Pyrazoles fluoromethyl

This method has been extended to heterocycles bearing a hydroxymethyl-substituted nitrogen. Thus, ethyl l-(hydroxymethyl)pyrazole-4-carboxylate (10) is converted into ethyl 1-(fluoromethyl)pyrazole-4-carboxylate (11) in 76% yield with cesium fluoride/methanesulfonyl fluoride/18-crown-6 system.167 Potassium fluoride did not react at all and tetrabutylammonium fluoride leads to decomposition and formation of coupling products. 

Ethyl-l-(Fluoromethyl)pyrazole-4-carboxylate (11) Typical Procedure 167... 

As noted above, the first monomeric pyrazol-l-ylborane was isolated as its trimethyl-amine adduct The compound (CH3)3N—BH2[pz-3,5-(Cp3)2] (Hpz = pyrazoie) was obtained as a distillable material on reaction of (CH3)3N—BH3 with 3,5-bis(tri-fluoromethyl)pyrazole = H[pz-3,5-(Cp3)2] = Hpz. Surprisingly, when THP—BH3 (THF = tetrahydrofuran) was employed as reagent, the dimeric species H2B(p-pz )2BH2, a pyrazabole (see Sect. IV.), was obtained without difficulty Apparently, the two-coordinate nitrogen of the pyrazolyl group in THP—BH2[pz-3,5-(Cp3)2] is sufficiently basic to displace THP but this base displacement cannot occur in the corresponding (CH3)3N—BH2[pz-3,5-(Cp3)j]. 

Despite their hazardous preparation and handling, trifluorodiazoethanes have been employed in cycloaddition reactions with various dipolarophiles, both alkenes and alkynes, to give tri-fluoromethyl-substituted pyrazoles and pyrazolincs. - ... 

Chemical Name 5-Amino-l-(2,6-dichloro-4-(tri-fluoromethyl)phenyl)-4-((l,R,S)-(trifluorome-thyl)sulfinyl)-l-fT-pyrazole-3-carbonitrile Chemicae Abstracts Service Registry Number CAS 120068-37-3 Synonym Eiprole... 

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