61. “Über die thermische, katalytische und photochemische Stickstoff-Eliminierung des 1-Diazo-3-(1-methylcyclopenta-2,4-dienyl)-2-propanons”
    Burger, U.; Zellweger, D.
    Helv. Chim. Acta 1986, 69, 676-682.

The synthesis of the title compound 12 is described. This diazoketone, distinguished by its C_s-symmetry and by a built-in cisoid diene unit, gives 5-methyltricyclo[3.3.0.0^2,8]oct-6-ene-3-one (13) when subjected to thermal or catalytic denitrogenation with rhodium (II) acetate or copper (II) acetylacetonate. Direct irradiation of 12 at 350 nm causes Wolff rearrangement, whereas the benzophenone-sensitized photolysis gives again ketone 13. A 1,4-carbene or carbenoid addition was never observed under the conditions described. The ketone 13equilibrates thermally or under base catalysis with 1-methyltricyclo[3.3.0.0^2,8]oct-6-ene-3-one (17). The key step of this apparent CH₃migration is shown to be a Cope rearrangement of the corresponding enols (hydroxysemibullvalenes).

DOI : 10.1002/hlca.19860690318 

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