(MeCN)4CuBF4 to the peptide resin as a dry powder, immediately followed by addition of the TFA cleavage cocktail and incubation at rt for 3 h (Figure ). Again, standard ether precipitation and air drying afforded the crude DBCO peptide 1a. Incubation of 1a with 6-azidohexanoic acid demonstrated a successful SPAAC (Figures and).