Lithium chlorodifluoroacetate

Lithium chlorodifluoroacetate in preparation of perfluoroolefins from perfluoroalkyl ketones, 48, 119... 

The procedure illustrates a fairly general method for the preparation of -substituted perfiuoroolefins. The method has been applied to the synthesis of 2-cyclohexyl- (70%), 2-benzyl- (61%), and 2-(/>-fluorophenyl)perfluoropropenes (67%), and it is probably applicable to any a-trifluoromethyl ketone. Olefins containing a perfluoroalkyl group other than trifluoromethyl can be prepared by the same procedure by the substitution of lithium chlorodifluoroacetate for sodium chlorodifluoroacetate.7 Other routes to / -substituted perfiuoroolefins are not general or convenient. Routes to perfiuoroolefins generally yield the a-substi-tuted olefin rather than the /3-substituted olefin. 

The sodium salt is generally used, but lithium chlorodifluoroacetate is more effective, particularly in diglyme (see Houben-Weyl, Vol. E19b, p 1478). Added alkali metal fluoride salts usually greatly accelerate the decomposition of the difluorocarbene source, but this has not applied to the preparation of 1,1-difluorocyclopropanes. 

Metal, Metalloidal, and Non-metal Fluoroacetates.— Fluorine Magnetic Resonance Studies.I.para-Substituted P-DifluorostyTeae [thepP-difluorostyrenesp-XC,H(-CH CFs (X — NMe OMe, Me, H, F, Cl, or CN) were obtained via the CF,Cl-CO,Na-Ph,P-aldehyde route]. Reaction of Difluorocarbene with 2-Benzylidenecyclohexanones to afford Phenylfluorofurans (CF2 generated via thermal decomposition of CF CI-COjNa). Cyclodecapentaene Derivatives (reaction of CF, from CFjCI-COjNa with 1,4,5,8-tetrahydronaphthalenes). Action of Sodimn and Lithium Chlorodifluoroacetates on... 

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)... 

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... 

ICOBu-0 - cell (w Molhyllllhium). lym-Dinuoroletrachloroacetone (K.OBu-r) — CFCI. Ethyl trichloroacetale (NaOCHi) -< CX lj. Lithium ethoxide, generation of 2,2-diphenyl-cyclopropylidene. Phenyl(bromodichloro)mercury (80°) —> CBrj. Phenyl(trichloromethyl)-mercury (47 hrs. at 80° or Nal at 25°) -> CCli. Sodium chlorodifluoroacetate (heat) - CFs. Sodium trichloroacetate (heat) -> CCIj. 

Slagel12 reports that the lithium salt of chlorodifluoroacetic acid is superior to the sodium salt for generation of difluorocarbene and difluoromethylenetriphenylphos-phorane. Thus the yield of 4,5-dicarbethoxy-l,l-difluoronorcarane from the lithium salt was 50.6% and from the sodium salt was 25.7%. 

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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