Synthesis
Step 1: Under vigorous stirring, 1.1 g of sodium metal pre-sliced into thin slices was slowly added to 11 ml of methanol. The resulting solution was heated to reflux followed by the slow addition of 3.0 g of methyl 3-[(2-methoxy-2-oxoethyl)thio]propionate (completed in about 10 minutes). After maintaining the reflux state for 30 minutes, the solution was allowed to cool to room temperature. The reaction mixture was poured into about 100 ml of ice water under continuous stirring, continued for 30-40 min and acidified with concentrated hydrochloric acid to pH 2. The aqueous phase was extracted five times with dichloromethane, the organic phases were combined and concentrated by rotary evaporation after drying to afford 1.7 g of the crude product in the form of an oil.GC-MS analysis showed that the crude product contained about 3% of the isomer (tetrahydro-3-oxa-2- methyl thiophenecarboxylate) (HPLC retention time = 2.53 min). The crude product was purified using a Flash Master Personal system and a STRATA column pre-filled with Phenomenex silica (20 g). The crude product was dissolved in a dichloromethane:hexane (1:1) solvent mixture, dried, upsampled and eluted with the same ratio of solvent mixture. Finally 1.12 g of white solid product was obtained in 54% yield.
References
[1] Patent: US2008/275023, 2008, A1. Location in patent: Page/Page column 9
[2] Patent: WO2006/97449, 2006, A1. Location in patent: Page/Page column 24-25
[3] Tetrahedron, 1991, vol. 47, # 27, p. 4847 - 4860
[4] Patent: WO2013/50508, 2013, A1. Location in patent: Page/Page column 42; 55
[5] Organic Process Research and Development, 2016, vol. 20, # 5, p. 982 - 988
