Synthesis of γ‑Pyrones from Formal [4 + 2] Cyclization of Ketene Dithioacetals with Acyl Chlorides

A formal
[4 + 2] cyclization of easily available ketene dithioacetals
with acyl chlorides has been developed. Mediated by lithium bis­(trimethylsilyl)­amide,
a series of γ-pyrones were obtained with a broad substrate scope.
This unprecedented formal [4 + 2] cyclization provides a novel mode
for ketene dithioacetals as versatile synthons. The synthesized γ-pyrones
could be successfully transformed to 2-aryl/amino γ-pyrones
and 2,3-dihydroimidazo­[1,2-a]­pyridin-7­(1H)-ones mainly via the cleavage of the C–S bond.