In Situ Generated TEMPO Oxoammonium Salt Mediated Tandem Cyclization of β‑Oxoamides with Amine Hydrochlorides for the Synthesis of Pyrrolin-4-ones

A novel in situ generated TEMPO oxoammonium
salt mediated one-pot
tandem reaction has been developed for the straightforward construction
of pyrrolin-4-ones from readily available β-oxoamides with amine
hydrochlorides. The reaction tolerates various functional groups and
represents a reliable method for the synthesis of highly substituted
pyrrolin-4-ones in good yields under mild conditions. Detailed mechanistic
studies disclosed that TEMPO oxoammonium salt generated in situ was
crucial for the transformation involving the formation of enaminone
precursors in situ by condensation of the β-oxoamides with amines,
followed by sequential oxidative coupling with β-oxoamides,
intramolecular cyclization, and 1,2-alkyl migration steps.