Thermolysis and Photolysis of the Azoalkane 4,5-Diaza-7,8,8-trimethyltricyclo3,7>non-4-ene: 1,3-Diradical and Diazoalkane Formation

Article abstract of DOI:10.1021/jo00205a007

On benzophenone-sensitized photolysis at 350 nm the azoalkane 3 denitrogenates exclusively into 2,3,3-trimethyltricyclo<2.2.1.0^2,6>heptane (5), while direct photolysis at 350 nm affords the tricycloheptane 5 as major product and 2,3,3-trimethyl-4-vinylcyclopentene (6) as minor product.With increasing temperature the vinylcyclopentene 6 increases in the direct photolysis.On preparative laser photolysis at 333 nm the diazo-2-(2,3,3-trimethylcyclopenten-4-yl)ethane (8) accumulates, which on subsequent photolysis is shown to produce the vinylcyclopentene 6 via the corresponding carbene intermediate.The diazoalkane 8 does not cyclize back to the azoalkane 3.The thermolysis leads essentially quantitatively to the tricycloheptane 5, with only traces of the vinylcyclopentene 6.These results are rationalized mechanistically in terms of a diazenyl diradical as common intermediate for all three denitrogenation modes.It is proposed that the divergent chemical behavior of the diazenyl diradicals produced in the three forms of activation (triplet-sensitized and direct photolysis and thermolysis) is best understood in terms of distinct spin multiplicities and electronic configurations of the diradical intermediates.In this tritopic process it is shown by means of a Salem diagram that the D_?,? diazenyl diradical serves as precursor to the tricycloheptane 5 via the 1,3-diradical 4, while the D_?,? diradical is responsible as intermediate for the vinylcyclopentene 6 via the diazoalkane 8.