Synthesis of Imidazopyridines via Copper-Catalyzed, Formal Aza-[3 + 2] Cycloaddition Reaction of Pyridine Derivatives with α‑Diazo Oxime Ethers

The Cu-catalyzed, formal aza-[3 +
2] cycloaddition reaction of
pyridine derivatives with α-diazo oxime ethers in trifluoroethanol
was used to synthesize imidazopyridines via the release of molecular
nitrogen and elimination of alcohol. These methods enabled modular
synthesis of a wide range of N-heterobicyclic compounds
such as imidazo­pyridazines, imidazo­pyrimidines, and imidazo­pyrazines
with an α-imino Cu-carbenoid generated from the α-diazo
oxime ethers and copper.