Mechanistic Study on the Bidentate Nitrogen-Ligated Iodine(V) Reagent Promoted Oxidative Dearomatization of Phenols

Danqi Zhang, Yingbo Shao, Hanliang Zheng, Biying Zhou, Xiao-Song Xue
2021 Huaxue xuebao  
Hypervalent iodine reagents, as a type of environmentally friendly and economical oxidants, have received extensive attention from synthetic chemistry in recent years. There are two kinds of common hypervalent iodine reagents: iodine(III) and iodine(V) reagents. Among various iodine(V) based reagents, 2-iodoxybenzoic acid (IBX) is one of the most commonly used oxidants in organic chemistry and has been widely used in selective oxidation of phenols, alcohols, thioethers and many other compounds.
more » ... Although the IBX can efficiently oxidize electron-rich phenols to obtain o-quinones, which have important applications in catalysis and materials science, the synthesis of electron-deficient o-quinones is still challenging and remains an unsolved problem. Recently, a novel bidentate nitrogen-ligated iodine(V) reagent has been found to efficiently and selectively promote the oxidative dearomatization of electron-deficient phenols to o-quinones. The bidentate-nitrogen ligand has been demonstrated to play a crucial role in the successful oxidative dearomatization of electron-deficient phenols. To understand the origin of the effect of bidentate-nitrogen ligand on oxidative dearomatization, we herein conducted a detailed mechanistic study on the oxidative dearomatization of phenols promoted by iodine(V) reagents with different ligands by using density functional theory (DFT). Geometry optimizations and frequency calculations were carried out at the M06-2X/[6-31G(d,p)+LANL2DZ(I)] level of theory. To obtain more accurate electronic energies, single-point energy were calculated at the M06-2X/[6-311+G(2d,p)+def2-TZVPP(I)] level of theory. The solvation model based on density (SMD) was used to account for the solvation effect of chloroform, the solvents used in the experiment. Calculations revealed that the bidentate-nitrogen ligand not only enhances the reactivity of iodine(V) reagent but also acts as a base to neutralize the strong acid generated in the reaction to prevent product degradation. The insights into the effect of the bidentate-nitrogen ligand on the reactivity of hypervalent iodine reagent obtained from this study would facilitate the future design of novel ligandregulated hypervalent iodine reagents for new reactions. Keywords bidentate-nitrogen ligand; iodine(V) reagent; oxidative dearomatization; o-quinone; DFT calculation 1 引言 高价碘试剂常展现出与过渡金属相似的反应性, 同 时兼具低毒价廉、环境友好、反应条件温和、选择性高 等优点, 近年来受到了合成化学研究者的广泛关注 [1] . 常见的高价碘试剂主要有三价和五价碘两类(图 1) [1] . 其 中, 五价碘试剂如 2-碘酰基苯甲酸(IBX)是当今有机化 学领域最为常用的氧化剂之一, 被广泛应用于苯酚、 醇、 硫醚等有机化合物的选择性氧化转化 [2] . 邻醌类化合物在催化、材料等领域有着非常重要的 应用 [3] . 虽然 IBX 可高效地将富电子苯酚氧化为邻醌, 但缺电子苯酚的选择性氧化却是长期困扰合成化学家 的难题 [4] . 最近, Wengryniuk 课题组通过使用新型双齿 氮配体螯合五价碘试剂 [5] [6] (Bi(bipy)-HVI, 图 2), 开发出
doi:10.6023/a21080358 fatcat:npt2qax3v5fd3cmcrgnnzgutw4