Diels‐alder adducts of a spirocyclopentenotriazoloazodienophile. Assignment of their ¹H and ¹³C NMR spectra

Abstract

1‐Phenyl‐cyclopenteno[1,2‐d]‐1,2,3‐rriazolo‐5‐spiro‐4′‐[perhydropyrazolino‐3′,5′‐dione] (5) afforded in situ, by oxidation with lead tetraacetate, the corresponding cyclopentenotriazolo‐spiropyrazolodione 6, which was trapped with dienes giving the hetero‐Diels‐Alder adducts 10–12 in good yields. The Diels‐Alder reactions were examined on the basis of AM1 MO calculations. Total assignment of the 1H‐ and 13C‐nmr chemical shifts as well as the relative configuration of these adducts was accomplished with the help of 2D (1H‐1H COSY, 1H‐1H NOESY, 1H‐13C XHCORR, 1H‐13C COLOC) and NOE difference spectroscopy. The structures of compounds 11a and 11b were also examined by molecular modeling.