Formation of salts from acetyl- and formylpyrroles,and pyrrole ring reactivity

With 2-acetyl- and 2-formylpyrrole, salt formation is via proton addition to the carbonyl oxygen. In salt formation with pyrrole derivatives having an acetyl or formyl group at position 2, position 5 is deactivated for electrophilic substitution. With salts of 3-acetyl- and 3-formylpyrroles, position 2 is also deactivated, while position 5 is activated.