Methyl chlorodifluoroacetate

The pyrolysis of sodium chlorodinuoroacetate is still a widely used, classical method for generating difluorocarbene, especially with enol and allyl acetates [48, 49, 50, 51] (equation 21) A convenient alternative that avoids the hygroscopic salt uses methyl chlorodifluoroacetate with 2 equivalents of a lithium chlonde-hexa-methylphosphoric triamide complex at 75-80 °C in triglyme [52], Yields are excellent with electron-rich olefins but are less satisfactory with moderately nucleophilic alkenes (4-5% yields for 2-bulenes)... 

Simultaneous elimination of chloride ion and carbon dioxide occurs dunng heating of methyl chlorodifluoroacetate with lithium chloride in hexamethyl-phosphoric tnamide (HMPA) The difluorocarbene generated in this way is trapped by electron-rich alkenes to form 1,1-difluorocyclopropanes [26] (equation 24)... 

An interesting application of the method is the reaction involving methyl chlorodifluoroacetate (Table 15) [95], the activation of which cannot be performed chemically. The reactions were best conducted in CH2CI2-DMF (90 10) as solvent instead of DMF. Here also a transmetallation has been invoked, on the basis of F NMR analysis of the reaction mixture. 

The generation of difluorocarbene has been the subject of intense investigation. Difluorocarbene has been successfully formed from a wide range of fluorinated precursors, including metal salts of chlorodifluoroacetic acid, methyl chlorodifluoroacetate, ethyl chlorodi-fluoroacetate, difluorodiiodomethane, " chlorodifluoromethane." " difiuorotris(trifluoro-methyl)-A -phosphane hexafluoropropylene oxide,tetrafluoroethylene... 

Heating a mixture of methyl chlorodifluoroacetate, lithium chloride and hexamelhylphosphoric triamidc in dichloromethane at reflux, or in diglyme at 80 C. results in the generation of difluorocarbene under relatively mild nonbasic conditions. Alternatively, difluorocarbene can... 

Methyl chlorodifluoroacetate decomposes to difluorocarbene on reaction with lithium chloride complexed with hexamethylphosphoric triamide or potassium fluoride with 18-crown-657 (Houben-Weyl, Vol. El 9b, p 1478), for example, formation of 13.21,57... 

Decarboxylation of methyl chlorodifluoroacetate with lithium chloride in HMPA in the presence of chlorodifluoroacetophenone yields mainly 1-chloro-l-phenyldifluoroethylene, probably by the mechanism shown in Scheme 11. Pyrolysis of the acid chlorides, CFs O CFs CFa COCl and HCF2 (CF2)6 COCl, causes loss of COFCl and formation of the olefins, CFs O-CFiCFs or HCF2 (CF2)3 CF CF2. Addition of bistrifluoromethylketen to bis-p-tolylcyclo-propenone yields triafulvene (13), which has a dipole moment of 7.42 D, suggestive of considerable charge separation. 

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