830326-14-2Relevant academic research and scientific papers
Metal 4-alkylidene-4H-pyridin-1-ides and 2H-imidazol-4-ones from novel highly N-(pyridin-4-yl)methyl-substituted azomethines
Hampe, Diana,Guenther, Wolfgang,Goerls, Helmar,Anders, Ernst
, p. 4357 - 4372 (2004)
Novel azomethines 3 synthesized from 4-(aminomethyl)pyridine (1) and various ketones 2 exhibit a higher acidity of the Ca-protons compared with other 4-alkylpyridines like 4-benzylpyridine or 4-(tosylmethyl)pyridine. Therefore, they can easily be metalated to give a variety of specific anions 3(-), which deserve interest for further synthetic applications. Important properties of compounds 3 and their lithiated derivatives 4 (lithium 4H-pyridin-1-ides, synthesized by deprotonation of the α-CH2 group in 3) can be controlled by the carbonyl reactant 2. These carbanions 3(-) are remarkable intermediates regarding their NMR properties. Comparing the NMR spectra of the lithium 4H-pyridin-1-ides 4 with their parent azomethines 3 reveal very distinct changes in the chemical shifts from which important structural and electronic properties of the carbanions can be deduced. The observation of E/Z isomers in the case of 3c and their mutual conversion at higher temperature inspire DFT calculations on the B3LYP/6-311++G(d,p) level of theory to get insight into the energetic demand of such isomerization processes. Moreover, calculations on the same level of theory were carried out on the model azomethine anion 5 and different monomeric lithium coordination isomers 6a-d. Experimentally, two selected examples will exemplify the reactivity of 4H-pyridin-1-ide anions towards heterocumulenes. The 2-(pyridin-4-yl)acetate 7 obtained from the reaction of 4e with carbon dioxide appears to be a CO2 storage molecule as it easily releases CO2 under protolysis conditions comparable with the vitamin B6 reaction mode. Interesting five-membered heterocycles were isolated after reaction of 4 with isocyanates followed by hydrolysis and oxidation. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
