Divergent Chemo‑, Regio‑, and Diastereoselective Normal Electron-Demand Povarov-Type Reactions with α‑Oxo-ketene Dienophiles

The
reactions between electron-rich 2-aza-dienes and α-oxo-ketenes
derived from the Wolff rearrangement of 2-diazocycloalkane-1,3-diones
chemo- and regioselectively produced spiro hydropyrid-4-ones with
good to excellent diastereoselectivities. These reactions are likely
to proceed via a domino Wolff/Friedel–Crafts/intramolecular
Mannich process. Prolonged domino sequences also allowed the expeditious
preparation of a series of pyrazolopyridine and pyridopyrimidine heterocycles.