Departamento de Química Orgánica, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain.
Chemistry. 2010 Oct 25;16(40):12147-57. doi: 10.1002/chem.201001714.
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 π* 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.
在密度泛函理论框架内，对过渡金属（Au(I)、Au(III)、Pd(II) 和 Pt(II)）辅助下丙二烯与连接的二烯（1,3 - 丁二烯和呋喃）之间的热 [4 + 3] 环加成反应进行了计算研究，并在活化能垒、相应过渡态的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。结果发现，金属介导的环加成反应是协同的，通过过渡结构发生，这些过渡结构甚至比它们的非有机金属类似物更具同步性和芳香性。然而，这些过程的活化能垒比涉及羟基烯丙基阳离子的母体环加成反应略高至中等程度。金属部分引起的键极化明显与过渡金属与烯丙基 π* 分子轨道的相互作用有关，烯丙基 π* 分子轨道构成初始反应物的最低未占分子轨道。最后，用呋喃取代 1,3 - 丁二烯导致在非有机金属和金属辅助过程中转化均逐步发生。
