N-Acylpyridinium Salts and Corresponding Fused Benzo-derivatives

Published information on the preparation, structure, and reactions of N-acylpyridiniurn salts and the corresponding benzo-derivatives is summarised. They comprise purely ionic structures with the acyl group attached to the nitrogen atom, which bears a positive charge (partly delocalised through the ring), and a halide counter-ion. In individual cases (quinolinium and isoquinolinium) the electron of the anion may be transferred to a non-bonding orbital of the heterocycle with formation of a charge-transfer complex. N-Acylated heterocyclic cations contain more than one reaction centre, and are capable of trans-acylation, ring opening, hetarylation, one-electron reduction, etc. Processes involving hetarylation are especially interesting, and permit the preparation of various difficultly accessible derivatives of pyridine, quinoline, isoquinoline, and acridine.
A list of 419 references is included.