Mechanism of dehydrogenation with nosylate What is the mechanism of the attached reaction? How could nosylate do the dehydrogenate the species?



The reaction is from this synthesis (46th IChO preparatory problem 26):
This is the reaction mechanism that I propose for this reaction. Though it does not show the complete reduction of the 3-nitrobenzene sulfonate, it could be reduced further through the nitroso-hydroxylamine pathway. This means that in total, a single nitrosyl anion could oxidize three molecules of the starting material. 

Extraction of a hydrogen by the nitro group. The hydrogen is extremely acidic compared to an ordinary aliphatic $\ce{C-H}$ bond due to the massive conjugation in the resulting ion:



Amide-imidic acid tautomerization: 



Resonance structures of the molecule, showing its extensive conjugation, and hence stability:



Radical reaction pathway and formation of the product. Every atom in product is $\mathrm{sp^2}$ hybridized and is conjugated over the entire system. It is much more stable than the starting material, and is the driving force of the entire reaction: