The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• completely new reaction Sakamoto has proposed a mechanism involving a ζ-hydrogen abstraction to form a biradical intermediate (Scheme 35, E). The resulting biradical cyclizes to form the spiro compound F upon recombination of the biradical. Re-aromatization affords the carboxylate G, which further attacks

• can take place to form a spiro compound; further re-aromatization to form the enol, lactolization and cyclization explains the formation of the benzoxepine structure [101]. Griesbeck et al. reported the formation of benzoxepines from the benzophenone analogue upon irradiation at slightly lower

A stable enol from a 6-substituted benzanthrone and its unexpected behaviour under acidic conditions

• Marc Debeaux,
• Kai Brandhorst,
• Peter G. Jones,
• Henning Hopf,
• Jörg Grunenberg,
• Wolfgang Kowalsky and
• Hans-Hermann Johannes

Beilstein J. Org. Chem. 2009, 5, No. 31, doi:10.3762/bjoc.5.31

• stable enol 4, which is converted by dehydrogenation into the benzanthrone derivative 7. Under acidic conditions 4 isomerises to the spiro compound 11 and the bicyclo[4.3.1]decane derivative 12. Furthermore, the formation of 7 and the hydrogenated compound 13 is observed. A mechanism for the formation of

• under these reaction conditions. Spiro compound 11 (11% yield) was characterised by NMR spectroscopy, mass spectrometry and single crystal X-ray crystallography (see below). The 1H NMR spectrum (600 MHz) of 11 shows two aliphatic triplets at δ = 2.16 and 3.42 ppm (J = 6.2 Hz) which are assigned to the

• internal Friedel-Crafts alkylation provides the spiro compound 11. Alternatively, protonation of 4 at C-5 generates the benzylic cation 17, which by intramolecular electrophilic attack leads to the bicyclo[4.3.1]decane derivative 12. Finally, the formation of 13 is a formal hydrogenation of the starting