title: Oxidative dimerization of (E)- and (Z)-2-propenylsesamol with O2 in the presence and absence of laccases and other catalysts: selective formation of carpanones and benzopyrans under different reaction conditions.
abstract: The oxidative dimerization of 2-propenylsesamol to carpanone with O(2) as the oxidant, which probably proceeds as a domino phenol oxidation/anti-β,β-radical coupling/intramolecular hetero Diels-Alder reaction, can be efficiently catalyzed by laccases. Experiments with laccases and other catalysts like a Co(salen) type catalyst and PdCl(2) clearly demonstrate that the diastereoselectivity of the carpanone formation does not depend on the catalyst but on the double-bond geometry of the substrate. With (E)-2-propenylsesamol as the substrate, carpanone and a so far unknown carpanone diastereoisomer are formed in a 9:1 ratio. When (Z)-2-propenylsesamol is used as starting material, carpanone is accompanied by two carpanone diastereoisomers unknown so far in a 5:1:4 ratio. All three carpanone diastereoisomers have been separated by HPLC, and their structures have been elucidated unambiguously by NMR spectroscopy, DFT calculations, and spin work analysis. When the oxidation of 2-propenylsesamol with O(2) is performed in the absence of any catalyst two diastereoisomeric benzopyrans are formed, probably as the result of a domino oxidation/intermolecular hetero Diels-Alder reaction. Under these conditions, carpanone is formed in trace amounts only.
authors.affiliation: Bioorganische Chemie, Institut für Chemie, Universität Hohenheim, Garbenstraße 30, D-70599 Stuttgart, Germany.
authors.forename: Mihaela-Anca
authors.initials: MA
authors.lastname: Constantin
authors.forename: Jürgen
authors.initials: J
authors.lastname: Conrad
authors.forename: Elena
authors.initials: E
authors.lastname: Merişor
authors.forename: Katja
authors.initials: K
authors.lastname: Koschorreck
authors.forename: Vlada B
authors.initials: VB
authors.lastname: Urlacher
authors.forename: Uwe
authors.initials: U
authors.lastname: Beifuss
mesh_terms: D052117:Benzodioxoles / Q000737:chemistry*; D001578:Benzopyrans; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D019281:Dimerization; D006576:Heterocyclic Compounds, 4 or More Rings; D042845:Laccase; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: C574729:(Z)-2-propenylsesamol; D052117:Benzodioxoles; D001578:Benzopyrans; D006576:Heterocyclic Compounds, 4 or More Rings; D010636:Phenols; C532598:carpanone; D042845:Laccase; D010100:Oxygen