Thermal Ring Closure Reaction of 4‐Methyl‐7‐(1,1‐Disubstituted Propyn‐2‐Yloxy)Chromen‐2‐Ones: The Effects of the Substituents at Propargylic Position on Reactivity and Products

Abstract

The thermal ring closure of 4‐methyl‐7‐(1,1‐disubstituted propyn‐2‐yloxy)chromen‐2‐ones (1) with gem‐dihydro‐ or dimethyl‐group at the propargylic position was carried out at high temperature such as refluxing in N,N‐diethylaniline and resulted in the analogues of 4‐methyl‐2H‐pyrano[6,5‐h]2H‐chromen‐2‐one (2). As the substituents at the propargylic position became bulkier, this ring closure could occur in much milder conditions such as refluxing in acetone or stirring in DMF at 80–90°C. The five‐membered products, 4‐methyl‐furano[2,3‐h]2H‐chromen‐2‐ones (3) gradually became the main products.

Keywords:

• Aryl propargylether
• 4‐methyl‐7‐(1,1‐disubstituted propyn‐2‐yloxy)chromen‐2‐ones
• Thermal ring closure reaction

Acknowledgment

This research was supported by a grant from National Science Foundation of China (20272010 and 30200348) awarded to P. Xia and Y. Chen, respectively.