Abstract In search to find levels of density functional theory (DFT) for the accurate prediction of vibrational circular dichroism (VCD) spectra of cacalolides, we undertook the evaluation of isomeric quinols. To gain compounds that provide experimental VCD spectra for comparative purposes to the calculated spectra, we prepared the hexanes extracts of the roots of Psacalium aff. sinuatum (Cerv.) H. Rob. & Brettell. They afforded the known furotetralin cacalol (1a), the isomeric quinols cacalone (2a) and epi‑cacalone (3a), and the furodehydrotetralin cacalohastine (4). In an earlier work we found that the absolute configuration (AC) determination of 1a by VCD required the study of its acetyl derivative 1b when comparing the experimental data with DFT spectra calculated at the commonly used B3LYP/DGDZVP level of theory. Herein the AC of acetylcacalone (2b) and of non-acetylated 3a were addressed using the same VCD methodology for which it is difficult to predict which DFT level of theory would provide satisfactory results for the uncommon quinol chromophores. It turned out that epi‑cacalone (3a) required the B3PW91/DGDZVP2 level of theory, while in the case of natural occurring 2a it was necessary, as in the case of 1a, to study the acetyl derivative 2b since in 2a the tertiary hydroxy group is prone to intermolecular associations in solution. In addition, the dihydronaphthofuran 4 required the PBEPBE/DGDZVP level of theory, mainly used for aromatic compounds, to be modeled satisfactorily.

中文翻译：

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来自 Psacalium aff 的 quinol cacalolides 的振动圆二色性行为。窦房结

摘要 为了寻找密度泛函理论 (DFT) 的水平以准确预测 cacalolides 的振动圆二色性 (VCD) 光谱，我们进行了异构喹啉的评估。为了获得提供实验 VCD 光谱以与计算光谱进行比较的化合物，我们制备了 Psacalium aff 根的己烷提取物。sinuatum (Cerv.) H. Rob。＆布雷特尔。他们提供了已知的呋喃四林 cacalol (1a)、异构喹啉 cacalone (2a) 和表 cacalone (3a)，以及呋喃四氢萘 cacalohastine (4)。在早期的工作中，我们发现当将实验数据与在常用 B3LYP/DGDZVP 理论水平计算的 DFT 光谱进行比较时，通过 VCD 确定 1a 的绝对构型 (AC) 需要研究其乙酰衍生物 1b。在本文中，乙酰卡卡隆 (2b) 和非乙酰化 3a 的 AC 使用相同的 VCD 方法进行处理，对于这种方法，很难预测哪种 DFT 理论水平将为不常见的醌醇生色团提供令人满意的结果。结果表明，epi-cacalone (3a) 需要 B3PW91/DGDZVP2 理论水平，而在天然存在的 2a 的情况下，有必要像 1a 的情况一样研究乙酰衍生物 2b，因为在 2a 中叔羟基组在溶液中容易发生分子间缔合。此外，二氢萘呋喃 4 需要 PBEPBE/DGDZVP 理论水平，主要用于芳族化合物，才能令人满意地建模。