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 spirocompound F upon recombination of the biradical. Re-aromatization affords the carboxylate G, which further attacks
can take place to form a spirocompound; 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
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 spirocompound 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.
Spirocompound 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 spirocompound 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
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Graphical Abstract
Scheme 1:
Behaviour of benzanthrone (1) towards phenylmagnesium chloride (a), phenyl lithium (b), and bipheny...