title: Protecting-group-free total synthesis of isoquinoline alkaloids by nickel-catalyzed annulation of o-halobenzaldimine with an alkyne as the key step.
abstract: An efficient short total synthesis of benzo[c]phenanthridine alkaloids including oxyavicine, oxynitidine, and oxysanguinarine is described. Thus, N-methyl-o-bromobenzaldimines 1 b-d undergo regioselective cyclization with 4-(benzo[d][1,3]dioxol-5-yl)but-3-yn-1-ol (2 b) in the presence of [Ni(cod)(2)] (cod=1,5-cyclooctadiene). In situ oxidation of the resultant isoquinolinium salts gives isoquinolinone derivatives 5 b-d with benzo[d][1,3]dioxol-5-yl substitution at the C(3) atom and a (CH(2))(2)OH group at the C(4) atom. Later, oxidation of the alcohol group in 5 b-d to the aldehyde moiety followed by acid-catalyzed cyclization and dehydration completes the total syntheses to give oxyavicine, oxynitidine, and oxysanguinarine in 67, 65, and 60 % yields, respectively. The synthesis requires four steps from o-bromobenzaldehyde derivatives. Transformations of these alkaloids to the other alkaloids in this family are also discussed herein.
authors.affiliation: Department of Chemistry, National Tsing Hua University, Hsinchu, 30013, Taiwan.
authors.forename: Rajendra Prasad
authors.initials: RP
authors.lastname: Korivi
authors.forename: Chien-Hong
authors.initials: CH
authors.lastname: Cheng
mesh_terms: D000470:Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry; D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D003500:Cyclization; D006846:Hydrocarbons, Halogenated / Q000737:chemistry*; D007097:Imines / Q000737:chemistry*; D007546:Isoquinolines / Q000138:chemical synthesis* / Q000737:chemistry; D009532:Nickel / Q000737:chemistry*; D010084:Oxidation-Reduction; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D000470:Alkaloids; D000480:Alkynes; D006846:Hydrocarbons, Halogenated; D007097:Imines; D007546:Isoquinolines; D009532:Nickel