Synthesis of Ethyl 3-(2,2-dimethoxyethyl)-4-oxo-2-thioxothiazolidin-5-yl-glyoxylate – DMAP as Catalyst

D.H.R. Barton, E.Buschmann, J.Hausler, C.W.Holzapfel, T. Sheradsky, and D.A.Taylor, J .Chem .Soc. Perkin I, 1107, (1977)

1. A solution of 3-(2,2-dimethoxyethyl)-2-thioxothiazolidin-4-one (4.21 g), pyridine (3.16 g), DMAP (122 mg), ethoxalyl chloride (4.7 mL), in anhydrous dichloromethane (50 mL) is heated under reflux for 3 h.
2. Dichloromethane (50 mL) is added to the reaction mixture which is then repeatedly washed with water, dried, and evaporated.  The residue is taken up with ether, and after 15 h a small amount of solid filtered off.  The rhodanine salt is precipitated by the addition of saturated aqueous potassium hydrogen carbonate, filtered, washed with ether and then with a small amount of hydrogen carbonate solution.
3. The crude salt (5.5 g, 78%) is suspended in water and acidified with citric acid (10 g).  Chloroform is added to dissolve the precipitate; the chloroform solution is dried and evaporated.  Tituration of the residue with light petroleum and crystallization from ether-light petroleum affords ethyl 3-(2,2-dimethoxyethyl)-4-oxo-2-thioxothiazolidin-5-yl-glyoxylate (4.11 g, 64%) as yellow needles, m.p. 80-81°C.