Chiral auxiliaries for asymmetric radical cyclization reactions: application to the enantioselective synthesis of (+)-triptocallol.
[figure: see text] A series of epimeric 8-aryl menthyl derivatives 5a-d and 6a-l, prepared from the same chiral source (R)-pulegone, were employed as chiral auxiliaries in the asymmetric radical cyclization reactions of beta-keto esters mediated by Mn(OAc)3. Chiral precursors 8c and 8d provided the cyclization products 10c and 10d, respectively, as single isomers (dr > 99:1), whereas the cyclization of precursor 9k gave 13k with good stereoselectivity (dr = 24:1). Diastereomer 13e was employed as the key intermediate in the enantioselective synthesis of (+)-triptocallol in 90% ee.
Yang
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Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong. yangdan@hku.hk
Xu
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Bian
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D001685:Biological Factors / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D003500:Cyclization; D000081005:Cyclohexane Monoterpenes; D004224:Diterpenes / Q000138:chemical synthesis / Q000737:chemistry; D004852:Epoxy Compounds; D008610:Menthol / Q000031:analogs & derivatives / Q000737:chemistry; D015394:Molecular Structure; D039821:Monoterpenes; D010616:Phenanthrenes; D010944:Plants / Q000737:chemistry*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013729:Terpenes / Q000138:chemical synthesis* / Q000737:chemistry
D001685:Biological Factors; D000081005:Cyclohexane Monoterpenes; D004224:Diterpenes; D004852:Epoxy Compounds; D039821:Monoterpenes; D010616:Phenanthrenes; D013729:Terpenes; C430468:triptocallol; D008610:Menthol; C001899:triptolide; C039648:pulegone