Visible light promoted oxygenation of oxazolidinones by an anthraquinone-resorcinol based donor-acceptor polymer as a heterogeneous photocatalyst

Abstract

Direct conversion of 2-oxazolidinone into a high-value-added product, oxazolidine-2,4-dione, is a desired goal for medicinal chemistry. This transformation can be achieved by C(sp³)-H bond activation of 2-oxazolidinone. Heterogeneous photocatalysis has been established as a promising strategy for enabling C(sp³)-H bond activation of diversified molecules. The active species generated in the photocatalytic reaction system under mild conditions activate the inert C–H bond in 2-oxazolidinone and promote chemical conversion. Herein, we have employed anthraquinone-resorcinol based donor-acceptor (D-A) heterogeneous polymer (ACP) as an active photocatalyst for C(sp³)-H bond activation. ACP, a metal-free semiconductor that mediates various photocatalytic reactions. Upon light irradiation, ACP functions as a photo-base and enables proton-coupled electron transfer (PCET). Upon excitation, the electron on the quinone moiety abstracts a proton from the substrate, while the hole on the resorcinol unit accepts an electron simultaneously. Thus, the PCET from substrate to catalyst selectively cleaves the C(sp³)-H bond of oxazolidine-2-ones, with the resulting radical species being trapped by molecular oxygen (O₂). This reaction affords the synthesis of a wide range of 1,3-oxazolidine-2,4-dione derivatives. The mechanistic study of 2-oxazolidinones conversion into 1,3-oxazolidine-2,4-diones derivatives is supported by DFT calculations. ACP can generate the singlet state (¹O₂) through an energy transfer (ET) process. However, experimental results and DFT calculations indicate that the transformation predominantly proceeds through the PCET pathway rather than via ET, or photoinduced electron transfer (PET) pathways.