4- Azaazulenes protonation

Interestingly in these cases protonation takes place at the ring carbon, whereas for 5-azaazulene protonation occurs at the -equivalent nitrogen, thus retaining the aromatic rr-electron structure.239... 

Deprotonation by alkali or amines to azaazulenes is commonly observed with jV-protonated pyrrolotropylium salts, often reversing their formation. Examples are those of bicyclic species like 603 (to give 604, Scheme 162 ... 

The formation of azaazulenium or pyrrolotropylium salts by protonation of azaazulenes is exemplified by the acenaphtho-fused com-... 

Protonation of 4-azaazulenones and tautomerism of 4-azaazulenes, which have been studied mainly by H-NMR spectroscopy, are covered in Sections III,B and III,A, respectively. 

H-NMR spectra have been compared for the only uncharged, fully conjugated 4-azaazulene (10) and its 6,7-dihydro derivative. The 6,7-double bond gives rise to a 0.3 to 0.6-ppm high-field shift of the remaining protons (83JHC37). 

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