Geminal difluoride

Alkylacetylenes form geminal difluorides by reaction with hydrogen fluoride, neat or in ether solution, at -50 to 0 [7) or by reaction with the pyridinium... 

Table 6. Conversion of Aryl Hydrazones to Geminal Difluorides...

Geminal difluorides usually require a strong base for conversion to vinylic fluorides, but some aluminum oxides such as neutral y-alumina or Woelm alumi-... 

N P Cl (NEt2) 2 (as monitored by F nmr and glc) with antimony trifluoride gives the cis non-geminal difluoride while the use of potassium fluorosulfate gives the cis geminal difluoride. The tetrafluoro derivative, cis-2,4-N P F (NEt, ) can be obtained from... 

Ethylene dithioacetals of benzophenone and its 4-fluoro-, 4-bromo-, 4,4 -difluoro-, 4,4 -dichlo-ro-, and 3,5-dimethyl-substituted analogs react with sulfuryl chloride or sttlfuryl chloride fluoride in hydrogen fluoride/ pyridine at — 78 C to room temperature to give the corresponding geminal difluorides in 85-90% yield. The reaction is, however, not applicable to dialkyl or alkyl aryl ketones as they undergo chlorination under these conditions.73... 

Geminal difluorides usually require a strong base for conversion to vinylic fluorides, but some aluminum oxides, such as neutral y-alumina or Woelm aluminum oxide, result in ready de-hydrofluorination under unexpectedly mild conditions. Just stirring the geminal difluorides 49 and 51 with a large excess of alumina at room or slightly elevated temperature affords products 50 and 52, respectively.84-85... 

Acidic media favor the hydrolysis, and alkaline reagents, usually, but not without exceptions,141 142 do not attack geminal difluorides. Thus, perfluorocyclobutene with potassium hydroxide gives trifluoro-3-hydroxycyclobut-2-enone derivative 3.142... 

The substitution of geminal difluoride groups with hydroxylamines or hydrazines leads to the corresponding oximes31 or hydrazones.3,32 Diamines, amino alcohols or amino thiols give rise to N,N, N,0- or /V.A-acetals, respectively.33 Yields are especially good when perfluoro-O-silyl enol ethers (e.g., 5) are used instead of the corresponding ketones.2,33... 

The reaction of alkynes and HF more commonly gives geminal difluoroalkanes, usually in high yield. Terminal alkynes afford 2,2-difluoroalkanes (equation 10) and internal alkynes yield geminal difluorides (equation ll).4-23-24 26... 

These reactions are generally carried out at temperatures of -70 to +15 °C using either liquid HF,24 or HF in ether or acetone.26 The latter process affords regioisomeric mixtures of geminal difluorides when unsymmetrical internal alkynes, such as 2-pentyne, are employed. 

Yields of geminal difluorides of 70-75% are also obtained from the reaction of terminal or internal alkynes with the (HF)x CjHjN reagent.21... 

The usual reaction of diethylaminosulfur trifluoride (DAST) with a carbonyl group is the replacement of carbonyl oxygen by two atoms of fluorine, thus generating geminal difluorides. 

The reaction in Explanation 43 is not a typical hydrolysis of geminal difluorides. A simple example of hydrolysis of geminal difluorides is conversion of 1,1-difluorocyclohexane to cyclohexanone. It is not easy, and takes place in alkaline or acidic media under very energetic conditions [66],... 

The outcome of the action of sulfur tetrafluoride on epoxides mainly depends on the substituents present on the epoxide ring. 1-Aryl-, 1,1-diaryl- and 1,1-dialkyloxiranes give rearranged geminal difluorides in low to moderate yield. From 1,2-diaryloxiranes, (chloromethyl)oxi-... 

Diethylaminosulfur trifluoride gives results similar to those of the reaction of sulfur tetrafluoride with epoxides, but mixtures of geminal difluorides, vicinal difluorides and bis(2-lluoroalkyl) ethers are obtained in low to moderate yield, depending on the structure of the epoxide.41... 

Substituted aryl hydrazones can be converted to geminal difluorides in satis factory yields by molecular fluonne [S4, iodine fluoride [ 5], and N bromo-suc-cimmide-pyridinium polyhydrogen fluoride or Af-bromosuccinimide-polyvi-nylpyridinium polyhvdrogen fluoride [56] (equation 21) (Table 6)... 

Difluoroiodo)arenes react with aryl-substituted alkenes to afford the rearranged, geminal difluorides, owing to the migration of the aryl group [32,33]. Likewise, the reaction of substituted cyclic alkenes with difluoroiodotoluene and EtsN/SHF results in a fiuorinative ring-contraction with the selective formation of difluoroalkyl substituted cycloalkanes. Thus, the fluorination of 1-methylcyclohexene derivatives 26 affords... 

The reaction of carbonyl groups with excess DAST under formation of geminal difluorides (Scheme 21) resembles the transformation of alcohols into fluoroal-kanes by the DAST route (see Scheme 6). Inasmuch as similar side reactions have also been observed in both cases, this special section is included here. As will be seen, many questions are still left unanswered. 

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