Dibromodifluoromethane, reaction

Condensatron between lithium acetylides and dibromodifluoromethane [124] or dichlorofluoromethane [125] leads to fluorohaloacetylenes (equation 107) Sodium alkyl malonates are also alkylated by dihalogenodifluoromethanes [124] (equation 108) These reactions involve difluorocarbene as intermediate (for the mechanism of the Cp2Br2 condensation, see equation 15)... 

Much better known are the fluonnatedphosphoranes, which have been widely used m the Wittig reaction for the preparation of fluoroolefms Difluoromethylena tion reactions have been effected by using a variety of conditions Treatment of dibromodifluoromethane with two equivalents of tns(dimethylammo)phosphine m carefully dried tnglyme yields a solution of bromodifluoromethylphosphonium broomide, which very effectively converts ketones to difluoromethylene derivatives A more sensitive reagent is prepared by the addihon of two equivalents of the phosphine to the reaction mixture of fluorohalomethane and a carbonyl compound [39, 40] (equation 40) (Table 14)... 

A similar distribution of copper reagents can be obtained via the du ect reaction of copper metal with dibromodifluoromethane or bromochlorodifluoromethane in DMF at 85-95 °C [2J2] The oligomerization can be supressed via the addition of alkali metal fluorides to the reaction mixture [272] When HMPAis added to the trifluoromethylcopper solution, decomposition is slowed, and this solution can be used to trifluoromethylate aromatic iodides [270] (equation 143). 

The use of dibromodifluoromethane with zinc [26] or lead metal [27] is a simple, economical method for generating difluorocarbene under mild conditions, but the reaction is limited to highly nucleophilic olefins (equation 8)... 

Difluorocarbene cannot be generated (<1%) under liquiddiquid phase-transfer catalytic conditions [29] owing to the rapid hydrolysis of the carbene at the interface [30], although it has been indicated that it is possible to obtain low yields of 1,1-difluorocyclopropanes under soliddiquid conditions [1]. More successful is the reaction of dibromomethane and dibromodifluoromethane under basic conditions. It is assumed that the initially formed dibromomethyl anion is transported into the organic phase where an equilibrium reaction with dibromodifluoromethane produces the bromodifluoromethyl anion and, subsequently, the difluorocarbene [31]. 

A. (1,3-Dibromo-3,3-difluoropropyl)trimethylsilane (Note 1). A 250-mL pressure tube (Note 2) equipped with a magnetic stirring bar is charged with vinyltrimethylsilane (20 g, 30.8 mL, 0.20 mol), ethanolamine (6.11 g, 6.04 mL, 0.10 mol), dibromodifluoromethane (83.9 g, 36.5 mL, 0.4 mol), copper(l) chloride (0.18 g, 1.8 mmol), and tert-butyl alcohol (15 mL) (Notes 3 and 4). The tube is sealed and stirred for 20 hr in an oil bath at 90°C (Note 5). The reaction mixture is combined with that from another run at the same scale and diluted with 40 mL of hexane (the mixture separates into a cloudy supernatant and a brown resin). The hexane layer is... 

Radical addition of dibromodifluoromethane to alkenes followed by sodium borohydride reduction is a convenient two-step method for the introduction of the difluoromethyl group.5 Either one or both carbon-bromine bonds in the intermediate dibromides may be reduced, depending on the reaction conditions. In the case of acyclic dibromodifluoromethane-alkene adducts, the reduction occurs regioselectively to yield the relatively inaccessible bromodifluoromethyl-substituted alkanes. The latter are potential building blocks for other fluorinated compounds. For example, they may be dehydrohalogenated to 1,1-difluoroalkenes an example of this methodology is illustrated in this synthesis of (3,3-difluoroallyl)trimethylsilane. 

The trialkyl(trifluoromethyl)tin can also be prepared via the reaction of triphenylphosphine and dibromodifluoromethane followed by the treatment with potassium fluoride and trialkyltin chloride [104,105] (Scheme 37). 

Reaction of Dibromodifluoromethane and tris(Dimethylamino)phosphine with Fluorinated Ketones... 

Reaction of Dibromodifluoromethane and 4-Chloro-3-nitrobenzotrifluoride with Copper... 

Tetrafluoroethylene was the only fluorine-containing product obtained from attempted coupling reactions with 1,2-dibromo- and 1,2-diiodotetrafluoroethane, and dibromodifluoromethane, perhaps via unstable copper compounds 200). 

The phosphoranium salts obtained in this way are soluble in polar solvents and can be used without isolation in olefination reactions. For example, if triphenylphosphane is reacted with dibromodifluoromethane in diglyme at room temperature, the corresponding bromo(di-fluoro)methyl triphenylphosphonium salt precipitates quantitatively... 

Table 4. Reactions of Dibromodifluoromethane and Tribromofluoromethane with Tfialkyl Phosphites (RO),P ...

The carbene is easily obtained in situ by the reaction of dibromodifluoromethane with activated 7. nc dust. The reaction is run at room temperature without solvent. Only ketones give reasonable yields. Aromatic aldehydes react with poor yields aliphatic aldehydes form tars in this reaction. 

Grignard reaction, other examples n-Butyl borate (see Phenylboronic add). r-Butylhydro-peroxide. /-Butylperbenzoate. Dibromodifluoromethane. Diethyl sulfate. Ester synthesis (see 3-Dimethylaminopropylamine). Ethoxymethyleneaniline. Ethyl chloroformate. Ethylene dibromide (entrainment). Ethylene oxide. Ethyl formate. Ethynylmagnesium bromide. Sulfur. Triethyl orthoformate. Trimethylene oxide. See also Dichloroformoxime. 

The lipophilic ion pair produced after the deprotonation of dibromomethane, HCBr2l U4, undergoes halophilic reaction with dibromodifluoromethane within the organic phase to form tribromomethane and the ion pair CBrF2NBu4. The latter splits into tetrabutylammonium bromide and difluorocarbene, which reacts with alkene to form 1,1-difluorocyclopropane (for an alternative possibility, see ref 17). 

The yields of 1,1-difluorocyclopropanes increase if the reaction is carried out in the presence of catalytic amounts of 18-crown-6 and if dibromodifluoromethane and triphenylphosphane are used in excess to the alkene. ... 

Dibromodifluoromethane (21.0 g, 9.3 mL, 100 mmol) was added to a solution of PhjP (26.2 g, 100 mmol) in DME (50 mL) and a white precipitate formed instantaneously. About halfof this suspension was poured into a vigorously stirred mixture of the alkene (50 mmol), KF (11.6 g, 200 mmol) and 18-crown-6 (1.3 g, 4.9 mmol) in DME (50 mL) and, after 5 h, the other half of the suspension was added. After stirring for an additional 5 h, always at 25 °C, the reaction mixture was diluted with pentane (250 mL) and centrifuged. The supernatant clear liquid was either distilled immediately or, more frequently, after thoroughly washing with a 2% aq NaOH (4 x 250 mL) (for more examples, see Table 1). 

Tetraisopropyl difluoromethylenediphosphonate has been prepared in 40% yield by the reaction of dibromodifluoromethane with sodium diisopropyl phosphite in hexane at -78°C. The reaction is believed to proceed via metal-halogen exchange to give a stabilized carbanion, which reattacks the diisopropyl bromophosphate formed during the transmetallation step. ... 

Diethyl 1-bromo-1,1-difluoromethylphosphonate is usually obtained from the Michaelis-Arbuzov reaction between triethyl phosphite and dibromodifluoromethane in Et2O at reflux for 24 h (Scheme 3.46). ° Other dialkyl 1-bromo-1,1-difluoromethyIphosphonates were obtained in the same way (Table 3.11). When the reaction is performed in triglyme, the yields are significantly lower.- 2 Recently, it has been shown that the reaction time can be shortened to 1.5 h by using refluxing THE. ... 

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