Organic-Dye-Catalyzed Visible-Light-Mediated Regioselective C-3 Alkoxycarbonylation of Imidazopyridines by Carbazates

Abstract

A mild and eco-friendly visible-light-mediated regioselective C–H alkoxycarbonylation of imidazo­[1,2-a]­pyridine heterocycles using rose bengal as a photoredox catalyst at room temperature has been developed. Biologically important alkoxycarboxylated imidazo­[1,2-a]­pyridines at the C-3 position as well as coumarins and quinoxalin-2­(1H)-ones have been prepared. The present approach has the advantage of having a user- and eco-friendly catalyst, a carbonyl source, as well as extremely mild conditions for direct and regioselective C–H alkoxycarbonylation mediated by visible light as a green energy source.

Oxidative Cross-Dehydrogenative C–H Bond Amination of Imidazo[1,2-a]pyridines in Aqueous Media under Metal-Free Conditions

“…11b In 2019, Aiwen Lei and group reported electrochemical intramolecular cross-dehydrogenative C–H/N–H bond coupling of imidazo[1,2- a ]pyridines (Scheme 1c ). 11c In continuation of our work 12 on the C-3 functionalization of imidazopyridine, in this report we disclose a metal-free, straightforward, selective oxidative C–H/N–H cross-dehydrogenative coupling of imidazoheterocycles in aqueous environments.…”

Photoinduced Regioselective Chalcogenation and Thiocyanation of 4H‐Pyrido[1,2‐a] pyrimidin‐4‐ones Under Benign Conditions

“…Of late, visible light mediated techniques for catalytic CÀ H functionalization of heterocycles have evolved and found extremely beneficial for late-stage functionalization of pharmaceutically significant drug relevant scaffolds. [16] In continuation of our work [17] on CÀ H functionaliza- tion and visible light mediated reaction, herein we described extremely mild procedure using visible light as an inducer, for the regioselective selenylation, sulfenylation and thiocyanation of 4H-pyrido[1,2-a] pyrimidin-4-ones.…”

Visible Light Assisted Direct C3–H Arylation of Pyrido[1,2-a]pyrimidin-4-ones and Thiazolo[3,2-a]pyrimidin-5-ones

“…Moreover, the susceptible nature of the pyrido­[1,2- a ]­pyrimidin-4-one framework to the harsh conditions results in decomposition or thermal rearrangement of the main skeletal structure, which is the deterring factor for suitable derivatization of this class of scaffold. , Consequently, to meet the demand of C3 arylated pyrido­[1,2- a ]­pyrimidin-4-one derivatives to enhance the drug discovery process, development of transition-metal-free, convergent, mild, and efficient methods for direct C3 arylation of 4 H -pyrido­[1,2- a ]­pyrimidin-4-one is highly essential. Recently, visible light promoted photo redox catalysis has been developed as a powerful synthetic tool and attracted significant interest from the synthetic community for a wide range of synthetic transformations under mild conditions. , In continuation of our efforts on development of novel methods via visible light mediated, metal-free, organic-dye photoredox catalysis for synthesis of biologically important heterocyclic compounds, herein we reveal the visible light promoted, eosin-Y catalyzed, direct C3–H arylation of 4 H -pyrido­[1,2- a ]­pyrimidin-4-one under very mild conditions (Scheme e).…”