Amine addition to nitro group
A reasonable mechanism for the transformation is shown below. Since this is under basic conditions, I've written a mechanism that avoids cationic intermediates. Deprotonating the hydrazine gives a very nucleophilic nitrogen that can attack the nitro group. Proton transfer gives a nitrogen anion, which can kick out hydroxide. Two additional proton transfer steps lead to the product, HOBt.



A SciFinder search didn't reveal any examples of the intermolecular variant of this reaction, although I didn't find this exact intramolecular reaction either.