2- Nitrosopyridine, reaction with nitrile oxides

Cycloaddition of 2-nitrosopyridine 48 with nitrile oxides can give either di-A -oxides such as 49 or 3-mono-A -oxides such as 50 (93JHC287). In general, greater electron withdrawing character in the aromatic substituent appears to favor formation of the di-A -oxides. Sulfur ylides such as compound 51 are obtained from aryl isothiocyanates and l-amino-2-methylthiopyridinium iodides (84JCS(P1)1891) nitrogen ylides can be obtained from a similar reaction (86H(24)3363). 

Reactions of 2-nitrosopyridine with nitrile oxides afford, depending on structure of the latter, either l,2,4-triazolo[l,5-a]pyridine 1,3-di-N-oxides (370) or the corresponding 1.2.4-triazolo, 5-a Ipyridine 3-oxides (371) (419). 

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