Interaction of Acylethynyl Pyrroles and Pyrrolyl Propynoates with Hydrazines: Synthesis of Pyrrolylethynyl Hydrazides and Pyrrol–Pyrazole Ensembles

Abstract

2-Acylethynylpyrroles cyclize with hydrazines (hydrazine hydrate and phenylhydrazine, EtOH, 40°C, 0.5 h) to form pyrrolylpyrazoles in 63–95% yield. Unlike acylethynylpyrroles, pyrrolylpropynoates react with hydrazine hydrate and phenylhydrazine differently: interaction with hydrazine hydrate at a low temperature (EtOH, 0°C, 1 h) leads to the selective formation of pyrrolylethynylhydrazides (yield, 90–97%), whereas under reflux (EtOH, 1 h) in reactions with hydrazine and phenylhydrazine pyrrolylpyrazolones or pyrrolylpyrazolones are formed (yield, 88–97%).