Synthesis of novel chiral fluorinating agents, (+)- and (−)-N-fluoro-3-methyl-3-(4-methylphenyl)-2H-benzo[e][1,2]thiazine-1,1,4-triones

Treatment of N-t-butylbenzenesulfonamide with an excess of BuLi, followed by the reaction with methyl 2-(4-methylphenyl)propanoate, gave the corresponding 2-carboxybenzenesulfonamide, which underwent a sequence of consecutive N-deprotective cyclization process mediated by TMSCl-NaI-MeCN reagent to afford the N-sulfonylimine. Following the bromination and ring expansion, 3-methyl-3-(4-methylphenyl)-2H-benzo[e][1,2]thiazine-1,1,4-trione was obtained. Optical resolution of the racemic benzosultam using (−)-menthoxyacetyl chloride, furnished the optically pure (+)- and (−)-3-methyl-3-(4-methylphenyl)-2H-benzo[e][1,2]thiazine-1,1,4-triones, which were fluorinated with FClO3 to produce the corresponding chiral N-F agents.