Mechanism and proton activating factors in base-induced β-elimination reactions of N-[2-(4-pyridyl)ethyl]quinuclidinium and N-[2-(2-pyridyl)ethyl]quinuclidinium salts

Abstract

β-Elimination reactions of N-[2-(4-pyridyl)ethyl]quinuclidinium and N-[2-(2-pyridyl)ethyl]quinuclidinium salts (N) in acetohydroxamate–acetohydroxamic acid buffer, H₂O, μ = 1 M KCl, 50 °C, with the formation of 4- or 2-vinylpyridine, respectively, proceed by an E1cb mechanism with carbon deprotonation occurring in the substrates protonated at the pyridine ring (NH⁺). The formation of the intermediate carbanion has a high degree of reversibility. The systems consistently present H/D exchange. NH⁺ is much more reactive than N; this can be attributed to the strong stabilization of the intermediate carbanion formed from NH⁺ due to resonance.