Transition-metal-catalyzed coupling reactions have become a versatile tool for chemical bond formation. From the variation of the coupling partners, coupling reactions can be classified into three models: traditional coupling, reductive coupling and oxidative coupling. The oxidative coupling, which is different from the traditional coupling, occurs between two nucleophiles. This critical review focuses on transition-metal-catalyzed oxidative coupling reactions involving organometallic reagents as nucleophiles. Since the scope of the oxidative coupling is highly diversified, this paper only reviews the oxidative coupling reactions concerning C-C bond formation, including the coupling between organometal reagents and hydrocarbons as well as coupling between two organometal reagents. Since terminal alkynes are normally activated by metal salts and in situ form the alkynyl metal reagents in coupling reactions, they are directly considered as organometal reagents in this review. Intramolecular oxidative couplings and oxidative cyclizations are not included in this critical review. Moreover, there are many examples of oxidative coupling leading to the formation of functional materials, such as the oxidative polymerization of thiophenes. Since several reviews in these areas have been published they are not included in this review either (99 references).

The first copper-catalysed oxidative alkenylation of simple ethers to construct allylic ethers was successfully achieved. Different substituted olefins and simple ethers could be cross-coupled well to generate the corresponding alkenylation products. Notably, open-chain ethers were also found to be efficient coupling partners in this reaction. This reaction is likely to proceed via a radical process.

No abstract

Controlling selectivity is of central importance to radical chemistry. However, the highly reactive and unstable radical intermediates make this task especially challenging. Herein, a strategy for taming radical redox reactions has been developed, in which solvent-bonding can alter the reactivity of the generated radical intermediates and thereby drastically alter the reaction selectivity at room temperature. Various β-oxy sulfoxides and β-hydroxy sulfides can be facilely obtained, some of which are difficult to synthesize by existing methods. Notably, neither a metal catalyst nor any further additives are necessary in these processes.

No abstract

No abstract

Highly selective radical/radical cross-coupling is paid more attention in bond formations. However, due to their intrinsic active properties, radical species are apt to achieve homo-coupling instead of cross-coupling, which makes the selective cross-coupling as a great challenge and almost untouched. Herein a notable strategy to accomplish direct radical/radical oxidative cross-coupling has been demonstrated, that is metal tuning a transient radical to a persistent radical intermediate followed by coupling with another transient radical. Here, a transient nitrogen-centered radical is tuned to a persistent radical complex by copper catalyst, followed by coupling with a transient allylic carbon-centered radical. Firstly, nitrogen-centered radical generated from N-methoxybenzamide stabilized by copper catalyst was successfully observed by EPR. Then DFT calculations revealed that a triplet diradical Cu(II) complex formed from the chelation N-methoxybenzamide nitrogen-centered radical to Cu(II) is a persistent radical species. Moreover, conceivable nitrogen-centered radical Cu(II) complex was observed by high-resolution electrospray ionization mass spectrometry (ESI-MS). Ultimately, various allylic amides derivatives were obtained in good yields by adopting this strategy, which might inspire a novel and promising landscape in radical chemistry.

The selective radical/radical cross-coupling of two different organic radicals is a great challenge due to the inherent activity of radicals. In this paper, a copper-catalyzed radical/radical C sp 3 ÀH/PÀH cross-coupling has been developed. It provides a radical/radical cross-coupling in a selective manner. This work offers a simple way toward b-ketophosphonates by oxidative coupling of aryl ketone o-acetyloximes with phosphine oxides using CuCl as catalyst and PCy 3 as ligand in dioxane under N 2 atmosphere at 130 8C for 5 h, and yields ranging from 47 % to 86 %. The preliminary mechanistic studies by electron paramagnetic resonance (EPR) showed that, 1) the reduction of ketone o-acetyloximes generates iminium radicals, which could isomerize to a-sp 3 -carbon radical species; 2) phosphorus radicals were generated from the oxidation of phosphine oxides. Various aryl ketone oacetyloximes and phosphine oxides were suitable for this transformation.