The condensation of 4-(methylsulfanyl)benzaldehyde (I) with 4-fluorophenylacetic acid (II) in refluxing acetic anhydride containing one equivalent of triethylamine, followed by aqueous hydrolysis, provided the diarylpropenoic acid (III). Curtius rearrangement of acid (III) by treatment with diphenylphosphoryl azide in cold toluene, and subsequent hydrolysis of the intermediate isocyanate afforded diarylethanone (IV), which was then brominated in a solution of HBr in acetic acid to give bromoketone (V). The cyclization of this bromoketone with 2-chlorothiobenzamide (VI) in refluxing acetonitrile gave rise to thiazole (VII), and then, oxidation with meta-chloroperbenzoic acid in dichloromethane provided the target sulfone.
Treatment of benzoin (I) with methanesulfonyl chloride and LiCl, followed by condensation with thioacetamide afforded 2-methyl-3,4-diphenylthiazole (II). Subsequent selective chlorosulfonation at the most reactive 5-phenyl group of (II) provided sulfonyl chloride (III). This was finally converted to the target sulfonamide upon treatment with ammonium hydroxide.