Acylmethylpyridinium salts

In the laboratory of P. Kocovsky, novel pyridine-type P,A/-ligands were prepared from various monoterpenes. The key step was the Krohnke pyridine synthesis, and the chirality was introduced by the a,(3-unsaturated ketone component, which was derived from enantiopure monoterpenes. One of these ligands was synthesized from (+)-pinocarvone which was condensed with the acylmethylpyridinium salt under standard conditions to give good yield of the trisubstituted pyridine product. The benzylic position of this compound was deprotonated with butyllithium, and upon addition of methyl iodide the stereoselective methylation was achieved. The subsequent nucleophilic aromatic substitution (Sw/ r) gave rise to the desired ligand. 

Mono- or bicyclic pyridines or their hydrogenated derivatives have been used as starting materials. Acylmethylpyridinium salts (157) could be easily reacted with hydrazines to give (158) (Equation (30)) <69JOC2i29, 86EJM417>. Instead of (157), 2-chloro-l-propargylpyridinium bromide was also used successfully <84JHC1765>. 

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