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.
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Hauser et al. (1986) studied this question.
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