Efficient one-pot syntheses of dibenzo[a,i]xanthene-diones and evaluation of their antioxidant activity

Facile and convenient procedures for the synthesis of dibenzo[a, i] xanthene-diones have been described. The process employs one-pot condensation of aldehydes, 2-hydroxynaphthalene-1,4-dione, and 2-naphthol/2,7-dihydroxynaphthalene/2,6-dihydroxynaphthalene using catalytic sulfuric acid in water under reflux. Task-specific ionic liquid, 1-butyl-3-methylimidazolium hydrogen sulfate ([bmim]HSO4), has also been found to be an effective catalyst for this transformation. The protocols defined herein prove to be efficient in terms of high yields, operational simplicity, easy workup, and short reaction time. Also, these compounds were screened for antioxidant activity by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay.