[N:1]1[CH:6]=[CH:5][C:4]([CH2:7][C:8]([C:10]2[CH:15]=[CH:14][C:13]([Cl:16])=[CH:12][CH:11]=2)=[O:9])=[CH:3][CH:2]=1.BrCBr.[C:20](=[S:22])=[S:21].[C:23](=O)([O-])[O-].[K+].[K+]>CC(C)=O>[Cl:16][C:13]1[CH:12]=[CH:11][C:10]([C:8](=[O:9])[C:7](=[C:20]2[S:22][CH2:23][S:21]2)[C:4]2[CH:5]=[CH:6][N:1]=[CH:2][CH:3]=2)=[CH:15][CH:14]=1To a solution of 2-(4-pyridyl)-1-(4-chlorophenyl)ethanone (70.0 g, 0.3 mol) prepared in a similar manner as the compound of Step 1 of Example A-19, dibromomethane (200 mL) and carbon disulfide (25.9 g, 0.34 mol) in acetone (800 mL) was added potassium carbonate (83.0 g, 0.6 mol). The reaction mixture was stirred at room temperature for 24 hours. An additional two equivalents of potassium carbonate and one equivalent of carbon disulfide was added and the stirring was continued for another 24 hours. Solvent was removed and the residue was partitioned between dichloromethane and water. The organic layer was washed with brine, dried over magnesium sulfate and filtered. The filtrate was concentrated and the crude was stirred with 1000 mL of a mixture of ethyl acetate and ether (1:9) to give 78.4 g of pure product, 1-(4-chlorophenyl)-2-(1,3-dithietan-2-ylidene)-2-(4-pyridinyl)ethanone, as a yellow solid (82%), mp: 177-179° C. Anal. Calc'd. for C15H10ClNOS2: C, 56.33; H, 3.15; N, 4.38. Found: C, 55.80; H, 2.84; N, 4.59.
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