Construction of 2‑Pyrone Skeleton via Domino Sequence between 2‑Acyl-1-Chlorocyclopropanecarboxylate and Amines

A base-promoted
domino reaction of 2-acyl-1-chlorocyclopropaneformic
esters with amines is described. In the presence of inorganic bases
like Cs2CO3 or Mg­(OEt)2, the reaction
proceeded smoothly in acetonitrile to afford 2-pyrone derivatives
in modest to excellent yields (up to 97%). This reaction provides
a straightforward and transition metal-free protocol to efficiently
construct 2-pyrone skeleton. A possible mechanistic process involving
1,2-elimination of hydrogen chloride, aza-Michael addition, ring-opening,
and intramolecular lactonization was suggested to rationalize the
formation of the target 2-pyrone derivatives.