Synthesis of Pyrazolo[5,1‑a]isoindoles and Pyrazolo[5,1‑a]isoindole-3-carboxamides through One-Pot Cascade Reactions of 1‑(2-Bromophenyl)buta-2,3-dien-1-ones with Isocyanide and Hydrazine or Acetohydrazide

A novel and efficient method for the construction of the pyrazolo­[5,1-a]­isoindole scaffold via a one-pot three-component cascade reaction of 1-(2-bromophenyl)­buta-2,3-dien-1-one with hydrazine and isocyanide promoted by a Pd catalyst is described. This cascade process proceeds through initial condensation of the allenic ketone with hydrazine followed by Pd-catalyzed isocyanide insertion into the C–Br bond and intramolecular C–N bond formation. Interestingly, when acetohydrazide was used in place of hydrazine, a more sophisticated procedure involving condensation, isocyanide insertion into C–H and C–Br bonds, deacetylation, and formation of C–C, C–O, and C–N bonds occurred to afford pyrazolo­[5,1-a]­isoindole-3-carboxamides with good efficiency.