A new group of regioisomeric 2,3‐diaryl‐1,3‐benzdiazinan‐4‐ones, possessing a methyl sulfonyl pharmacophore, were synthesized and their biological activities were tested for cyclooxygenase‐2 (COX‐2) inhibitory activity. In vitro COX‐1/COX‐2 inhibition studies identified 3‐(p‐fluorophenyl)‐2‐(4‐methylsulfonylphenyl)‐1,3‐benzdiazinane‐4‐one (2b) as a potent and highly selective (IC50 = 0.07 µM; selectivity