Oxygen-nitrogen bond, cleavage

Decarboxylation of isoxazole-3-carboxylic acids is related to the nucleophilic cleavage of the isoxazole ring as far as the nature of the reaction products is concerned. It occurs at temperatures above 200°C and is accompanied by the cleavage of the nitrogen-oxygen bond of the heterocyclic ring to yield a j8-ketonitrile. It was first reported by Claisen with 5-methyl- and 5-phenyl-isoxazole-3-carboxylic acids (153- 154).Under the reaction conditions, j8-ketonitriles condense... 

The reduction of isoxazoles is often rather peculiar and its course depends on the nature both of the isoxazole and of the reducing agent. Together with a normal reduction of groupings in the side chain, cleavage of the nitrogen-oxygen bond of the heterocyclic nucleus often occurs. 

Catalytic cleavage of the nitrogen-oxygen bond occurs very frequently as in reduction of nitro compounds, oximes, and various heterocyclics these reactions are discussed in separate chapters. Considered here are N-oxides, hydroxylamincs, and N- and C-nitroso compounds. 

Amino alcohols are also good substrates for aziridination under Mitsunobu conditions. The rfs-1,4-amino alcohols 48, obtained by reductive cleavage of the nitrogen-oxygen bonds of the hetero Diels-Alder adducts 47, underwent syn-SN2 -type displacement on treatment with PPh3 and DEAD to give cyclic vinylaziridines 49 (Scheme 2.15) [27]. 

Heteroatoms, such as nitrogen, oxygen and sulphur, promote cleavage of an adjacent carbon-carbon single bond by forming an ion in which the lone-pair electrons participate in resonance stabilization ... 

A bond between nitrogen and oxygen was hydrogenolyzed in a cyclic derivative of hydroxylamine, 2-methyl-6-[ -pyridyl]-l,2-oxazine, which on treatment with zinc dust in acetic acid gave, on ring cleavage, 84.5% of 1-hydroxy-4-methylamino-1 -[ -pyridyl]butane [739]. 

Pre-treatment of the cathode produces a finely divided copper surface and this catalyses the hydrogenolysis of phenylhydroxylamine to aniline which becomes the principal reaction product. The reaction probably involves promotion of nitrogen-oxygen bond cleavage in the chemisorbed phenylhydroxylamine intermediate. 

Nitrobenzenes with an ortho or a para hydroxyl or amino function form an exceptional group of compounds in which the nitro function can readily be reduced to amino in alkaline solution. Heterolytic cleavage of the nitrogen-oxygen bond in the phenylliydroxylamine intermediate is promoted by any 2- or 4-substituent which can donate a lone pair of electrons. Further reduction steps then lead to the overall... 

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