Red-Light Driven Supramolecular Photocatalysis: Functionalization of Photoinert N-Propargyl amides to Substituted oxazole

Chelation-assisted photoactivation of inert organic molecules using the long-wavelength red light (620-750 nm) becomes a new synthetic avenue than the widely applied blue light as the photo-stimulated source due to its superior penetration depth. Herein, we have demonstrated a mechanistic model of a solid-state electron catalytic reaction to account for the reactivity of potassium tert-butoxide (KOtBu), providing the potassium ions as the chelate cations to the synthesis of 2,5-disubstituted oxazoles from 2-halo N-propargyl benzamide under the irradiation of red light (620-750 nm) at ambient conditions. Potassium tert-butoxide (KOtBu) has been utilized to form a 6-member chelate (2nd order inner metallic complex) complex between K+-ion and N-propargyl benzamide characterized by fluorescence and mass spectroscopy to generate a bright yellow-colored charge transfer complex. This in-situ generated charge transfer (CT) complex is believed to be the initiator of this electron catalysis and, further, in the presence of red light, splits into a radical anion and a radical, which eventually cyclizes to form the desired oxazole. We utilized HRMS to detect the chelate complex, UV-Vis, and PL enhancement experiment to provide support towards the CT complex formation. Again, EPR analysis supported the single electron transfer (SET) mechanism involved in this chemical transformation.