Synthetic studies towards pentacyclic quassinoids: total synthesis of unnatural (-)-14-epi-samaderine E and natural (-)-samaderine Y from (S)-(+)-carvone |
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Authors: | Shing Tony K M Yeung Ying-Yeung |
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Institution: | Department of Chemistry and Center of Novel Functional Molecules, The Chinese University of Hong Kong, Shatin, NT, Hong Kong, China. tonyshing@cuhk.edu.hk |
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Abstract: | First total syntheses of unnatural (-)-14-epi-samaderine E (5) and natural (-)-samaderine Y (2) were accomplished from (S)-(+)-carvone (6) in 18 and 21 steps, respectively. The syntheses are short, efficient (with an average yield of 80 % plus for each transformation), enantiospecific, and produce nine new chiral centers. The crucial points of the syntheses included a regioselective allylic oxidation on ring C, regio- and stereoselective reduction of ketone, a stereocontrolled epoxidation, an epoxymethano-bridge formation, a chemoselective Grignard reaction, an intramolecular Diels-Alder reaction, an intramolecular aldol addition, and a newly developed manganese(III)-catalyzed allylic oxidation on ring A. |
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Keywords: | allylic oxidation antitumor agents cycloaddition quassinoids total synthesis |
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