Photo-induced C–H bond activation of N,N′-dialkylethylenediamine upon aza-Michael addition to 1,8-pyrenedione: facile synthesis of fluorescent pyrene derivatives
We discovered a reaction between 1,8-pyrenedione and N,N′-dialkylethylenediamine to form highly fluorescent products, via aza-Michael addition followed by double C–H activation facilitated by visible light. Remarkably, the reaction intermediates and mono C–H bond activation product could only be formed when the reaction was carried out in the presence of a base and UV-light (254 nm). Dehydrogenation of the intermediate under room lighting converts it to the final products. The reaction is a general one as it works with a number of ethyleneamines with different substituents with a (N)–CHn (n = 1, 2) linkage. The reaction mechanisms suggested that nucleophilic addition of the amine followed by dehydrogenation occurs to restore aromaticity and give an amine substituted 1,8-pyrenedione intermediate. The C–H activation requires photoexcitation via a radical mechanism. Our work opens a new avenue for the construction of novel molecules with a pyrene core as a fluorophore with good quantum yields.