1.2- Diazabicyclo hexa-2,5-dienes

Similarly, 2,3-diazabicyclo[2.2.2]oct-2-enes underwent photoelimination of nitrogen via singlet 1,4-diradicals15 to give bicyclic cyclobutanes (Houben-Weyl, Vol. 4/4, pp 40-44). However, the parent compound on photolysis at 185 nm gave bicyclo[2,2.0]hexane (11 a) in only 9% yield,10 while benzophenone sensitized or direct photolysis resulted in mixtures of bicy-clo[2.2.0]hexane and hexa-1,5-diene (27 73 or 42 58, respectively).16 In a separate study, a triplet 1,4-cyclohexadiyl was trapped with molecular oxygen.17... 

Irradiation of substituted 2,3-diazabicyclo[2.2.2]oct-2-enes 12 gave remarkable quantities of the bicyclo[2.2.0]hexanes 13 in addition to the hexa-1,5-dienes. 

Diazabicyclo[2.2.0]hexa-2,5-diene, perfluoro-IR spectra, 7, 360 Diazabicyclo[2.2.0]hexadienes thermal isomerization, 7, 360 Diazabicyclo[3.1.0]hexane, 7, 56... 

Earlier work on the photolytic or thermal rearrangement of polyhalogenated pyridazines to corresponding pyrazines has been continued,14,161,774,1690 but the fascinating results offer little of preparative value. It has been reported that 300-nm irradiation of 3,4,5,6-tetra-tert-butylpyridazine (66) gave a quantitative yield of the Dewar isomer (3,4,5,6-tetra-tert-butyl-l,2-diazabicyclo [2.2.0]hexa-2,5-diene 67] that subsequently afforded 2,3,5,6-tetra-tert-butylpyrazine (68) in 18% yield on 254-nm irradiation.1464... 

The photolytic rearrangement of 3,4,5,6-tetra-tm-butyl-l,2-diazabicyclo[2.2.0]-hexa-2,5-diene into 2,3,5,6-tetra-tcrt-butylpyrazine has been covered in Section 2.1.12. 

However, more detailed study of the products showed that perfluoro-1,4-di-isopropy 1-2,5-diazabicyclo [2.2.0] hexa-2,5-diene was formed (Scheme 41).103 This result excluded the mechanism in Scheme 40. A similar isomerization of perfluoro-3,6-methylpyridazine to the 2,5-substituted pyrazine was reported.104... 

Dewer benzene —> Bicyclo[2.2.0] hexa-2,5-diene Diacetylene —> 1,3-Butadiyne 1,4-Diazabicyclo [2.2.2]octane ZCCC (average) CHoCHo Z 111.4 C—N 1.472 ED... 

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