Electrochemical Reduction of 1H‐Thioxanthene‐1,4,9‐trione and 3‐Methyl‐1H‐thioxanthene‐1,4,9‐trione – Representatives of a New Class of Heterocycles Related to Thioxanthenone

A convenient synthetic route was proposed for the synthesis of 3-methyl-1H-thioxanthene-1,4,9-trione. This compound and its 3-H congener are representatives of a new class of thioxanthone-like heterocycles, which can be used as building blocks for materials used in organic electronics. Electrochemical reduction (ECR) of 1H-thioxanthene-1,4,9-trione and its 3-methyl derivative in DMF and acetonitrile is a three-stage process leading to the formation of the corresponding long-lived radical anions and unstable dianions at the first and second stages, respectively. In a protolytic equilibrium, dianions are converted into 1-oxy-4-hydroxy-1H-thioxanthene-9-one anions. Their one-electron reversible ECR leads to the corresponding radical dianions, followed by the formation of (3-methyl/H)-1,4-dihydroxy-1H-thioxantene-9-ones as the final products. The latter compounds can be converted into the initial (3-methyl/H)-1H-thioxanthene-1,4,9-triones. The main intermediates were characterized using a combination of cyclic voltammetry, EPR spectroscopy, 3D spectroelectrochemistry, and DFT calculations at the (U)B3LYP/6-31+G*/PCM level of theory. A general ECR scheme was proposed for both types of compounds.