title: Pyramidalized Double Bonds Containing Endoperoxide Linkages: Photooxygenation of Dimethyl cis-3,8-Dihydroheptalene-3,8-dicarboxylate.
abstract: Diels-Alder cycloaddition utilizing singlet oxygen as the dienophile with dimethyl cis-3,8-dihydroheptalene-3,8-dicarboxylate (5) has been investigated, and monoaddition product 7 has been isolated. The addition of a second singlet oxygen to the cycloheptatriene unit in 7 gave syn-bis(norcaradiene) bis(endoperoxide) 4. (1)H NMR spectral studies and theoretical calculations indicate the increased pyramidalization in syn-4 compared with carbon analogue. The increased pyramidalization results from hyperconjugation between the central pi-bond and the four adjacent C-O bonds and by rehybridization at C3, C4, C5, and C6. Furthermore, the increased reactivity for syn-4, which is probably arising from further folding of the central double bond, is also in agreement with theoretical calculations.
authors.affiliation: Departments of Chemistry, Atatürk University, 25240 Erzurum, Turkey, Bilkent University, 06533 Ankara, Turkey, and Middle East Technical University, 06531 Ankara, Turkey.
authors.forename: Nurullah
authors.initials: N
authors.lastname: Saraçoglu
authors.forename: Abdullah
authors.initials: A
authors.lastname: Menzek
authors.forename: Safak
authors.initials: S
authors.lastname: Sayan
authors.forename: Ulrike
authors.initials: U
authors.lastname: Salzner
authors.forename: Metin
authors.initials: M
authors.lastname: Balci