Akhmedov Novruz G, Myshakin Evgeniy M, Hall C Dennis
Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200, USA.
Magn Reson Chem. 2004 Jan;42(1):39-48. doi: 10.1002/mrc.1306.
The 1H and 13C NMR spectra of methyl-8-(2-furyl)-5-methyl-1,3-dioxo-3,3a,4,6,8,9,9a,9b-octahydrofuro[3,4-f]isoquinoline-7(1H)-carboxylate (1) and trimethyl 8-methyl-3-phenyl-3,4,4a,7-tetrahydro-2,5,6(1H)-isoquinolinetricarboxylate (2) at room temperature displayed doubling of the majority of signals, suggesting the presence of two rotational conformers (rotamers) in a ratio approximately 1:1.2 (in a mixture of CDCl3 and C6D6), approximately 1:1 (in CD2Cl2) and approximately 1:1.4 (in C6D6). On the basis of the temperature-dependent 1H NMR spectra of 1 and 2, the barrier to interconversion of the rotamers was calculated to be approximately 16 kcal mol(-1). The average chemical shifts and spin-spin coupling constants were analyzed for the resolution-enhanced 300 MHz 1H NMR spectrum of 1 at 333 K in CDCl3 solution. From analysis of the spin-spin coupling constants, it is proposed that the nitrogen-containing ring is in a chair conformation with C-2-H equatorial. Low- and room-temperature NOESY experiments in conjunction with theoretical ab initio calculations supported the hypothesis that the two rotamers interchange via rotation about the C-N bond. Spectral assignments of all proton and carbon resonances were made on the basis of one- and two-dimensional NMR experiments (DEPT, DQCOSY, NOESY, HETCOR and gHMBC).
8-(2-呋喃基)-5-甲基-1,3-二氧代-3,3a,4,6,8,9,9a,9b-八氢呋喃并[3,4-f]异喹啉-7(1H)-羧酸甲酯(1)和8-甲基-3-苯基-3,4,4a,7-四氢-2,5,6(1H)-异喹啉三羧酸三甲酯(2)在室温下的1H和13C NMR谱显示，大多数信号出现双峰，这表明存在两种旋转异构体(旋转异构体)，其比例约为1:1.2(在CDCl3和C6D6的混合物中)、约1:1(在CD2Cl2中)和约1:1.4(在C6D6中)。根据1和2的温度依赖性1H NMR谱，计算出旋转异构体相互转化的势垒约为16 kcal mol(-1)。对1在CDCl3溶液中333 K下分辨率增强的300 MHz 1H NMR谱的平均化学位移和自旋-自旋耦合常数进行了分析。通过对自旋-自旋耦合常数的分析，提出含氮环呈椅式构象，C-2-H处于平伏键。低温和室温NOESY实验结合理论从头算计算支持了两种旋转异构体通过绕C-N键旋转而相互交换的假设。所有质子和碳共振的光谱归属是基于一维和二维NMR实验(DEPT、DQCOSY、NOESY、HETCOR和gHMBC)进行的。
