Diazaazulene synthesis

H-3a,4-Diazaazulenes synthesis, 4, 297 Diazabicycloalkanes anion complexes, 7, 747 conformation, 7, 737 Diazabicyclo[k. /. m]alkanes conformation, 7, 739-740 Diazabicydodecanes synthesis, 5, 315... 

The synthesis of diazaazulenes was investigated as mentioned earlier in Section 13.04.2, during the study of the nature of aromaticity of numerous nonbenzenoid carbocyclic and heterocyclic conjugated 7i-electron systems. The synthetic approaches started with reactions of semicyclic 1,5-diketones with various hydrazines to give partially saturated cyclopenta[c]-l,2-diazepines. Then several methods were used to dehydrogenate, as described earlier, the cyclopenta-l,2-diazepines to the respective diazaazulenes without much success <2001TH1>. 

Many attempts were made to synthesize the diazaazulene derivative 4,7-diphenyl-5,6-diazaazulene 34. A directed synthesis of diazaazulene 34 by [6+4] cycloaddition of fulvenes with 1,2,4,5-tetrazenes when attempted with 2-cyclopenta-dienyliden-l,3-dioxolane led to the formation of cyclopcnta[z/ pyridazines via a [4+2] cycloaddition pathway <2001TH1>. 

After the failure of the direct synthesis of the completely unsaturated heterocycle 34, an attempt was made to synthesize the partially saturated cyclopenta[t]-l, 2-diazcpine, which then could be dehydrogenated to the 5,6-diazaazulene 34. However, this approach by starting with a 1,2-diazepine ring 36 (made successfully by following published method) and its [3+2] palladium-catalyzed cycloaddition with allyl chlorosilane 35 to the bicyclic diazepine 37 failed (Scheme 8). 

---