Metal-Catalyzed Oxidative Amide Synthesis

Some synthetic approaches to pyrazines relied on metal-assisted reactions. A synthesis of 6-substituted 5H-pyrrolol2,3-bJpyrazines via Pd-catalyzed heteroannulation from W-(3-chloropyrazin-2-yl)methanesulfonamide and alkynes was developed <04TL8087>, and 3- and 5-substituted 2(l//)-pyrazinones were prepared by Suzuki and Heck reactions using 3,5-dichloro-2(l//)-pyrazinones <04TL1885>. An improved synthesis of 6-substituted-5//-pyrrolo 2,3-iiJ-pyrazines via microwave-assisted Pd-catalyzed heteroannulation was developed <04TL8631>, and the reaction of a-diazo-P-keto esters with Boc amino acid amides in the presence of a Rh catalyst gave, after air oxidation, pyrazin-6-ones 111, which were then converted into tetrasubstituted pyrazines 112 <04OL4627>. 

Ishida T, Watanabe H, Take T, Hamasaki A, Tokunaga M, Haruta M (2012) Metal oxide-catalyzed ammoxidation of alcohols to nitriles and promotion effect of gold nanoparticles for one-pot amide synthesis. Appl Catal A Gen 425 26 85-90... 

Transition metal complexes are used as catalysts and as reagents in the synthesis of imides. Molybdenum hexacarbonyl activates strained aziridines and allows the nucleophilic attack of caibanions. Intramolecular rearrangement and a final oxidation yields imides completely stereospecifically (equation 59).38> Dicobalt octacarbonyl catalyzes the conversion of 3,7-unsaturated amides to imides in the presence of carbon monoxide (equation 60). ... 

A sequential one-pot synthesis of unsymmetrical aryl urea derivatives was developed by arylation of N-substituted cyanamides under metal-free conditions, followed by a second N-arylation under copper-catalyzed conditions [96]. Chen and Chen devised the arylation of pyridine N-oxides with At21X via initial O-arylation followed by a 1,3-radical rearrangement to o-pyridinium phenolates, and arylation of pyridine N-amidates delivered o-pyridinium anilines (Scheme 5d) [97]. 

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