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首页> 外文期刊>Chemistry: A European journal >DFT study of a 5-endo-trig-type cyclization of 3-alkenoic acids by using Pd-spiro-bis(isoxazoline) as catalyst: Importance of the rigid spiro framework for both selectivity and reactivity
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DFT study of a 5-endo-trig-type cyclization of 3-alkenoic acids by using Pd-spiro-bis(isoxazoline) as catalyst: Importance of the rigid spiro framework for both selectivity and reactivity

机译：使用Pd-螺双-（异恶唑啉）作催化剂的DFT研究3-链烯酸的5内-trig型环化：刚性螺环骨架对选择性和反应性的重要性

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摘要

The reaction pathway of an enantioselective 5-endo-trig-type cyclization of 3-alkenoic acids catalyzed by a chiral palladium-spiro-bis(isoxazoline) complex, Pd-SPRIX, has been studied by density functional theory calculations. The most plausible pathway involves intramolecular nucleophilic attack of the carboxylate moiety on the C=C double bond activated by Pd-SPRIX and β-H elimination from the resulting organopalladium intermediate. The enantioselectivity was determined in the cyclization step through the formation of a π-olefin complex, in which one of the two enantiofaces of the olefin moiety was selected. The β-H elimination occurs via a seven-membered cyclic structure in which the acetate ligand plays a key role in lowering the activation barrier of the transition state. In the elimination step, the SPRIX ligand was found to behave as a monodentate ligand due to the hemilability of one of the isoxazoline units thereby facilitating the elimination. Natural population analysis of this pathway showed that the more weakly electron-donating SPRIX ligand, compared with the bis(oxazoline) ligand, BOX, facilitated the formation of the π-olefin complex intermediate, leading to a smaller overall activation energy and a higher reactivity of the Pd-SPRIX catalyst. Robust yet flexible! DFT calculations of a 5-endo-trig-type cyclization of 3-alkenoic acids have been performed to elucidate the reaction mechanism, a rate-limiting cyclization via an organopalladium transition state followed by an acetate-assisted reductive β-H elimination via a seven-membered metallacycle transition state (see scheme). Enantioselectivity is induced in the cyclization step by the chiral environment created by the spiro-bis(isoxazoline) (SPRIX) firmly chelated to the Pd~(II) center.
机译：通过密度泛函理论计算研究了手性钯-螺-双（异恶唑啉）配合物Pd-SPRIX催化的3-链烯酸对映选择性5-内-trig型环化反应的反应路径。最合理的途径涉及通过Pd-SPRIX激活的C = C双键上的羧酸酯部分的分子内亲核攻击以及从所得有机钯中间体中消除β-H。对映选择性是在环化步骤中通过形成π-烯烃络合物确定的，其中选择了烯烃部分的两个对映体之一。 β-H消除是通过七元环结构发生的，其中乙酸酯配体在降低过渡态的活化势垒中起关键作用。在消除步骤中，由于异恶唑啉单元之一的半球形性，发现SPRIX配体表现为单齿配体，从而促进了消除。该途径的自然种群分析显示，与双（恶唑啉）配体BOX相比，供电子较弱的SPRIX配体促进了π-烯烃络合物中间体的形成，从而导致较小的总活化能和更高的反应性Pd-SPRIX催化剂。坚固而灵活！为了阐明反应机理，已进行了DFT计算，以阐明3-链烯酸的5内-trig型环化反应，通过有机钯过渡态进行限速环化，然后通过7位乙酸盐辅助还原性β-H消除。元金属环过渡态（见方案）。对映选择性是在环化步骤中由螺-双（异恶唑啉）（SPRIX）牢固螯合到Pd〜（II）中心所产生的手性环境诱导的。

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