Ruthenium Catalyzed Formation of Fused Pyridine Derivatives or Substituted Indoles from Hydrazine‐Derived Enamines and Propargyl Alcohols

Abstract New ruthenium‐catalyzed transformations of secondary propargyl alcohols with hydrazine‐derived enamines are presented, affording fused pyridines or substituted indoles depending on the hydrazine derivative used. The cascade reactions are catalyzed by an air‐ and moisture‐stable bifunctional ruthenium complex and proceed via redox‐isomerization of the propargyl alcohol, subsequent Michael addition and cyclocondensation. In case of phenylhydrazine a Fischer indole synthesis also takes place, prior to the final release of the products. The produced heterocyclic motifs are important scaffolds in medicinal and agricultural chemistry.