Copper bromide-Dimethyl sulfide

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. 

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). 

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... 

Note 11). The residual activated magnesium is rinsed once with 200 mL of dry diethyl ether, and the supernatant layer is transferred via cannula to the copper bromide-dimethyl sulfide slurry (Note 12). The reaction mixture is slowly warmed to -10°C, and then 16.78 g (17.42 mL, 125 mmol) of hexanoyl chloride is added dropwise via syringe after which the reaction mixture is warmed to room temperature. After stirring for 3 hr, the reaction mixture is filtered through a 75-g layer of Celite 545 (Note 13) and the filter cake rinsed with three 100-mL portions of diethyl ether. Concentration of the filtrate under reduced pressure yields the a-silyl ketone which is utilized without further purification (Note 14). 

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... 

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. 

Stannane 6a underwent facile transmetalation in tetrahydrofuran at — 78 °C on treatment with butyllithium to afford 6b. Addition of the lithium reagent 6b to a solution of 1.1 equivalents of copper(I) bromide-dimethyl sulfide in 1 1 diisopropyl sulfide/tetrahydrofuran at — 78 °C gave the copper reagent 6c, which reacted with methyl vinyl ketone at —78 "C in the presence of boron trifluoride-diethyl ether65, producing 7 in 55% yield65. 

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... 

Cuprous bromide/dimethyl sulfide Copper, bromo[th1obis[methane]]- (9) (54678-23-8)... 

DIENES Bcn/.yldtlotobis(Iriphenyl-phosphine)palladium(ll). Copper(I) bromide-Dimethyl sulfide. Palladium(Il) chloride. Tetrakis(triphenyEphosphine)-palladium. Titanium IVichloride-Lithium aluminum hydride. 

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

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