Dibromomethane, reaction

Numerous other conversions of 5-(2,2 -bipyridyl)-3,3,7,7-tetramethyl-tran -5-nickelatri-cyclo[4.1.0.0 ]heptane (9) have been reported. Upon treatment with maleic anhydride, tetra-cyanoethene or triphenyl phosphite, 3,3,6,6-tetramethyl-trani -tricyclo[3.1.0.0 ]hexane was formed. With triphenyl phosphite, bi(2,2-dimethylcyclopropyl) and l-(2,2-dimethylcyclo-propyl)-3-methylbuta-l,3-diene were obtained as additional products. Similarly, bi(2,2-dimethylcyclopropyl) was obtained upon acidolysis of the metallacycle. The bicyclopropyl was also released with triethylaluminum. Reaction with phenol gave an intermediate complex 3-[2,2 -bipyridyl(phenoxy)nickela-l,T-bi(2,2 -dimethylcyclopropyl). Dibromomethane reaction of the nickelacyclopentane 9 gave the tricyclo[3.1.0.0 ]hexane system and 3,3,7,7-tetramethyl-rrani-tricyclo[4.1.0.0 ]heptane. On the other hand, treatment of the nickelacyclopentane 9 with trifluoroborane gives 3,3,6,6-tetramethylcyclohexa-l,4-diene. ... 

With special techniques for the activation of the metal—e.g. for removal of the oxide layer, and the preparation of finely dispersed metal—the scope of the Refor-matsky reaction has been broadened, and yields have been markedly improved." The attempted activation of zinc by treatment with iodine or dibromomethane, or washing with dilute hydrochloric acid prior to use, often is only moderately successful. Much more effective is the use of special alloys—e.g. zinc-copper couple, or the reduction of zinc halides using potassium (the so-called Rieke procedure ) or potassium graphite. The application of ultrasound has also been reported. ... 

In another reaction tetraalkylmethylenediphosphonates, obtained by Arbusov reaction from triisopropyl phosphite and dibromomethane [see Eq. (58)], were... 

A modified version of the Simmons-Smith reaction uses dibromomethane and in situ generation of the Cu-Zn couple.171 Sonication is used in this procedure to promote reaction at the metal surface. 

Several modifications of the Simmons-Smith procedure have been developed in which an electrophile or Lewis acid is included. Inclusion of acetyl chloride accelerates the reaction and permits the use of dibromomethane.174 Titanium tetrachloride has similar effects in the reactions of unfunctionalized alkenes.175 Reactivity can be enhanced by inclusion of a small amount of trimethylsilyl chloride.176 The Simmons-Smith reaction has also been found to be sensitive to the purity of the zinc used. Electrolytically prepared zinc is much more reactive than zinc prepared by metallurgic smelting, and this has been traced to small amounts of lead in the latter material. 

The lithium tetramethylpiperidide solution from Part A is cooled with a dry ice-acetone bath. When the solution of ethyl 1-naphthoate and dibromomethane has cooled to -74°C or below (internal solution temperature), addition of the dry ice-acetone cooled solution of lithium tetramethylpiperidide is begun. Addition is made via a double-ended (16 gauge) needle over a 40 to 50-min period using a slight positive nitrogen pressure in the 500-mL flask (Note 7). During this time, the addition rate is slowed or stopped as needed to maintain the reaction temperature below -67 C. 

Reiter and co-workers found in the course of their extended research on fused [l,2,4]triazines <1994JHC997> that the N-protected methylthiotriazine derivative 110 when reacted with carbon disulfide under strongly basic conditions yields a mixture of two products 111 and 112. When this mixture was treated with dibromomethane, product 113 was easily removed from the reaction mixture, and workup of the mother liquor allowed the isolation of the [l,2,4]triazolo[l,5-c][l,3,5]thiadiazine derivative 114 in 49% yield (Scheme 21). The same authors carried out ring closure of the ring-closed semithiocarbazide 115 to the triazolothiadiazine derivative 118 as shown in Scheme 21 <1997JHC1575>. The starting compound was treated with triethyl orthoformiate. The authors assume that first intermediate 116 is formed which cyclizes to a second intermediate 117 and, finally, ethanol elimination yields the isolated product 118. 

Table 1 contains details of experimental conditions used in the preparation of the polyethers. It can be seen that the reduced viscosity of the polymers which were obtained increased with the concentration of the aqueous KOH solution and was inversely related to the amount of dibromomethane used in the reaction. 

Hydro ythiophenols react with dibromomethane to produce 1,3-benzoxathioIes [27] (Table 4.6). 1,3-Benzoxathioles have also been obtained by the one-pot base-catalysed ring opening of 1,3-benzoxathiol-2-ones and subsequent reaction with dibromomethane in the presence of Aliquat [28]. 

Predictably, 1,2,4-triazole is alkylated preferentially at the 1-position [36, 38,39]. Specific alkylation at the 4-position can be achieved by the initial reaction with dibromomethane to form the bis-triazol-l-ylmethane (see below), followed by quat-emization of the triazole system at the 4-position and subsequent C-N cleavage of the 1,1 -methylenebistriazolium salts [40]. 1,2,3-Benztriazole yields a mixture of the isomeric 1- and 2-alkylated derivatives [41]. The 1-isomer predominates, but the ratio depends on whether the reactions are conducted in the presence, or absence, of a nonpolar organic solvent (Table 5.33). Higher ratios of the 1-isomer are obtained under solidrliquid two-phase conditions. Thus, alkylation of 1,2,3-benztriazole with benzyl chloride produces an overall yield of 95% with the l- 2-isomer ratio of ca. 5.7 1 similar reactions with diphenylmethyl and triphenylmethyl chlorides gives overall yields of 95% (9 1 ratio) and 70% (100% 1-isomer), respectively [38], 6-Substituted purines are alkylated at the N9-atom and reaction with 1-bromo-3-chloropropane yields exclusively the 9-chloropropyl derivative (cf. reaction wi phenols) [42]. 

Although aliphatic azides can be prepared under liquidrliquid phase-transfer catalytic conditions [3-5], they are best obtained directly by the reaction of a haloalkane with sodium azide in the absence of a solvent [e.g. 6, 7]. Iodides and bromides react more readily than chlorides cyclohexyl halides tend to produce cyclohexene as a by-product. Acetonitrile and dichloromethane are the most frequently used solvents, but it should be noted that prolonged contact (>2 weeks) of the azide ion with dichloromethane can produce highly explosive products [8, 9] dibromomethane produces the explosive bisazidomethane in 60% yield after 16 days [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 bromide was introduced in the reaction instead of a fluoride in performing the anodic oxidation of a-stannyl ethers in dibromomethane solvent with tetrabutyl-ammonium perchlorate as the electrolyte (Scheme 19) [28]. The bromide ion was generated by the reduction of the solvent at the cathode of an undivided cell. 

Class and Ballschmitter (1988) suggested that 1,2-dibromoethane may be produced naturally in sea water from a dibromomethane precursor via a halogen exchange reaction. The dibromomethane is produced by brown algae via haloperoxidase enzymes and released to sea water. 

Consecutive condensations of 2-naphthol, allylamine, and dibromomethane comprised another route to naphthalene-condensed 1,3-oxazines. A preheated mixture of allylamine and dibromomethane was reacted with 2-naphthol 152 to yield the aminophenol intermediate 520, which was cyclized with the salt formed in the reaction of dibromomethane and diethylamine to give 3-allyl-3,4-dihydro-2//-naphth[l,2-< ][l,3]oxazine 521 on further reaction (Scheme 98) <2004SC2253>. 

Carbon tetrachloride, chloroform, dibromomethane, tribromometh-ane, tribromochloromethane, and tetrabromomethane were examined as telogens, and bromomethanes were found2"0 to follow reaction pathways more complicated than those for chlorinated compounds. Thus, chloroform reacts exclusively by hydrogen transfer, giving rise to 423 and a small proportion of higher telomers whereas, for dibromo-... 

Employment of Zn—Cu couple is representative of another approach. For example, reaction of perfluoroalkyl iodides with carbonates gives fluorocarboxylic esters (equation 107)132. Similarly, reaction of perfluoroalkyl iodides with Zn—Cu couple and C02 or S02 in DMSO affords the perfluorocarboxylic acids and sulfonyl chlorides, respectively133. A double methylene inserted product is formed when dibromomethane is used as a substrate (equation 108)134. 

The reaction of dibromomethane with antimony(III) fluoride in the presence of antimony ) chloride at 85-90r C under nitrogen produces bromofluoromethane in ca. 30% yield,74 while treatment of tribromomethane with antimony(III) fluoride/bromine provides dibromofluoromethane in 62% yield.75... 

Dibromomethane [74-95-3] (methylene bromide), CH2Br2, is a similar liquid, mp — 52.7° C, bp 96.9°C, Water solubility is 1.17 g/100 g at 15°C. It is prepared by the same methods as bromochloromethane, allowing the reaction to proceed to completion. A laboratory preparation involves removing a bromine from bromoform using sodium arsenite (86). The compound is used as a solvent, as a gauge fluid, and in producing pesticides. Both of these dihalomethanes can be used as dense, readily volatile media for mineral and salt separations. 

Trimethylamine N-oxide, 325 Vinyltrimethylsilane, 343 Other reactions (Phenylsulfonyl)allene, 247 Cyclodehydration Diethoxytriphenylphosphorane, 109 Hexamethylphosphoric triamide, 142 Cycloprop anation Simmons-Smith reaction Diiodomethane-Diethylzinc, 276 Simmons-Smith reagent, 275 by other reagents which add CH2 to a carbon-carbon multiple bond Dibromomethane-Zinc-Copper(I) chloride, 93... 

This notation blends smoothly with the plus-minus notation to indicate sequences of reactions or multifunctional reagents. In the simple, hypothetical transformation in Scheme 20, dibromomethane might serve as a reagent for the synthon (5). A slash (/) separates the two symbols (-/ ) to indicate that (5) will behave separately as a nucleophilic site and a radical site, rather than as a radical anion. The more rigorous notation of Seebach avoids this confusion. Related transformations have actually been executed by Wilcox and Gaudino.76... 

In the second reaction, dibromomethane acts as the reagent. Since this requires working in a two-phase system, the phase-transfer catalyst Adogen 464 methyltrialkyl(Ca-C ammonium chloride] is added. 

The initial report of the reaction of an imidazoline with thionyl chloride to give a triazocine was found to be in error, the correct structure being an imidazolidone (56JA6144). However, condensation of tristosyltriamine 232 with dibromomethane did afford triazocine 233 (83MI3) 1,3-diazocines were also prepared by this method (see Section lll,B,l,c). 

More interestingly diiodomethane reacts with Pd2(dpm)3 to form the methylene-bridged complex III (X = I). Dibromomethane reacts similarly to form III (X = Br), but fortunately, under these conditions, dichloromethane does not react with Pd2(dpm)3, so it may be used as the solvent for these reactions. Complex III is expected to possess an A-frame structure similar to that of Pd2(dpm)2( and... 

The preparation of dibenzo-fused dithiepins was usually catalyzed by BF3 Et20. For example, the synthesis of dibenzo[7//][l,3]dithiepin from 1,1 -binaphthalene-2,2 -dithiol and dibromomethane and diiodomethane, respectively, failed however, reaction of the dithiol with dimethoxymethane in the presence of BF3-Et20 afforded the desired dithiepin in 71% yield <1995T787>. 

Catechol and other o-dihydroxy aromatic systems may be protected by the formation of the methylenedioxy compound, most conveniently achieved by the following PTC procedure.44 A mixture of water (20 ml), dibromomethane (0.15 mol) and Adogen 464 (1 mmol), is vigorously stirred and heated to reflux. The air in the system is displaced by nitrogen. A solution of the appropriate o-dihydroxybenzene (0.1 mol) and sodium hydroxide (0.25 mol) in water (50 ml) is added at such a rate that addition is complete after 2 hours. After addition is complete, the reaction mixture is stirred and refluxed for a further hour. The product is isolated by standard work-up procedures. 

Since the free carbene ( CH2) is not thought to be present, the reagent (40) is termed a carbenoid. The activity of the zinc surface is of crucial importance to the smoothness and success of the reaction. Failure to ensure appropriate activation procedures may cause the reaction to fail, or the onset of the exothermic reaction may be delayed and then proceed with excessive vigour. The recent use of ultrasonic activation of the zinc surface from the outset of the reaction results in a smoother, less unpredictable reaction rate, and leads to satisfactory yields.118 Furthermore, sonication enables the cheaper dibromomethane to be employed.1 lb... 

---