Preeparation of a building block for a pyrazole expanded porphyrin and isolation of a tripyrrolyl ketone decomposition product

Dipyrrolylpyrazole 3, obtained from 1,3-di-(1H-pyrrol-2-yl)propane-1,3-dione (2), was prepared as a building block for pyrazole-based binuclear expanded porphyrins. An unusual transformation of 2, in solution or on chromatography, afforded 1,3,3-tri-(1H-pyrrol-2-yl)prop-2-en-l-one (4) in good yield. HRMS indicated the presence of an unstable pyrazole-based expanded porphyrin 1 and its trinuclear Mg derivative 5 on condensation of 3 with benz-aldehyde.