A mild and efficient method for the direct difluoromethylenephosphonation of imidazopyridines has been developed using rose bengal (RB) as a photoredox catalyst. Bis(pinacolato)diboron (B 2 pin 2 ) is found to be a crucial additive in the present reaction. The present methodology is also applicable to other heterocycles like imidazo[2,1-b]thiazole, benzo [d]imidazo-[2,1-b]thiazole, and indole. The reaction possibly proceeds through a single electron transfer (SET) process.

A Ru(II)-catalyzed facile and controllable protocol for C−H alkylation and spirocyclization of 2-arylquinoxalines with maleimides has been achieved under ambient air in high yields. Sequential ortho-C−H activation and C-annulation results in the formation of diverse polyheterocycles containing spiro[indeno[1,2b]quinoxaline-11,3′-pyrrolidine]-2′,5′-diones, which are of potent interest in medicinal chemistry. Mechanistic investigations suggest a reversible cleavage of the ortho-C−H bond in the turnover-limiting step.

A visible-light-promoted regioselective C­(sp2)–H/C­(sp3)–H cross-dehydrogenative coupling between 2H-indazoles and ethers has been achieved using a catalytic amount of rose bengal as an organophotoredox-catalyst and tert-butyl hydroperoxide (TBHP) as an oxidant at ambient temperature under aerobic conditions. A variety of C-3 oxyalkylated 2H-indazoles have been synthesized in moderate to good yields. Mechanistic studies suggest a radical pathway of the present reaction.

A new iodine(III)-mediated oxidative dearomatization of 2H-indazoles has been developed to afford N-1 indazolyl indazolones. In this methodology, PIFA shows duo character: as an oxidant as well as a carbonyl...

C−H activation and functionalization is quite promising in recent days as the strategy offers a go‐to general method for different bond formations and hence grants synthetic versatility. At the same time, imidazopyridine, a fused bicycle of imidazole moiety with pyridine ring, has a profound impact due to its ubiquitous and prodigious application in medicinal as well as material chemistry. The presence of N‐1 atom in 2‐arylImidazo[1,2‐a]pyridine facilitates the coordination with metal catalysts leading to the formation of ortho‐substituted products. This review summarizes all the articles on ortho C−H functionalization of 2‐arylImidazo[1,2‐a]pyridines published till August 2021.