title: An entry to the azocino[4,3-b]indole framework through a dehydrogenative activation of 1,2,3,4-tetrahydrocarbazoles mediated by DDQ: formal synthesis of (±)-uleine.
abstract: It is presented that hexahydro-1,5-methano[4,3-b]indoles were efficiently synthesized in high yields (up to 89% yield) through the cyclization reaction of starting tetrahydrocarbazoles bearing a monoalkylaminocarbonylmethyl moiety at the C-2 position mediated by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ). A mechanistic proposal is also given that mainly includes two cascade reactions: (i) formation of a vinylogous iminium cation via DDQ-mediated dehydrogenation of tetrahydrocarbazole functionality and (ii) intra-molecular and syn-selective addition of the amide functionality as the nucleophile to the vinylogous iminium cation. Furthermore, this cyclization reaction was successfully utilized in the formal total synthesis of (±)-uleine, an Aspidospermatan skeletal type alkaloid.
authors.affiliation: Department of Chemistry Education, Faculty of Education, Hacettepe University, 06800 Beytepe, Ankara, Turkey. patir@hacettepe.edu.tr
authors.forename: Süleyman
authors.initials: S
authors.lastname: Patir
authors.forename: Erkan
authors.initials: E
authors.lastname: Ertürk
mesh_terms: D000470:Alkaloids / Q000138:chemical synthesis / Q000737:chemistry*; D001392:Azocines / Q000138:chemical synthesis* / Q000737:chemistry; D016227:Benzoquinones / Q000737:chemistry*; D001952:Bridged-Ring Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D002227:Carbazoles / Q000138:chemical synthesis* / Q000737:chemistry; D003500:Cyclization; D007211:Indoles / Q000138:chemical synthesis* / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D013237:Stereoisomerism
chemical_list: D000470:Alkaloids; D001392:Azocines; D016227:Benzoquinones; D001952:Bridged-Ring Compounds; D002227:Carbazoles; D007211:Indoles; C557359:azocino(4,3-b)indole; C428545:uleine; C000928:dichlorodicyanobenzoquinone; C030374:indole; C409925:1,2,3,4-tetrahydrocarbazole