Thionyl Chloride → 3-Chlorothiophene-2-carbonyl chloride

Excess thionyl chloride (3.5 ml, 48.0 mmoles) was added to 0.85 g (5.2 mmoles) of 3-Chloro-2-thiophenecarboxylic acid (prepared according to Corral, C., et al., Heterocycles 23:1431 (1985)) dissolved in 50 ml of toluene and stirring at room temperature. After addition the solution was refluxed for 3 hours to form 3-chloro-2-thiophenecarbonyl chloride. Concentration of the reaction solution gave the acid chloride as a white solid. The acid chloride was then dissolved in 4 ml of N,N-dimethylformamide and slowly added to a cooled (ice/water bath) stirring solution of 5-chloro-2-oxindole-1-carboxamide (1.0 g, 4.71 mmoles) and 4-(N,N-dimethylamino)pyridine (1.3 g, 10.5 mmoles) in 10 ml of N,N-dimethylformamide. After 45 minutes the solution was allowed to warm to room temperature and after 2 hours was worked-up by pouring into a mixed ice/6 N hydrochloric acid solution. A yellow precipitate formed. The precipitate was filtered, washed with water and dried to give 1.3 g of impure product as a yellow solid. Recrystallization with acetic acid/heptane (2:1) gave 0.77 g (2.2 mmoles) of pure title compound as yellow needles, m.p. 222-224° C. Total yield of product was 42%.