Proton loss from a ring nitrogen atom

4 Proton loss from a ring nitrogen atom 

The position of alkylation can depend on counter ion, solvent and reagent. Thus, Ag salts tend to give O-alkylation, whereas Na or K salts predominantly undergo A-alkylation (see CHEC 2.05.2.5). 

Reaction of pyridones with diazoalkanes involves deprotonation as the first step, forming an alkyldiazonium cation which then rapidly alkylates the pyridone anion 2-pyridone gives mainly 0-methyl derivatives, but 4-pyridone gives mixed 0- and A-methyl derivatives. 

Perimidines with a free NH-group (360) in basic media form readily oxidizable anions (361). The latter can be A-alkylated in inert atmosphere, the reaction being sensitive to steric interference from 2-and 4(9)-substituents (81RCR1559). 

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Azole anions are derived from imidazoles, pyrazoles, triazoles or tetrazoles by proton loss from a ring NH group. In contrast to the neutral azoles, azole anions show enhanced reactivity toward electrophiles, both at the nitrogen (Section 3.4.1.3.6) and carbon atoms (Section 3.4.1.4.1.i). They are correspondingly unreactive toward nucleophiles. 

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