Methyl pentafluorobenzoate

In 1998, Ube Industries, Ltd. discovered that pentafluorobenzoates, such as methyl pentafluorobenzoate (62), can be used as additives in small quantities [92], Also, in 1999, Toyota Central R D Labs found that fluorinated benzoates, such as methyl 2,6-difluorobenzoate (63), can be used as additives in small quantities [93], and in 2002, Ube Industries, Ltd. found that pentafluorophenol compounds, such as pentafluorophenyl methanesulfonate (64) and methyl pentafluorophenyl carbonate (65), can be used as additives in small quantities [94]. 

Other derivatives unsubstituted at N 119 were synthesized in one step by condensation of hydrazine monohydrate and pentafluoroaryl ketones 118 in excellent yield (Scheme 38) [64], Interestingly, in the case of methyl pentafluorobenzoate 118 (R=OMe), the desired indazole is obtained in low yield (28 %) due to the fact that substitution of the fluorine by hydrazine occurs ortho- and para- to the ester group so, besides 4,5,6,7-tetrafluoro-lH-indazol-3-ol (119, R=OH)), the methyl 2,3,5,6-tetrafluoro-4-hydrazinylbenzoate is also formed. 

More recently, the same group reported another novel procedure for the synthesis of pyridines by cyclization of ketoxime acetates with ruthenium as the catalyst (Scheme 3.46) [95]. Here, a methyl carbon on DMF performed as a source of a one carbon synthon. For different propiophenone oxime carboxylates tested, such as propionate, tert-butyrate, and benzoate, showed similar reactivity as the corresponding acetate derivative. Only a trace of product was observed with pentafluorobenzoate. 

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