With the optimized conditions in hand we started to explore the scope of amino acids present on the urea. Carrying out the reaction on scope scale (0.3 mmol) using the model substrate afforded 4a in 76% yield. Simple glycine or alanine gave the corresponding alkynylated azapeptides 4b and 4c in good yields. Product 4b could be obtained in 97% yield on a 1 mmol scale. More sterically demanding valine only afforded 38% of 4d. Aromatic residues are tolerated in the reaction and good yields can be obtained for phenylalanine (2e) and tryptophan (2f). However, lower efficiency was observed with tyrosine (2g), probably due to the presence of an unprotected phenol. Methionine derived azapeptide (2h) could be alkynylated in 58% yield with no side reactivity of the sulfur atom with the hypervalent iodine reagent. 11 With serine, product 4i could be obtained in a moderate 29% yield. Amino acids bearing additional nitrogen atoms, such as protected lysine (2j) or asparagine (2k) were alkynylated selectively on the azaglycine affording 4j and 4k in 76% and 56% yields, respectively. Protected glutamic acid (2l) was well tolerated in the reaction. Finally, using a methyl carbamate protected azaglycine, we could access 4m in 60% yield. Replacing the protecting group with a bulkier tert-butyl carbamate (2n) led to a drop in yield. Scheme 2. Scope of amino acids. a a conditions: azapeptide 2a-n (1.0 equiv.), TIPS-EBX (3a) (1.0 equiv.), CuI (5 mol%), Cs2CO3 (1.5 equiv.), DCM (0.1 M), 40 °C, 1 h, reactions were carried out under air on a 0.3 mmol scale. Reaction was performed on 1 mmol scale.