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 (B2pin2) is ...found to be a crucial additive in the present reaction. The present methodology is also applicable to other heterocycles like imidazo2,1-bthiazole, benzodimidazo-2,1-bthiazole, and indole. The reaction possibly proceeds through a single electron transfer (SET) process.
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 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 spiroindeno1,2-bquinoxaline-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.
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-arylImidazo1,2-apyridine 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-arylImidazo1,2-apyridines published till August 2021.
We disclose a new general strategy for the site-selective difluoroalkylation of nonprefunctionalized heteroarenes, such as quinoxaline at the C-8 position, and benzothiadiazole, benzoxadiazole, and ...benzothiazole at the C-4 position via consecutive organophotoredox-catalyzed radical–radical cross-coupling and base-assisted hydrogen abstraction reactions. The current methodology represents a site-selective direct difluoroalkylative strategy to allow broad functional group tolerance and a wide substrate scope in good to excellent yields. Careful experimental investigations and detailed DFT calculations revealed the exact site-selectivity of the heteroarenes and a possible mechanistic pathway.
The synthesis of N-substituted indolo2,3-bquinoxalines has been developed through a Ru(II)-catalyzed ortho C–H functionalization of 2-arylquinoxalines with sulfonyl azides and further oxidation ...with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in one pot. This double C–N bond formation strategy provides a new efficient route for the preparation of a series of biologically relevant 6H-indolo2,3-bquinoxaline derivatives in up to 94% yield, suggesting a broad substrate scope applicability. The preliminary mechanistic studies reveal that the sequential C–N bond formations proceed through the formation of a five-membered ruthenacyclic intermediate in the first step and a radical mechanism in the second step.
A visible-light-promoted regioselective C(sp2)-H/C(sp3)-H cross-dehydrogenative coupling between 2 H-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 2 H-indazoles have been synthesized in moderate to good yields. Mechanistic studies suggest a radical pathway of the present reaction.
A visible light-mediated regioselective C3-ethoxycarbonylmethylation of imidazopyridines with ethyl diazoacetate (EDA) was achieved under mild reaction conditions. In contrast to the carbene ...precursors from α-diazoester a first C3-ethoxycarbonylmethylation of imidazopyridines
via
a radical intermediate has been established. The present methodology provides a concise route to access pharmacologically useful esters with wide functional group tolerance in high yields.
A visible-light-promoted regioselective ethoxycarbonylmethylation of imidazoheterocycles has been developed using an α-diazoester
via
a radical pathway.
A facile, efficient, and transition-metal-free chemodivergent C-3 functionalization of 2H-indazoles was developed under aerobic conditions using carboxylic acid and DMSO as the combined source of the ...carboxylic acid ester group and DMSO as the formylating agent. A series of formylated indazoles and carboxylic acid esters of indazole derivatives were produced in moderate to excellent yields. The mechanistic studies suggest that the reactions probably proceed through a radical pathway.
PDF