6 -chloro-3-nitropyridine formation

A special, isotope-labeled case of the azide-tetrazole equilibrium was studied by Cmoch et al. <2000JP0480>, and the results are shown in Scheme 23. 2-Chloro-3-nitropyridine 86 was treated with potassium azide containing a doubly labeled (15NN15N) azide anion. The authors detected formation of two differently labeled tetrazolopyridines the 2,4- 87 and the 1,3-labeled 88 derivatives. 

All these amination reactions show exclusive SNH substitution. There is hardly any indication for the formation of 3-nitropyridines, in which the chloro or methoxy group was replaced by an amino group, even when these leaving groups are present at the reactive a-position of the pyridine ring. It seems to be a characteristic feature of the oxidative amination... 

There are also some reports on the formation of the oxathiine derivatives 31-33, resulting from cyclizations of 2-chloro-3-nitro- and 4-chloro-3-nitropyridines with l,4-0,S-bifunctional nucleophiles (Scheme 32) (81JHC479 80JHC589 79TL5035 80JHC1153). 

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