Efficient synthesis of 9,10-dihydropyrano[2,3-h]chromene-2,8-dione derivatives in ionic liquid and the study of their antioxidant activity.

Ionic liquid N,N,N',N'-tetramethylguanidinium trifluoroacetate (TMGT) has been applied as a green and reusable catalyst for the one-pot synthesis of 10-aryl substituted-9,10-dihydropyrano[2,3-h]chromene-2,8-diones via reaction of various aromatic aldehydes, 5,7-dihydroxycoumarin derivatives and Meldrum's acid. The reactions were rapid, clean and the products were prepared in good yield. The ionic liquid was stable during the reaction process and reused without significant loss of its activity. The synthesised compounds were evaluated for their antioxidant activity by a 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay.