Reactions of an Aluminum(I) Reagent with 1,2-, 1,3-, and 1,5-Dienes: Dearomatization, Reversibility, and a Pericyclic Mechanism
Reactions of an Aluminum(I) Reagent with 1,2-, 1,3-, and 1,5-Dienes: Dearomatization, Reversibility, and a Pericyclic Mechanism
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DOI：
10.1021/acs.inorgchem.9b03701
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发表时间：
2020-04-06
影响因子：
4.6
通讯作者：
Crimmin, Mark R.
中科院分区：
文献类型：
--
作者：
Bakewell, Clare;Garcon, Marti;Crimmin, Mark R.
本文报道了铝试剂[{（ArNCMe）（2）CH}Al]（Ar = 2，6-二异丙基苯基）对一系列环状和非环状1，2-，1，3-和1，5-二烯的加成反应。在1，3-二烯的情况下，反应通过周环反应机理，特别是螯合环加成反应发生，以形成含铝环戊烯的产物。该机制已通过立体化学实验和密度泛函理论计算进行了验证。立体化学实验表明，（4 + 1）环加成遵循的superfacial拓扑结构，而计算支持一个协调的，虽然异步的途径，其中过渡态表现出芳香族字符。值得注意的是，（4 + 1）环加成反应的底物范围包括苯乙烯、1，1-二苯基乙烯和蒽。在这些情况下，二烯基序部分或全部包含在芳环内，并且反应随着底物的脱芳化而发生，并且可以是可逆的。在1，2-环壬二烯或1，5-环辛二烯的情况下，观察到互补的反应性; C=C π键（1，2-二烯）和均共轭体系（1，5-二烯）的正交性质都不利于（4 + 1）环加成。相反，反应途径由初始（2 + 1）环加成决定，以形成铝环丙烷中间体，其又可以经历另外的C=C π-键的插入，导致结合稠合烃环的复杂有机金属产物。
Addition of the aluminum(I) reagent [{(ArNCMe)(2)CH}Al] (Ar =2,6-di-iso-propylphenyl) to a series of cyclic and acyclic 1,2-, 1,3-, and 1,5-dienes is reported. In the case of 1,3-dienes, the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene-containing products. This mechanism has been examined by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4 + 1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4 + 1) cycloaddition includes styene, 1,1-diphenylethylene, and anthracene. In these cases, the diene motif is either in part, or entirely, contained within an aromatic ring and reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2-cyclononadiene or 1,5-cyclooctadiene, complementary reactivity is observed; the orthogonal nature of the C=C pi-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavor a (4 + 1) cycloaddition. Rather, reaction pathways are determined by an initial (2 + 1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C=C pi-bond, leading to complex organometallic products that incorporate fused hydrocarbon rings.