Bhai Surjit, Jana Kalyanashis, Ganguly Bishwajit
Computation and Simulation Unit, Analytical and Environmental Science Division and Centralized Instrument Facility, CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar, Gujarat 364002, India.
ACS Omega. 2018 Sep 11;3(9):10945-10952. doi: 10.1021/acsomega.8b01165. eCollection 2018 Sep 30.
We have examined the π-facial stereoselectivity in the Diels-Alder reactions of phosphole oxides computationally. The experimentally observed syn-cycloadditions have been rationalized with the Cieplak model and distortion-interaction model. The natural bond orbital analysis suggests that the hyperconjugative interactions are energetically preferred between the antiperiplanar methyl group present in the -P=O unit and the developing incipient (-C-C-) bond in syn-adducts in accordance with the Cieplak model. The distortion-interaction analysis carried out for syn and anti transition states of Diels-Alder reactions of 1-substituted phosphole 1-oxide with different dienophiles reveals that the syn selectivity is favored by distortions and interaction energies compared with the anti selectivity. The formation of a syn adduct is also stabilized by the π-σ* orbital interaction, and the repulsive n-π interaction destabilizes the anti adduct that leads to the 7.0 kcal/mol thermodynamic preference for the former adduct. Furthermore, the distortion-interaction model rationalizes the formation of stereospecific products in these Diels-Alder reactions, which however is not explicable with the much-debated Cieplak model.
我们通过计算研究了氧化膦在狄尔斯-阿尔德反应中的π-面立体选择性。利用齐普拉克模型和畸变-相互作用模型对实验观察到的顺式环加成反应进行了合理解释。自然键轨道分析表明，根据齐普拉克模型，在-P=O单元中存在的反式共平面甲基与顺式加合物中正在形成的初生（-C-C-）键之间，超共轭相互作用在能量上更有利。对1-取代氧化膦与不同亲双烯体的狄尔斯-阿尔德反应的顺式和反式过渡态进行的畸变-相互作用分析表明，与反式选择性相比，顺式选择性受畸变和相互作用能的影响。顺式加合物的形成也通过π-σ*轨道相互作用得以稳定，而排斥性的n-π相互作用使反式加合物不稳定，导致前者加合物具有7.0千卡/摩尔的热力学优势。此外，畸变-相互作用模型解释了这些狄尔斯-阿尔德反应中立体专一性产物的形成，然而，这是备受争议的齐普拉克模型无法解释的。
