The transition-metal-catalyzed amination of aryl halides has been the most powerful method for the formation of aryl amines over the past decades. Phenols are regarded as ideal alternatives to aryl halides as coupling partners in cross-couplings. An efficient palladium-catalyzed formal cross-coupling of phenols with various amines and anilines has now been developed. A variety of substituted phenols were compatible with the standard reaction conditions. Secondary and tertiary aryl amines could thus be synthesized in moderate to excellent yields.

Aryl halides are very useful electrophiles for synthesizing various substituted aromatic compounds via metal-catalyzed cross-coupling reactions. Because of the high cost associated with their synthesis and the stoichiometric halide waste produced when using aryl halide feedstocks, cheaper and more sustainable alternatives have been explored, such as phenols. However, phenols have a very reactive hydroxyl group and a C–O bond with high dissociation energy. To overcome such challenges, earlier studies focused on finding ways to reduce the energy of the C–O bond while removing the active proton by transforming phenols into phenol derivatives (e.g., sulfonates, esters, carbamates, ethers, and metal salts). A greater ambition is to directly cross-couple phenols with nucleophiles via C–O cleavage. In this Perspective, we briefly summarize efforts and accomplishments concerning the cross-coupling of phenol derivatives and phenols.

The facile iodination of aromatic compounds under mild conditions is a great challenge for both organic and medicinal chemistry. Particularly, the synthesis of functionalized aryl iodides by light has long been considered impossible due to their photo-lability, which actually makes aryl iodides popular starting materials in many photo-substitution reactions. Herein, a photoinduced halogen exchange in aryl or vinyl halides has been discovered for the first time. A broad scope of aryl iodides can be prepared in high yields at room temperature under exceptionally mild conditions without any metal or photo-redox catalysts. The presence of a catalytic amount of elemental iodine could promote the reaction significantly.A ryl and heteroaryl iodides are ubiquitous precursors and fundamental building blocks used in chemistry for many important transformations, such as metalation processes, 1,2 nucleophilic aromatic substitutions, 3 and transition-metalcatalyzed cross-coupling reactions. 4,5 Furthermore, aryl iodides and their radiolabeled analogues have proven to be very useful in nuclear medicine and radiotherapy science, such as hypothyroidism treatment, 6 single-photon-emission computed tomography, 7 and preclinical X-ray imaging. 8 The various radioactive iodine isotopes ( 131 I, 125 I, and 123 I) make it possible to label the same target agent with different isotopes, increasing the flexibility in pharmacokinetic studies. 9 However, compared to the less reactive aryl bromides and chlorides, the corresponding aryl iodides are much more difficult to obtain. 10 The routine iodination methods usually result in poor yields or require stoichiometric amount of transition-metal reagents. 11−13 Substrate scope also suffers from severe limitations due to the harsh reaction conditions. More recently, great efforts have been devoted and several useful strategies have been developed to synthesize functionalized (hetero)aromatic iodides with high yield and broad substrate scope. One of the major improvements has been made via the palladium-catalyzed C−H bond iodination assisted by directing groups. 14−18 Another pivotal progress is the copper-or nickel-catalyzed aryl halide exchange process assisted by ligandsthe so-called aromatic Finkelstein reactionwhich was first reported by Buchwald and co-workers. 19−22 Despite the tremendous progresses achieved, the current transition-metal-catalyzed iodination methods are still not straightforward and atom economical enough, especially compared to the classical Finkelstein reaction, in which alkyl chlorides and bromides (aryl, vinyl, and tertiary alkyl halides are unreactive) can be converted into the corresponding alkyl iodides simply using a solution of sodium iodide in acetone. Furthermore, the difficulty associated with metal or ligand residue has led to growing concerns about the pharmaceuticals and materials. In this respect, a transition-metal-free iodination approach to access aryl iodides more efficiently and under milder and environmentally benign conditions is h...

A highly efficient Pd-catalyzed direct coupling of phenolic lignin model monomers and analogues with anilines to give cyclohexylamines using sodium formate as hydrogen donor is described.