Enantioselective Synthesis of Spirorhodanine-Pyran Derivatives via Organocatalytic [3+3] Annulation Reactions between Pyrazolones and Rhodanine-Derived Ketoesters

A series of novel biselectrophilic beta,gamma-unsaturated alpha-ketoesters were designed and synthesized from rhodanine. Under the catalysis of chiral squaramides, the enantioselective [3 + 3] annulation reaction of these novel ketoesters with pyrazolones was developed. This reaction offers an efficient method for the synthesis of chiral 2'-thioxo-5,6-dihydrospiro [pyrano [2,3-c]pyrazole-4,5'-thiazolidin]-4'-ones.