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

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. (c) 2005 Elsevier B.V. All rights reserved.