抄録
Asymmetric Diels-Alder reaction of di-l-menthyl acetoxymethylenemalonate with cyclopentadiene under high pressure was examined. The yield, proportion of exo isomer, and diastereomeric excess (d.e.) of the adduct increased with increase of pressure when the reactions were carried out without any catalyst. The absolute structure of the major diastereoisomer of the endo adduct corresponded to the natural configuration, which could be transformed to a precursor of aristeromycin, while the exo adduct had the unnatural configuration. The same diastereoselectivity was also observed when diethylaluminum chloride (capable of chelating with only one carbonyl group of the dienophile) was used as the catalyst. On the contrary, both endo and exo isomers obtaiend from the high-pressure-mediated Diels-Alder reaction in the presence of zinc chloride or tris(6, 6, 7, 7, 8, 8, 8-heptafluoro-2, 2-dimethyl-3, 5-octanedionato)ytterbium (capable of chelating with the two carbonyl groups of the dienophile at the same time) had the natural configuration. Possible mechanisms of these selectivities are proposed.
