Visible-Light-Induced Functionalization of Oxindole Enol Ethers via EDA Complex Photoactivation

Abstract

Light-mediated reactions offer a powerful platform for exploring chemical reactivity through controlled photoexcitation. This project focuses on advancing photoinduced reactions via electron donor-acceptor (EDA) complex activation, where interactions between an electron-rich donor and an electron-deficient acceptor generate reactive radicals under visible-light irradiation. Crucially, this approach operates without external catalysts—such as traditional metal-based photocatalysts—or sacrificial additives, enhancing synthetic efficiency. Central to our study is the functionalization of oxindoles, a privileged scaffold in medicinal chemistry due to the potent bioactivity of its derivatives. To achieve this, we designed and synthesized an oxindole-derived enol ether (donor 1) and paired it with Katritzky salts (acceptors 3 and 4) as complementary EDA complex partners. UV-visible spectroscopy confirmed EDA complex formation through the characteristic charge-transfer band (CT), while also identifying the optimal irradiation wavelength to maximize product formation and minimize byproduct generation. These findings establish a foundation for developing a mild, efficient, and catalyst-free methodology for oxindole functionalization. Future work will expand the scope of this reactivity and refine reaction conditions to enhance synthetic utility.