Ring–Ring Interconversions of Nitrosoimidazoles. The Effect of some Condensed Six-Membered Rings on the Reactivity

The study of the effect of a condensed ring on the reactivity of nitrosoimidazoles with hydrochloric acid has been extended to some six-membered rings: thus, the reactivity of 2-(4-chlorophenyl)-3-nitrosoimidazo[1,2-a]pyridine (6), 6-chloro-2-(4-chlorophenyl)-3-nitrosoimidazo[1,2-b]pyridazine (7), 2-(4-chlorophenyl)-3-nitrosoimidazo[1,2-a]pyrimidine (8a) and 2-(4-chlorophenyl)-3-nitrosoimidazo[1,2-a]pyrazine (9) has been examined. The striking differences observed in the reactivity of compounds 6–9 (denitrosation, ring-opening with ammonia elimination, ring–ring interconversion with the unexpected loss of a C3 fragment and decomposition, respectively) have been discussed.