α‐Amino Acids Mediated C−C Double Bonds Cleavage in Diastereoselective Synthesis of Aza‐Spirocyclic Pyrazolones

An efficient and reagent‐free synthesis of highly functionalized aza‐spirocyclic pyrazolones are achieved from easily available α‐amino acids and alkylidene pyrazolones by means of amination, C−C‐double bonds cleavage, and decarboxylative annulation process. These highly diastereoselective reactions are promoted simply by α‐amino acids and involve in situ generated azomethine ylides as reactive intermediates. This newly developed protocol involves the formation of three new bonds (one C−N and two C−C) and four new contiguous stereo‐centers including a quaternary carbon center in a single pot cascade process.