Table . Optimization of the reaction conditions. Entry Flow rate 1 st reactor Flow rate 2 nd reactor SOCl2/acid ratio Yield (%) [a] Reactions performed on a 0.5 mmol scale of carboxylic acid 1, using 2.5 equivalents of triethylamine and 4-1.1 equivalents of thionyl fluoride. [b] Yields were determined by 19 F NMR analysis, using 1,2difluorobenzene as internal standard. [c] Reaction performed using 3 equivalents of Et3N.