Picci, Giacomo, Milia, Jessica, Lippolis, Vito, Carlo Ricci, Pier, Frontera, Antonio, Gomila, Rosa M., Ojah, Emmanuel O., De Silva Weerakonda Arachchige, Randima D., Orton, James, Coles, Simon J., Busschaert, Nathalie and Caltagirone, Claudia (2026) Synthesis of a highly fluorescent quinoxalino[2,3-b]quinoxaline polycyclic derivative via intramolecular michael addition to a squaramide ring. Journal of Organic Chemistry, 91 (10), 3751-3758. (doi:10.1021/acs.joc.5c03075).
Abstract
In the presence of TBAOH, bis-indolylsquaramide (1) converts into the highly emissive, novel bis(3H-pyrrolo[1,2,3-de]quinoxaline) exa-cyclic derivative 2. This compound was fully characterized in solution and the solid state, with emission properties supported by DFT calculations. Derivative 2 exhibits high quantum yield in solution with aggregation-induced quenching, and a large spectral shift between solid state and solution. Reaction conditions were optimized, and a mechanism involving a double intramolecular Michael addition triggered by deprotonation, oxidation and photodecarbonylation was proposed on the basis of DFT calculations and LC-MS measurements. In addition to reporting a novel, highly π-conjugated emissive compound, this manuscript highlights an unprecedented squaramide reactivity under basic conditions, resulting in the first example of intramolecular quinoxaline moiety formation from a squaramide derivative.
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