Enamine–azide [2+3]-cycloaddition as a method to introduce functional groups into fluorescent dyes

摘要： Fluorescent dyes are a significant research tool with various applications in modern science. However, many experiments require the preparation of covalent dye conjugates, which is impossible without the presence of a functional group on the dye molecule. Unfortunately, the introduction of such groups is often a complicated task. Herein, we report a novel approach for the introduction of functional groups into fluorescent dyes, based on the [2+3]-cycloaddition reaction of 'terminal' enamines with azides. The synthesis of such 'terminal' enamines is carried out by the condensation of formamide acetals with a methyl group that is influenced by a strong electron withdrawing group. Thus, the proposed functionalization technique requires only the presence of a methyl group in the relevant position of the initial non-functionalized fluorescent dye.