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 alpha-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 alpha-amino acids and involve in situ generated azomethine ylides as reactive intermediates. This newly developed protocol involves the formation of three new bonds (oneC-Nand twoC-C) and four new contiguous stereo-centers including a quaternary carbon center in a single pot cascade process.