title: Electrocyclic ring-opening/pi-allyl cation cyclization reaction sequences involving gem-dihalocyclopropanes as substrates: application to syntheses of (+/-)-, (+)-, and (-)-gamma-lycorane.
abstract: The readily prepared gem-dibromocyclopropanes (+/-)-13 and (+/-)-19 each engage in a silver(I)-promoted electrocyclic ring-opening/pi-allyl cation cyclization sequence to deliver the hexahydroindole (+/-)-20, which participates in a Suzuki cross-coupling reaction with arylboronic acid 3 to give the tetracyclic compound (+/-)-21. Catalytic hydrogenation of this last compound proceeds in a completely stereoselective manner to give the saturated analogue (+/-)-24, which undergoes Bischler-Napieralski cyclization on reaction with phosphorus oxychloride. The resulting lactam (+/-)-25 is then reduced with lithium aluminum hydride to give (+/-)-gamma-lycorane [(+/-)-1]. By using (-)-menthyl-derived carbamates 27 and 28, this chemistry has been extended to the synthesis of the (+)- and (-)-modifications of the title compound.
authors.affiliation: School of Chemistry, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: M G
authors.initials: MG
authors.lastname: Banwell
authors.forename: J E
authors.initials: JE
authors.lastname: Harvey
authors.forename: D C
authors.initials: DC
authors.lastname: Hockless
authors.forename: A W
authors.initials: AW
authors.lastname: Wu
mesh_terms: D000470:Alkaloids / Q000138:chemical synthesis*; D047151:Amaryllidaceae Alkaloids; D000818:Animals; D002236:Carbohydrate Conformation; D003521:Cyclopropanes / Q000138:chemical synthesis*; D004187:Disaccharides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D005647:Fucosyltransferases / Q000037:antagonists & inhibitors*; D006026:Glycoside Hydrolases / Q000037:antagonists & inhibitors*; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation
chemical_list: D000470:Alkaloids; D047151:Amaryllidaceae Alkaloids; D003521:Cyclopropanes; D004187:Disaccharides; D004791:Enzyme Inhibitors; C412290:lycorane; D005647:Fucosyltransferases; C031692:galactoside 3-fucosyltransferase; D006026:Glycoside Hydrolases