title: Total synthesis of alkaloid 205B.
abstract: Concise and highly stereocontrolled total syntheses of racemic and enantiopure frog alkaloid 205B (1) were accomplished in 11 steps from 4-methoxypyridines 6 and 7 in overall yields of 8 and 8%, respectively. The assembly of the core of the natural product relies on a stereoselective Tsuji-Trost allylic amination reaction and a ring-closing metathesis. The synthesis features the use of an N-acylpyridinium salt reaction to introduce the first stereocenter and an unprecedented trifluoroacetic anhydride-mediated addition of an allylstannane to a vinylogous amide with complete facial selectivity. Deoxygenation of the C4 ketone proved difficult but was accomplished via a modified Barton-McCombie reaction in the presence of a catalytic amount of diphenyl diselenide.
authors.affiliation: Department of Chemistry, North Carolina State University , Raleigh, North Carolina 27695-8204, United States.
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Tsukanov
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Comins
mesh_terms: D000470:Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D006575:Heterocyclic Compounds, 3-Ring / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000470:Alkaloids; D006575:Heterocyclic Compounds, 3-Ring; D011725:Pyridines; C510161:alkaloid (-)-205B