Chiral Synthesis of Natural Products Employing Enantiofacial Discriminating Reaction

研究了具有反向电子需求的分子内杂原子Diels-桤木反应的对映选择性反应。由L-酒石酸二乙酯（1）制得的两种异构甘油醛（2）和（3）与Meldrum酸的反应经历了平稳的同时缩合和分子内的Diels-Alder反电子反应，以高度非对映选择性的方式得到相应的环加合物。发现E-亲二烯体（2）提供顺式-5/6-加合物（4），Z-亲二烯体（3）提供反式-5/6-加合物（5），各自作为单一差向异构体。利用两种加合物建立了杂育亨宾生物碱所有可能的立体异构体的正式路线。此外，以顺式-5/6-加合物（4）为单一前体，还开发了一条合成开环环烯醚萜类单萜（-）-亚麻酸甲酯（6）以及顺式和反式D/E环杂育亨宾生物碱（-）-四氢阿司他丁（7）和（-）-阿司他丁（8）的新路线。

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.