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Z. Naturforsch. 2012,
67b, 1289 – 1296
doi:10.5560/ZNB.2012-0214
Oxidative Rearrangement of Flavanones with Thallium(III) Nitrate, Lead Tetraacetate and Hypervalent Iodines in Trimethyl Orthoformate and Perchloric or Sulfuric Acid
1 Department of Organic Chemistry, University of Debrecen, H-4032 Debrecen, Hungary
2 Vascular Biology, Thrombosis and Hemostasis Research Group, Hungarian Academy of Sciences, University of Debrecen, H-4032 Debrecen, Hungary
Reprint requests to Prof. Dr. Sándor Antus. Fax: +36-52-512-744. E-mail:
antus.sandor@science.unideb.hu
Received August 2, 2012 / published online November 30, 2012
In memory of Professor Ándrás Lipták
An HPLC monitoring protocol has been developed to follow the reaction of flavanone [(±)-1] with thallium(III) nitrate, lead tetracetate, phenyliodonium diacetate (PIDA) or [hydroxyl(tosyloxy)iodo]benzene in trimethyl orthoformate. Besides the major ring-contraction product, the 2,3-dihydrobenzo[b]furan derivative (±)-4a, minor components were also identified, and their structures including the relative stereochemistry and a plausible mechanism of formation are reported and compared with literature data. The oxidation reactions were monitored by HPLC at different conditions, and the structure and the ratio of the products were determined and compared. The preferred formation of flavone (5) from (±)-flavanone (1) by PIDA is explained by quantum-chemical calculations on the intermediate formed by the addition of this reagent to the enol ether derivative of (±)-1.
Key words: Flavanones, Ring-contraction, Thallium(III) Nitrate, Lead Tetraacetate, Hypervalent Iodine