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Diversely functionalized chromeno-pyrimidine-2,5-dione/thione compounds were synthesized by cyclocondensation of 4-hydroxy coumarin, aldehydes and urea/thiourea using tannic acid as a green catalyst and 1:1 (EtOH:H2O) as a green solvent. Different acids were screened for their catalytic activity of chromeno-pyrimidine-2,5-dione/thione derivatives. Tannic acid (10 mol%) was used as a suitable catalyst with increased catalytic activity. By utilizing this protocol, chromeno-pyrimidine scaffolds were prepared in acceptable to excellent yield without the use of conventional volatile organic solvent and toxic metal catalyst. To our best of knowledge, this is the first report, in which tannic acid is utilized successfully as an eco-safe catalyst for synthesis of fused pyrimidines.
Puvithra et al. (Wed,) studied this question.