Visible-light-mediated C3-ethoxycarbonylmethylation of imidazo[1,2-a]pyridines and convenient access to Zolpidem

Photocatalytic sequential C-H functionalization expediting acetoxymalonylation of imidazo heterocycles

The importance of functionalized imidazo heterocycles has often been featured in several impactful research both from academia and industry. Herein, we report a direct C-3 acetoxymalonylation of imidazo heterocycles using relay C-H functionalization enabled by organophotocatalysis starring zinc acetate in the triple role of an activator, ion scavenger as well as an acetylating reagent. The mechanistic investigation revealed a sequential sp² and sp³ C-H activation, followed by functionalization driven by zinc acetate coupled with the photocatalyst PTH. A variety of imidazo[1,2-a]pyridines and related heterocycles were explored as substrates along with several active methylene reagents, all generating the products with excellent yields and regioselectivity, thus confirming excellent functional group tolerability.

Recent Developments in the Photochemical Synthesis of Functionalized Imidazopyridines

Imidazopyridines constitute one of the most important scaffolds in medicinal chemistry, as their skeleton could be found in a myriad of biologically active molecules. Although numerous strategies were elaborated for imidazopyridine preparation in the 2010s, novel eco-compatible synthetic approaches have emerged, conscious of climate change concerns. In this framework, photochemical methods have been promoted to conceive this heterocyclic motif over the last decade. This review covers the recently published works on synthesizing highly functionalized imidazopyridines by light induction.

Visible-light-induced Direct 3-Ethoxycarbonylmethylation of 2-Aryl-2H-Indazoles in Water

A visible-light-driven Rhodamine B-catalyzed transition-metal-free 3-ethoxycarbonylmethylation of 2-aryl-2H-indazoles and imidazo[1,2-a]pyridines (40 examples) using commercially available α-bromoesters was realized in water. This protocol features sustainable, operational simplicity, mild reaction conditions, and...