Synthesis of Novel Spiro Pyrano[2,3‐d]thiazolo[3,2‐a]pyrimidine via 1,3‐Dipolar Cycloaddition of Azomethine Ylide

The reaction involving 4-phenyl-octahydro-pyrano[2,3-d]pyrimidine-2-thione, ethyl chloroacetate and the appropriate aromatic aldehyde yielded 2-arylmethylidene-5-phenyl-5a,7,8,9a-tetrahydro-5H,6H-pyrano[2,3-d][1,3]thiazolo[3,2-a]pyrimidin-3(2H)-ones. The 1,3-dipolar cycloaddition of 2-arylmethylidene-5-phenyl-5a,7,8,9a-tetrahydro-5H,6H-pyrano[2,3-d][1,3]thiazolo[3,2-a]pyrimidin-3(2H)-ones with azomethine ylide generated by a decarboxylative route from sarcosine and acenaphthenequinone afforded 4′-aryl-1′-methyl-5″-phenyl-5a″,7″,8″,9a″-tetrahydro-2H,5″H,6″H-dispiro[acenaphthylene-1,2′-pyrrolidine-3′,2″-pyrano[2,3-d][1,3]thiazolo[3,2-a]pyrimidine]-2,3″-diones in moderate yields. The structures of the products were determined and characterized thoroughly by NMR, MS, IR, elemental analysis, and X-ray crystallographic analysis.