Strukturuntersuchungen an einem Produkt der intramolekularen Diels‐Alder‐Reaktion Konfigurations‐ und Konformationsanalyse von 5‐Methyl‐2‐phenyl‐1H‐2,3,3a,4,5,7a‐hexahydroisoindol‐1‐on

Structure Elucidation of a Product of Intramolecular Diels-Alder-Reaction: Configurational and Conformational Analysis of 5-Methyl-2-phenyl-1H,2,3,3a,4,5,7a-hexahydroisoindol-1-one N-Allyl-N-phenylsorbamide 1 cyclizes at 160°C to give 5-methyl-2-phenyl-1H,2,3,3a,4,5,7a-hexahydroisoindol-1-one 2. As a result of this intramolecular [4 + 2] cycloaddition four stereoisomeres 2a–2d can exist. The 1H and 13C n.m.r. data are given. The 1H n.m.r. studies demonstrate that the product of Diels-Alder cyclisation is the result of cis-fusion of the two rings. The nuclear Overhauser effect data provide further evidence for 2a in which the carbonyl group and methyl one are trans-arranged. The n.m.r. results are confirmed by X-ray studies.