Trifluoroacetamido reaction conditions

Cydocondensation of N-(trifluoroacetamido)-o-arylenediamines leads to a series of 2-trifluoromethylarylimidazoles with good yields on montmorillonite K10 in dry media under the action of microwave irradiation within 2 min. Using conventional heating under the same conditions, no reaction was observed [104] (Eq. (54) and Tab. 3.23). 

The main advantage of photochemical fluorodediazoniation lies in the fact that, under very mild conditions, UV irradiation promotes it more efficiently than most of the side reactions. Thus, this technique has been successfully applied to diazonium tetrafluoroborates which fail to deliver aryl fluorides thermally, such as 4,5-dimethoxy-2-[2-(trifluoroacetamido)ethyl]ben-zenediazonium tetrafluoroborate which is a precursor of 6-fluoro-substituted dopamine.251... 

Of further interest is that a trifluoroacetamido group, under conditions of a displacement reaction, gives N-attack only (entry 8), whereas, under conditions of solvolysis, ring contraction (see entries 9 and 10) and no participation is observed. The forced participation of a M-benzoylcarbamate group, depicted in entries 11 and 12, shows dependence in the mode of attack (0- or N-cyclisation) on the anomeric configuration. 

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