m-Chloroperbenzoic acid → 7-Chloro-6-fluoro-isoquinoline 2-oxide

50 g of 7-chloro-6-fluoro-isoquinoline (prepared according to WO 2007/012422) were dissolved in dichloromethane and cooled to 5° C. 69.6 g of m-chloro-perbenzoic acid (70%) were added portionwise. The mixture was stirred at room temperature. When conversion was complete, the mixture was diluted with 1.5 L of dichloromethane and washed three times with saturated sodium bicarbonate solution. The organic layer was dried over sodium sulphate and evaporated to dryness to give 47.6 g of the desired product 9. Rt=0.98 min (Method 5). Detected mass: 198.1 (M+H+).