Synthesis
General procedure for the synthesis of methyl tetrahydro-4-oxo-2H-thiopyran-3-carboxylate from dimethyl 3,3'-thiodipropionate: 2.7098 g of NaH (60%) was added to a dry 250 ml three-necked flask, followed by the addition of 40 ml of anhydrous tetrahydrofuran (THF) and stirring for 10 min at room temperature. Dimethyl 3,3'-thiodipropionate (10.1015 g) dissolved in THF was added slowly dropwise. After dropwise addition, the reaction mixture was heated to reflux for about 1 hour. The reflux was continued for 1 hour after rinsing the dropping funnel with 10 ml of THF. The reaction was stopped and cooled to room temperature. The pH of the reaction solution was adjusted to 6-7 with 2% hydrochloric acid and then extracted with dichloromethane (30 ml x 3). The organic layers were combined, washed with saturated sodium chloride solution, collected and dried over anhydrous sodium sulfate. After filtration, the solvent was removed under reduced pressure to give 7.5639 g of a yellow oily liquid product in 88.7% yield.
References
[1] Synthesis, 2007, # 10, p. 1584 - 1586
[2] Patent: CN104086562, 2016, B. Location in patent: Paragraph 0136; 0137
[3] Patent: CN105153190, 2017, B. Location in patent: Paragraph 0134; 0165; 0166
[4] Organic Letters, 2018, vol. 20, # 19, p. 6104 - 6107
[5] Journal of the American Chemical Society, 1997, vol. 119, # 18, p. 4285 - 4291
