Improved Method for the Synthesis of Dialkyl-substituted Thiophene 1, 1-Dioxides

Abstract

The peracid oxidation of substituted thiophenes to thiophene 1, 1-dioxides has been extensively investigated by Melles and Backer^1,2. Most oxidations, especially those of 3,4-disubstituted thiophenes, afford the sulfones in fair to good yields. Oxidation of 2,5-dimehtylthiophene, however, only yields 14% of the corresponding dioxide. As we needed considerable amounts of this dioxide and related compounds for oxidation studies³ and the preparation of cyclo-heptatrienes⁴, we had to improve the method of its synthesis. We found that using the commercially available m-chloroperbenzoic acid as the oxidant, freezing out (−55 °C) most of the m-chlorobenzoic acid formed and subsequently removing the residual acid with the aid of tert-amino-substituted macroreticular resins, the yield could be increased considerably (Table I). An additional advantage of using the above-mentioned ion-exchange resins is that they decompose any excess of the peracid. This procedure was also successfully applied to the synthesis of other 2,5- or 2,4-disubstituted thiophene 1,1-dioxides (see Table I).