Movahedi Mansooreh, Zabarjad Shiraz Nader, Ezabadi Ali, Samadizadeh Marjaneh, Talei Bavil Olyai Mohamad Reza
Department of Chemistry, Central Tehran Branch, Islamic Azad University, Tehran Iran.
Department of Chemistry, South Tehran Branch, Islamic Azad University, Tehran Iran.
Turk J Chem. 2021 Oct 19;45(5):1609-1620. doi: 10.3906/kim-2012-15. eCollection 2021.
The mechanism as well the stereochemistry of cascadecycloisomerization of 15-membered triazatriacetylenic macrocycle was investigated theoretically by using M062X/6-31+G(d,p) and M062X/LANL2DZ calculations. The results showed that the mechanism and outcome of the reaction depended on the absence and presence of a transition metal catalyst. So that, in thermal-induced condition, the reaction had to experience several suprafacial concerted reactions including Ene-reaction (DG=35.38 kcal/mol), Diels-Alder cycloaddition (DG = 17.16 kcal/mol), and sigmatropic H-shift rearrangement (DG = 56.21 kcal/mol) to produce diastereoselective fused cis-tetracyclic aromatic bearing a pyrrole moiety by following kinetic considerations. Also, the [2+2+2] cycloaddition mechanism was neglected in thermal-induced conditions because of high activation free Gibbs energy (DG = 63.90 kcal/mol). In the presence of palladium catalyst, Pd(0) formed an adduct by coordinating to C = C bonds and decreased the DG of the process to 29.58 kcal/mol, and consequently provided a facilitated media for the reaction to follow the [2+2+2] to produce more stable fused tetracyclic benzenoid aromatic by passing through the lower energy barrier.
采用M062X/6 - 31 + G(d,p)和M062X/LANL2DZ计算方法，对15元三氮杂三乙炔大环的串联环异构化反应机理及立体化学进行了理论研究。结果表明，反应的机理和结果取决于过渡金属催化剂的有无。因此，在热诱导条件下，该反应必须经历几个同面协同反应，包括烯反应（ΔG = 35.38 kcal/mol）、狄尔斯-阿尔德环加成反应（ΔG = 17.16 kcal/mol）和σ迁移H-重排反应（ΔG = 56.21 kcal/mol），以动力学为依据生成具有吡咯部分的非对映选择性稠合顺式四环芳烃。此外，由于高活化自由吉布斯能（ΔG = 63.90 kcal/mol），在热诱导条件下[2 + 2 + 2]环加成机理被忽略。在钯催化剂存在下，Pd(0)通过与C = C键配位形成加合物，将该过程的ΔG降低至29.58 kcal/mol，从而为反应提供了一个有利的介质，使其通过较低的能垒遵循[2 + 2 + 2]反应生成更稳定的稠合四环苯型芳烃。
