Concerted and Stepwise Mechanisms in Metal-Free and Metal-Assisted [4+3] Cycloadditions Involving Allyl Cations
Concerted and Stepwise Mechanisms in Metal-Free and Metal-Assisted [4+3] Cycloadditions Involving Allyl Cations
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DOI：
10.1002/chem.201001714
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发表时间：
2010-01-01
影响因子：
4.3
通讯作者：
Luis Mascarenas, Jose
中科院分区：
文献类型：
--
作者：
Fernandez, Israel;Cossio, Fernando P.;Luis Mascarenas, Jose
在密度泛函理论框架下，研究了过渡金属（Au-I、Au-III、Pd-II和Pt-II）辅助下烯与系链二烯（1,3-丁二烯和呋喃）之间的热[4+3]环加成反应，并在相应过渡态的激活势垒、同步性和芳香性方面与类似的非有机金属过程进行了比较。研究发现，金属介导的环加成反应是协调一致的，并且通过过渡结构发生，这种过渡结构比它们的非有机金属类似物更同步，更芳香。然而，与羟基烯丙基阳离子的母体环加成相比，该过程表现出略至中等程度的活化障碍。金属部分引起的键极化明显与过渡金属与烯丙基pi*分子轨道的相互作用有关，这构成了初始反应物的LUMO。最后，呋喃取代1,3-丁二烯，使得非有机金属和金属辅助工艺的转化逐步发生。
The thermal [4+3] cycloaddition reaction between allenes and tethered dienes (1,3-butadiene and furan) assisted by transition metals (Au-I, Au-III, Pd-II, and Pt-II) was studied computationally within the density functional theory framework and compared to the analogous non-organometallic process in terms of activation barriers, synchronicity and aromaticity of the corresponding transition states. It was found that the metal-mediated cycloaddition reaction is concerted and takes place via transition structures that can be even more synchronous and more aromatic than their non-organometallic analogues. However, the processes exhibit slightly to moderately higher activation barriers than the parent cycloaddition involving the hydroxyallylic cation. The bond polarization induced by the metal moiety is clearly related to the interaction of the transition metal with the allylic pi* molecular orbital, which constitutes the LUMO of the initial reactant. Finally, replacement of the 1,3-butadiene by furan caused the transformation to occur stepwise in both the non-organometallic and metal-assisted processes.