Some peculiarities in electrophilic substitutions in azaindoles could possibly be ascribed to protonation of the axaindole cycle (1).
For elucidating the structures of cations for 5-azaindole,l-substituted 5-czaindole and 2,~dihydroderivatives we have recorded PIFiR-spectra of neutral and protonated 5-azaindole(I),5-azaindoline(II),l-phenyl-5-azaindole (III),l-phenyl-~-azaindoline(IV),l-acetyl-~-azaindoline(V) and Icaminopyridine(VI>. The eqerimental data are swnnarized in the Table .
The spectra of 5-azaindole(1) show that protonation of molecule results in marked deahielding of protons of the pyrrol moiety (0,41-0,54ppm),whereaa the chemical shift changes of the protons,located atdand B -positions to the pyridinic nitrogen are considerably smaller than those observed on protonation of pyridine(0,02-0,03 and 0,5'/ppm for a(-and?-protona in azaindole against 0,s and 1,04ppm for respective valuea in pyridine (3,4).A similar variation of proton deshielding had been observed earlier for 4-aminopyridine on its protonation, and the resulting cation was formulated as VIa(4).5-azaindolines(I1 and IV) exhibit even stronger similarity to 4-aminopyridine than the >-azaindoles, and protonation of II and IV produces an upfield shift of