2,2-Difluorovinyl ketones

Nitroalcohols undergo addition to isopropyl 2,2-difluorovinyl ketone and isopropyl 3,3-difluoroacrylate in the presence of amines [6] (equation 5)... 

FIGURE 3.69 Synthesis of 1-substituted 5-fluoropyrazoles from 2,2-difluorovinyl ketones. 

Ichikawa, J. Kobayashi, M. Noda, Y Yokata, N. Amano, K. Minami, T. Regiocon-trolled syntheses of 3- or 5-fluorinated pyrazoles from 2,2-difluorovinyl ketones. J. Org. Chem. 1996, 61, 2763-2769. 

An alternative method for the synthesis of 5-fluoropyrazoles is depicted in Scheme 6. The target molecules 17 were obtained in high yields (76-95 %) and excellent regioselectivities (96/4-100/0) upon condensing 2,2-difluorovinyl ketones 16 with alkyl and arylhydrazines [9]. Reactions with alkylhydrazines occurred in aqueous ethanol at rt whereas, with arylhydrazines, the use of n-butyUithium was requisite to generate the anion of the hydrazine (Scheme 6). 

Trifluoroethanol is an extremely attractive building block. The alcohol is available in industrial quantities and is a stable liquid with a rich chemistry. The initial contributions in the area were made by Nakai et al. [126] conversion to the tosylate (itself a stable, crystalline commercial material) followed by exposure to LDA in THF at -78 °C led to the formation of difluorovinyl tosylate which reacted efficiently with hard electrophiles such as aldehydes and ketones. Ichikawa has converted this initial result into a powerful and versatile metho-... 

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