title: Synthetic studies towards pentacyclic quassinoids: total synthesis of unnatural (-)-14-epi-samaderine E and natural (-)-samaderine Y from (S)-(+)-carvone.
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.
authors.affiliation: Department of Chemistry and Center of Novel Functional Molecules, The Chinese University of Hong Kong, Shatin, NT, Hong Kong, China. tonyshing@cuhk.edu.hk
authors.forename: Tony K M
authors.initials: TK
authors.lastname: Shing
authors.forename: Ying-Yeung
authors.initials: YY
authors.lastname: Yeung
mesh_terms: D000470:Alkaloids / Q000138:chemical synthesis*; D000498:Allyl Compounds / Q000737:chemistry; D000972:Antineoplastic Agents, Phytogenic / Q000138:chemical synthesis*; D002384:Catalysis; D003500:Cyclization; D000081005:Cyclohexane Monoterpenes; D008958:Models, Molecular; D039821:Monoterpenes / Q000737:chemistry*; D010084:Oxidation-Reduction; D036702:Quassins / Q000138:chemical synthesis*; D013237:Stereoisomerism
chemical_list: D000470:Alkaloids; D000498:Allyl Compounds; D000972:Antineoplastic Agents, Phytogenic; D000081005:Cyclohexane Monoterpenes; D039821:Monoterpenes; D036702:Quassins; C517587:samaderine E; C514130:samaderine Y; C006923:carvone