Synthesis and structure of pyrazolo[5,1‐ a ]isoindol‐8‐ones from Aromatic Ortho Diesters

The title compounds 2 , have now been shown to arise in certain cases from condensation of aromatic ortho ‐diesters with ketone, where formerly only indeno[1,2‐ c ]pyrazol‐4(1 H )‐ones 3 have been reported from such reaction. Heretofore 2 was obtained in a less direct fashion from phthalaldehydic acid esters. When hetero‐aromatic diesters were employed, new heterocyclic ring systems as represented by 2a,b ,c were prepared for the first time. Structures of 2 have been verified from detailed 1 H and 13 C nmr studies, while representative intermediates 4–9 in the condensation of diesters to 2 have been isolated and identified.