title: Cycloaddition Reaction of Vinylphenylfurans and Dimethyl Acetylenedicarboxylate to [8 + 2] Isomers via Tandem [4 + 2]/Diradical Alkene-Alkene Coupling/[1,3]-H Shift Reactions: Experimental Exploration and DFT Understanding of Reaction Mechanisms.
abstract: An experimental test of designed [8 + 2] reaction of vinylphenylfuran and dimethyl acetylenedicarboxylate (DMAD) has been carried out, showing that the reaction gave unexpected addition products under different conditions. When the reaction was conducted under thermal conditions in toluene, expoxyphenanthrene, which was named as a [8 + 2] isomer, was generated. The scope of this reaction has been investigated in the present study. In addition, experiments and DFT calculations have been conducted to investigate how the reaction between vinylphenylfuran and DMAD took place. Surprisingly, the reaction did not involve the expected [8 + 2] intermediate, o-quinodimethane. Instead, the reaction starts from intermolecular Diels-Alder reactions between DMAD and the furan moiety of vinylphenylfuran, followed by unexpected intramolecular alkene-alkene coupling. This step generates a diradical species, which then undergoes [1,3]-H shift to give the experimentally observed expoxyphenanthrene. DFT calculations revealed that, the [8 + 2] cycloadduct cannot be obtained because the [1,5]-H shift process from the [1,5]-vinyl shift intermediate is disfavored kinetically compared to the [1,3]-H shift to the [8 + 2] isomer.
authors.affiliation: Key Laboratory of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology , Guangzhou 510640, People's Republic of China.
authors.forename: Kai
authors.initials: K
authors.lastname: Chen
authors.affiliation: Key Laboratory of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology , Guangzhou 510640, People's Republic of China.
authors.forename: Feng
authors.initials: F
authors.lastname: Wu
authors.affiliation: Key Laboratory of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology , Guangzhou 510640, People's Republic of China.
authors.forename: Lijuan
authors.initials: L
authors.lastname: Ye
authors.affiliation: College of Chemistry, Peking University , Beijing 100871, People's Republic of China.
authors.forename: Zi-You
authors.initials: ZY
authors.lastname: Tian
authors.affiliation: College of Chemistry, Peking University , Beijing 100871, People's Republic of China.
authors.forename: Zhi-Xiang
authors.initials: ZX
authors.lastname: Yu
authors.affiliation: Key Laboratory of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology , Guangzhou 510640, People's Republic of China.
authors.forename: Shifa
authors.initials: S
authors.lastname: Zhu