title: Enantioselective Organocatalyzed Bromolactonizations: Applications in Natural Product Synthesis.
abstract: Asymmetric bromolactonization reactions of δ-unsaturated carboxylic acids have been investigated in the presence of 10 chiral squaramide hydrogen-bonding organocatalysts. The best catalyst enabled the cyclization of several 5-arylhex-5-enoic acids into the corresponding bromolactones with up to 96% ee and in high to excellent chemical yields. The reported catalysts are prepared in a straightforward manner in two steps from dimethyl squarate. The utility of the developed protocol was demonstrated in highly enantioselective syntheses of the sesquiterpenoids (-)-gossoronol and (-)-boivinianin B. Both natural products were obtained in ≥99% enantiomeric excess.
authors: Department of Pharmaceutical Chemistry, School of Pharmacy, University of Oslo , P.O. Box 1068, Blindern, N-0316 Oslo, Norway.
authors: Marius
authors: M
authors: Aursnes
authors: Department of Pharmaceutical Chemistry, School of Pharmacy, University of Oslo , P.O. Box 1068, Blindern, N-0316 Oslo, Norway.
authors: Jørn E
authors: JE
authors: Tungen
authors: Department of Pharmaceutical Chemistry, School of Pharmacy, University of Oslo , P.O. Box 1068, Blindern, N-0316 Oslo, Norway.
authors: Trond V
authors: TV
authors: Hansen
mesh_terms: D001688:Biological Products / Q000138:chemical synthesis*; D001966:Bromine / Q000737:chemistry*; D066241:Carbon-13 Magnetic Resonance Spectroscopy; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D003500:Cyclization; D007783:Lactones / Q000737:chemistry*; D066244:Proton Magnetic Resonance Spectroscopy; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism
chemical_list: D001688:Biological Products; D007783:Lactones; D001966:Bromine