Triacetic lactone, 4-hydroxycoumarins and 2-chloromethyl-5-hydroxy-4-pyrone were subjected to anodic oxidation in methanol containing LiClO4 or NaCN to afford the corresponding methoxy or cyano compounds. In basic media, however, bispyrone and biscoumarol were produced from triacetic lactone (4-hydroxy-6-methyl-2-pyrone) and 4-hydroxycoumarin, respectively. The formation processes of these oxidation products are discussed.
Triacetic lactone, 4-hydroxycoumarins, and kojic acid derivative were subjected to anodicoxidation in MeOH containing LiClO4 or NaCN to afford the corresponding methoxy or cyano compounds. In a basic media, however, dipyrone and dicoumarol were produced from triacetic lactone and 4-hydroxycoumarin, respectively. The formation process of 3-methoxytriacetic lactone as well as of 3-cyanotriacetic lactone
formaldehyde under basic condition. Similarly, the electrochemical oxidation and the treatment of 6 under Knoevenagel reaction conditions are the other alternative procedure described for the preparation of these bis compounds. However, the first method lacks generality as it involves aqueous reaction media and the second procedure is useful to obtain only the methylene bridged bispyrone derivatives
Using the synthesis of the heterodimeric phloroglucinyl pyrone arzanol as a benchmark reaction, a carba-version of the Betti multicomponent reaction has been developed. Capitalizing on the fluorous activation of the phenolic component and the use of iminium ions as bivalent and "transmissive" aldehyde equivalents, the reaction has been used to colonize a biologically privileged but previously inaccessible
Et2AlCl Promoted Coupling Reactions of 4-Hydroxy-2-pyrone or 4-Hydroxycoumarine with Aldehydes: Synthesis of Methylenebis-(4-hydroxy-2-pyrone) or Methylenebis-(4-hydroxycoumarine) Derivatives
Methylenebis(4-hydroxy-2-pyrone) or methylenebis(4-hydroxy-coumarine) derivatives (5) have been synthesized from 4-hydroxy-2-pyrones (6) and (8) or 4-hydroxycoumarine (10) with aldehydes (4) in the presence of diethylaluminum chloride.