M. Abe, W. Adam*, W. Nau
Oct 27, 1998
Citations
0
Influential Citations
34
Citations
Journal
Journal of the American Chemical Society
Abstract
The direct and benzophenone-sensitized photodenitrogenation of the azoalkane 2,3-diazabicyclo[2.2.1]hept-2-ene-7,3‘-spiro-2‘,2‘-diphenyloxirane 1 at ambient temperature (ca. 15 °C) in benzene afforded exclusively the 6-oxabicyclo[3.2.0]hept-1-ene 3. The labile oxetane 3 is proposed to be formed by the selective cleavage of the C−O bond in the epoxy ring of the initially photogenerated, spiroepoxy-substituted, localized cyclopentane-1,3-diyl diradical 1,3-DR to the 1,4-DR diradical and subsequent cyclization of the latter. Even at −100 °C, the highly strained (strain energy estimated to be ca. 94 kcal/mol) spiroepoxy housane 2 could not be observed by 1H NMR (600 MHz) spectroscopy. In MeOH, instead of the oxetane 3, the two regioisomeric MeOH adducts 6 (trapping product of the diradicals 1,3-DR and 1,4-DR) and 6‘ (methanolysis product of 3) were obtained in high yields. For the first time methanol trapping of a cyclopentane-1,3-diyl singlet diradical was achieved; the required dipolar character is presumab...