Flexible protocol for the chemo- and regioselective building of pyrroles and pyrazoles by reactions of Danishefsky’s dienes with 1,2-diaza-1,3-butadienes

The versatility of the Mukaiyama-Michael-type addition/heterocyclization of Danishefsky’s diene with 1,2-diaza-1,3-butadienes was applied to the synthesis of both 4H-1-aminopyrroles and 4,5H-pyrazoles. Thus, the same reagents furnished different types of highly functionalized azaheterocycles essentially depending on their structure: as a matter of fact, the ester or the amide moiety differently affects the acidity of the proton at the adjacent carbon. An unexpected formation of 5H-1-aminopyrroles from the reactions carried out in water was also observed.