The present article describes the synthesis of dihydrobenzo[4,5]imidazo[1,2-a]pyrimidin-4-one (2a-h) under microwave irradiation. The product was obtained in excellent yield (74-94%) in a shorter reaction time (2 min). These molecules (2a, b) further reacted with various substituted 4-bromomethylcoumarins (3a-f) to yield a new series of coumarin substituted dihydrobenzo[4,5]imidazo[1,2-a]pyrimidin-4-ones (4a-h). The structure of all the synthesized compounds were confirmed by spectral studies and screened for their in vitro antibacterial activity against three Gram-positive bacteria viz., Staphylococcus aureus, Enterococcus faecalis, Streptococcus mutans and three Gram-negative bacteria viz., Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa and antifungal activity against Candida albicans, Aspergillus niger, Aspergillus fumigatus, Aspergillus flavus, Fusarium oxysporum, Penicillium chrysogenum and anticancer activity against Dalton's Ascitic Lymphoma (DAL) cell line. In general, all the compounds possessed better antifungal properties than antibacterial properties. The coumarin substituted dihydrobenzo[4,5]imidazo[1,2-a]pyrimidin-4-one (4g) (R = i-Pr, R₁ = 6-Cl) was found to be the most potent cytotoxic compound (88%) against Dalton's Ascitic Lymphoma cell line at the concentration of 100 μg/mL.