C−O Activation by a Rhodium Bis(N‐Heterocyclic Carbene) Catalyst: Aryl Carbamates as Arylating Reagents in Directed C−H Arylation

Abstract

Despite recent progress in the catalytic transformation of inert phenol derivatives as alternatives to aryl halides and triflates, attempts at the cross-coupling of inert phenol derivatives with the C-H bonds of arenes have met with limited success. Herein, we report the rhodium-catalyzed cross-coupling of aryl carbamates with arenes bearing a convertible directing group. The key to success is the use of an in situ generated rhodium bis(N-heterocyclic carbene) species as the catalyst, which can promote activation of the inert C(sp )-O bond in aryl carbamates.

A comprehensive overview of directing groups applied in metal-catalysed C–H functionalisation chemistry

“…Sparse examples of oxazolines as DGs are generally reported in papers mostly dealing with other DGs, but a few specific investigations have been recently published. Arylation with aryl halides or aryl carbamates was reported by Ackermann and Chatani using Ru, Co or Rh catalysis ( Scheme 160A–C ), 653 , 985 , 986 typically requiring preformed catalysts or the addition of a ligand to reach good results. An example of intramolecular alkylation leading to the formation of heterocycles was reported by Zhu ( Scheme 160D ).…”

B(C6F5)3‐Catalyzed Tandem Friedel‐Crafts and C−H/C−O Coupling Reactions of Dialkylanilines

“…It is worth noticing that the reported catalysts of the C−H/C−O couplings are quite different from those of FC reactions due to the difference of their reaction mechanisms and the specifity of the catalysts. Besides, comparing with the abundant achievements on metal‐catalyzed C−C bond formation, processes promoted by metal‐free catalyst are still rare and full of challenges…”

“…Many famous reactions have been developed for the C−C bond formation . Among them, C−H/C−O coupling and Friedel‐Crafts (FC) reactions are two effective strategies …”

“…Hence, the C−H/C−O coupling to produce C−C bond is full of challenges. Until now, effectively accessing this coupling reaction still requires metal‐based catalysts, such as compounds containing Ni, Fe, Co, Mn, Rh, Ir, or Pd . It is worth noticing that, besides the use of highly active metal‐based catalysts, some of these reported C−H/C−O coupling reactions also require pre‐active substrates, such as Grignard reagent, organolithium reagent, or organoboron compound …”

Single‐Electron‐Transfer‐Initiated Sequential Direct Arylation Reaction of Pyrrole with Aryl Diazonium Salts

“…[3] Over the past decade, the direct CÀ H arylation reaction of heteroarenes has gained much attention in the field of organic chemistry as it provides an alternative to the conventional cross-coupling-reaction-based methodologies. [4][5][6][7][8] In direct CÀ H arylation reactions, CÀ C bonds are generated by the coupling reaction between a (hetero)aryl CÀ H bond and a (hetero)aryl halide. These reactions offer several important benefits such as the need for fewer reaction steps and the generation of products without any stoichiometric metal wastes (Scheme 1a).…”