Chemodivergence in Pd-catalyzed desymmetrization of allenes: enantioselective [4+3] cycloaddition, desymmetric allenylic substitution and enynylation.
Chemodivergence in Pd-catalyzed desymmetrization of allenes: enantioselective [4+3] cycloaddition, desymmetric allenylic substitution and enynylation.
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DOI：
10.1039/d3sc04581a
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发表时间：
2023-10-11
期刊：
影响因子：
8.4
通讯作者：
Shao, Zhihui
中科院分区：
文献类型：
--
作者：
Luo, Pengfei;Li, Long;Mao, Xinfang;Sun, Zheng;Wang, Yingcheng;Peng, Fangzhi;Shao, Zhihui
首次引入了一类前手性联烯型双亲电试剂作为三原子配体参与环加成反应，并成功地发展了一种新型的过渡金属催化的对映选择性顺序联烯取代[4+3]环加成反应，使具有挑战性的七元环外轴手性联烯以良好的产率和对映选择性得到了合成.通过加入催化量的邻氨基苯胺或邻氨基苯酚，有效地抑制了[4+3]环加成产物的外消旋化。机理研究表明，难以捉摸的Pd催化的对映选择性分子内的丙二烯取代，而不是分子间的丙二烯取代是在这个环加成的对映体决定步骤。通过调节配体，实现了钯催化的对映选择性去对称丙二烯取代反应，得到线性轴向手性三取代丙二烯，或钯催化的串联去对称丙二烯取代/β-乙烯基氢消除（缩甲醛烯炔化）反应，得到多官能化的1，3-烯炔。钯催化的对映选择性的丙二烯[4+3]环加成反应、去对称丙二烯取代反应或串联去对称丙二烯取代/β-乙烯氢消除反应可以通过配体控制化学不对称地实现。
A class of prochiral allenylic di-electrophiles have been introduced for the first time as three-atom synthons in cycloadditions, and a new type of [4+3] cycloaddition involving transition metal-catalyzed enantioselective sequential allenylic substitution has been successfully developed, enabling challenging seven-membered exocyclic axially chiral allenes to be accessed in good yields with good enantioselectivity. Through the addition of a catalytic amount of ortho-aminoanilines or ortho-aminophenols, the racemization of the [4+3] cycloaddition products is effectively suppressed. Mechanistic studies reveal that elusive Pd-catalyzed enantioselective intramolecular allenylic substitution rather than intermolecular allenylic substitution is the enantio-determining step in this cycloaddition. By tuning the ligands, a Pd-catalyzed enantioselective desymmetric allenylic substitution leading to linear axially chiral tri-substituted allenes or a Pd-catalyzed tandem desymmetric allenylic substitution/β-vinylic hydrogen elimination (formal enynylation) leading to multi-functionalized 1,3-enynes is achieved chemodivergently. Pd-catalyzed enantioselective allenylic [4+3] cycloaddition, desymmetric allenylic substitution or tandem desymmetric allenylic substitution/β-vinylic hydrogen elimination (formal enynylation) can be realized chemodivergently by ligand control.
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