Copper salts, as catalysts

Copper-complexes prepared with other type of N-chelating ligands have been also prepared and evaluated as catalysts for the Diels-Alder reaction. Eng-berts et al. [103] studied enantioselective Diels-Alder reaction of 3-phenyl-l-(2-pyridyl)-2-propen-l-one with cyclopentadiene in water (Scheme 39). By using coordinating chiral, commercially available a-amino-adds and their derivatives with copper salts as catalysts, they obtained the desired product with yields generally exceeding 90%. With L-abrine (72 in Scheme 39) as chiral moiety, an enantiomeric excess of 74% could be achieved. Moreover, the catalyst solution was reused with no loss of enantioselectivity. 

Phenols such as 2.6-dimethyIphenol are converted rapidly and in high yield to high molecular weight polymers at room temperature with oxygen in the presence of amine complexes of copper salts as catalyst. Much of the work described in the literature has been performed with copper (I) chloride as catalyst and pyridine as ligand and solvent. Other amines, primary, secondary or tertiary can be used as ligands for the catalyst. Autoxidation of copper (I) chloride in pyridine results in the... 

When 2,6-dimelhylphenol is oxidized with oxygen in the presence of an amine complex of a copper salt as catalyst a high-molecular weight polyether (PPO) is formed. 

In cases where it is not necessary to introduce the nitro group directly at a position of the azole ring poorly susceptible to electrophilic attack it is possible to use the Sandmeyer reaction or its modifications (Scheme 53). The use of copper salts as catalysts is not essential in a number of cases [392, 393],... 

Carbonates are often formed as by-products even in the synthesis of oxalates or acrylates. The catalytic system for such a synthesis does not require the presence of palladium, however, since it can be achieved by using only copper salts as catalysts. 

The cyclopropanation of )- and (Z)-/S-methylstyrene (393 and 394) led to essentially the same ratio of ( ) and (Z) cyclopropane derivatives 395 and 396, indicating that the reactions proceeded stereospecihcally (81MI4 83BCJ2687). As electron-deficient olefins such as acrylate and acrylonitrile reacted even in the absence of copper(II) bromide, while the reaction of styrenes required the copper salt as catalyst, it was concluded that the reaction mechanism may vary, depending on the nature of the olefin. 

More recently, Yamamoto [16] reported a comparative study between different copper salts as catalysts for the reaction of n-butylmagnesium chloride with trun.s-allylic phosphate 108 and showed that CuCN -2LiCl gives the best results for the selectivity in favor of the Sn2 product 110 [Eq. (34) and Table 5]. 

Nucleophilic aromatic substitutions are a type of reactions frequently applied in the synthesis of chemical intermediates and fine chemicals. In general, these processes are performed in the liquid phase, batchwise, with dissolved copper salts as catalysts [1]. It is of interest to investigate the possibilities of heterogeneous catalysis, as a more convenient catalyst recycle can thus be achieved. 

The reaction of cycloprop-2-enecarboxylates with hydrogen cyanide in the presence of a copper salt as catalyst resulted in ring opening. 

The proposed iminium intermediate 2 in the oxidative alkylation reaction implied that other C-H based nucleophiles could undergo oxidative addition reactions to the C-H bond of tertiary amines. Li and co-workers demonstrated the cross-coupling of indoles 18 with tertiary amines 6 using simple copper salts as catalyst (Scheme 11) [27]. 

The chemical synthesis uses copper salt as catalyst for the hydration of acrylonitrile and has several disadvantages ... 

The Baudisch reaction295 makes it possible simultaneously to introduce a nitroso and a hydroxyl group in the ortho-position to one another. In this reaction NOH radicals are produced by oxidation of hydroxylamine or reduction of nitrous acid these radicals, in conjunction with an oxidizing agent and in the presence of a copper salt as catalyst attack the aromatic nucleus. Yields are seldom very high, but few o-nitrosophenols are easily prepared in other ways. Cronheim296 has reported the first preparation of fifty mono-and di-substituted n-nitrosophenols by the Baudisch reaction. 

Greater preparative importance attaches to oxidative ring opening of cycloalkanols and cycloalkanones, which then afford alkanedioic acids containing an unchanged number of carbon atoms. Thus, for instance, adipic acid is obtained in up to 90% yield from cyclohexanol or cyclohexanone by means of about 60% nitric acid containing vanadium and copper salts as catalyst 125... 

Oxidation of rc-butanal with cobalt and copper salts as catalyst gives peracid and acid. The values of the rate coefficient obtained with various... 

Carbene complexes, generated by the reaction between metal salts and diazo compounds can insert into C-H bonds in a form of CH activation (see Chapter 3 for other CH activation reactions). While early reactions involved the use of copper salts as catalysts (Schemes 8.143 and 8.144), rhodium complexes are now more widely used. In molecules such as cyclohexane, there is no issue of regioselectivity, but this issue is critical for the use of the reaction in synthesis. Both steric and electronic factors influence selectivity. Carbon atoms where a build up of some positive charge can be stabilized are favoured. Hence, allylic positions and positions a- to a heteroatom such as oxygen or nitrogen, are favoured. The reaction at tertiary C-H bonds, rather than primary C-H bonds is also favoured for the same reason, but, in this case, are also disfavoured by steric effects. Reactivity and selectivity are also influenced by both the structure of the catalyst, and the... 

In addition to the use of copper salts as catalysts, a variety of discrete organosoluble copper compounds have been generated and used to promote the synthesis of triazoles. An example of this chemistry entailed the use of an Af-heterocyclic carbene as the stabi-lizing/solubilizing ligand for the copper (Scheme 3.108) [113]. lodoalkynes were used as... 

The yield of ketones can be sometimes improved by working in the presence of copper salts as catalyst (1 to 5%), especially in the case of methyl and s- or t-alkyl-manganese chlorides (Scheme 13.18). 

It was reported that iron salts catalyzed the oxidative a-phosphonation of A,A-dimethylanilines with (R0)2P(0)H in the presence of tert-butylhydroperoxide [196]. In the study electrochemical C-H bond activation was utilized to generate iminium species, followed by C-P bond formation. An efficient dehydrogenative coupling reaction involving iminium salt as a possible intermediate was also reported with copper salt as catalyst and molecular oxygen as oxidant [197]. 

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