Complex with copper bromide

Regioselective deactivation of the dianions of carbohydrate diols by complexing with copper salts (see Sect. 3.5) has been employed for their effective monobenzylation [165, 166]. When benzyl iodide was used, the yield of monosubstituted product was higher than 85 % in almost every instance, the rest being accounted for an unreacted starting material. In no case was any disubstituted product isolated. Benzyl bromide gave <20% of alkylation in a reasonable time, benzyl chloride showed no reaction at all. 

UUmann ether synthesis. The original Ullmann ether synthesis9 involved melting the salt of a phenol with an aryl bromide in the presence of copper metal. Yields are low. Williams et al.10 found that the reaction can be carried out at lower temperatures by using as solvent pyridine, which forms a complex with copper salts (cuprous chloride preferred), which provides catalysis for the reaction reflux temperature is then sufficient. 

Several complexes of cuprous halides with acrylonitrile 69> and acrolein 70> have been investigated. The enthalpies of complexing have been found from vapour pressure measurements the enthalpy of formation of the complex from solid copper chloride and liquid acrylonitrile was -29.3 kJ mole-1, while with copper bromide this was -1.3 kJ mole-1. The corresponding value for the acrolein complex was -17.3 kJ mole-1 the enthalpy values for the formation from the gaseous olefinic compounds were -62.3, -34.3 and -49.2 kJ mole-1 respectively. 

The rodlike ligand Lm was also found to form a polymeric complex with copper (226), but the complex obtained by reaction of LM with 1 molar equivalent of Cul in thf, [Cu2l2(Lg4)2] thf, is surprisingly not isostructural of the corresponding complex of the bromide. Instead, it... 

Helquist and his co-workers find that the dimethyl sulphide-copper(i) bromide complex with methylmagnesium bromide will add to simple terminal acetylenes in stoicheiometric amounts, or in only a small excess (10—15%) this procedure allows a more efficient means of constructing stereochemically defined methyl trisubstituted olefins found in natural isoprenoids (Scheme 10). 

Whereas acyclic sulfoxides form complexes with various metal salts, thiirane oxides react with copper(II) chloride or bromide in benzene at room temperature to give the thiolsulfonate 146a. In alcoholic solution below 0°C the major products are sulfinates (149). Similar results are obtained in the reaction of thiirane oxides with ethanesulfinyl chloride as summarized in equation 60. 

Early studies [170] of copper(II) complexes of thiosemicarbazones were 2-formylpyridine iV-methylthiosemicarbazone, 30, 6-methyl-2-formylpyridine Ai-methylthiosemicarbazone, 31, and 2-formylpyridine " JV-dimethylthiosemi-carbazone, 32. With copper(II) chloride and bromide, monomeric complexes of stoichiometry [Cu(L)A2] were isolated for each of these thiosemicarbazones. All six complexes had a band in the 14000-15000 cm spectral region, but their stereochemistry was not specified. 

The Rh2(OAc)+-catalyzed reaction between crotyl bromide and ethyl diazoacetate at or below room temperature follows the pathway 129 - 131 - 132 exclusively. At higher temperature, when ethyl bromoacetate and increasing amounts of the [1,2] rearrangement product 126 are found additionally, the 129 -> 130 - 132 -f 133 route becomes a competing process. With copper catalysts, this situation may be applicable at all temperatures, but it has been suggested that the route via complex 130 operates solely, when copper bronze is the catalyst154). 

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. 

Allenyl alcohols 10 react with lithium bromide in the presence of a palladium(II) catalyst to afford tetrahydrofurans and tetrahydropyrans 11 in good yield (Scheme 17.6) [7]. The mechanism of the reaction is similar to that discussed in Sect 17.2.1. i.e. it proceeds via a 2-bromo(jt-allyl)palladium(II) complex. In this case, however, the second nucleophile is not bromide ion but the alcohol moiety. As stoichiometric oxidant p-benzoquinonc (BQ) or copper(II) together with oxygen can be used. 

The enantioselective lithiation of anisolechromium tricarbonyl was used by Schmalz and Schellhaas in a route towards the natural product (+)-ptilocaulin . In situ hthi-ation and silylation of 410 with ent-h M gave ewf-411 in an optimized 91% ee (reaction carried ont at — 100°C over 10 min, see Scheme 169). A second, substrate-directed lithiation with BuLi alone, formation of the copper derivative and a quench with crotyl bromide gave 420. The planar chirality and reactivity of the chromium complex was then exploited in a nucleophilic addition of dithiane, which generated ptilocaulin precnrsor 421 (Scheme 172). The stereochemistry of componnd 421 has also been used to direct dearomatizing additions, yielding other classes of enones. ... 

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... 

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. 

CH3(CH2)4CH = CHCH = CHC00CH2CH3, C12H20O2, Mr 196.29, bp6i> 70-72 °C, has been identified in pears and has the typical aroma of Williams pears. Synthesis of ethyl 2-trans-4-cw-decadienoate starts from cis-l-heptenyl bromide, which is converted into a 1-heptenyllithium cuprate complex with lithium and copper iodide. Reaction with ethyl propiolate yields a mixture of 95% ethyl 2-trans-A-cis- and 5% ethyl 2-tranx-4-tranx-decadienoate. Pure ethyl 2-trans-A-cis-decadienoate is obtained by fractional distillation [25]. A biotechnological process for its preparation has been developed [26]. 

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