Visible light-induced C3-carbamoylation of quinoxalinones via the formation of intermolecular EDA complex

Patra, Shefali (2022) Visible light-induced C3-carbamoylation of quinoxalinones via the formation of intermolecular EDA complex. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Shefali Patra (17MS027)) 17MS027_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

Quinoxalin-2(1H)-ones are privileged structures given their diverse pharmacological properties and various applications in chemical industries. As such, the functionalization of quinoxalinones, particularly at the C3-position, has attracted considerable interest to generate a repertoire of derivatives with various applications. However, despite its numerous uses, methods to access the carbamoylated quinoxalinone scaffold are scarce. Moreover, existing protocols require transition metals, additives and/or high temperatures. In this work, a novel visible light-mediated, photocatalyst-free direct C–H carbamoylation using oxamic acids has been developed using the concept of electron donor-acceptor (EDA) complex photochemistry. At room temperature and without any additive, a range of oxamic acids was found to couple well with quinoxalinones generating 42 examples, including 18 new compounds, in yields up to 85%. Starting materials were prepared using simple reported procedures, followed by optimization studies that ascertained irradiation of the model reaction mixture with 390 nm light using 4:1 v/v DCE-H2O solvent as the ideal conditions. Following the examination of the substrate scope, mechanistic studies were carried out. UV-Visible absorbance spectra strongly indicated the formation of an EDA complex with an optimal binding stoichiometry of 1:1, and radical trapping experiments supported the idea of a radical-mediated pathway. Two probable mechanisms mediated by an EDA complex between the quinoxalinones and the oxamic acid were proposed. This is the first report of a direct C3-carbamoylation protocol for quinoxalinones using visible light as the energy source without any additive, unlike previously reported methods.

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