Novel cis-trans enantiomeric conglomerates: triage and absolute configurations via anomalous X-ray scattering. A photochemical second order asymmetric transformation

摘要

Three tricyclic imides were prepared by a Diels-Alder reaction of 6-arylfulvenes and maleic anhydride, followed by treatment with NH3. The exo isomers were found to exist as conglomerates when the aryl group was either p-tolyl or p-anisyl (although not phenyl). Triage of the p-tolyl racemate, followed by reaction with p-toluenesulfonyl chloride in CH2Cl2/Et3N, led to the crystalline enantiopure N-tosylimides (these were also conglomerates). X-ray diffraction analysis of the N-tosylimides via the anomalous dispersion technique led to assignment of the absolute configurations (as either E or Z). The original p-tolyl imide enantiomers were found to racemize under UV irradiation in CHCl3. Based on this, a possible second order asymmetric transformation under photochemical conditions was attempted, and indeed led to the isolation of crystalline imide with a small ee (similar to 15%). (c) 2006 Elsevier Ltd. All rights reserved.