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.
- Publication Type
- Journal contribution (peer reviewed)
- Authors
- Constantin, M.-A.; Conrad, J.; Merişor, E.; Koschorreck, K.; Urlacher, V.B.; Beifuss, U.
- Year of publication
- 2012
- Published in
- J. Org. Chem.
- Band/Volume
- 77/
- DOI
- 10.1021/jo300263k
- Page (from - to)
- 4528-4543
The oxidative dimerization of 2-propenylsesamol to carpanone with O2 as the oxidant, which probably proceeds as a domino phenol oxidation/anti-beta,beta-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 PdCl2 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 diastereomer are formed in a 9:1-ratio. When (Z)-2-propenylsesamol is used as starting material carpanone is accompanied by two carpanone diastereomers 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 O2 is performed in the absence of any catalyst two diasteromeric benzopyrans are formed - probably as the result of a domino oxidation/intermolecular hetero Diels-Alder reaction. Under these conditions carpanone is formed in traces only.