Synthesis of 2,2-di(pyrazol-1-yl)enones via the 2:1 coupling of pyrazoles and acylbromoacetylenes in solid alumina

Pyrazoles were reacted with acylbromoacetylenes in solid Al₂O₃ at room temperature to afford 2,2-di(pyrazol-1-yl)enones in 22–69% yield. The reaction proceeds via isolable intermediates, (Z)-2-bromo-2-(pyrazol-1-yl)enones. This unexpected 2:1 coupling is in contrast to similar reactions of pyrroles, furans and thiophenes, which give the corresponding acylethynyl derivatives. This reaction opens a one-pot route to inaccessible gem-dipyrazolylenones, which have potential applications as bidentate chelating ligands and building blocks for drug design.