Rhodium(II)‐Catalyzed C−H Bond Carboxylation of Heteroarenes with CO₂

Abstract

A method of RhII‐catalyzed C−H carboxylation of 2‐(imidazo[1,2‐a]pyridin‐2‐yl)phenols via CO2 fixation under redox‐neutral conditions was reported, providing an access to a range of coumarin derivatives. A suitable diphosphine ligand was crucial for this reaction. This reaction could be performed under relatively lower temperature or in a shorter time than the alternative base‐promoted protocol.

C−H Bond Carboxylation with Carbon Dioxide

“…Remarkably, the reaction occurs selectively on the less nucleophilic phenyl group through promotion by a phosphine ligand, which overrides the site selectivity dictated by the well‐known Kolbe–Schmitt‐type reaction. Later, they successfully applied this Rh II catalysis approach to similar types of substrate …”

Dirhodium: carbene transformations and beyond

“…This innovative strategy could also be extended to the aryl C–H carboxylation of 2-pyridylphenols and imidazo[1,2- a ]pyridine with good efficiency. 85…”

Cationic organotin cluster [t‐Bu2Sn(OH)(H2O)]22+2OTf−‐catalyzed one‐pot three‐component syntheses of 5‐substituted 1H‐tetrazoles and 2,4,6‐triarylpyridines in water

“…Substituted 2,4,6-triarylpyridines have been extensively exploited as chemosensors, [13] as photosensitizers [14] and as intermediates in the synthesis of therapeutic drugs, insecticides, herbicides and surfactants. [15] Consequently, various synthetic methods have been developed for the synthesis of 2,4,6-triarylpyridines, [16] such as the coupling of aryl aldehydes with aromatic keto-oxime acetates, [17] oxidative cleavage of C&bond;N bonds of benzyl amines with aromatic ketones [18] and the reactions of aromatic ketones with benzylamines, [19] acetophenoneoximes with aldehydes [20] or epoxy styrenes, [21] benzyl halides with acetophenones, [22] and chalcones with enaminones. [23] The cyclocondensation reaction of acetophenones, benzaldehydes and ammonium acetate is known as one of the most conventional pathways for the synthesis of 2,4,6-triarylpyridines in the presence of various catalysts such as PEG 1000 -DAIL, [24] ionic liquid, [25] PFPAT, [26] MIL-101-SO 3 H, [27] DPTA, [28] ZrOCl 2, [29] TiO 2 -SO 3 H, [30] TCT, [31] Fe 3 O 4 @TiO 2 @O 2 PO 2 (CH 2 ) 2 NHSO 3 H, [32] HClO 4 /SiO 2 [33] or without catalyst.…”