For the preparation of 4 both reagents (3 and Kryptofix 22) were dissolved in fresh anhydrous toluene in separate round-bottom flasks and sonicated until dissolved. Both were added via syringe to a third round-bottom flask filled with more anhydrous toluene cooled by means of an ice bath. The speed of addition was not important for this reaction as both slow addition over 1 h by means of a syringe pump and fast addition over 1 minute gave roughly equivalent yields. The reaction was complete after 1 h at room temperature and did not require overnight stirring as described in some literature reports. Compound 5 was obtained by refluxing 4 in BH3 . THF overnight and was used without further purification. Reduction of the nitro group of 5 was achieved by using fine zinc dust instead of powder, giving K222-NH2 after purification on a C18 cartridge. FSO2N3 was prepared as described in the literature and reacted with K222-NH2 to form K222-N3 after purification by column chromatography on silica. NHS-ester activated dibenzocyclooctyne (DBCO-NHS) was reacted with K222-NH2, forming K222-DBCO as evidenced by LC-MS. This compound was then utilised further without purification.