Copper catalysis aerobic oxidation

The Wacker process (Eq. 1) was developed nearly 50 years ago [1-3] and represents one of the most successful examples of homogeneous catalysis in industry [4-9]. This palladium-catalyzed method for the oxidation of ethylene to acetaldehyde in aqueous solution employs a copper cocatalyst to facilitate aerobic oxidation of Pd° (Scheme 1). Despite the success of this process, certain features of the reaction have Umited the development of related aerobic oxidation reactions. Many organic molecules are only sparingly sol-... 

Finally, C—N bond formation has been also accomplished through aerobic oxidative amination of arylboronic acids (Evans-Chan-Lam coupling) under poly-NHC-copper(II) catalysis. In particular, azoles and aromatic amines were successfully coupled with arylboronic acid using catalyst 73, with catalytic efficiencies comparable to those of other previously reported copper(II)-based catalytic systems for this reaction. 

Intramolecular carbon-nitrogen bond formation may result from the Ullmann coupling of l,3-bis(2-iodoaryl)propan-2-amines catalysed by copper. Using (i )-BINOL, l,l -Bi-2-naphthol, ligands, the enantioselective formation of indolines and 1,2,3,4-tetrahydroquinolines was achieved. Copper catalysis has also been used in the intramolecular formation of imidazobenzimidazole derivatives. The reaction is likely to involve the formation of intermediates, such as (16), which on aerobic oxidation yield the product. There is evidence for an intramolecular 0- -N Smiles rearrangement, as... 

Tabler, A., Hausser, A., Roduner, E. (2013). Aerobic one-step oxidation of benzene to phenol on copper exchanged HZSM5 zeolites a mechanistic study. Journal of Molecular Catalysis A Chemical, 379, 139—145.

Intramolecular cyclization reactions with ureas and related nitrogen sources usually require a base at least at one stage of the reaction. As a result, aerobic reaction conditions for terminal reoxidation cannot be realized in this type of intramolecular vicinal difunctionalization. In order to demonstrate the general feasibility of such a process, Muniz employed a platinum catalyst in the cycHzation of six-membered annelation products 132 (Scheme 16.33). Aminometallation under platinum catalysis is known to proceed under neutral conditions, and hence without the requirement of a base addition [92]. The resulting intermediate AA is oxidized by copper(II) to a platinum(IV) intermediate AB, which induces reductive elimination to 133. 

Since traces of cations like copper can catalyze the oxidation of reduced GSH by molecular oxygen, it seemed possible that the effect of these metals might be an indirect one associated with a catalysis of the reoxidation of GSH by O2. That this is not the case was shown by comparing results obtained aerobically with those obtained anaerobically. Representative results are shown in Table III. It is clear that the amount of GSH formed is not increased under anaerobic conditions. The inhibiting cations appear to have an effect on the protein itself, and the nature of the more effective inhibitors suggests that free SH groups are necessary for enzyme activity. 

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