title: An application of the phosphine-catalyzed [4 + 2] annulation in indole alkaloid synthesis: formal syntheses of (+/-)-alstonerine and (+/-)-macroline.
abstract: [reaction: see text] An application of the phosphine-catalyzed [4 + 2] annulation in the formal synthesis of alstonerine and macroline is reported. A phosphine-catalyzed [4 + 2] reaction between imine 7a and allene 8 formed the D ring of the target indole alkaloids. A subsequent intramolecular Friedel-Crafts acylation provided the C ring of the bridged tetracycle. Deprotection, followed by methylation of the bridged nitrogen, deoxygenation of the C6 ketone, and reduction of the C16 carbethoxy group provided the previously known intermediate 3.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles 607 Charles E. Young Drive East, Los Angeles, California 90095-1569, USA.
authors.forename: Yang S
authors.initials: YS
authors.lastname: Tran
authors.forename: Ohyun
authors.initials: O
authors.lastname: Kwon
mesh_terms: D000085:Acetates / Q000737:chemistry; D047151:Amaryllidaceae Alkaloids / Q000138:chemical synthesis / Q000737:chemistry; D001897:Boronic Acids / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray; D004987:Ethers / Q000737:chemistry; D026121:Indole Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry; D000078183:Oxindoles; D010720:Phosphines / Q000737:chemistry*; D012238:Rhodium / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000085:Acetates; D047151:Amaryllidaceae Alkaloids; D001897:Boronic Acids; D004987:Ethers; D026121:Indole Alkaloids; D000078183:Oxindoles; D010720:Phosphines; C510442:alstonerine; C412290:lycorane; C512190:macroline; D012238:Rhodium; C044646:phosphine; C010686:benzeneboronic acid; D009584:Nitrogen