Synthesis and Properties of Nitrosoazulenes

Ethyl 2-amino-3-nitrosoazulene-1-carboxylate (II) was synthesized from ethyl 2-aminoazulene-1-carboxylate by treatment with isoamyl nitrite. The structure of the amino-nitrosoazulene was proved by the reductive acetylation of the azulene to give ethyl 2,3-diacetylaminoazulene-1-carboxylate. This nitrosation method was then applied to several azulenes possessing different substituents; it yielded some stable nitrosoazulene derivatives. The spectral properties of the nitrosoazulenes will be discussed. The condensation reactions of II with aromatic amines failed to give azo-dyes, but with diethyl malonate and malononitril they gave the corresponding pyrazinoazulene derivatives.