Efficient synthesis of a novel series of indeno-fused pyrido[2,3-d]pyrimidines using a deep eutectic solvent system comprised of choline chloride/urea

A series of 13 aryl indeno[2′,1′:5,6]pyrido[2,3-d]pyrimidine-2,4,6-(3H,5H,11H)-triones, eight of which are new, were synthesised regioselectively in high yields by a three-component reaction of 1,3-indanedione, an araldehyde and 6-aminopyrimidin-2,4(1H,3H)-dione in the presence of a deep eutectic solvent comprised of choline chloride/urea (1:2) as the catalyst. The reaction conditions were mild and did not require additional catalysts. Given the inexpensive, nontoxic and recyclable nature of the deep eutectic solvent, these reaction conditions are simple to carry out and environmentally friendly.