The Photochemical Synthesis and Denitrogenation of 8,9-Diazodibenzoisobullvalene

Article abstract of DOI:10.1002/hlca.19890720809

Starting from dibenzocyclooctene (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-?-methane rearrangement sequence.The synthesis is completed by a stepwise hydrolytic oxydation of the ensuing triazolidinedione 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 cyclobutaphenanthrene 8 and two further carbene-derived C16H12 products.Photolysis of 1 at 350 nm leads in modest yield (12percent), via a diazenyl diradical, to an unstable bridged bicyclobutane 10 (dibenzooctavalene).MNDO calculations suggest the latter to have a rapidly inverting, twisted structure of C₂ symmetry.