[CH3:1][O:2][C:3]1[C:7]([O:8][CH3:9])=[CH:6][S:5][CH:4]=1.[CH2:10]([C:12]([CH2:17][CH3:18])(CO)CO)[CH3:11].C1(C)C(S(O)(=O)=O)=CC=CC=1>C1(C)C=CC=CC=1>[CH2:10]([C:12]1([CH2:17][CH3:18])[CH2:1][O:2][C:3]2=[CH:4][S:5][CH:6]=[C:7]2[O:8][CH2:9]1)[CH3:11]3,4-Dimethoxythiophene (5.0 g, 34.7 mmol), 2,2-diethyl-1,3-propanediol (36.4 mmol), toluenesulfonic acid (0.2 g), and dry toluene (200 mL) were placed in a 500 mL round bottom flask equipped with a soxhlet extractor that contained a molecular sieve (4A)-filled extraction thimble. The solution was refluxed for 12 h under argon atmosphere, then cooled to 25° C. The solvent was removed under reduced pressure, the mixture diluted with 250 mL diethyl ether, extracted with 5% ammonium hydroxide (200 mL), and the extracted with water (2×200 mL). The organic layer was dried over anhydrous magnesium sulphate and the ether distilled off under reduced pressure, leaving an oil. This oil was further purified using column chromatography (silica and hexanes/ethyl acetate, 90/10) to yield 3,3-diethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine as a colourless oil in 68% yield.
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