Water → 3-[(5-Chloro-1,3-benzodithiol-2-ylidene)amino]butanoic acid, ethyl ester

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A solution of 5-chloro-N-methyl-N-phenyl-1,3-benzodithiol-2-iminium iodide (12.59g), 4-aminobutanoic acid, ethyl ester, hydrochloride (5.02g), and anhydrous sodium carbonate (3.18g) in 300 ml of anhydrous dimethylformamide is heated at 120° C under nitrogen for three hours. The reaction mixture is poured into water (1000 ml) and extracted with three 200 ml portions of benzene. The combined benzene extracts are washed with water and brine, dried over sodium sulfate, and concentrated in vacuo. The resultant crude product is chromatographed on silica gel (1000 ml) eluting with 1) pentane (1000 ml), 2) pentane/dichlormethane (1:1, 4000 ml) and 3) dichloromethane (9000 ml). The fractions containing product with Rf =0.4 (silica gel, 1% ethyl acetate/dichloromethane) are concentrated in vacuo. The resultant solid is recrystallized from pentance to yield 3.02g of the title compound, melting point 60°-61° C.

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