N[C:2](N)=[S:3].[OH:5][CH2:6][CH2:7][O:8][CH2:9][CH2:10][O:11][CH2:12][CH2:13][O:14][CH2:15]COS(C1C=CC(C)=CC=1)(=O)=O.[OH-].[Na+].Cl>C(O)C.O>[SH:3][CH2:2][CH2:15][O:14][CH2:13][CH2:12][O:11][CH2:10][CH2:9][O:8][CH2:7][CH2:6][OH:5]A solution of thiourea (0.94 g, 12.35 mmol) and toluene-4-sulfonic acid 2-{2-[2-(2-hydroxy-ethoxy)-ethoxy]-ethoxy)-ethyl ester (4.09 g, 11.75 mmol) in absolute alcohol (32 ml) was heated to reflux under argon atmosphere for 24 h. The mixture was cooled and a solution of NaOH (1.23 g, 30.75 mmol) in 15 ml of ethanol/water (9:1, v/v) was added. Refluxing was continued for another 2.5 h under argon. The reaction mixture was then cooled to ambient temperature and acidified to pH 2 using concentrated hydrochloric acid and then concentrated under reduced pressure. The residue was purified by flash chromatography using ethyl acetate/absolute ethanol (10:1) to afford the product as a colourless oil. Yield 1.55 g (66%).
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