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Oligomers of 2-vinylpyridine have been prepared by addition of 2-vinylpyridine to T H F solutions of alkali salts of 2-ethylpyridine followed by termination with CH31. With Li and Na as counterions, these oligomers were highly (>95%) isotactic as determined with 'H and 13C NMR. With K and larger counterions, the formation of dimers is not stereoselective. Epimerization of these types of compounds yields statistically expected mixtures of stereoisomers. Thus stereoselection appears kinetically controlled. Dimerization of 4-vinylpyridine or addition of kinylpyridine t o lithio-2-ethylpyridine followed by methylation is not stereoselective. The results particularly with the Li and Na salts indicate that the stereochemistry of methylation and 2-vinylpyridine addition is identical. A mechanism is proposed taking the chirality of the ion pair itself into account. For the Li and Na salts of the living oligomers, the cation appears to be coordinated with the nitrogen lone pair of the penultimate 2-pyridine unit. In such a case, one of the two possible diastereomeric ion pairs is expected to be favored, and this is most likely the reason for the observed stereoselectivity. Electrophilic attack is apparently occurring in a "syn" fashion.

We have recently shown that oligomers [7] and [8] of 2-vinylpyridine prepared with Li and Na salts as initiators in THF [eq. (l)] are predominantly Q 95%) isotactic (1,2). -- C2I-C61C7I-C121 C21. C71 n=l; 131. CSI ~2 ; 141.C91 n=3; C51. [lo] 11.5-6; [6]. [ I 1 1 n=6-12 1123 n -Thus, the methylation of and the 2-vinylpyridine addition to anion [2] occurs with the same meso stereochemistry. Moreover, with a 4-pyridyl unit in ultimate position or both ultimate and penultimate positions the methylation of such an anion is not stereoselective. With larger or more extensively coordinated cations the methylation stereoselectivity of [2] is decreased dramatically. These results have been shown to be consistent with the occurrence of diastereomeric ion pairs [13] and [14]. With Li and Na as counterions these ion pairs most likely exist in their respective chelated forms [13a] and [14a] (3): -*qJ paw n+ 2-Py 2-Py 2-Py 2-Py C13Jl C14al Since [13a] should be preferred because of butane gauche and PCHz-chain end pyridine lone-pair interactions, the stereoselectivity [eq. (l)] is consistent

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