中国科学院化学研究所左智伟团队报道了用单一醇脱乙酰催化剂对立体富集的倍增增强作用。相关研究成果于2023年10月27日发表于国际顶尖学术期刊《科学》。

通过去乙酰化对外消旋混合物进行立体化学富集，必须克服不利的熵效应以及微观可逆性原理。最近，由光的能量输入揭示的光化学反应途径导致了这方面的创新，最常见的是通过烧蚀立体C（sp3）–H键。

研究人员报道了一种光化学驱动的去乙酰化方案，其中单个手性催化剂影响两个不同的机制步骤，C–C键切割和C–C形成，以实现立体诱导的倍增增强，从而导致高水平的立体选择性。由手性磷酸或双恶唑啉配位的钛催化剂的配体-金属电荷转移激发有效地富集了外消旋醇，该外消旋醇具有相邻和完全取代的立体中心，对映体比高达99:1。机制研究表明通过一种常见的前手性中间体进行顺序自由基介导的键断裂和键形成的途径，并表明，尽管总体立体富集度较高，但每个单独步骤的选择性中等。

附：英文原文

Title: Multiplicative enhancement of stereoenrichment by a single catalyst for deracemization of alcohols

Author: Lu Wen, Jia Ding, Lingfei Duan, Shun Wang, Qing An, Hexiang Wang, Zhiwei Zuo

Issue&Volume: 2023-10-27

Abstract: Stereochemical enrichment of a racemic mixture by deracemization must overcome unfavorable entropic effects as well as the principle of microscopic reversibility; recently, photochemical reaction pathways unveiled by the energetic input of light have led to innovations toward this end, most often by ablation of a stereogenic C(sp3)–H bond. We report a photochemically driven deracemization protocol in which a single chiral catalyst effects two mechanistically different steps, C–C bond cleavage and C–C bond formation, to achieve multiplicative enhancement of stereoinduction, which leads to high levels of stereoselectivity. Ligand-to-metal charge transfer excitation of a titanium catalyst coordinated by a chiral phosphoric acid or bisoxazoline efficiently enriches racemic alcohols that feature adjacent and fully substituted stereogenic centers to enantiomeric ratios up to 99:1. Mechanistic investigations support a pathway of sequential radical-mediated bond scission and bond formation through a common prochiral intermediate and reveal that, although the overall stereoenrichment is high, the selectivity in each individual step is moderate.

DOI: adj0040

Source: https://www.science.org/doi/10.1126/science.adj0040