title: DFT and experimental exploration of intramolecular [2 + 2 + 2] cycloaddition of oxanorbornadienedicarboxylates and analogues.
abstract: The facile intramolecular [2 + 2 + 2] homo-Diels-Alder cycloadditions of oxanorbornadienedicarboxylates and analogues have been investigated by theoretical calculations using B3LYP and M06-2X density functional methods and experimental confirmation. The oxanorbornadienedicarboxylates formed from furans and but-2-ynedioates undergo the resulting intramolecular [2 + 2 + 2] cycloaddition in a concerted but asynchronous fashion, requiring energy barriers of about 30 kcal/mol to construct five- and three-membered rings simultaneously. Bridgehead substitutents have little influence on the regioselectivity, whereas 5-substitutents involving steric hindrance or electron-acceptor groups are predicted to attenuate the cycloaddition at the substituted side. Furthermore, the linker length, unsaturated bonds, and bridge-ring size are very sensitive to the cyclization rate. Additionally, aza- and norbornadienedicarboxylates demonstrate less reactivity, while thionorbornadienedicarboxylates show more reactivity with the challenge of their synthesis. The intermolecular version was also evaluated in comparison with the intramolecular version. Finally, our experimental tests verified the calculational prediction of the regioselectivity and reactivity.
authors: State Key Laboratory of Chemical Resource Engineering, Department of Organic Chemistry, Faculty of Science, Beijing University of Chemical Technology, 100029 Beijing, People's Republic of China.
authors: Xinyao
authors: X
authors: Li
authors: Jiaxi
authors: J
authors: Xu
mesh_terms: D003500:Cyclization; D008956:Models, Chemical; D015394:Molecular Structure; D009636:Norbornanes / Q000138:chemical synthesis* / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D009636:Norbornanes