Hypofluorite

Fluorine forms very reactive halogen fluorides. Reaction of CI2 and F2 at elevated temperatures can produce GIF, CIF, or CIF 3 be obtained from the reaction of Br2 and F2. These halogen fluorides react with all nonmetals, except for the noble gases, N2, and O2 (5). Fluorine also forms a class of compounds known as hypofluorites, eg, CF OF (6). Fluorine peroxide [7783-44-0], O2F2, has also been reported (6). 

Eused-ring polycycHc fluoroaromatics can be made from the corresponding amino fused-ring polycycHc or from preformed fluoroaromatics, eg, 4-fluorophenyl-acetonitrile [459-22-3] (275). Direct fluorination techniques have been successfully appHed to polycycHc ring systems such as naphthalene, anthracene, benzanthracenes, phenanthrene, pyrene, fluorene, and quinoHnes with a variety of fluorinating agents xenon fluorides (10), acetyl hypofluorite (276), cesium fluoroxysulfate (277), and electrochemical fluorination (278,279). 

Survey of Fluorinaling Agents Table 7. Organic Hypofluorites... 

Diazoketones react with trifluoromcthyl hypofluorite to give a mixture of a,a-difluoro ketones and o-fluoro-a-trifluoromethoxy ketones [70, 71] With elemental fluorine, two fluorine atoms replace the nitrogen in both diazoketones and unactivated diazo eompounds [70, 72, 73] (equation 9)... 

Isocyanides react with fluorine [75 to yield difluoromethylene imines, which tend to dimerize In an inert solvent, imines accept fluorine fioin trifluoromethyl hypofluorite [76, 77] (equation 11)... 

Although fluonnation of peroxoanions [S2] has been examined, the major emphasis in the fluonnation of oxygenated material is the preparation offhioroxy compounds The simplest, trifluoromethyl hypofluorite, can be prepared almost quantitatively by the action of fluorine on carbonyl fluoride (fluorophosgene) in the presence of various catalysts [Si, 84] Addition of fluorine to trifluoroacetic acid [S5] or its sodium salt [S6] gives rise to FjCF(OF)2 Long-chain fluoroxy compounds can also... 

In addition, fluonne [97, 98], trifluoromethyl hypofluorite [99, 100], bisftri-fluoromethyOperoxide [100, 101], trifluoromethyl disulfide [100]. and xenon difluoride [102, lOi, 104] react with phosphines to give the corresponding diflu-orophosphoranes in yields ranging from 25% to near quantitative. Phosphites are fluorinated by carbonyl fluoride [95, 96] or 2-hydroperfIuoropropyl azide [f05J (equation 15). 

The product from fluonnation of sodium acetate is acetyl hypofluorite [64], which IS isolated and characterized [65] The value of this reagent lies in its relative mildness, because it reacts cleanly with most olefins adding the elements of acetoxyl and fluorine [66] Tnfluoroacetyl hypofluorite adds cleanly only to benzylic or electron-rich double bonds... 

Fluoroxytrifluoromethane (trifluoromethyl hypofluorite) and acetyl hypofluorite are the most commonly used neutral hypofluontes, cesium fluoroxysultate is an inorganic anionic fluoroxy derivative... 

Fluoroxy reagents became of general synthetic utility after the discovery of a relatively simple preparation of acetyl hypofluorite [i5] (equation 2)... 

The synthetic procedure has been extended to the preparation of trifluoro-acetyl hypofluorite [16, 17], long-chain perfluorinated hypofluorites [18, 19], and radiolabeled hypofluorites [II, 12],... 

The white cesium fluoroxy sulfate precipitates from the reaction medium and may be kept for several months in the cold (0 to -15 °C) Metal surfaces can cause detonation of the reagent. The reaction scope of cesium fluoroxysulfate seems narrower than that of acetyl hypofluorite because of its limited solubility in organic solvents Cesium fluoroxysulfate has not been prepared with a fluorine-18 label. 

Fluororesorcinol can be prepared from derivatives of resorcinol and fluo-roxytrifluoromethane [15, 24] (equation 4) or by fluorination of resorcinol with cesium fluoroxysulfate [25] (equation 5). Reaction of acetyl hypofluorite with M-acetyl-O-methyltyrosine methyl ester provides a good route to 3-fluorotyrosine derivatives [26] (equation 6). 

Acyl hypofluorites react readily with ends, enol acetates, vinyl ethers, and enolates [39, 40, 41] (Table 2, entries 1-7) Steroidal enol acetates are also fluorinated smoothly [39] (equations 17-19)... 

Vinyl acetates are also fluormated by mixtures contammg both acyl hy-pofluorite and perfluoroalkyl hypofluorite, obtained from fluorinatton of the carboxylic acid salts [16 19] (equations 20 and 21)... 

Fluorine is well known for its ability to fluonnate seleeti vely terttary carbon-h drogen bonds that are slightly activated by polar substituents Hypofluorite reagents also react with carbon-hydrogen bonds, both secondary and tertiary but tertiary bonds react better [6]... 

Acetyl hypofluorite is very effective m the fluorination of the aryl-metal (Hg, Ge, or Si) bond, but yields are frequently low. With aryl silicon compounds some competition exists for replacement of an aromatic hydrogen [5i, 52, 55, 54] (equations 25-27). Fluoroxytrifluoromethane fluorinates p-methoxypheny 1 mercuric acetate to givep-fluoroanisole in 86% yield [52]... 

The aryl tin compounds are better substrates for fluorination because they give high yields of fliiorinated aromatics and they may be fluorinated with acetyl hypofluorite, cesium fluoroxysulfate, or fluorine [52, 54 (equation 28). Aryl boronic esters react with cesium fluoroxysulfate to produce fluoroaromatics [55] (equation 29). 

Acetyl hypofluorite gas is used in a reaction with an arylmercunc acetate to produce a derivative of L-DOPA [56] (equauon 30). 

Table 3. Comparison of Electrophilic Fluorination of Aromatic Amino Acids with [ F]fluorine or [ F]acetyl Hypofluorite" [25]...

A, [ F]fluorine diluted with an unreactive gas B, [ F]acetyl hypofluorite. For companson with F]F2, the radiocherracal yields obtained with acetyl hypofluonte need to be divided by 2... 

Preparation of o- and p-Fluoroacetanilide, 164, 165 Fluorination witli Acetyl Hypofluorite... 

The very reactive yellow SF5OF, which is one of the few known hypofluorites, can be made by... 

In the absence of CsF the product is SOF4 (p. 687) and this can then be isomerized in the presence of CsF to give a second hypofluorite, SF3OF. Derivatives of -SF5 are usually reactive volatile liquids or gases, e.g. ... 

Two further oxofluorides of Se can be prepared by reaction of Se02 with a mixture of P2/N2 at 80° the main product is the hypofluorite PsSeOP whereas at 120° the peroxide PsSeOOSePs predominates. The compounds (Table 16.7) can be purified by... 

The syn addition of pentafluoroethyl hypofluorite (CF3CF2OF), generated in situ by the action of anhydrous, hydrogen-fluoride-free fluorine gas on sodium trifluoroacetate, to 5-acetyl-5//-dibenz[/i,/]azepine (11) has been reported to yield 12.135... 

Fluorination. Direct fluorination of quinoline was accompanied by extensive fragmentation of the heteroring, but trifluoromethyl hypofluorite in trichlorofluoromethane at -70°C converted 5-fluoro-8-hydroxyquino-line into the 5,7-difluoro-8-hydroxy product (72JMC987). Quinoline, itself, was perfluorinated by fluorine and cobalt(III) fluoride (56JCS783), whereas cesium tetrafluorocobaltate at around 350°C converted it into a mixture of saturated polyfluoro compounds (82JFC413). It is much more satisfactory to introduce fluorine by nucleophilic methods. 

In a related procedure, even benzene and substituted benzenes (e.g., PhMe, PhCl, xylenes) can be converted to phenols in good yields with sodium perborate F3CS020H. " Aromatic amines, N-acyl amines, and phenols were hydroxylated with H2O2 in SbFs—HF. Pyridine and quinoline were converted to their 2-acetoxy derivatives in high yields with acetyl hypofluorite AcOF at -75°C. ... 

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