Synthesis of some 2,10-dioxo-4-methyl-2[H],10[H]benzo[1,2-b:5,6-b′]dipyran-8-carboxylic acids

Dimethylacetylenedicarboxylate on condensation with 7-hydroxy-4-methylbenzopyran-2[H]-one 1 furnishes an inseparable cis-trans mixture of 4-methyl-7-(dimethylethene-dicarboxylate)oxybenzopyran-2[H]-one 2. It is then hydrolysed to give corresponding cis-trans mixture of acids 3, which are cyclised with conc. H2SO4 to give 2,10-dioxo-4-methyl-3[H], 10[H]-benzo[1,2-b:5,6-b']dipyran-8-carboxylic acid 4. Esterification of 4 with dimethyl sulphate gives the corresponding methyl ester 5. Similarly 2,5-dioxo-4,10- dimethyl-2[H], 6[H]benzo[1,2-b:4,5-b']dipyran-8-carboxylic acid 10 and 2,5-dioxo-4-methyl of the above carboxylic acids 2[H], 5[H]-benzo[1,2-b:3,4-b']dipyran-7-carboxylic acid 15 are prepared from 7-hydroxy-4,8-dimethylbenzopyran-2[H]-one and 6-hydroxy-4-methylbenzopyran 2[H]-one 11.