COC1C=CC(P2(SP(C3C=CC(OC)=CC=3)(=S)S2)=[S:10])=CC=1.[CH3:23][O:24][C:25]([CH:27]1[CH2:31][C:30](=O)[S:29][CH2:28]1)=[O:26]>C1(C)C=CC=CC=1>[CH3:23][O:24][C:25]([CH:27]1[CH2:31][C:30](=[S:10])[S:29][CH2:28]1)=[O:26]207 g (0.51 mol) of Lawesson reagent are added at room temperature to a suspension of 149 g (0.93 mol) of tetrahydro-5-oxo-3-thiophenecarboxylic acid methyl ester in 1.23 litres of absolute toluene, and the mixture is boiled at reflux for 16 hours. Then the solvent is removed by distillation in vacuo, the residue is boiled at reflux for 20 minutes four times in one litre of a solvent mixture of petroleum ether and diethyl ether 1:1 each time, and the extract phase is in each case decanted off and concentrated. After distillation of the crude substance at 130°-140° C./0.03 mbar using a bulb tube, 129.5 g of orange oil are obtained.
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