methanesulfonyl chloride; triethylamine in dichloromethane 3 h; temperature < 15 deg C;

dipyridinium dichromate in dichloromethane 18 h;

Multi-step reaction with 2 steps 1: 1.) n-BuLi / 1.) THF, hexane, 1 h, -78 deg C, 2.a) THF, 2 h, -78 deg C, 2.b) 30 min, room temperature2: 41.6 percent / 0.2 N aq. HCl / dioxane / 90 h / Ambient temperature