Pyrazoles difluoromethyl

Scheme 12.1 shows a synthetic example via route A, which provides tri and difluoromethylated pyrazole analogues in reasonable yields. Condensation of 4-aryl-l,l,l-trifluoro-2,4-butanedione 26 with aryl hydrazine 27 in aqueous A,A-dimethy-lacetamide provides the desired pyrazoles 28 in good yields with an excellent regioselectivity (3-CF3-5-aryl >99.5-99.8%). The high regioselectivity arises from... 

A coupling between the fluorine nuclei and methylene protons on C3, 1/hf of 2.4-2.5 Hz, has been reported by Boltacheva et for l- 2-amino-6-methylpyrimidin-4-yl)-5-difluoromethyl-3-phenyl-4,5-dihydro-lH-pyrazol-5-ol synthesized by them during their studies on the reactions of fluoroallqrl-substituted lithium 1,3-diketonates with various hetarylhydrazines. 

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