Copper bromide-dimethyl sulfide complex

The beneficial effect of added phosphine on the chemo- and stereoselectivity of the Sn2 substitution of propargyl oxiranes is demonstrated in the reaction of substrate 27 with lithium dimethylcyanocuprate in diethyl ether (Scheme 2.9). In the absence of the phosphine ligand, reduction of the substrate prevailed and attempts to shift the product ratio in favor of 29 by addition of methyl iodide (which should alkylate the presumable intermediate 24 [8k]) had almost no effect. In contrast, the desired substitution product 29 was formed with good chemo- and anti-stereoselectivity when tri-n-butylphosphine was present in the reaction mixture [25, 31]. Interestingly, this effect is strongly solvent dependent, since a complex product mixture was formed when THF was used instead of diethyl ether. With sulfur-containing copper sources such as copper bromide-dimethyl sulfide complex or copper 2-thiophenecarboxylate, however, addition of the phosphine caused the opposite effect, i.e. exclusive formation of the reduced allene 28. Hence the course and outcome of the SN2 substitution show a rather complex dependence on the reaction partners and conditions, which needs to be further elucidated. 

An oven-dried, 1-L, round-bottomed flask is equipped with a magnetic stirring bar and a rubber septum. The flask is charged with 25.61 g of copper bromide-dimethyl sulfide complex (124 mmol) and 250 mL of dry diethyl ether, and the resulting slurry is cooled to -78°C with a dry ice-acetone bath. The Grignard reagent solution prepared above is added to the copper bromide-dimethyl sulfide slurry via cannula... 

Lithium wire (3.2 mm diam.), carbon tetrachloride, triphenylphosphine, MgBrEtaO, copper bromide-dimethyl sulfide complex, hexanoyl chloride, methyllithium, p-toluenesulfonic acid monohydrate, potassium hydride, and 18-crown-6 were purchased from Aldrich Chemical Company, Inc. and used without further purification. 

Schmidt s group15 reported the first synthesis of the lactosyl ceramides 44 (Scheme 6). Reaction of excess n-tetradecylmagnesium bromide with 35 in THF at 60°C afforded a 1 1 mixture of d-arabino- and L-xylo-octadecanetetrol derivatives, 36a and 36b, respectively. Reactions at lower temperature or in different solvent did not result in a dramatic change in the ratio of 36a and 36b. It is interesting, however, that the addition of salts, such as the copper bromide-dimethyl sulfide complex or titanium tetrachloride, as a catalyst led... 

Commercial copper bromide or its dimethyl sulfide complex contains impurities that are deleterious to the reaction. Therefore, the copper(l) bromide-dimethyl sulfide complex is prepared according to the method of House from copper(l) bromide generated by reduction of copper(ll) bromide (Aldrich Chemical Company, Inc., 99%) with sodium sulfite. Best results ctre obtained using copper(l) bromide-dimethyl sulfide complex freshly recrystallized according to the following procedure. 

A 100-mL conical flask equipped with a condenser and a nitrogen inlet is charged with copper(l) bromide-dimethyl sulfide complex (15 g). Anhydrous dimethyl sulfide (50 ml) is added via syringe and the mixture heated gently until all the solid dissolves. The heating bath is removed and pentane (25 mL) is added to the warm solution. The solution... 

As discussed in the last sections, addition of sodium methoxide-alkenylborane complexes to copper bromide-dimethyl sulfide at 0 °C immediately gives conjugated dienes. However, if the temperature is lowered to —15 °C, the dark blue-black complex formed is stable and can be trapped by allylic halides to afford a stereochemically defined synthesis of (4 )-1,4-dienes (Eq. 93) 148). 

Copper(l) bromide-dimethyl sulfide complex Copper, bromo[1hiobis[methane]]- (9) (54678-23-8)... 

Copper(l) bromide-dimethyl sulfide complex, (CuBr SMe2), 99%, was obtained from Aldrich Chemical Company, Inc. and purified prior to use as follows 10 g of CuBrSMez was dissolved in 20 mL of dimethyl sulfide and triturated with 30 mL of... 

S)- (113162-02-0), 70, 47 (E)-Clnnamaldehyde, 70, 197, 240 Citric acid, 70, 54 CONJUGATED ENYNES, 70, 215 Copper(l) bromide-dimethyl sulfide complex, 70, 218 Copper cyanide (544-92-3), 70, 196 Copper(l) thiophenoxide, 70, 206 Copper-zinc organometallic, 70, 196 Crown ethers, chiral, 70, 65... 

Reaction Procedure (Scheme 4.4) Aryl bromide (1.0 mmol) in THF (2 mL) was added to Rieke zine (4 mL, 5 g/100 mL suspension in THF). After the addition, the reaetion mixture was heated at reflux and then concentrated in vacuo. The aryl zine was dissolved in DMA (4 mL) and transferred via cannula onto a solid copper(i) bromide-dimethyl sulfide complex (20 mg, 0.1 mmol). Oxidant (147 mg, 0.5 mmol) in DMA (2 mL) was then added and the solution was kept stirring for 1 h at room temperature. The reaction mixture was filtered through a plug of silica eluting with hexane and EtOAc. The filtrate was concentrated in vacuo and the residue purified by flash eolumn chromatography on silica gel. 

The nucleophilic addition of cuprates onto internal alkynes is not possible and onto 1-alkynes is quite tricky. The best results have so far been obtained with a complex made from methylmagnesium bromide and copper bromide-dimethyl sulfide. 

Alkynylepoxy alcohols of high enantiomeric purity, obtained via Sharpless oxidation of allylic alcohols (see Section D.4.5) react smoothly with excess dialkylcuprate/magnesium bromide to give (/Vf.25)-3.4-alkadiene-1.2-diols in reasonable overall yield and with high anti selectivity when performed at low temperature and by using the dimethyl sulfide complex of copper(I) bromide to synthesize the cuprates42. 

Reaction of 4 with lithium dimethylcuprate (2 equiv.) in THF effects /3-addition and intramolecular alkylation to 5, but in only 15% yield. Use of methylmagnesium chloride (2 equiv.) and the dimethyl sulfide complex of copper(l) bromide (1 equiv.) increases the yield to 25%. The product is easily dehydrated by TsOH to two isomeric pseudoguaianes (70% yield). 

Copper(0)-lsonitrile complexes, 122 Copper(I) bromide, 332-333 Copper(I) bromide-Dimethyl sulfide, 70, 468, 469... 

Copper(II) acetate-Morpholine, 115 Copper(II)-amine complexes, 114-115 Copper(l) bromide, 116-117 Copper(I) bromide-Dimethyl sulfide, 117-118, 235 Copper(II) bromide, 196 Copper(I) f-butoxide, 311 Copper(l) chloride, 118-119, 288 Copper(I) chloride-Tetra-n-butylam-monium chloride, 119... 

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