DFT (density functional theory) studies on cycloisomerization of 15–membered triazatriacetylenic macrocycle |
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Authors: | Mansooreh MOVAHEDI Nader ZABARJAD SHIRAZ Ali EZABADI Marjaneh SAMADIZADEH Mohamad Reza TALEI BAVIL OLYAI |
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Affiliation: | 1. Department of Chemistry, Central Tehran Branch, Islamic Azad University, Tehran, Iran ; 2. Department of Chemistry, South Tehran Branch, Islamic Azad University, Tehran, Iran |
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Abstract: | The mechanism as well the stereochemistry of cascade cycloisomerization 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. |
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Keywords: | DFT (density functional theory), triazatriacetyle, cycloisomerization, Ene– Reaction, Pd, [2+2+2] reaction |
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