Chiral Bifunctional Phosphine Ligand Enabling Gold-Catalyzed Asymmetric Isomerization of Alkyne to Allene and Asymmetric Synthesis of 2,5-Dihydrofuran
Chiral Bifunctional Phosphine Ligand Enabling Gold-Catalyzed Asymmetric Isomerization of Alkyne to Allene and Asymmetric Synthesis of 2,5-Dihydrofuran
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DOI：
10.1021/jacs.8b12833
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发表时间：
2019-03-06
影响因子：
15
通讯作者：
Zhang, Liming
中科院分区：
文献类型：
--
作者：
Cheng, Xinpeng;Wang, Zhixun;Zhang, Liming
炔不对称异构化为联烯是制备这类多功能轴向手性结构的最有效、最完全原子经济的方法。然而，现有技术限于具有必需的酸性炔丙基C-H键的烷-3-炔酸叔丁酯底物。本文报道了一种基于金催化的策略，该策略通过设计的手性双官能联苯基膦配体来实现。它允许异构化的炔与非酸性的α-C-H键，因此提供了一个急需的通用解决方案。用手性炔丙醇作为底物，在一个步骤中以通常良好的产率和良好至优异的非对映选择性形成2，5-二取代的2，5-二氢呋喃。使用非手性底物，形成具有良好至优异的对映体过量的2，5_二氢呋喃。一种新的中心手性的方法被开发，以实现立体控制的效果类似于一个轴向手性的手性配体设计。机理研究表明，由于阳离子金催化剂的流动轴，催化剂前体轴向差向异构体都转化为催化活性的阳离子金催化剂。
The asymmetric isomerization of alkyne to allene is the most efficient and the completely atom-economic approach to this class of versatile axial chiral structure. However, the state-of-the-art is limited to tertbutyl alk-3-ynoate substrates that possess requisite acidic propargylic C-H bonds. Reported here is a strategy based on gold catalysis that is enabled by a designed chiral bifunctional biphenyl-2-ylphosphine ligand. It permits isomerization of alkynes with nonacidic alpha-C-H bonds and hence offers a much-needed general solution. With chiral propargylic alcohols as substrates, 2,5-disubstituted 2,5-dihydrofurans are formed in one step in typically good yields and with good to excellent diastereoselectivities. With achiral substrates, 2,5-dihydrofurans are formed with good to excellent enantiomeric excesses. A novel center-chirality approach is developed to achieve a stereocontrol effect similar to an axial chirality in the designed chiral ligand. The mechanistic studies established that the precatalyst axial epimers are all converted into the catalytically active cationic gold catalyst owing to the fluxional axis of the latter.