Fluoroaromatic amines

The required A-arylhydroxylamines may also be generated in situ by treatment of the corresponding nitrobenzenes with mild reductive metals in liquid hydrogen fluoride323 (former reports324-325). Examples of the reduction of nitroaromatic compounds 12 to fluoroaromatic amines 11 arc given below.323... 

Fluoroaromatics are produced on an industrial scale by diazotization of substituted anilines with sodium nitrite or other nitrosating agents in anhydrous hydrogen fluoride, followed by in situ decomposition (fluorodediazoniation) of the aryldiazonium fluoride (21). The decomposition temperature depends on the stabiHty of the diazonium fluoride (22,23). A significant development was the addition of pyridine (24), tertiary amines (25), and ammonium fluoride (or bifluoride) (26,27) to permit higher decomposition temperatures (>50° C) under atmospheric pressure with minimum hydrogen fluoride loss. 

Studies of the S Ar mechanism have involved theuse of 2,4-dmitrofluoroben-zene as a substrate The S, jAr reaction of fluoroaromatics is catalyzed by both aromatic and alphatic amines [42. 43 44, 45, 46 47, 48, 49] Diamines [50] and... 

The decomposition of arenediazonium tetrafluoroborates in the resulting fluoroarene as solvent has also been utilized.179 This method is very fruitful in the synthesis of fluorobenzene (96% yield) or fluorotoluenes (85-88% yield for the three isomers) but fails with substrates such as anisolediazonium tetrafluoroborates which probably arylate the reactive fluoroaromatic solvent. In contrast, perfluorinated tertiary amines (EF-L 174, F-C 40), perfluorinated alkyl tetrahydropyran (EF-L 102), perfluorodecahydronaphthalene (Flutec PP7) or other per-fluorocycloalkanes (Flutec s) are claimed to be the best media for fluorodediazoniation of all types of diazonium tetrafluoroborates.224 These media seem to be more efficient, at least in the synthesis of 1,2-difluorobenzene, than silicone oil which has also been claimed to improve fluorodediazoniation.225... 

Not only is thermal fluorodediazoniation possible, but the corresponding pliotochemically induced process is also possible (see Vol. E 10a, p 703). Several aromatic fluorides can be prepared viti diazotization and pliotochemically induced fluorodediazoniation of aromatic amines in anhydrous hydrogen fluoride-organic base solutions. In general, no fluoroaromatic compounds can be isolated if the fluorodediazoniation stage is carried out without photochemical irradiation under similar conditions (rt). 

General method for nucleophilic displacement (by primary amines) ofjluor-oaromatic substituents to introduce a nudeophile into precursors (at R ) of the acyl iminium cyclization (not applicable in Scheme 19) A 2 m solution of a primary amine in DMSO (5 mb, 66.7 equiv.) was added to the resin bearing the fluoroaromatic substituent (0.5 g, 0.15 mmol, 1 equiv.) and the suspension was shaken (vortexed) at ambient temperature for 16 h. The resin was then filtered off and washed with CH2CI2 (2 x 10 mb) and DMF (3 x 10 mb) to give the desired product. 

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