Tautomerism of quinazolin-4-ones with 2,3-annulated hydrogenated 1,3-diazaheterocycles. Synchronous and asynchronous double proton transfer in cyclic hydrogen-bonded associates
作者:A. S. Morkovnik、L. N. Divaeva
DOI:10.1007/s11172-009-0111-6
日期:2009.5
It was shown by quantum chemical methods and 1H NMR spectroscopy that in the series of prototropic tautomeric quinazolin-4-ones with hydrogenated 1,3-diazaheterocycles annulated at positions 2 and 3, namely, imidazole, pyrimidine, or [1,3]diazepine (compounds 1–3, respectively), the 1H-tautomeric form strongly predominates in the gas phase and in solutions regardless of the nature of these cycles. Tautomerization of tricycles 1–3 occurs via the intermolecular mechanism to form as intermediates hydrogen-bonded cyclodimers of these compounds or their cyclosolvates with proton-donor solvents. The key step of the reaction is the intraassociated concerted double proton transfer, which can proceed in nearly synchronous and asynchronous modes. In particular, double proton transfer in cyclodimers of quinazolinones 1–3 is asynchronous and proceeds with the formation of solvate-stabilized polar transition states, which are similar in structure to ionic intermediates of the nonconcerted double proton transfer.
量子化学方法和 1H NMR 光谱显示,在原向同分异构喹唑啉-4-酮系列中,氢化的 1,3-二氮杂环在第 2 位和第 3 位环化,即咪唑、嘧啶或 [1,3]diazepine(分别为化合物 1-3),无论这些循环的性质如何,1H-同分异构形式在气相和溶液中都占主导地位。三环 1-3 的同分异构反应是通过分子间机理进行的,中间产物是这些化合物的氢键环二聚体或它们与质子供体溶剂的环溶剂化物。反应的关键步骤是联合体内部协同的双质子转移,它可以以近乎同步和异步的模式进行。特别是,喹唑啉酮环二聚体 1-3 中的双质子转移是异步的,并以形成溶胶稳定的极性转变态的方式进行,这种转变态的结构与非一致双质子转移的离子中间体相似。