A novel, one-pot, simple, efficient procedure for 4H-pyrimido[2,1-b]benzothiazole (4a-h), pyrazole (6a-d) and benzylidene (7a-d) derivatives of curcumin under solvent and solvent free conditions in microwave with good yield is have been synthesized. The synthesized compounds were evaluated for their antibacterial activity against gram-positive and gram-negative bacteria viz. Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella typhi, Escherichia coli, Bacillus cereus and Providencia rettgeri and antifungal activity against fungi viz Aspergillus niger, Aspergillus fumigates, Aspergillus flavus. Detailed mechanistic study shows reaction proceeds through Knoevenagel type intermediate 3a which has been suggested as key intermediate for reaction (Fig. 3).