Metal carbenes play a pivotal role in transition-metal-catalyzed synthetic transfer reactions. The metal carbene is generated either from a diazo compound through facile extrusion of N2 with a metal catalyst or in situ generated from other sources like triazoles, pyriodotriazoles, sulfoxonium ylides and iodonium-ylide. On the other hand, Co(III), Rh(III) & Ir(III)-catalyzed C-H functionalizations have been well established as a key synthetic step to enable the construction of various synthetic transformations. Interestingly, in recent years, merging of these two concepts C-H activation and carbene migratory insertion gained much attention, in particular group 9 metal-catalyzed arene C-H functionalizations with carbene precursors via carbene migratory insertion. In this review, we summarize recent advances in Co(III), Rh(III) & Ir(III)-catalyzed direct C-H alkylation/alkenylation/arylation with carbene precursors and also discuss key synthetic intermediates within the catalytic cycles.

Co(III), Rh(III) & Ir(III)-Catalyzed Direct C-H Alkylation/Alkenylation/Arylation with Carbene Precursors.

The past decade has witnessed tremendous developments in transition-metal-catalyzed C-H bond activation and subsequent carbene migratory insertion reactions, thus assisting in the construction of diverse arene/heteroarene scaffolds. Various transition-metal catalysts serve this purpose and provide efficient pathways for an easy access to substituted heterocycles. A brief introduction to metal-carbenes has been provided along with key mechanistic pathways underlying the coupling reactions. The purpose of this review is to provide a concise knowledge about diverse directing group-assisted coupling of varied arenes/heteroarenes and acceptor-acceptor/donor-acceptor diazo compounds. The review also highlights the synthesis of various carbocycles and fused heterocycles through diazo insertion pathways, via C-C, C-N and C-O bond forming reactions. The mechanism usually involves a C-H activation process, followed by diazo insertion leading to subsequent coupling.

Transition-Metal-Catalyzed C-H Bond Functionalization of Arenes/Heteroarenes via Tandem C-H Activation and Subsequent Carbene Migratory Insertion Strategy

The diazo quinone or quinone diazide class of compounds has been extensively utilised to introduce phenol/naphthol moieties into hydrocarbons or nitrogen-containing heterocycles under transition metal catalysis. The reactions proceed via C–H insertion or migratory insertion of metal carbenes. In many cases, the site-selectivities were obtained via the guidance of directing groups. Various rearrangement reactions were explored with the metal carbenes generated from these diazo compounds. Further, interesting asymmetric reactions were studied to obtain phenol/naphthol containing compounds having stereogenic centers or axial chirality with high enantioselectivity. In this review, the recent progress on synthetic studies of metal carbenes generated from quinone diazide moieties has been summarized.

Recent quinone diazide based transformations via metal–carbene formation

Privileged biaryl frameworks, BINOL and NOBIN, were efficiently constructed with sole 1-DNQs as arylation reagents under one set of reaction conditions. The judicious selection of palladium catalytic system plays a pivotal role in the excellent selectivities. This transformation accommodated fairly broad substrate generality for both 2-naphthol and N-Boc-2-naphthylamine and afforded the structurally diversified BINOLs and NOBIN derivatives in high efficiency. Notably, the bromo substituent which cannot be survived in conventional palladium catalyzed reactions were well-compatible with this set of conditions, providing an effective handle for further enriching the library of BINOLs and NOBINs. Preliminary attempts on the asymmetric variant of this reaction were also performed with up to 80:20 er for BINOLs synthesis.

https://link.springer.com/content/pdf/10.1007/s11426-021-1003-9.pdf

Synthesis of structurally diversified BINOLs and NOBINs via palladium-catalyzed C-H arylation with diazoquinones

Looking deep into C-H functionalization: the synthesis and application of cyclopentadienyl and related metal catalysts.

Ir(iii)-Catalyzed direct C-H functionalization of N-phenylacetamide with α-diazo quinones: a novel strategy for producing 2-hydroxy-2'-amino-1,2'-biaryl scaffolds.

Xingjun Li

Papers

Ir(iii)-Catalyzed direct C-H functionalization of N-phenylacetamide with α-diazo quinones: a novel strategy for producing 2-hydroxy-2'-amino-1,2'-biaryl scaffolds.