[Cl-].[Mg+2].[Cl-].[C:4]([O:12][CH2:13][CH3:14])(=[O:11])[CH2:5][C:6]([O:8][CH2:9][CH3:10])=[O:7].[S:15]1[C:19]2[C:20](C(Cl)=O)=[CH:21][CH:22]=[CH:23][C:18]=2[N:17]=[N:16]1.Cl>C(#N)C.C(N(CC)CC)C>[S:15]1[C:19]2[C:20]([CH:5]([C:6]([O:8][CH2:9][CH3:10])=[O:7])[C:4]([O:12][CH2:13][CH3:14])=[O:11])=[CH:21][CH:22]=[CH:23][C:18]=2[N:17]=[N:16]14.8 g of magnesium chloride in 50 ml of acetonitrile are treated with 7.6 ml of diethyl malonate and 14 ml of triethylamine, with ice-cooling and stirring. The mixture is stirred for 20 minutes and then treated at 0°-5° C. with portions of a suspension of 9.6 g of benzo-1,2,3-thiadiazole-7-carboxylic acid chloride in 50 ml of acetonitrile, the temperature being maintained at between 5° C. and 15° C. The resulting beige suspension is stirred for a further hour in an ice-bath at 0° C. and subsequently overnight at room temperature. On the next day, it is cooled again to 0° C., brought to pH 4.5 using 15% hydrochloric acid, and extracted with ethyl acetate. The extracts are dried over sodium sulfate, filtered over silica gel and evaporated. This results in the title compound in a yield of 83.2% of theory and with a melting point of 72°-74° C.
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