Synthesis of 2-Arylpyridines and 2-Arylbipyridines via Photoredox-Induced Meerwein Arylation with in Situ Diazotization of Anilines

International audienceWe report herein a sustainable method for the preparation of 2-arylpyridines through C-H arylation of pyridines using in situ formed diazonium salts (from commercially available aromatic amines) in the presence of a photoredox catalyst under blue light-emitting diode (LED) irradiation. The reaction is tolerant to a wide range of functional groups (e.g., halogen, nitrile, formyl, acetyl, ester). Applications to the C-H bond arylation of bipyridine ligands is also presented

Application of Palladium-Catalyzed C(sp(2))-H Bond Arylation to the Synthesis of Polycyclic (Hetero)Aromatics

International audienceRecently, the use of the palladium-catalyzed inter-and/or intra-molecular C-H bond arylations in the building of various π-extended (hetero)aromatic structures has emerged as a suitable alternative to the previous multi-steps synthesis. Such new methodology even allowed to prepare unprecedented π-extended molecules owing a perfect control of the reaction sites. This review gives an overview of various synthesis of Polycyclic Aromatic Hydrocarbons (PAHs) and PolyCyclic Heteroaromatics (PCHs) with planar, bowl-shaped, and helical structures prepared in high efficiency and selectivity via Pd-catalyzed C-H bond arylations

Synthesis of 2,2'-Bipyridines through Catalytic C-C Bond Formations from C-H Bonds

International audienceThe present review describes the homogenous catalytic methodologies for the synthesis of 2,2'-bipyridines involving C-C bond formation from C-H bond. There are three main approaches to build well-decorated 2,2'-bipyridines from C-H bond cleavage: i) the formation of C2-C2 ' bond by the dimerization of (activated) pyridines, ii) the C-H bond heteroarylation of activated pyridine, or iii) the late-stage functionalization of (activated) 2,2'-bipyridines including photoredox processes. Besides the scope and limitation of each methodologies, the relevant mechanisms of reaction are also discussed

Direct access to 2-(hetero)arylated pyridines from 6-substituted 2-bromopyridines via phosphine-free palladium-catalyzed C-H bond arylations: the importance of the C6 substituent

International audienceA phosphine-free palladium catalytic system was found to be very active to promote C-H bond activation/arylation of 5-membered ring heterocycles or electron-deficient arenes with 6-substituted 2-bromopyridines, providing a general, straightforward and environmentally benign synthetic approach to a broad variety of 2-(hetero)arylpyridines. The reactivity of 2-bromopyridines is strongly dependent on the substituent at the C6 position. Several C6 substituents such as Br, CF3, CH3, CHO, or morpholine have been employed. Moreover, the use of 2,6-dibromopyridine as the coupling partner allowed the synthesis in high yields of sym. and unsym. 2,6-di(hetero)arylpyridines, as well as 2-heteroarylpyridines after the C-Br bond cleavage

3‑Sulfonylindoles via Gold- or Silver-Catalyzed Cyclization1,3-Sulfonyl Migration Sequences under Visible Light Irradiation

A pathway for the synthesis of 3-sulfonylindoles has been devised. Upon blue LED irradiation, in the presence of a gold(I) or a silver(I) salt, ortho-alkynyl N-sulfonyl precursors readily undergo a 5-endo-dig cyclization concomitant with a 1,3-sulfonyl migration. While the gold-catalyzed reaction takes place in photocatalyst-free conditions, an iridium photocatalyst (Ir[dF(CF3)ppy]2(dtbbpy)PF6) is necessary with silver catalysis. Mechanistic studies featuring the generation of a sulfonyl radical support this dichotomy

Reactant-induced photoactivation of in situ generated organogold intermediates leading to alkynylated indoles via Csp2-Csp cross-coupling

International audienceAbstract Photosensitization of organogold intermediates is an emerging field in catalysis. In this context, an access to 2,3-disubstituted indoles from o -alkynyl aniline and iodoalkyne derivatives via a gold-catalyzed sequence under visible-light irradiation and in the absence of an exogenous photocatalyst was uncovered. A wide scope of the process is observed. Of note, 2-iodo-ynamides can be used as electrophiles in this cross-coupling reaction. The resulting N -alkynyl indoles lend themselves to post-functionalization affording valuable scaffolds, notably benzo[a]carbazoles. Mechanistic studies converge on the fact that a potassium sulfonyl amide generates emissive aggregates in the reaction medium. Static quenching of these aggregates by a vinylgold(I) intermediate yields to an excited state of the latter, which can react with an electrophile via oxidative addition and reductive elimination to forge the key C-C bond. This reactant-induced photoactivation of an organogold intermediate opens rich perspectives in the field of cross-coupling reactions