Telescoped Flow Process for the Syntheses of N-Aryl Pyrazoles

N -Aryl pyrazoles were prepared from anilines in a three step telescoped approach. An aniline was diazotized to give the diazonium fluoroborate, followed by reduction with tin(II) chloride to give the corresponding hydrazine, which in turn reacted with a ketoenamine to give the N -aryl pyrazole. The deprotection of the methyl ether was accomplished with PhBCl 2 to give the final product. The continuous flow methodology was used to minimize accumulation of the highly energetic and potentially explosive diazonium salt and hydrazine intermediates to enable the safe scale-up of N -aryl pyrazoles. The heterogeneous reaction mixture was successfully handled in both lab scale and production scale. A continuous extraction was employed to remove organic impurities from the diazotization step, which eliminated the need for chromatography in the purification of the final N -aryl pyrazole.