Hexane → 3-Thiophenecarboxylic acid, tetrahydro-4-oxo-, methyl ester

A solution of 3-methoxycarbonylmethylsulfanyl-propionic acid methyl ester (32) (58 g, 300 mmol) in dry T HF (800 mL) was added slowly within 4 h to a refluxing solution of hexane washed NaH (60% in mineral oil, 13.24 g, 331 mmol) in THF. The solution was further refluxed for 5 h. The solution was cooled and the solvent was evaporated. The residue was taken in water, acidified to pH˜1 by cold HCl solution, and extracted by CH2Cl2. The combined organic phase was dried over MgSO4 and concentrated under vacuum to get a viscous residue. The residue was purified by flash chromatography eluting with hexane to yield 17 g (35%) of 4-oxo-tetrahydro-thiophene-3-carboxylic acid methyl ester as colorless viscous oil which solidified on keeping overnight under vacuum. MP 51° C.; 1H NMR (400 MHz, CDCl3) δ 3.17-3.82 (m, 6.5 H), 10.94 (s, 0.5H) ppm. The isomeric mixture was used to next step without further purification.