Fluoroacylation

Acylation of various oxygen functions by use of common and commercially available fluonnated carboxylic acid denvatives such as trifluoroacetic anhydride or the corresponding acyl halides have already been discussed sufficiently in the first edition [10] Therefore only exceptional observations will be described in this section In the past 15 years, many denvatizations of various nonfluonnated oxygen compounds by fluoroacylation were made for analytical purposes. Thus Mosher s acid chlorides for example became ready-to-use reagents for the determination of the enantiomeric purity of alcohols and amines by NMR or gas-liquid chromatographic (GLC) techniques [//] (equation 1)... 

For most cases, common fluoroacyl derivatives are sufficiently reactive and selective Thus conversion of perfluoroglutaric dichloride to a monomethyl ester by methanol proceeds smoothly under the appropriate reaction conditions [17] (equation 9) Perfluorosuccinic acid monoester fluoride, on the other hand, is prepared most conveniently from perfluorobutyrolacetone (equation 10) Owing to the strong acidity of a fluorinated carboxylic acids, Fischer esten-ficaiton with most aliphatic alcohols proceeds autocatalytically [79 20]... 

Fluoroacetylation of hydrogen sulfide, mercaptans, and thiocyanates have already been discussed in the first edition [10] A useful extension of this particular chemistry is the fluoroacylation of trifluoromethyldisulfane [30] (equation 19)... 

Ruonnated carboxylic anhydrides and acyl halides as common acylating reagents to convert amines to amides and to acy late suitable heterocyclic nitiogen atoms have already been described in the first edition [10] Like in the acylation at oxygen, much synthetic activity was concentrated m the past few years on the denvatization of biomolecules by fluoroacylation reactions, that is, tnfluoroacetylation of amino sugars,... 

By contrast, reaction of XeFi with the iridium carbonyl complex cation [Ir(CO)3(PEt3)2] in CH2CI2 results in addition across one of the Ir-CO bonds to give the first example of a metal fluoroacyl complex ... 

Sodium salts of fluoroacids react with chlorine fluoride at —112 to —78°C to give explosively unstable fluoroacyl hypochlorites. Trifluoroacetyl hypochlorite and its pentafluoropropionyl, heptafluorobutyryl, difluoroacetyl and chlorodifluo-roacetyl analogues explode without fail if the partial pressure exceeds 27-67 mbar. Hexafluoroglutaiyl dihypochlorite explodes above — 10°C [1]. Of the 4 compounds prepared, acetyl, propionyl, isobutyryl and pivaloyl hypobromites, the 2 latter appeared stable indefinitely at —41°C in the dark, while the 2 former exploded unpredictably as isolated solids [2],... 

D. Block, H.H. Coenen, G. Stocklin, N.C.A. F-Fluoroacylation via fluorocarboxylic acid esters, J. Label. Compds Radiopharm. 15 (1988) 185-200. 

Nucleocidine is a nucleoside that has been isolated from cultures of Streptomyces clavus, a bacteria found in the ground of India. This nucleoside has an intriguing structure it bears a fluorine atom in the 4 position of the ribose cycle. This fact seems to exclude the possibihty of its biosynthesis from a fluoroacyl fragment. 

The addition of chlorine monofluoridc across the C = 0 bonds in difluorophosgene, per-fluoroacyl fluorides, and perfluoroketones with the formation of hypochlorites occurs only in the presence of the catalysts potassium fluoride, rubidium fluoride, cesium fluoride80,81 or the strong Lewis acids hydrogen fluoride, boron trifluoride, or arsenic(V) fluoride.82 The cesium fluoride catalyzed reactions are carried out in an autoclave for 2-3 hours at — 20"C or left overnight.80... 

An allenic structure possessing two ester groups at one carbon atom is dihydroxylated at the double bond closer to the ester groups to afford a-fluoroacyl-x-hydroxymalonate (Table 11 ).90... 

The simultaneous elimination of fluorine and chlorine from a-fluoroacyl halides results in the formation of a,/i-unsaturated compounds 2.192... 

Arsoranes that contain fluoroacyl groups have been obtained by the methods described in the following paragraphs. 

Reactions of carbomethoxymethylene triphenylarsorane with per-fluoroacyl chlorides gave perfluoroacylcarbomethoxymethylene triphenyl-arsoranes (26) (42). 

For compounds 5 to 11 with fluoroacyl substituents, the base peak was the ion formed by the elimination of the fluoroalkyl group. 

The asymmetric catalytic aldol reaction of silyl allenolates ICH=C=CR2OSiMe3 with aldehydes R CHO has been achieved by Li et al. by using N-C3F7CO oxazaborolidine as the catalyst [43], The fluoroacyl group of the catalyst was found to be crucial for control of enantioselectivity. The reaction provides the first enantioselective approach to / -halo Baylis-Hillman-type adducts. 

F]Fluoroacylation with [18F]fluoroacetic acid and [2-18F]fluoropropionic acid derivatives... 

NCA a-[18F]Fluoro-substituted acetic and propionic acid esters have been obtained169 by aminopolyether (APE 2.2.2) supported nucleophilic exchange as shown in equation 76 and applied169 for NCA 18F-fluoroacylation of ethanol (equation 77) and of -butylamine (equation 78). The above reactions are relevant to 18F-labelling of biomolecules such as peptides170. 

Sulfonyl Fluorides. Sulfonyl fluorides inhibit serine proteases by reacting with the active-site serine residue. Previously we investigated the rates of inhibition of human leukocyte elastase and cathepsin G by a variety of sulfonyl fluorides and found relatively little selectivity or reactivity (38). However, we have discovered recently that the introduction of fluoroacyl groups into the sulfonyl fluoride structure gives considerable reactivity and selectivity for elastase (39). 

In a similar vein, the addition of XeF2 to [Ir(CO)3(PR3) 2]+ results in addition of F2 across an Ir—C bond to give the fluoroacyl derivative,... 

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