1: 100 percent / dicyclohexyl carbodiimide, dimethyl sulfoxide, pyridine, trifluoroacetic acid / benzene / 5 h / Ambient temperature 2: 1.) conc HCl, 2.) dicyclohexyl carbodiimide, dimethyl sulfoxide, pyridine, trifluoroacetic acid / 1.) methanol, reflux, 2 h; 2.) benzene, r.t., 5 h View Scheme