9-mesityl-10-methylacridinium perchlorate (Mes-Acr-Me+ClO4−) as a novel metal-free donor–acceptor (D–A) photocatalyst: visible-light-induced access to tetrahydrobenzo[b]pyran scaffolds through a single-electron transfer (SET) pathway

Abstract

A green radical synthetic approach for the production of tetrahydrobenzo[b]pyran scaffolds, which utilizes a Knoevenagel–Michael cyclocondensation reaction of aldehydes, malononitrile, and dimedone, has been devised. This innovative technique has been designed to achieve environmental sustainability. A novel single-electron transfer photocatalyst was employed for the synthesis in an aqueous ethanol solution under an air atmosphere at room temperature and stimulated with blue LED illumination serving as a renewable energy source. The objective of this undertaking is to cultivate a metal-free donor–acceptor (D–A) photocatalyst that is highly affordable and universally accessible. 9-Mesityl-10-methylacridinium perchlorate (Mes-Acr-Me⁺ClO₄⁻) is recognized for its expeditious and effortless applicability, high efficiency in yielding products, low energy consumption, and commendable eco-friendliness. This capability facilitates the investigation into the temporal alterations of environmental and chemical constituents. A research inquiry was conducted with the primary objective of determining the turnover number and turnover frequency associated with tetrahydrobenzo[b]pyran scaffolds. Furthermore, the attainment of cyclization at a gram-scale level offers substantiation for its feasibility as a viable solution for industrial implementation.