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Computational Analysis of the Selective Formation of the C4α—C8′ Bond in the Intermolecular Coupling of Catechin Derivatives
The Journal of Organic Chemistry ( IF 3.3 ) Pub Date : 2020-03-18 , DOI: 10.1021/acs.joc.0c00261 Keisuke Fukaya 1 , Akiko Saito 2 , Noriyuki Nakajima 3 , Daisuke Urabe 1
The Journal of Organic Chemistry ( IF 3.3 ) Pub Date : 2020-03-18 , DOI: 10.1021/acs.joc.0c00261 Keisuke Fukaya 1 , Akiko Saito 2 , Noriyuki Nakajima 3 , Daisuke Urabe 1
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Procyanidin B3 is a natural flavonoid composed of two catechins connected via a C4α—C8′ bond. The couplings of catechin derivatives, promoted by Lewis acids, have been widely applied to the syntheses of procyanidin B3 and related flavonoids because the reactions construct the C4α—C8′ bond in a highly stereo- and regioselective manner. However, the structural complexity of the catechin derivatives has complicated the exploration of a detailed mechanism for this selectivity. Here, we report the results of a computational study to provide plausible origins for the selective C4α—C8′ bond formation of catechin derivatives 1 and 2 by using models 5 and 7. Although a systematic search did not provide SN2-like transition states, we successfully identified transition states TS-A, TS-B, and TS-C for the SN1-type C4α—C8′, C4β—C8′, and C4α—C6′ bond formations, respectively, from a total of 233 transition states to justify the stereo- and regioselectivity of the experimental results. The analysis of these structures by NCIPLOT mapping and the distortion/interaction strain model suggests that the eclipsed interaction at the forming C—C bond between the electrophile and the nucleophile destabilizes TS-B, while the strain of the electrophile destabilizes TS-C. Consequently, the C4α—C8′ bond is formed via the lowest energy transition state TS-A.
中文翻译：
儿茶素衍生物分子间偶联中C4α-C8'键选择性形成的计算分析
原花青素B3是天然黄酮，由两个通过C4α-C8'键连接的儿茶素组成。路易斯酸促进的儿茶素衍生物偶联已广泛用于原花青素B3和相关类黄酮的合成，因为该反应以高度立体和区域选择性的方式构建C4α-C8'键。然而，儿茶素衍生物的结构复杂性使对该选择性的详细机理的探索变得复杂。在这里，我们报告计算研究的结果，以通过使用模型5和7为儿茶素衍生物1和2的选择性C4α-C8'键形成提供合理的起源。尽管系统搜索没有提供S N类似2的过渡态，我们成功地确定了S N 1型C4α-C8'，C4β-C8'和C4α-C6'键形成的过渡态TS-A，TS-B和TS-C，从总共233种过渡态中证明了实验结果的立体选择性和区域选择性。通过NCIPLOT映射和畸变/相互作用应变模型对这些结构的分析表明，亲电试剂和亲核试剂之间形成的CC键处的蚀变相互作用使TS-B不稳定，而亲电试剂的应变使TS-C不稳定。因此，经由最低的能量跃迁状态TS-A形成C4α-C8'键。
更新日期：2020-03-19
中文翻译：
儿茶素衍生物分子间偶联中C4α-C8'键选择性形成的计算分析
原花青素B3是天然黄酮，由两个通过C4α-C8'键连接的儿茶素组成。路易斯酸促进的儿茶素衍生物偶联已广泛用于原花青素B3和相关类黄酮的合成，因为该反应以高度立体和区域选择性的方式构建C4α-C8'键。然而，儿茶素衍生物的结构复杂性使对该选择性的详细机理的探索变得复杂。在这里，我们报告计算研究的结果，以通过使用模型5和7为儿茶素衍生物1和2的选择性C4α-C8'键形成提供合理的起源。尽管系统搜索没有提供S N类似2的过渡态，我们成功地确定了S N 1型C4α-C8'，C4β-C8'和C4α-C6'键形成的过渡态TS-A，TS-B和TS-C，从总共233种过渡态中证明了实验结果的立体选择性和区域选择性。通过NCIPLOT映射和畸变/相互作用应变模型对这些结构的分析表明，亲电试剂和亲核试剂之间形成的CC键处的蚀变相互作用使TS-B不稳定，而亲电试剂的应变使TS-C不稳定。因此，经由最低的能量跃迁状态TS-A形成C4α-C8'键。
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