[O:1]=[C:2]1[N:6]2[CH2:7][CH2:8][CH2:9][CH:10]([C:11]([O:13][C:14]([CH3:17])([CH3:16])[CH3:15])=[O:12])[N:5]2[C:4](=[O:18])[CH2:3]1.[H-].[Na+].[C:21]([S:24][CH2:25]CBr)(=[O:23])[CH3:22]>CN(C)C=O>[C:21]([S:24][CH2:25][C:3]1([CH2:25][S:24][C:21](=[O:23])[CH3:22])[C:2](=[O:1])[N:6]2[CH2:7][CH2:8][CH2:9][CH:10]([C:11]([O:13][C:14]([CH3:15])([CH3:17])[CH3:16])=[O:12])[N:5]2[C:4]1=[O:18])(=[O:23])[CH3:22](c) A solution of 1.27 g of tert.butyl hexahydro-1,3-dioxo-1H-pyrazolo[1,2-a]pyridazine-5-carboxyate in 10 ml of dimethylformamide was added to a suspension of 0.4 g of sodium hydride in dimethyformamide. The mixture was stirred at room temperature until the evolution of gas had ceased. 1.86 g of S-bromoethyl thioacetate were added and the mixture was heated at 75° C. for 5 hours. Working-up in the same manner as described in paragraph (D) (a) earlier gave 0.15 g (7%) of tert.butyl 2,2- bis(acetylthiomethyl)-hexahydro-1,3-dioxo-1H-pyrazolo[1,2-a]pyridazine-5-carboxylate in the form of a white solid having a melting point of 85°-86° C. (from diethyl ether/hexane).
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