Lightening Copper: Unleashing Radical Reactivity of Diazo Arylidene Succinimides to Enable One Step Synthesis of PMDI Core

Visible light promoted direct and convenient synthesis of pyromellitic diimides (PMDI) starting from vinyl diazo arylidene succinimides via copper catalysis has been achieved in one step. This novel and convenient transformation involves an unusual formation of carbon radicals directly from diazo arylidene succinimides instead of the traditional reactive carbene intermediate. This unprecedented and efficient copper-catalyzed chemoselective radical cyclization proceeds through the proton transfer (PT) followed by the electron transfer (ET) process. Notably, the choice of NaSCN along with the copper catalyst plays a pivotal role in this overall photoinduced transformation. Additionally, we have synthesized a known PMDI molecule in a single step, which displayed prominent aggregation-induced emission (AIE) properties. The protocol has been further extended for direct access to unsymmetrically substituted PMDI from two different diazo arylidene succinimides. A detailed controlled experiment, UV-visible spectroscopic as well as EPR studies have been performed to gain mechanistic insights into the reaction pathway.