Reactions with Oxidising Agents

2-Bromo- and 2-chloropyridines can be made extremely efficiently by reaction with the halogen, at 0-5°C in the presence of the pyridine-palladium chloride complex.  

The salt formed by the interaction of pyridine with mercuric acetate at room temperature can be rearranged to 3-acetoxymercuripyridine by heating to only 180 C. This process, where again there is C-attack by a relatively weakly electrophilic reagent, like that described for mercuric sulfate-catalysed sulfonation, may involve attack on an equilibrium concentration of free pyridine. 

In most situations carbon-substituents can be oxidised with survival of the ring, thus alkylpyridines can be converted into pyridine carboxylic acids with a variety of reagents. Some selectivity can be achieved only a- and y-groups are attacked by selenium dioxide.  

Pyrroles which have a ketone or ester substituent are more resistant to ring degradation and high yielding side-chain oxidation can be achieved using cerium(IV) ammonium nitrate with selectivity for an a-alkyl.  

Pyrrole and its derivatives do not react with nucleophilic reagents by addition or by substitution, except in the same type of situation which allows nucleophilic substitution in benzene chemistry the two examples below are illustrative.  

A key step in a synthesis of Ketorolac involves an intramolecular nucleophilic displacement of a methanesulfonyl group activated by a 5-ketone.  

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