2H‐benzimidazoles. Part 5. Convenient synthons for tricyclic heterocycles

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Abstract
The readily available 5‐nitrospiro[2H‐benzimidazole‐2,1′‐cyclohexane] (1) was converted into the carbonitrile 5 and the 4‐phenylthio derivative 4. The NO2 or the PhS substituents in 4 could be replaced regiospecifically by reaction with Me3SiN3 or NaN3, respectively. The 5‐azido derivative 8, resulting from NO2‐group replacement was made to cyclize photolytically to give the angular spiro[cyclohexane‐imidazophenothiazine] 18. The azide 9 obtained from the PhS replacement in 4 cyclized spontaneously to give the angular spiro[cyclohexane‐imidazobenzoxadiazole] 10 which, on reductive hydrolysis, furnished benzofurazan‐4,5‐diamine 14. The diamine 14 was converted by conventional methods into a imidazobenzoxadiazole 15, oxadiazoioquinoxaline 16, and selenadiazoloxadiazole 17. The carbonitrile 5 was converted, in simple steps, into the ‘stretched‐out’, angular pteridine and purine analogues, 25 and 28, respectively.

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