1: With Ellman resin; toluene-4-sulfonic acid in dichloromethane T=20°C; 72 h; 2: With hexamethyl-distannane in benzene T=80°C; 20 h; UV-irradiation; 3: With toluene-4-sulfonic acid in methanol; dichloromethane T=20°C; 10 h; Further stages.;