Synthesis
Step 3: 2-(carboxymethoxy)-4-chlorobenzoic acid (11.5 g, 50 mmol) obtained from step 2 was dissolved in acetic anhydride (100 ml) and anhydrous sodium acetate (10.0 g, excess) was added. The reaction mixture was heated to 150 °C and maintained for 4 hours. During the reaction, the color of the mixture changed to deep red. Upon completion of the reaction, the mixture was cooled to room temperature and quenched carefully with ice-cold water. The resulting red solid was collected by filtration and washed well with water. The washed red solid was suspended in 1N HCl and refluxed for 2 hours. After the reaction, 6-chlorobenzofuran-3(2H)-one precipitated from the mixture as a deep red solid. The product was isolated by filtration, washed well with water and dried at 40 °C and used in subsequent steps without further purification. Yield: 5.8 g (69%); MS data: (M + H): 169.
References
[1] Patent: US2009/54454, 2009, A1. Location in patent: Page/Page column 22
[2] Patent: WO2004/99191, 2004, A2. Location in patent: Page 49
[3] Patent: US2005/4162, 2005, A1. Location in patent: Page/Page column 12
