Other copper(I) and copper(II) salts could also be used as the catalysts (entry 9 and 10). Notably, the use of less airsensitive copper(II) catalysts allowed the reaction to be set up under an air atmosphere affording 13 in a similar yield (entry 11). The copper(II) salts were expected to be reduced in situ by the organozinc reagents to form the active copper(I) catalysts. Moreover, the loading of the diazonium salts could be reduced while the desired product was formed in good yields (entry 12 and 13), although our later study revealed that unreacted alkyl iodides occasionally complicated the purification of difluoromethylated products. Therefore, 2.5 equiv. of 4a was used in the entire study to ensure the full consumption of the alkyl iodides. Finally, control experiments have shown that no desired products were formed in the absence of either the diazonium salt or the copper catalyst (entry 14 and 15). The alkyl iodide remained intact when the diazonium salt was omitted in the reaction, consistent with the argument that copper catalysts alone were not reactive toward unactivated alkyl iodides.