[C:1]1([O:11][CH2:12][C:13]([O:15][CH3:16])=[O:14])[C:10]2[CH2:9][CH2:8][CH2:7][CH2:6][C:5]=2[CH:4]=[CH:3][CH:2]=1.[S:17]1[CH:21]=[CH:20][CH:19]=[C:18]1[C:22](Cl)=[O:23].[Cl-].[Al+3].[Cl-].[Cl-].Cl>C(Cl)Cl>[C:18]1([C:22]([C:4]2[C:5]3[CH2:6][CH2:7][CH2:8][CH2:9][C:10]=3[C:1]([O:11][CH2:12][C:13]([O:15][CH3:16])=[O:14])=[CH:2][CH:3]=2)=[O:23])[S:17][CH:21]=[CH:20][CH:19]=1To a solution maintained at 0° C. of 12.5 g of the ester obtained according to (a) and 8.79 g thiophene-2-carboxylic acid chloride in 130 ml methylene chloride, there are added little by little 7.9 g aluminium chloride. The mixture is then maintained at reflux temperature for 6 hours and then poured into a mixture of ice and hydrochloric acid. The final product is recrystallised from methanol. There are obtained, with an 85% yield, 16.35 g of the ester which melts at 85° C.
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