Pyridine, 2,3,5-trichloro-, reaction with nucleophiles

Since the nitrogen in pyridine is electron attracting it seemed reasonable to predict that the trihalopyridynes would also show the increased electrophilic character necessary to form adducts with aromatic hydrocarbons under similar conditions to those employed with the tetra-halogeno-benzynes. The availability of pentachloropyridine suggested to us and others that the reaction with w-butyl-lithium should lead to the formation of tetrachloro-4-pyridyl-lithium 82 84>. This has been achieved and adducts obtained, although this system is complicated by the ease with which pentachloropyridine undergoes nucleophilic substitution by tetrachloro-4-pyridyl lithium. Adducts of the type (45) have been isolated in modest yield both in the trichloro- and tribromo- 58) series. 

The solvents included both, some that were less polar and some that were more polar than the amines involved. This as well as the definite stoichiometry of their involvement makes it improbable that the amines accelerate the reaction by means of a general solvent effect and suggests their actual participation in a rate-affecting transition state. Similar amine catalysis has been demonstrated for a nucleophilic displacement on a heterocyclic ring. The reaction of trichloro-s-triazene with aniline in benzene is catalyzed by triethyl-amine, pyridine, and aniline (78). 

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