Oligomerization of vinyl monomers 18. Stereochemistry of anionic oligomerization of 4‐vinylpyridine

Oligomers of 4‐vinylpyridine were prepared by reaction in vacuo of 4‐vinylpyridine with lithio‐4‐ethylpyridine at −78°C, followed by reaction with CH3I(13CH3I) or CH3OH. The stereochemistry was studied by NMR and GC. Methylation and the addition of 4‐vinylpyridine occurred in a stereochemically nonselective manner. The data also indicated that in contrast to the oligomerization of 2‐vinylpyridine the stereoisomeric meso and racemic 4‐pyridyl carbanions propagated with equal reaction rates. The stereochemistry was readily explained by an absence of coordination of the Li ion by the nitrogen of the penultimate pyridine ring observed in the corresponding oligomerization of 2‐vinylpyridine.