Aromatic fluorine, hydrogenolysis

Hydrogenolysis (23S) of perchloryl aromatic compounds yields ArH and not ArOH, thus confirming the presence of a —Cl bond. Another useful reaction of FCIO3 involves the replacement of the active hydrogens of methylene compounds by fluorine (145, 262, 284). A typical example is the fluorination of malonic esters ... 

Polyhalo aromatic compounds with different halogens may be selectively hydrogenolyzed, usually in the order of increasing ease of hydrogenolysis fluorine < chlorine < bromine < iodine. Thus, 4-bromo-2,6-dichlorophenol was selectively debrominated to give 2,6-dichlorophenol over palladium catalyst in benzene-cyclo-... 

Hydrogenolysis of aromatic halides using catalytic hydrogenation takes place easily with rates of replacement of halogen decreasing in the order I > Br > Cl > F. For example, replacement of chlorine in preference to fluorine takes place in chlorofluoropyridines (equation 21)."... 

Hydrogenolysis of polyfluoro and perfluoro aromatics by lithium aluminum hydride has already been shown in equations (24) and (25). Additional examples are replacement of fluorine by hydrogen in pentafluorobenzene, where the predominant product is 1,2,4,5-tetrafluorobenzene (20), resulting from the reduction by lithium aluminum hydride para to the hydrogen (equation 38), and replacement of fluorine in the -position in 1,2,3,4-tetrafluoronaphthalene (equation 39). ... 

Very recently, a different synthetic approach to fluorinated p-lactams involving catalytic hydrogenolysis of the N-O bond of isoxazohdines appeared in the literature. The method involves the synthesis of isoxazohdines (71) by 1,3-cycloaddition of aromatic nitrones to fluorinated alkenes, followed by N-O bond cleavage by hydrogenolysis using palladium catalyst (Scheme 2.34). ... 

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