To a stirred suspension of commercially available (10.0 g, 47 mmol) and triethylamine (14.4 mL, 0.10 mol) in dichloromethane (100 mL), diphosgene (3.0 mL, 25 mmol) was added dropwise at 0 °C and the mixture was stirred for 1 h at the same temperature. After concentration in vacuo, the residue was poured into water to precipitate crystals. The crystals were collected by filtration, successively washed with 10% HCl and H2O, and dried in vacuo at 50–60 °C for 3 h to afford 593a as colorless crystals (10.9 g, 97%).
