2,4-Pentanediol → 2,4-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine

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A three-neck round bottom flask is vacuum dried, fitted with a stir bar, thermometer, and drying tube and maintained under nitrogen. About 500 milliliters (ml) of anhydrous xylene is cannulated into the flask. Two ml of 3,4-dimethoxy thiophene 1 (DMOT) (0.0166 mol), 4.85 ml of 2,4-pentanediol 2 (0.0332), and 0.61 ml of catalyst dodecylbenzene sulfonic acid (DBSA) (0.0025 mol) are added to the flask sequentially with previously degassed disposable syringes through the rubber septa fitted on one of the necks of the flask. The molar proportion between DMOT:diol:DBSA is 1.00:2.00:0.15. The reaction is set to run for five days under stirring at a temperature of around 100° C. The reaction is monitored on a daily basis by gas chromatography-mass spectrometry (GC-MS). After five days, the reaction is cooled to ambient temperature and filtered to remove any solid particulates. The xylene is stripped using a rotary evaporator to result in a green oil. The oil is taken up in a small amount of chloroform and extracted with water three times using sodium chloride to break any emulsion. The chloroform is stripped leaving a green oil. The crude mixture is purified by column chromatography using 70:30 toluene:n-hexane as the eluting solvent. The first fractions contain the product 2,4-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine 3 (aDM-ProDOT) and subsequent fractions contain DMOT 1 starting material. The aDM-ProDOT 3 is isolated as a white solid that is dried under vacuum. The final product was confirmed by GC-MS and 1H-NMR.

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