Polarized ketene dithioacetals: 55: synthesis of novel 5-aryl-2-methylthio 4H-pyran-4-ones-from cinnomyl ketene dithioacetals

Abstract

A novel method for the synthesis of 5-aryl-2-methylthio-4H-pyran-4-ones 4a-h has been developed from the corresponding cinnamoylketene dithioacetals 1a-h in three successive steps. In the first step, 1a-h were oxidized with alkaline hydrogen peroxide to give the corresponding (ß-aryl-,a,ß-epoxypropanoyl)ketene dithioacetals 2a-h in 78-89% overall yields. In the second step the epoxyketones 2a-h were subjected to rearrangement in the presence of ether-boron trifluoride complex to give the corresponding (a-formyl-a-phenylacetyl)ketene dithioacetals 3a-h, which were then cyclized in the third step by refluxing in acetic acid/ethanol to afford the title compounds in good yields.