A Theoretical Stereoselectivity Model of Photochemical Denitrogenations of Diazoalkanes Toward Strained 1,3-Dihalogenated Bicyclobutanes
A Theoretical Stereoselectivity Model of Photochemical Denitrogenations of Diazoalkanes Toward Strained 1,3-Dihalogenated Bicyclobutanes
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重氮烷光化学脱氮对应变 1,3-二卤双环丁烷的立体选择性理论模型
DOI：
10.1021/acs.joc.0c02905
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Lopez, Steven A.
中科院分区：
文献类型：
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作者：
Li, Jingbai;Stein, Rachel;Lopez, Steven A.
光化学反应是一种“绿色”化学，是在温和的光照条件下合成高应变分子的重要工具。双环偶氮烷烃的光促进脱氮得到官能化的立体富集的双环[1.1.0]丁烷。这些反应进行了重新审视与多参考计算和非绝热分子动力学（NAMD）模拟，提供了一个详细的分析，一系列的二氮杂双环[2.1.1]己烯的物理，反应性，和无法解释的立体选择性。我们使用完全活性空间自洽场（CASSCF）计算，采用（8，8）活性空间和ANO-S-VDZP基组，CASSCF能量用CASPT 2（8，8）/ANO-S-VDZP校正。本文报道的二氮杂双环[2.1.1]己烯的电子激发性质为n → π*，范围为3.77至3.91 eV。最小能量路径计算表明，逐步C-N键断裂，并直接导致最小能量交叉点，对应于立体化学的“双反转”产品。二氮杂双环[2.1.1]己烯的维格纳采样提供了692 NAMD轨迹的初始条件。我们确定了竞争完整的立体选择性和立体化学的混乱途径。立体选择性途径的特点协同双环丁烷转化和N2挤出。的立体化学乱序途径涉及N2挤出，然后由双环丁烷平面化，导致立体化学乱序。预测的非对映异构体过量（d.e.）几乎完全符合实验（calc.d.e.= 46% vs exp.d.e.= 47%）。我们对1-F、1-Cl和1-Br的NAMD模拟，用672、568和596条轨道预测了双反转产物的ad.e.为94-97%。由于超共轭相互作用，卤代显着扰动势能面（PES）对保留产物。nC→ σ*C-X（X = F，Cl，Br）的超共轭效应导致PES上双反转的肩区变宽。
Photochemical reactions exemplify “green” chemistry and are an essential tool for synthesizing highly strained molecules under mild conditions with light. The light-promoted denitrogenation of bicyclic azoalkanes affords functionalized, stereoenriched bicyclo[1.1.0]butanes. These reactions were revisited with multireference calculations and non-adiabatic molecular dynamics (NAMD) simulations to provide a detailed analysis of the photophysics, reactivities, and unexplained stereoselectivity of a series of diazabicyclo[2.1.1]hexenes. We used complete active space self-consistent field (CASSCF) calculations with an (8,8) active space and ANO-S-VDZP basis set; the CASSCF energies were corrected with CASPT2 (8,8)/ANO-S-VDZP. The nature of the electronic excitation is n → π* and ranges from 3.77 to 3.91 eV for the diazabicyclo[2.1.1]hexenes reported here. Minimum energy path calculations showed stepwise C–N bond breaking and led directly to a minimum energy crossing point, corresponding to a stereochemical “double inversion” product. Wigner sampling ofdiazabicyclo[2.1.1]hexeneprovided initial conditions for 692 NAMD trajectories. We identified competing complete stereoselective and stereochemical scrambling pathways. The stereoselective pathways feature concerted bicyclobutane inversion and N2extrusion. The stereochemical scrambling pathways involve N2extrusion followed by bicyclobutane planarization, leading to stereochemical scrambling. The predicted diastereomeric excess (d.e.) almost exactly matches the experiment (calc.d.e.= 46% vs exp.d.e.= 47%). Our NAMD simulations with 672, 568, and 596 trajectories for1-F,1-Cl, and1-Brpredicted ad.e.of 94–97% for the double inversion products. Halogenation significantly perturbs the potential energy surface (PES) toward the retention products due to hyperconjugative interactions. The nC→ σ*C–X, X = F, Cl, Brhyperconjugative effect leads to a broader shoulder region on the PES for double inversion.