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

The readily available 5‐nitrospiro[2 H ‐benzimidazole‐2,1′‐cyclohexane] ( 1 ) was converted into the carbonitrile 5 and the 4‐phenylthio derivative 4 . The NO 2 or the PhS substituents in 4 could be replaced regiospecifically by reaction with Me 3 SiN 3 or NaN 3 , respectively. The 5‐azido derivative 8 , resulting from NO 2 ‐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.