Abstract
Background: From an industries and academic perspective, there is a need for a method for producing 3-nitro-4-aryl-2H-chromen-2-ones from aryl alkynoate esters that is both economic and environmental benign. In this context, superoxide ion-assisted radical cascade reaction can be an efficient and greener protocol.
Objective: Herein, we have demonstrated an unprecedented methylene blue (MB) visible light photocatalysis for the production of a series of 3-nitro-4-aryl-2H-chromen-2-ones from readily available aryl alkynoate esters and a nitrating agent in solution.
Methods: Synthesis of 3-nitro-4-aryl-2H-chromen-2-ones has been performed in the presence of aryl alkynoate ester, TBAN, DIPEA, solvent, catalyst and molecular oxygen under visible light irradiation at room temperature. The products were purified by column chromatography using silica gel, and the mixture of ethyl acetate/petroleum ether as an eluting solvent and characterized by IR, NMR and mass spectroscopic analysis.
Results: A series of aryl alkynoate esters were successfully nitrated into corresponding 3-nitro-4- aryl-2H-chromen-2-ones with good isolated yields by this protocol, in which the key NO2-radicals formed by the action of superoxide ion (O2−·).
Conclusion: In contrast to the literature-reported methods of synthesis of 3-nitro-4-aryl-2Hchromen- 2-ones, the process described here for making 3-nitro-4-aryl-2H-chromen-2-ones uses methylene blue visible light photocatalysis, is inexpensive, mild, does not require a metal precursor or high temperatures, and is successful when using the direct sunlight.
