Regioselective synthesis of novel spiroheterocyclic framework via the 1,3-dipolar cycloaddition

A series of novel dispiro[oxindole-fused pyrimidine]pyrrolidine ring systems 4a-f were synthesized by the regioselective 1,3-dipolar cycloaddition reaction of the 2-arylmethylene-7-benzyl-9-(benzylidene)tetrahydropyrido[4,3-d]thiazolo[3,2-a]pyrimidin-3-ones 1a-f with azomethine ylides, generating by the decarboxylative route from isatin 2 and sarcosine 3, in moderate to good yields. The regiochemistry of designed dispiroheterocyclic compounds 4a-f was established by single crystal X-ray structure and spectroscopic techniques.