Compounds with an Additional Nitrogen in the Six-Membered Ring

5 Compounds with an Additional Nitrogen in the Six-Membered Ring 

In addition to the propensity for electrophilic substitution at C-l/C-3 (see above), the main feature of this class of heterocycle is that they undergo relatively easy nucleophilic attack in the six-membered ring, which is now distinctly electron-deficient through the incorporation of imine units - the analogy with the ease of nucleophilic addition to diazines versus pyridines, is obvious. Some are so susceptible to nucleophilic addition that they form hydrates even on exposure to moist air. Preparative Uthiations can, however, be carried out using less nncleophilic bases. 

Ring synthesis of such molecules can proceed from diazines nsing methods analogous to those described for the synthesis of azolo-pyridines from pyridines, for example the dipolar cycloaddition of an A-imide to an alkyne, or the bromine-promoted ring closure of hydrazones of 2-hydrazino-pyridines, -pyridazines (shown) or -pyrimidines.  

Varions routes from the five-membered ring component are also possible - some representative chemistry involving pyrroles is shown below. 

CI(CH2)2NH2 NaOH, TBAS HCO2H MeCN, reflux reflux 

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Compounds with an additional nitrogen in the six-membered ring... 

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