Thermolysis of Azoalkanes Containing the 2,3-Diazabicyclooct-2-ene (DBO) Skeleton

Article abstract of DOI:10.1021/ja00362a014

The effect of one and two bridgehead substituents on the thermal stability of DBO is assessed by monitoring the disappearance of four new compounds (8-11).Two cyclopropyl groups are found to lower ΔG^<*> for thermolysis by twice the amount of one such group; however, a second bridgehead phenyl substituent is much less effective than the first.Comparison of these results with those of the previously studied methyl and vinyl DBO suggests two mechanisms that are indistinguishable on the basis of available data.In the first one, symmetrical azoalkanes decompose by simultaneous scission of both C-N bonds while unsymmetrical azolakanes exhibit greater breaking of the C-N bond at the transition state.This idea is described in a More O'Ferrall-Jencks-Thornton diagram.The second possible mechanism is reversible cleavage of a weaker C-N bond followed by loss of nitrogen from an intermediate diazenyl radical.Incorporation of endocyclic fused rings into the DBO skeleton generally slow down thermolysis, perhaps by inhibiting planarization of the carbon atoms α to the azo group.