[F:1][C:2]1[CH:14]=[CH:13][C:5]([C:6]([CH2:8][C:9]([O:11][CH3:12])=[O:10])=O)=[CH:4][CH:3]=1.C1(C)C=CC([S:21]([N:24]=[N+:25]=[N-])(=O)=O)=CC=1.C(N(CC)CC)C.COC1C=CC(P2(SP(C3C=CC(OC)=CC=3)(=S)S2)=S)=CC=1>O1CCCC1.O.C(#N)C>[F:1][C:2]1[CH:14]=[CH:13][C:5]([C:6]2[S:21][N:24]=[N:25][C:8]=2[C:9]([O:11][CH3:12])=[O:10])=[CH:4][CH:3]=1A mixture of methyl 4-fluorobenzoylacetate (3.92 g), p-toluenesulfonyl azide (4.00 g), triethylamine (2.02 g) and acetonitrile (30 ml) was stirred at 0° C. for 1 hr. The reaction mixture was poured into water and extracted with ethyl acetate. The organic layer was washed with saturated brine, dried over anhydrous magnesium sulfate and concentrated to give a yellow oil. The Lawesson's reagent (8.10 g) and tetrahydrofuran (50 ml) were added to this yellow oil and the mixture was heated under reflux for 16 hrs. The reaction mixture was concentrated, and the residue was purified by silica gel column chromatography to give methyl 5-(4-fluorophenyl)-1,2,3-thiadiazole-4-carboxylate (1.95 g, yield 41%) as colorless crystals from a fraction eluted with ethyl acetate-hexane (1:3, v/v).
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