorobenzene to give 4‐chloromethylthiopyrano[2,3‐b]pyran‐2‐one and 4‐hydroxymethylthiopyrano[2,3‐b]pyran‐2‐one or several thieno[2,3‐b]pyran‐2‐ones.

Keywords:

• Phase transfer catalysis
• Claisen rearrangement
• [3,3] Sigmatropic rearrangement
• 4‐Mercapto‐6‐methyl‐pyran‐2‐one
• Thiopyrano[2,3‐b]‐pyran‐2‐one
• Heterocycles

Acknowledgment

We thank the CSIR (New Delhi) for financial assistance. One of us (S. S) is thankful to CSIR (New Delhi) for a Senior Research Fellowship.