Alkyl fluoroformates

Fluorodediazoniation of alkyl carbamates in hydrogen fluonde/pyndine (70/30) represents a novel route to alkyl fluoroformates [6, 9] (equation 4)... 

Class D Alkyl fluoroformates quaternary ammonium salts,... 

The conversion of alcohols to the corresponding alkyl fluorides by the pyridine or boron trifluoride catalyzed decomposition of alkyl fluoroformates formed by the addition of 2, or of carbonyl chloride fluoride, to alcohols has been reported.47,48... 

Chloroalkyl carbonates do not undergo direct nucleophilic substitution with fluorine on heating with potassium fluoride either neat or in solution in the presence of 18-crown-6. They easily fragment to aldehydes and fluoroformates. This reaction has been exploited to synthesize valuable tertiary alkyl fluoroformates and benzyl fluoroformate. fert-Butyl fluoroformate (Boc-F) is a superior reagent for the preparation of Boc-amino acids.51... 

Table 1. Preparation of Alkyl Fluorides by the Decomposition of Alkyl Fluoroformates...

The preparation of alkyl fluoroformates from alkyl chloroformates with thallium(I) fluoride has been described previously.1-3... 

An alkyl chloroformate was treated at rt with an equimolar amount of T1F, which was added with stirring over a period of a few h. The stirring was continued for an additional 12 h. The mixture was then heated for 30 min on a steam bath and the product distilled off in vacuo and purified by redistillation. Pure alkyl fluoroformates were obtained yields 50-65%. 

The decomposition of alkyl fluoroformates proceeds either by heating in pyridine or by addition of boron trifluoride to yield the corresponding alkyl fluoride (see also Sections 16.1.2. and 13.7.). 

Aliphatic carbamates (readily available from alcohols and sodium cyanate)313 have also been submitted to fluorodediazoniation16,90 314 to give alkyl fluoroformates 890 which are useful tools in peptide synthesis and also valuable precursors of alkyl fluorides.315... 

On treatment with a potassium fluoridc-crown ether complex, alkyl 1,2,2,2-tetrachloroethyl carbonates are cleaved at the carbonyl group-oxygen bond to give high yields of alkyl fluoroformates [ 5] (equation 25)... 

Aliphatic carbamates 6 have also been diazotized and subjected to Quorodediazoniation to yield the corresponding alkyl fluoroformates 7 (see Vol. ElOa, pp 729-731), which are useful as synthetic tools in the preparation of peptides and as intermediates in the preparation of alkyl fluorides. This preparation of alkyl fluoroformates from the readily available carbamates using hydrogen fluoridc/pyridine eliminates the need to employ phosgene or its derivatives in the synthetic process. ... 

Aliphatic alkyl fluoroformates. as well as chloroformates, undergo thermal decomposition by warming in the presence of a catalyst elimination of carbon dioxide lakes place and an alkyl fluoride is formed. " ... 

In the preferred literature, most fluoroformates are prepared from their analogous chloroformates through halogen exchange using excess KF activated by a little 18-Crown-6. However, this method proved to be impractical for tertiary alkyl fluoroformates and/or benzyl fluoroformates, either because the corresponding chloroformates are not stable or because of the lack of selectivity of the fluoride attack. Acylation of the respective alcohols with COF2 or COFCI requires complex equipment not accessible to standard laboratories and/or multipurpose plants. 

Alkyl fluoroformates can be decarboxylated, for example by heating in the presence of pyridine or BF, to give the corresponding fluoride [380,382], or they can be further treated with SF4 to produce ROCF, [1856b,1856c] ... 

Alkoxysilanes, however, react with COFj (at 0-20%) in a similar way to that described for COClj to give silyl fluoride and alkyl fluoroformate derivatives [1452] in high yields ... 

Alkyl fluoroformates. These substances can be obtained in 30-75% yield by diazotization of alkyl carbamates in polyhydrogen fluoride-pyridine. 

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