Synthesis of 4H,5H-pyrano [3,2-c] (1) benzopyran-4,5-diones

Claisen condensation of 3-acetyl-4-hydroxycoumarins with different esters in the presence of sodium/ether gave 4-hydroxy 3[1 -substituted-1,3-dioxo propyl] benzopyran-2-ones (IIa-p) which on further cyclization with sodium acetate and acetic acid gave corresponding 4H, 5H-pyrano [3,2-c](1) benzopyran-4,5-diones (IIIa-p). Alternate route for the synthesis of 7-methyl-4-hydroxy 3 [1-phenyl-1,3-dioxo prspyl] benzopyran-2-one (IIg) is also suggested.