N‐Heterocyclic Carbene‐Catalyzed Umpolung of Alkynyl 1,2‐Diketones

The umpolung of alkynyl 1,2‐diketones via N‐heterocyclic carbene (NHC) catalysis was achieved for the first time, allowing the rapid access to a large variety of synthetically and pharmaceutically important α‐pyrones under very mild conditions. A completely new NHC‐catalyzed umpolung pattern involving an O‐acylated allenolate as the key intermediate was proposed. Moreover, an unprecedented reaction pathway, featured by a series of group migrations and new bond formation, was postulated to demonstrate the formation of the products. magnified image