Chiral Synthesis of Natural Products Employing Enantiofacial Discriminating Reaction

研究了分子内杂diels - alder反应的对映选择性反应。由l -酒石酸二乙酯(1)制备的两种同分异构体甘油醛(2)和(3)与Meldrum's酸进行了平滑的同步缩合和分子内Diels-Alder反应，以反电子需求以高度非对映选择性的方式生成相应的环加合物。结果发现，e -亲二烯亲和物(2)和z -亲二烯亲和物(3)作为一个外聚体分别产生顺-5/6-加合物(4)和反-5/6-加合物(5)。利用两个加合物，建立了异育亨宾生物碱所有可能的立体异构体的形式路线。此外，还以顺式5/6-加合物(4)为前体，开发了合成二环环烯醚萜类单萜(-)-甲基烯酸酯(6)和顺式和反式d /E环异亨宾生物碱(-)-四氢alstonine(7)和(-)-ajmalicine(8)的新途径。

Enantioselective reaction employing intramolecular hetero-Diels-Alder reaction with reverse electron demand has been examined. Reaction of the two isomeric glyceraldehydes, (2) and (3), prepared from diethyl L-tartrate (1), with Meldrum's acid underwent smooth concurrent condensation and intramolecular Diels-Alder reaction with reverse electron demand to give the corresponding cycloadducts in highly diastereoselective manners. It was found that the E-dienophile (2) afforded the cis-5/6-adduct (4) and the Z-dienophile (3) afforded the trans-5/6-adduct (5) each as a single epimer. Using two adducts a formal route to all possible stereoisomers of the heteroyohimbine alkaloids has been established. Furthermore, a new route to the secoiridoid monoterpene, (-)-methyl elenolate(6), and both cis- and trans-D/E ring heteroyohimbine alkaloids, (-)-tetrahydro-alstonine (7) and (-)-ajmalicine (8), has been developed using the cis-5/6-adduct (4) as a single precursor.