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Publication 27  


  1. “The Photochemical Synthesis and Denitrogenation of 8,9-diazadibenzo[c, e]isobullvalene”
    U. Burger, Y.G. Mentha, P. Millasson, P.-A. Lottaz, J. Mareda
    Helv. Chim. Acta 1989, 72, 1722-1728.

Starting from dibenzo[a, c]cyclooctene (4) and 4-methyl-3H-1,2,4-triazol-3,5(4H)-dione (MTAD), the strained skeleton of the title azo compound 1 is assembled in a tandem photo-Diels-Alder addition/di-π-methane rearrangement sequence. The synthesis is completed by a stepwise hydrolytic oxidation of the ensuing triazolidine-dione 2 with nickel peroxide. Thermolysis of 1 in benzene solution is shown to be governed by an initial 1,3-dipolar cycloreversion which leads, via an intermediate diazo compound 11, to cyclobuta[1]phenanthrene 8 and two further carbene-derived C16H12 products. Photolysis of 1 at 350 nm leads in modest yield (12%), via a diazenyl diradical, to an unstable bridged bicyclobutane 10 (dibenzooctavalene). MNDO calculations suggest the latter to have a rapidly inverting, twisted structure of C2symmetry.

DOI : 10.1002/hlca.19890720809 

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