Ośmiałowski Borys, Kolehmainen Erkki, Gawinecki Ryszard
Department of Chemistry, Technical and Agricultural University, Seminaryjna 3, 85-326 Bydgoszcz, Poland.
Chemistry. 2003 Jun 16;9(12):2710-6. doi: 10.1002/chem.200204273.
Although there is a very fast (on the NMR timescale) double-proton transfer in (1Z,3Z)-3-hydroxy-4-quinolin-2-yl-1-quinolin-2(1H)-ylidenbut-3-en-2-one (the product of the condensation of ethyl oxalate with 2lithiomethylquinoline), it is the only species present in chloroform solution. Comparison of the product of condensation of ethyl oxalate with 2lithiomethyl derivatives of pyridine (recent studies) and quinoline (present studies) shows that benzoannulation considerably affects the tautomeric equilibrium. The observed changes are not only quantitative but also qualitative. Moreover, contrary to the proton transfer in the pyridine tautomers, this process is fast in the quinoline tautomers. Comparison of the experimental and ab initio/DFT GIAO-calculated (13)C and (15)N chemical shifts for the transition states in the proton-transfer reactions between (1Z,3Z)- 3-hydroxy-4-quinolin-2-yl-1-quinolin-2(1H)-ylidenbut-3-en-2-one and its tautomers support the theory that a concerted identity reaction takes place between the enolimine-enaminone and enaminone-enolimine tautomeric forms. As a consequence, the most stable tautomeric form, (1Z,3Z)-1,4-di(quinolin-2-yl)buta-1,3-diene-2,3-diol, is not present in the tautomeric mixture.
尽管在(1Z,3Z)-3-羟基-4-喹啉-2-基-1-喹啉-2(1H)-亚基丁-3-烯-2-酮（草酸乙酯与2-锂甲基喹啉缩合产物）中存在非常快速的（在核磁共振时间尺度上）双质子转移，但它是氯仿溶液中唯一存在的物种。草酸乙酯与吡啶的2-锂甲基衍生物（近期研究）和喹啉的2-锂甲基衍生物（本研究）的缩合产物比较表明，苯并环化对互变异构平衡有相当大的影响。观察到的变化不仅是定量的，也是定性的。此外，与吡啶互变异构体中的质子转移相反，这个过程在喹啉互变异构体中很快。对(1Z,3Z)-3-羟基-4-喹啉-2-基-1-喹啉-2(1H)-亚基丁-3-烯-2-酮及其互变异构体之间质子转移反应过渡态的实验和从头算/密度泛函理论GIAO计算的(13)C和(15)N化学位移进行比较，支持了烯醇亚胺-烯胺酮和烯胺酮-烯醇亚胺互变异构形式之间发生协同同一反应的理论。因此，最稳定的互变异构形式(1Z,3Z)-1,4-二（喹啉-2-基）丁-1,3-二烯-2,3-二醇不存在于互变异构混合物中。
