Remarkable Diastereoselectivity Eserted by Dienophile Configuration in Intramolecular Diels-Alder Reaction of Electron Deficient Heterodienes: New Chiral Entry into the Secoiridoid Monoterpenes and the Heteroyohibine Indole Alkaloids

Abstract
Reaction between the optically active glyceraldehyde (1Z) carrying Z-olefin and Meldrum''s acid furnished in one step the tricyclic adduct 3 with trans 5/6 ring juncture selectively under mild conditions by spontaneous condensation followed by the intramolecular Diels-Alder reaction. On the other hand, the E-olefin isomer (1E), under the same conditions, furnished the isomeric adduct 4 with cis 5/6 ring juncture selectively. The former gave a pair of the cis-fused bicyclic carbamates, (22) and (25), while the latter gave the trans-fused pair, (23) and (26), by the following transformations. Although these imply formal chiral route to the heteroyohimbine alkaloids, a new enantioselective route to a secoiridoid monoterpene, (-)-methyl elenolate (37), has also been developed.
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