Dibromodifluoromethane

Condensation of dibromodifluoromethane or bromochlorodifluoromethane with potassium phenoxides usually needs an initiation by a thiol and occurs by an ionic chain mechanism [/5, 16 (equations 14 and 15)... 

Thiolates react with dibromodifluoromethane by initial displacement of one of the larger halogens [54, 55, 56] (equation 48) see equation 15). 

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)... 

The ternary carbamon generated by the addition of fluoride anion to peifluoroi-sobutylene reacts with dibromodifluoromethane to give perfluoroneopentyl bromide... 

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)... 

Table 14. Synthetic Utility of Fluorinated Phosphonium Salts Prepared From Dibromodifluoromethane [40 ...

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)... 

The use of trifluroiodoethane or dibromodifluoromethane for alkylation of 5-aryloxadiazolin-2-ones or 5-arylox-adiazoline-2-thiones led exclusively to N-alkylated products 42a or 42b, respectively <1999MI161>. 

On the contrary, the cathodic reduction of dibromodifluoromethane generates difluorocarbene, which was successfully trapped with reactive olefines yielding 1,1-difluorocyclopropanes (Scheme 3.3.) [13]. 

Difluoromethylenation (79,80) of aldonolactones may be readily accomplished by treatment of the lactone derivative with tris(dimethyl-amino)phosphine, dibromodifluoromethane, and zinc in refluxing tetrahy-... 

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... 

Vinyltrimethylsilane, ethanolamine, copper(l) chloride (98+% ACS reagent grade), and dibromodifluoromethane were obtained from Aldrich Chemical Company, Inc. tert-Butyl alcohol was obtained from Fisher Scientific Company. 

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. 

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