A synthetically useful approach for one-pot preparation
of 1-aryl-3-trifluoromethylpyrazoles
using in situ generated nitrile imines and mercaptoacetaldehyde applied
as 1 equiv of acetylene is presented. This protocol comprises (3 +
3)-annulation of the mentioned reagents to form 5,6-dihydro-5-hydroxy-4H-1,3,4-thiadiazine, followed by cascade dehydration/ring
contraction reactions withp-TsCl. In addition, representative
nonfluorinated analogues functionalized with Ph, Ac, and CO2Et groups at the C(3)-position of the pyrazole ring were also prepared
by the devised method.