Peroxide-Free Pd(II)-Catalyzed Ortho Aroylation and Ortho Halogenation of Directing Arenes

Maleimide-Dependent Rh(III)-Catalyzed Site-Selective Mono and Dual C-H Functionalization of 2-Arylbenzo[d]thiazole and Oxazole Derivatives

The site-selective functionalization of aromatic compounds via C-H activation has emerged as a popular tool in organic synthesis. In this study, we report a regioselective coupling of maleimide to 2-arylbenzo[d]thiazoles in the presence of a rhodium(III) catalyst. Depending upon the nature of the substituent (R2-group) present in the maleimide substrate, either mono- or bis-1,4-addition products were observed in this methodology. In the case of R2 = aryl, cyclohexyl, and tert-butyl, mono coupling was observed, whereas substituents, such as methyl, ethyl, benzyl, and methyl thiophene, provided bis coupling as the major products. Similar selectivity was also observed in the case of 2-arylbenzo[d]oxazoles.

Transition-metal-catalyzed ortho C-H functionalization of 2-arylquinoxalines

Recently, direct C-H bond activation and functionalization has become a prodigious and hot topic among synthetic organic chemists due to its step-economic nature and substantial synthetic versatility. On the other hand, quinoxaline, a fused bicycle of benzene and pyrazine, has omnipresent applications in medicinal-, industrial- and materials chemistry. The presence of the N-1 atom in 2-arylquinoxaline enables chelation formation with a metal catalyst leading to the formation of ortho-substituted products. In this review, all articles related to the ortho C-H bond functionalization of 2-arylquinoxalines published up to May 2022 are highlighted.

Differential formation of nitrogen-centered radicals leading to unprecedented, regioselective bromination of N,N′-(1,2-phenylene)bisamides and 2-amidophenols

A highly efficient, site-selective, visible light-accelerated, remote C–H halogenation of unsymmetrical aromatic bisamides/amidoesters has been developed.

The palladium(ii)-catalyzed regioselective ortho-C-H bromination/iodination of arylacetamides with in situ generated imidic acid as the directing group: mechanistic exploration

In the present study, we report the palladium(ii)-catalyzed regioselective ortho-C-H bromination/iodination of challenging arylacetamide derivatives using N-halosuccinimides as halogenating agents. Diverse arylacetamides underwent the regioselective ortho-bromination and iodination of aromatic C-H bonds in the presence of a reactive benzylic C(sp3)-H bond without installing any bulky auxiliaries via unfavorable six-membered metallacycles. Weak coordination, the use of ubiquitous primary amides for challenging C-H functionalization, the simple catalytic system and the wide substrate scope are the key features of this transformation. Further, the halogenated amide derivatives were transformed into a variety of valuable synthons. Detailed mechanistic studies revealed some interesting aspects concerning the reaction pathway. We present for the first time strong evidence for the formation of imidic acid (in situ) from primary amides under Brønsted acid conditions that eventually aids in the stabilization of palladacycles of amide derivatives and drives regioselective C-X bond formation.

Transition metal catalysed C7 and ortho-selective halogenation of 2-arylbenzo[d]oxazoles

An approach to construct C–X bonds on the C7 or ortho-position of 2-arylbenzo[d]oxazoles by Rh and Ru catalysts has been reported.

Iron promoted C3–H nitration of 2H-indazole: direct access to 3-nitro-2H-indazoles

An efficient C3–H functionalization of indazole has been demonstrated. Notably, this method involves chelation-free radical C–H nitration on 2H-indazole. The radical mechanism was confirmed by control experiments and quantum chemical calculations. The synthetic utility has been proven by the synthesis of bio-relevant benzimidazoindazoles via reductive cyclization.

Synthesis of unsymmetrical multi-aroyl derivatives of ferrocene using palladium catalysed oxidative C–H aroylation

Palladium catalysed oxidative C–H aroylation of ferrocene: accessing the multi-aroyl derivatives of ferrocene.