Rhodium-catalyzed regioselective C-H functionalization via decarbonylation of acid chlorides and C-H bond activation under phosphine-free conditions

Efficient rhodium(I)-catalyzed regioselective functionalization of aromatic C-H bonds has been realized with acid chlorides as the coupling partners via decarbonylation and C-H activation under phosphine-free conditions.     

Pd-catalyzed selective addition of heteroaromatic C-H bonds to C-C triple bonds under mild conditions

Simple heteroarenes such as pyrroles and indoles undergo addition reactions to C-C triple bonds in the presence of a catalytic amount of Pd(OAc)(2) under very mild conditions, affording cis-heteroarylalkenes in most cases. The cleavage of aromatic C-H bonds is the possible rate-determining step in CH(2)Cl(2), and the addition of heteroaromatic C-H bonds to C-C triple bonds is in a trans-fashion.     

Rhodium-catalyzed selective C-H activation/olefination of phenol carbamates

Rh(III)-catalyzed ortho C-H activation/olefination of phenol carbamates has been developed. High regioselectivity is observed with a range of phenol carbamates enabling efficient coupling with acrylates and styrenes. This reaction exhibits different reactivity as compared to the Pd-catalyzed ortho-arylation reaction of phenol esters and provides a new approach for the synthesis of ortho-substituted phenols.     

Rhodium-catalyzed direct C-H addition of 4,4-dimethyl-2-oxazoline to alkenes

A new method for the preparation of 2-substituted oxazolines by rhodium-catalyzed coupling of alkenes with 4,4-dimethyl-2-oxazoline is reported. The oxazoline products are obtained in good yield with excellent selectivity for the linear product. A variety of alkene substitution patterns and functional groups are tolerated. This procedure represents an attractive alternative to hydroesterification because it does not involve the manipulation of CO gas.     

Rhodium-catalyzed selective olefination of arene esters via C-H bond activation

A new catalytic procedure of ortho-olefination of benzoates and benzaldehydes has been developed. Ester and carboxaldehyde units were revealed to be effective chelating groups in focusing the activation of aryl C-H bonds ortho to the directing moieties under the Rh-catalyzed oxidative conditions. The reaction is highly regioselective with a range of benzoates and benzaldehydes enabling the efficient olefination with acrylates, acrylic acid, and styrenes.     

Towards mild metal-catalyzed C-H bond activation

Functionalizing traditionally inert carbon-hydrogen bonds represents a powerful transformation in organic synthesis, providing new entries to valuable structural motifs and improving the overall synthetic efficiency. C-H bond activation, however, often necessitates harsh reaction conditions that result in functional group incompatibilities and limited substrate scope. An understanding of the reaction mechanism and rational design of experimental conditions have led to significant improvement in both selectivity and applicability. This critical review summarizes and discusses endeavours towards the development of mild C-H activation methods and wishes to trigger more research towards this goal. In addition, we examine select examples in complex natural product synthesis to demonstrate the synthetic utility of mild C-H functionalization (84 references).     

Palladium-catalyzed direct olefination of urea derivatives with n-butyl acrylate by C-H bond activation under mild reaction conditions

Pd(II)-catalyzed aromatic C-H bond activation using urea as a directing group was achieved in a p-TsOH/AcOH medium under mild reaction conditions. The direct olefination products of various urea derivatives were produced from aryl urea derivatives and butyl acrylate in moderate to good yields.     

Rhodium-catalyzed alkylation of aromatic azines with alkenes via C-H bond activation

The aromatic azines reacted with terminal alkenes under a rhodium catalyst [RhCl(coe)₂]₂ and Cy₃P to give the alkylated products with good to high isolated yields. The azines bearing H and o-CH₃, p-CH₃ and p-CH₃O groups have high reactivities, but m-CH₃O, p-Cl, p-F exhibit low reactivities.     

Rhodium-catalyzed alkylation of terephthaldialdimine with terminal alkenes via C-H bond activation

Terephthaldialdimine 1a reacted with alkenes to give 2,6-dialkylated products selectively in moderate to high isolated yields. In the case of terephthaldialdimine 1b having a substituent at site 2 in the phenyl ring, the alkylation takes place selectively at site 6 in the phenyl ring. In this alkylation, a meta-substituent affected the reactivity significantly because of the steric hindrance.     

C-H activation and palladium migration within Biaryls under Heck reaction conditions

[reaction: see text] Biaryl bromides such as 1 (R=NO(2), H, OMe) undergo the Heck reaction to give both the expected products 3 ("retention") as well as "crossover" products 4 derived from a migration of Pd and net transfer of reactivity from one aryl ring to the other. Under the conditions used, crossover is increasingly favored when electron-deficient arenes are involved. Crossover products derived from transfer onto the pyridine ring have also been observed.     

The diorgano dichalcogenides addition to benzyne under mild conditions

The reaction between diorgano dichalcogenides and o-(trimethylsilyl)phenyl triflate in the presence of CsF at room temperature produced o-bis(organochalcogenide)benzenes in moderate to good yields.     

Rhodium-catalyzed asymmetric conjugate addition of arylboronic acids to nitroalkenes using olefin-sulfoxide ligands

An efficient rhodium/olefin-sulfoxide catalyzed asymmetric conjugate addition of organoboronic acids to a variety of nitroalkenes has been developed, where 2-methoxy-1-naphthyl sulfinyl functionalized olefin ligands have shown to be highly effective and are applicable to a broad scope of aryl, alkyl, and heteroaryl nitroalkenes.     

Rhodium-catalyzed enantioselective conjugate addition of organoboronic acids to alpha,beta-unsaturated sulfones

[reaction: see text] A general method for the enantioselective catalytic conjugate addition to acyclic alpha,beta-unsaturated sulfones is described. Using metal-chelating alpha,beta-unsaturated pyridyl sulfones as substrates, the rhodium-catalyzed chiraphos-mediated addition of organoboric acids takes place in excellent yield and high enantioselectivity. The subsequent elimination of the pyridylsulfonyl group by Julia-Kociensky olefination provides a novel approach to the enantioselective synthesis of allylic substituted alkenes.     

Rhodium-catalyzed intermolecular amidation of arenes with sulfonyl azides via chelation-assisted C-H bond activation

We report the direct amidation of arene C-H bonds using sulfonyl azides as the amino source to release N(2) as the single byproduct. The reaction is catalyzed by a cationic rhodium complex under external oxidant-free conditions in the atmospheric environment. A broad range of chelate group-containing arenes are selectively amidated with excellent functional group tolerance, thus opening a new avenue to practical intermolecular C-N bond formation.     

Rhodium-catalyzed intramolecular C-H insertion of alpha-aryl-alpha-diazo ketones

Direct diazo transfer proceeds smoothly with alpha-aryl ketones. The derived alpha-aryl-alpha-diazo ketones cyclize efficiently with Rh catalysis to give the corresponding alpha-aryl cyclopentanones.