Synthesis of Pyrazolo[5,1‑<i>a</i>]isoindoles and Pyrazolo[5,1‑<i>a</i>]isoindole-3-carboxamides
through One-Pot Cascade Reactions of 1‑(2-Bromophenyl)buta-2,3-dien-1-ones
with Isocyanide and Hydrazine or Acetohydrazide
- Publication date
- Publisher
Abstract
A novel and efficient method for
the construction of the pyrazolo[5,1-<i>a</i>]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-<i>a</i>]isoindole-3-carboxamides with good efficiency