water; trifluoroacetic acid in dichloromethane T=20°C; 10.5 h;

Multi-step reaction with 2 steps 1: 88 percent / MeSO2Cl, Et3N / benzene / 12 h / 20 °C2: 2) t-BuOK / 1) THF, 50 deg C, 12 h; 2) THF, -78 deg C, 0.5 h