ASYMMETRIC DIELS-ALDER REACTION CATALYZED BY SOME CHIRAL LEWIS-ACIDS

Diels-Alder reaction between cyclopentadiene and various dienophiles (mainly methacrolein) at -78°C was catalysed by various chiral aluminum alcoholates. The catalysts were prepared by reaction of EtAlCl2 with several families of diol (or their monoether monoalcohol derivatives). The most enantioselective catalyst is derived from diol 5a. A detailed investigation in that case gives some light on the experimental parameters of the system, especially the reproductible preparation of the catalyst. Enantiomeric excess up to 86% (in exo cycloadduct 2a) could be achieved. Tentative structures are proposed for the transition state of the reaction. © 1990.