Theoretical Insight into Ligand- and Counterion-Controlled Regiodivergent Reactivity in Synthesis of Borylated Furans: 1,2-H vs 1,2-B Migration
Theoretical Insight into Ligand- and Counterion-Controlled Regiodivergent Reactivity in Synthesis of Borylated Furans: 1,2-H vs 1,2-B Migration
复制标题
硼化呋喃合成中配体和抗衡离子控制的区域发散反应性的理论见解：1,2-H 与 1,2-B 迁移
DOI：
10.1021/acscatal.8b02188
复制
发表时间：
2018
期刊：
影响因子：
12.9
通讯作者：
Zhang Dongju
中科院分区：
文献类型：
--
作者：
Yang Yiying;Li Jinghua;Zhu Rongxiu;Liu Chengbu;Zhang Dongju
通过调节催化条件，特别是改变辅助配体和/或抗衡离子，不同的催化反应可以通过受控的反应途径快速获得不同的分子支架。本研究提出了 Au(I) 催化的含硼炔基环氧化物向 C2 和 C3 硼化呋喃区域发散环异构化的计算研究。计算阐明了反应的机制细节以及两种金催化剂引起的区域分歧。所提出的催化循环涉及两个主要阶段：炔基环氧化物的扩环伴随着B(MIDA)基团迁移以形成am-硼呋喃基杂环中间体，以及正式的1,2-H或1,2-B迁移以形成C3-或C2-硼化呋喃。前者被认为是反应的瓶颈，该反应是通过环氧乙烷部分的σ激活而不是实验工作中提出的炔基部分的π激活来进行的，而后者控制区域发散。计算表明，金催化剂中的抗衡离子和配体在扩环中发挥的作用不太重要，但它们对于硼化呋喃的不同形成至关重要：具有(ArO)3P配体的OTf-抗衡离子有利于1,2-H迁移，导致C3-硼化呋喃的形成，而具有IPr配体的SbF6-阴离子促进1,2-B迁移，支持主要形成C2-硼化呋喃。理论结果合理化了观察到的区域选择性，并为含硼炔基环氧化物的迁移环异构化机制提供了关键见解。
Divergent catalytic reactions provide quick access to diverse molecular scaffolds through controlled reaction pathways by tuning the catalytic conditions, especially changing auxiliary ligands and/or counterions. This study presents a computational study of Au(I)-catalyzed regiodivergent cycloisomerizations of boron-containing alkynyl epoxides toward C2- and C3-borylated furans. The calculations clarified the mechanistic details of the reaction and the regiodivergence induced by two gold catalysts. The proposed catalytic cycle involves two major stages: ring expansion of alkynyl epoxide accompanied by B(MIDA) group migration to form am-boron furyl heterocyclic intermediate and a formal 1,2-H or a 1,2-B migration to form a C3- or C2-borylated furan. The former is identified as the bottleneck of the reaction, which proceeds via σ activation of the oxirane moiety rather than π activation of the alkynyl moiety proposed in experimental work, and the latter controls the regiodivergence. Calculations show that the counterion and ligand in the gold catalyst play a less important role in the ring expansion, but they are crucial for the divergent formation of borylated furans: an OTf–counterion with an (ArO)3P ligand favors the 1,2-H migration, leading to the formation of C3-borylated furan, whereas an SbF6–anion with an IPr ligand promotes the 1,2-B migration, supporting the predominant formation of C2-borylated furan. The theoretical results rationalize the observed regioselectivity and provide key insights into the mechanism of the migratory cycloisomerization of boron-containing alkynyl epoxides.