Beschreibung:
AbstractThe Diels‐Alder reaction of the cyclic methylene compound 3 with cyclopentadiene at ambient temperature leads to the adducts 4 and 5 with more than 95% face and more than 96% exo selectivity. The structure of the products has been verified by chemical correlation as well as by X‐ray diffraction analysis of the Diels‐Alder adduct 4. The mixture of 4 and 5 was converted to optically active (+)‐norbornenone 12. face Selectivity was dramatically decreased by Lewis acid catalysis with TiCl2(iPrO)2 or AlEtCl2 at lower temperatures.