Ethyl 5-(p-chlorobenzoyl)-3-ethoxycarbonyl-4-hydroxy-1-methylpyrrole-2-acetate (537 mg, 1.37 mmole) is added to a suspension of 70 mg of 50% sodium hydride (1.46 mmole prewashed with hexanes) in 5 ml of dry dimethylformamide (DMF) under nitrogen. After gas ceased to evolve, 150 μl of dimethylsulfate (1.57 mmole) is added all at once. The resulting yellow-orange solution is stirred for an additional 10 minutes before it is poured into 100 ml of water to precipitate the crude product. The mixture is stirred well followed by filtration. The collected residue is washed with water and dried in vacuo to afford 505 mg of crude ethyl-5-(p-chlorobenzoyl)-3-ethoxycarbonyl-4-methoxy-1-methylpyrrole-2-acetate.
