p-TsOH Catalyzed regioselective synthesis of 8,8'-methylene-bis-4- oxo-dihydrochromeno [4,3-c]pyrazoles

Abstract

The ethyl-5-[3-(ethoxycarbonyl)-4-hydroxybenzyl]- 2-hydroxybenzoate 3 is prepared by the usual esterification of 5-(3-carboxy-4-hydroxybenzyl)-2-hydroxy benzoic acid 2. Compound 3 on reacting with ethyl acetoacetate yields 3-acetyl-6-[(3-acetyl-4-hydroxy-2-oxo-2H-6- chromenyl)methyl]-4-hydroxy-2H-2-chromenone 4. The regioselective conversion, by cyclizing the hydrazone 5 of compound 4 to either 8,8'-methylene-bis-4-oxo-1,4-dihydrochromeno [4,3-c]pyrazoles 6 with p-toluene sulfonic acid in refluxing xylene or 8,8'-methylene-bis-4-oxo-2,4-dihydro chromeno[4,3-c]pyrazoles 7 with corresponding hydrazine hydrochloride in refluxing acetic acid is described.