N,O-diacetyl tyrosine and 3-(4-hydroxy-phenyl)-propanoic acid were converted into phosphoramidite derivatives and introduced to the 5'-end of oligonucleotides. The resulting oligonucleotides exhibiting a 4-hydroxyphenyl alkyl group were conjugated with 4-phenyl-1,2,4-triazoline-3,5-dione as a model of a Y-Click reaction. The reaction is fast (< 1h) and efficient (> 90%). A partial side reaction occurred on the C8 position of deoxyguanosine in single-stranded oligonucleotides. This side reaction does not take place on the G quadruplex and double-stranded oligonucleotides and when N2 position of guanine is protected. This Y-Click reaction could be applied to 1,2,4-triazoline-3,5-dione derivatives displaying a fluorescent dye, a carbohydrate or orthogonal functions (alkyne, azide, ketone or maleimide) for the labelling of oligonucleotides.