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Interestingly, an early example of perfluoroalkylations using silver salts was the synthesis of multi‐trifluoromethylated fullerene [44]. In 2001, Boltalina's group prepared mixtures of multi‐trifluoromethylated fullerenes by solid‐state trifluoromethylation with silver trifluoroacetate at 300 °C [45]. The silver salt could add up to 22 trifluoromethyl groups to C60, although other metal trifluoroacetates such as copper, palladium, and chromium salts could add only less than 8 trifluoromethyl groups. Several multi‐trifluoromethylated fullerenes, including isomers, were independently characterized by means of nuclear magnetic resonance (NMR) and mass spectroscopies by Boltalina and coworkers [46] and Taylor and coworkers [47]. In 2007, Goryunkov and coworkers successfully determined the X‐ray crystal structures of some of them and discussed the observed isomeric distribution in mixtures of C60(CF₃)_n compounds up to n = 6 [48].

In 2015, Zhang and coworkers reported an electrophilic trifluoromethylation of aromatic compounds with trifluoroacetic acid by using a silver catalyst (Scheme 2.24) [49]. The Ag₂CO₃ catalyst was considered to facilitate the generation of CF₃ radical from trifluoroacetic acid via decarboxylation, and then this radical mediates aromatic trifluoromethylation. The resulting Ag(I) species is reoxidized by K₂S₂O₈, used as an additive.

Zhang's conditions have been applied to several types of fluoroalkylations using fluorine‐containing carboxylic acids. Nielsen and coworkers performed a decarboxylative difluoromethylation of N‐heteroaromatic compounds with difluoroacetic acid (Scheme 2.25a) [50]. Wan, Hao, and coworkers reported an aryldifluoromethylation of isocyanides with potassium difluoroarylacetate, affording phenanthridines bearing an arylated difluoromethene motif (Scheme 2.25b) [51, 52]. Wan, Hao, and coworkers [53] and Deng and coworkers [54] independently reported an oxindole synthesis by the reaction of N‐arylacrylamides with potassium difluoroarylacetate or its acid form in the presence of persulfate salts (Scheme 2.25c). Hashmi and coworker employed ethynyl benziodoxolone, as the coupling partner, in a decarboxylative aryldifluoromethylation with difluoroarylacetic acids (Scheme 2.25d) [55].

Scheme 2.24 Silver‐catalyzed electrophilic trifluoromethylation.

Scheme 2.25 Silver‐catalyzed fluoroalkylations with various fluorinated carboxylic acids. DMSO, dimethylsulfoxide; MS4Å, molecular sieves 4Å.