1, 2-Dibromomethane

A versatile oxirane synthesis via (64) is the sulfur ylide approach (B-75MI50504, cf. 76TL457), which in effect inserts a CR2 group into a carbonyl group (Scheme 71). Older, less generally useful versions of this insertion utilize diazomethane or dibromomethane-butyllithium. 

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... 

The less efficient dibromomethane also reacts presumably with C-Br bond rapture, although some examples of reacting at a C-H bond are known (ref. 1). 

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. 

COMPOUND NAME CHLORODIFLUOROMETHANE DICHLOROFLUOROMETHANE CHLOROFORM HYDROGEN CYANIDE DIBROMOMETHANE DICHLOROMETHANE FORMALDEHYDE FORMIC ACID METHYL BROMIDE METHYL CHLORIDE METHYL FLUORIDE METHYL IODIDE NITROMETHANE METHANE METHANOL METHYL MERCAPTAN METHYL AMINE METHYL HYDRAZINE METHYL SILANE... 

The photocycloaddition of maleic anhydride to acenaphthylene has been studied by Hartmann and Heine.(107a> Irradiation of acenaphthylene in the presence of maleic anhydride in light-atom solvents (dioxane, acetone, or acetonitrile) yields only dimers or copolymers of acenaphthylene. In heavy-atom solvents (dichloromethane, dibromomethane, or iodomethane), however, dimerization is suppressed and cycloaddition with maleic anhydride predominates ... 

Ethylenediamine Ethylene dibromide, see 1,2,-Dibromomethane Ethylene dichloride, see 1,2-Dichloroethane 1... 

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. 

Tetramethylpiperidine, dibromomethane (99%) and 1,1,1,3,3,3-hexamethyldisilazane (98%) were purchased from Aldrich Chemical Company, Inc., and used without further purification. Use of less hindered secondary amines (such as diisopropylamine) in place of tetramethylpiperidine results in lower yields because of the formation of carboxamide by-products. 

Alkylation of 31 with dibromomethane and 1,2-dibromoethane was performed under solvent-PTC conditions with good yields and short irradiation times (15 min) [16]. The synthesis of original benzimidazo-[l,2-c]-quinazoline dimers 32(a,b) was successfully achieved by use of potassium carbonate in the microwave active DMF solvent (Scheme 8.13). 

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