4-(2-fluorobenzyl)-2H-benzo[b][1,4]thiazin-3(4H)-one (1 g, 3.66 mmole) and methyl 4-formylbenzoate (1.2 g) were dissolved in THF (20 mL) and to the solution was added NaOEt (1 g). The reaction solution was heated at 70° C. overnight and aqueous HCl (5%, 10 mL) was added to quench the reaction. The mixture was extracted with EtOAc (50 mL) twice and combined organic layers were dried over anhydrous magnesium sulfate. After filtration, the solvent was removed under vacuum to give 4-((Z)-(4-(2-fluorobenzyl)-3,4-dihydro-3-oxobenzo[b][1,4]thiazin-2-ylidene)methyl)benzoic acid (1.13 g, 71%).
