Thermal king 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

Article abstract of DOI:10.1081/SCC-200043203

The thermal ring closure of 4-methyl-7-(1,1-disubstituted propyn2-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-A]2H-chromen-2-ones (3) gradually became the main products.