Verjuice as a green and bio-degradable solvent/catalyst for facile and eco-friendly synthesis of 5-arylmethylenepyrimidine-2,4,6-trione, pyrano[2,3-d]pyrimidinone and pyrimido[4,5-d]pyrimidinone derivatives

Abstract

Verjuice (unripe grape juice), a natural mixture of organic acids, which is identified by pH-metric and TGA analysis, is efficiently used for the promotion of the synthesis of 5-arylmethylenepyrimidine-2,4,6-triones, via Knovenagel condensation reaction between barbituric or thiobarbituric acid and aldehydes. Verjuice is also employed for the effective synthesis of pyrano[2,3-d]pyrimidinone derivatives via a three-component reaction of barbituric acid or its thio analogue, aldehydes and malononitrile. In the same way, pyrimido[4,5-d]pyrimidinone derivatives are simply produced via the reaction of barbituric acid, aldehydes and urea or thiourea in the presence of verjuice. This green methodology rewards notable advantages including simple procedures, acceptable reaction times, easy work-up, high yields, circumventing the use of any expensive starting materials, volatile and hazardous organic solvents during the reaction and work-up process, and use of a natural, low-cost, reusable, and bio-degradable catalyst.