Diethyl Oxalate → 5-Methoxy-2-thiopheneglyoxylic acid ethyl ester

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Reaction Steps

2-Methoxythiophene (15.4 g) is dissolved in 100 ml anhydrous THF and butyl lithium (0.135 moles) in hexane is added dropwise. The solution is stirred at room temperature 15 hr and then heated at reflux for 1 hr. After cooling, the clear solution is transferred to a dropping funnel by means of a siphon. The solution of thienyl lithium is added dropwise to a solution of diethyl oxalate (19.7 g) in 150 ml THF at -78° C. After stirring 2 hr at -78° C, the mixture is brought to -10° C and treated with saturated NH4C1 solution. The aqueous fraction is separated and extracted several times with ether. The combined ether extracts are washed with water and brine, dried (MgSO4) and concentrated. Chromatography on silica gel (eluant = benzene) gives 5-methoxy-2-thiopheneglyoxylic acid ethyl ester (2; X1 = CH3O, X2 and X3 = H and R10 = C 2 H5); mp 136 -137° C after recrystallization from benzene-hexane.

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