trifluoroacetic acid in dichloromethane T=20°C; 1 h;

1: 1) N-methylmorpholine, iBuOCOCl / 1) THF, below -15 deg C, 2) THF, -20 deg C to -15 deg C, 30 min, r.t., 1 h 2: aq. HCl / dioxane / 0.5 h / Ambient temperature View Scheme