A retro Diels-Alder method for the preparation of pyrrolo[1,2-a] pyrimidinediones from diexo-aminooxanorbornenecarboxamide

Abstract Through the reactions of diexo -3-amino-7-oxanorbornene-2-carboxamide 1 with the oxocarboxylic acids: 4-oxopentanoic acid, p -chlorobenzoylpropionic acid or 2-formylbenzoic acid, the pyrrolo[1,2- a ]pyrimidinediones 2 and 3 or pyrimido[1,2- a ]isoindoledione 4 were formed on cyclization and thermolysis, when the parent cycles decomposed via the loss of furan to give 2 – 4 in a retro Diels–Alder reaction. With cis -or trans -2-aroylcyclohexanecarboxylic acids as starting compounds, the 1-aroylhexahydroisoindol-3-ones ( 5 – 8 ) were formed; the phenyl-substituted derivatives gave diastereomeric mixtures. The structures of the new compounds were established by NMR spectroscopy and, for 3 and 6 , also by single-crystal X-ray structure determination.