Copper catalysts bonds

Nerol, geraniol, and linalool, known as the rose alcohols, are found widely in nature. Nerol and geraniol have mild, sweet odors reminiscent of rose flowers. They are manufactured by the hydrochlorination of mycene at the conjugated double bonds when a copper catalyst is used (88,89). 

Dehydrochlorination of 1,1,2-trichloroethane at 500°C in the presence of a copper catalyst gives a different product, ie, cis- and /n7 j -l,2-dichloroethylene. Addition of small amounts of a chlorinating agent, such as chlorine, promotes radical dehydrochlorination in the gas phase through a disproportionation mechanism that results in loss of hydrogen chloride and formation of a double bond. The dehydrochlorination of 1,2-dichloroethane in the presence of chlorine, as shown in equations 19 and 20, is a typical example. 

The enantioselective 1,4-addition addition of organometaUic reagents to a,p-unsaturated carbonyl compounds, the so-called Michael reaction, provides a powerful method for the synthesis of optically active compounds by carbon-carbon bond formation [129]. Therefore, symmetrical and unsymmetrical MiniPHOS phosphines were used for in situ preparation of copper-catalysts, and employed in an optimization study on Cu(I)-catalyzed Michael reactions of di-ethylzinc to a, -unsaturated ketones (Scheme 31) [29,30]. In most cases, complete conversion and good enantioselectivity were obtained and no 1,2-addition product was detected, showing complete regioselectivity. Of interest, the enantioselectivity observed using Cu(I) directly in place of Cu(II) allowed enhanced enantioselectivity, implying that the chiral environment of the Cu(I) complex produced by in situ reduction of Cu(II) may be less selective than the one with preformed Cu(I). 

Several other examples of regioselective cyclopropanation of 1- and 2-substituted butadienes in the presence of copper catalysts are known (Scheme 5). 2-Trimethyl-siloxy-1,3-butadiene parallels the behavior of other 2-substituted butadienes (see Table 9) in that the electron-rich double bond is cyclopropanated 60. With the 1-methoxy-, acetoxy- or trimethylsilyloxy-substituted butadienes 17, 18 and 19, both double bonds are cyclopropanated, thus giving rise to sometimes unseparable mixtures of regio- and stereoisomers 79). Perhaps, the yields of separated and isolated regioisomers in some cases do not reflect the true regioselectivity as considerable... 

The dominant role of the traditional copper catalysts, generally used under heterogeneous conditions, has not been challenged as yet. Only a few reports shed light on the efficiency of alternative catalysts. Copper(II) triflate allows high-yield intramolecular cyclopropanation of y,8-unsaturated diazoketone 182160) it is superior to CuS04 (53 % yield 192 ) or Rh2(OAc)4160). The solvent is crucial for an efficient conversion If the reaction is carried out in ether, the solvent competes with the double bond for the electrophilic metal carbene to give 184, presumably via an oxonium ylide intermediate. 

Similar to the intramolecular insertion into an unactivated C—H bond, the intermolecular version of this reaction meets with greatly improved yields when rhodium carbenes are involved. For the insertion of an alkoxycarbonylcarbene fragment into C—H bonds of acyclic alkanes and cycloalkanes, rhodium(II) perfluorocarb-oxylates 286), rhodium(II) pivalate or some other carboxylates 287,288 and rhodium-(III) porphyrins 287 > proved to be well suited (Tables 19 and 20). In the era of copper catalysts, this reaction type ranked as a quite uncommon process 14), mainly because the yields were low, even in the absence of other functional groups in the substrate which would be more susceptible to carbenoid attack. For example, CuS04(CuCl)-catalyzed decomposition of ethyl diazoacetate in a large excess of cyclohexane was reported to give 24% (15%) of C/H insertion, but 40% (61 %) of the two carbene dimers 289). 

In order to rationalize the catalyst-dependent selectivity of cyclopropanation reaction with respect to the alkene, the ability of a transition metal for olefin coordination has been considered to be a key factor (see Sect. 2.2.1 and 2.2.2). It was proposed that palladium and certain copper catalysts promote cyclopropanation through intramolecular carbene transfer from a metal carbene to an alkene molecule coordinated to the same metal atom25,64. The preferential cyclopropanation of terminal olefins and the less hindered double bond in dienes spoke in favor of metal-olefin coordination. Furthermore, stable and metastable metal-carbene-olefin complexes are known, some of which undergo intramolecular cyclopropane formation, e.g. 426 - 427 415). 

The regioselectivity of the C-H insertion is very dependent on the nature of the catalysts. A good example of this is the reaction of 2-methylbutane (Equation (6)).56 As can be seen in the reactions with 2-methylbutane, the silver and copper catalysts TpBf3Cu and Tp(GFs)2Ag resulted in competitive C-H insertions at the tertiary and secondary C-H bonds. In contrast, the more electrophilic silver catalyst TpBf3Ag was less discriminating and all four possible products were formed, comparable to the earlier results with the rhodium catalysts. 

The second well-known and much-used carbon-carbon bond forming reaction is a [4 + 2]-cycloaddition, the Diels Alder reaction. Very many chiral Lewis acid catalysts have been used to promote this reaction and a pot-pourri of organo-aluminium, -boron and -copper catalysts are described, in brief, below. 

Arylation of activated double bonds with diazonium salts in the presence of copper catalysts is known as the Meerwin reaction. The reaction is postulated to either proceed through an organocopper intermediate or through a chlorine atom transfer from chiral CuCl complex to the a-acyl radical intermediate. Brunner and Doyle carried out the addition of mesityldiazonium tetrafluoroborate with methyl acrylate using catalytic amounts of a Cu(I)-bisoxazoline ligand complex and were able to obtain 19.5% ee for the product (data not shown) [79]. Since the mechanism of the Meerwin reaction is unclear, it is difficult to rationalize the low ee s obtained and to plan for further modifications. 

Palladium-catalysed C-C bond formation under Heck reaction conditions, which normally requires anhydrous conditions and the presence of copper(I) salts, is aided by the addition of quaternary ammonium salts. It has been shown that it is frequently possible to dispense with the copper catalyst and use standard two-phase reactions conditions [e.g. 18, 19]. Tetra-/i-butylammonium salts catalyse the palladium-catalysed reaction of iodoarenes with alkynes to yield the arylethynes in high yield [20, 21], whereas the reaction with 3-methylbut-1 -yn-3-ol (Scheme 6.30) provides a route to diarylethynes [22]. Diarylethynes are also formed from the reaction of an iodoarene with trimethylsilylethyne [23], Iodoalkynes react with a,p-unsaturated ketones and esters to produce the conjugated yne-eneones [19],... 

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

Bobianko and Gorokhovatskil 152) and Roiter, Golodets, and Pyatnit-skii 153) found correlations between the rates of the total oxidation of alkenes and alkanes on copper catalysts and the strength of the C—C bond, which is ruptured in the rate-determining step (series 137, six reactants series 138, seven reactants). 

At this stage, sulfoximines had been shown to function as chiral ligands for various palladium and copper catalysts which led to enantioselectivities of >95% ee in various reactions. Furthermore, most of those catalyzed reactions were C-C bond formations. Obvious questions were, therefore, whether sulfoximines could also be applied in combination with other metals and whether reductions and oxidations could be catalyzed as well. A structural comparison of the sulfoximines leading to high ee values such as 55, 60, 81, and 85 revealed that all of them had a two-carbon distance between the two coordinating atoms (which were all nitrogen in these cases). 

The addition of dichlorocarbene, produced from CHCl3-NaOH in the presence of a phase transfer catalyst, to the 10,11-bond of 5//-dibenz[6,/]azepine is accompanied by formylation at nitrogen (78CPB942), whereas the A-methyl derivative with diiodo- or dichloro-methane and a zinc-copper catalyst forms the 10,11-cyclopropanoderivative (137 X = CH2, R = Me) in 55% yield (76CPB2751). 

Copper was also effective in the creation of carbon-nitrogen bonds. N-(o-halophenyl)-guanidines gave 2-aminobenzimidazoles in the presence of a copper-1,10-phenantroline catalyst system. While the iodo and bromo derivatives in the presence of the copper catalyst gave the cyclized product in 83% and 96% yields respectively, the analogous palladium catalysed transformation showed similar efficiency in both cases, resulting in 88% and 86% yields.52... 

A low-cost route to 1,4-butanediol and tetrahydrofuran based on maleic anhydride has been disclosed (Davy process).343,344 Here dimethyl or diethyl maleate is hydrogenated over a copper catalyst. Rapid saturation of the C—C double bond forms diethyl succinate, which subsequently undergoes further slower transformations (ester hydrogenolysis and reduction as well as dehydration) to yield a mixture of y-butyrolactone, 1,4-butanediol, tetrahydrofuran, and ethanol. After separation both ethanol and y-butyrolactone are recycled. 

Intermolecular cyclopropanation of 2-substituted terminal diene 121 with rhodium or copper catalysts occurs preferentially at the more electron-rich double bond (equation 109)37162. With a palladium catalyst, considerable differences in regiocontrol can occur, depending on the substituent of the diene. In general, palladium catalysed cyclopropanation occurs preferentially at the less substituted double bond (equation 110). However, with a stronger electron-donating substituent present in the diene, e.g. as in 2-methoxy-l, 3-butadiene, the catalytic process results in exclusive cyclopropanation at the unsubstituted double bond (equation 110)162. 

The cyclopropanation of alkenes, alkynes, and aromatic compounds by carbenoids generated in the metal-catalyzed decomposition of diazo ketones has found widespread use as a method for carbon-carbon bond construction for many years, and intramolecular applications of these reactions have provided a useful cyclization strategy. Historically, copper metal, cuprous chloride, cupric sulfate, and other copper salts were used most commonly as catalysts for such reactions however, the superior catalytic activity of rhodium(ll) acetate dimer has recently become well-established.3 This commercially available rhodium salt exhibits high catalytic activity for the decomposition of diazo ketones even at very low catalyst substrate ratios (< 1%) and is less capricious than the old copper catalysts. We recommend the use of rhodium(ll) acetate dimer in preference to copper catalysts in all diazo ketone decomposition reactions. The present synthesis describes a typical cyclization procedure. 

Barbier-type reactions, 9, 433 in catalyzed C-C bond formation, 9, 438 in C-C bond formations, 9, 435 in C-heteroatom bond formations, 9, 440 with copper catalysts, 9, 442 non-catalyzed reactions, 9, 443 miscellaneous reactions, 9, 444 in oxidations, 9, 443 in reduction reactions, 9, 444 Bismuth(V) compounds... 

Cross-coupling reactions 5-alkenylboron boron compounds, 9, 208 with alkenylpalladium(II) complexes, 8, 280 5-alkylboron boron, 9, 206 in alkyne C-H activations, 10, 157 5-alkynylboron compounds, 9, 212 5-allylboron compounds, 9, 212 allystannanes, 3, 840 for aryl and alkenyl ethers via copper catalysts, 10, 650 via palladium catalysts, 10, 654 5-arylboron boron compounds, 9, 208 with bis(alkoxide)titanium alkyne complexes, 4, 276 carbonyls and imines, 11, 66 in catalytic C-F activation, 1, 737, 1, 748 for C-C bond formation Cadiot-Chodkiewicz reaction, 11, 19 Hiyama reaction, 11, 23 Kumada-Tamao-Corriu reaction, 11, 20 via Migita-Kosugi-Stille reaction, 11, 12 Negishi coupling, 11, 27 overview, 11, 1-37 via Suzuki-Miyaura reaction, 11, 2 terminal alkyne reactions, 11, 15 for C-H activation, 10, 116-117 for C-N bonds via amination, 10, 706 diborons, 9, 167... 

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