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Asymmetric Diels-Alder reactions with 5-menthyloxy-2(5H)-furanones

(2006) Jong, Johannes Cornelis de

At the beginning of the reseach described in this thesis the catalytic asymmetric Diels-Alder reaction had scarcely been investigated. No good catalytic processes with high enantiomeric excess were known at that time. At the same time the Diels-Alder reactions with chiral dienophiles needed further improvement as the number of diastereoselective cycloaddition reactions was limited to a few cases only. In most cases no complete diastereoselectivity was obtained. Besides, most chiral auxiliaries which were used were rather expensive or had to be synthesized by a multistep syntheses. The inherent problem of the chiral dienophiles used sofar was their conformational freedom leading to low selectivities, although the results were considerably improved by means of Lewis acid complexation. The disadvantage of Lewis acids is that they also catalyze the polymerization of dienes. Therefore, in most catalyzed reactions the dienes are limited to the most simple and cheap ones like butadiene or cyclopentadiene.
The general purposes of our research was: (i) to synthesize a chiral dienophile which would meet all the criteria described in Section 1.1, i.e. both enantiomers should be available, the absolute configuration of the Diels-Alder adducts should be predictable and the starting material should be a crystalline compound; (ii) to synthesize a number of substituted chiral dienophiles; (iii) to study these dienophiles in the thermal Diels-Alder reaction. Furthermore these dienophiles should have low conformational freedom, resulting in a high diastereoselectivity, and no Lewis acid catalysis should be needed in the cycloaddition reactions with these dienophiles.