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DFT Study on Oxidative Cyclization of o‐ Alkynylbenzoates Mediated by Hypervalent Iodine Reagent: Mechanism and Substituent Effect
Author(s) -
Zhou Jianguo,
Song XinXin,
Zhao ChengBin,
Wang LingLing,
Zhang XiaoQian,
Chen Yu,
Zhang Lei
Publication year - 2020
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.202000106
Subject(s) - chemistry , substituent , hypervalent molecule , nucleophile , intramolecular force , electrophile , medicinal chemistry , chemoselectivity , transition state , reagent , reaction mechanism , cationic polymerization , density functional theory , stereochemistry , computational chemistry , organic chemistry , catalysis
The reaction mechanisms of PhICl 2 ‐mediated oxidative cyclization were characterized by density functional calculations with the m06 method, in order to unveil the plausible reaction pathway and the substituent effect on the chemoselectivity observed. The reaction of methyl o ‐alkynylbenzoate 1 a and PhICl 2 was used as a model, and the proposed pathway leading to the cyclization product involves the elementary steps of electrophilic attack, cyclization, intramolecular I/Cl exchange, and nucleophilic substitution, with the rate‐limiting activation barrier of 25.6 kcal/mol. The competing mechanisms of the p ‐OMe‐substituted substrate 1 b and PhICl 2 were comparatively characterized, and the exclusive formation of dichlorinated products rather than cyclization product should be a result of the kinetic discrimination. The free‐energy barriers of the dichlorination were computed to be 1–4 kcal/mol lower than those of the cyclization. The substituent effect was probed on the basis of geometric parameters and molecular orbitals. It was proposed that the electron‐donating property of the p ‐OMe group could stabilize the alkenyl cationic intermediate, which serves a branch point of several competing pathways.