Ru‐Catalyzed Dehydrogenative C−O Bond Formation with Anilines and Phenols

The Ru catalyzed cross‐dehydrogenative C?O bond formation between anilines and phenols is described and discussed. The exclusive C?O versus C?N bond‐formation selectivity, moreover in the absence of chelating–assisting directing groups and while leaving the N?H position untouched, is a remarkable feature of this metal‐catalyzed radical cross‐dehydrogenative coupling.     

Variable Reactivity of a N‐Heterocyclic Phosphenium Complex: P−C Bond Activation or “Abnormal” Deprotonation

The reaction of an N‐heterocyclic phosphenium complex of manganese with MeLi/Et₃NHCl under formal addition of CH₄ to the Mn=P double bond can be reversed upon UV photolysis, providing a rare example for selective P−C(alkyl) bond activation. Action of LDA on the phosphenium complex does not proceed via attack at phosphorus but rather via C4‐deprotonation to yield a unique P‐analogue of an “abnormal” carbene. A transmetalation product of the original complex was fully characterized. The C‐metalation is also applicable to bis‐phosphenium complexes of other metals.     

Supramolecular Recognition Allows Remote,Site‐Selective C−H Oxidation of Methylenic Sites in Linear Amines

Site‐selective C−H functionalization of aliphatic alkyl chains is a longstanding challenge in oxidation catalysis, given the comparable relative reactivity of the different methylenes. A supramolecular, bioinspired approach is described to address this challenge. A Mn complex able to catalyze C(sp³)‐H hydroxylation with H₂O₂ is equipped with 18‐benzocrown‐6 ether receptors that bind ammonium substrates via hydrogen bonding. Reversible pre‐association of protonated primary aliphatic amines with the crown ether selectively exposes remote positions (C8 and C9) to the oxidizing unit, resulting in a site‐selective oxidation. Remarkably, such control of selectivity retains its efficiency for a whole series of linear amines, overriding the intrinsic reactivity of C−H bonds, no matter the chain length.     

Base‐Mediated Transition‐Metal‐Free Dehydrative C−C and C−N Bond‐Forming Reactions from Alcohols

In recent years, there has been an increasing interest in using alcohols as alkylating agents for C?C and C?N bond‐forming processes employing mainly TM‐catalysts. Although BH‐catalysis looks like a green atom economy process since water is the only by‐product, it often suffers from one or more drawbacks, such as the use of expensive noble metal complexes, capricious ligands, and toxic organic solvents. Therefore, straightforward, efficient, atom economy and environmentally benign alternative protocols are desirable. This review aims to summarize the current knowledge within the published literature about dehydrative processes developed without TM‐catalysts. The most recent contributions to this topic have been reviewed keeping into account the new findings reported in this area. The features, strengths, and limitations of these alcohol‐based C?C and C?N bond‐forming processes has also been taken into account.     

Trapping σ‐Alkyl–Palladium(II) Intermediates with Arynes Encompassing Intramolecular C−H Activation: Spirobiaryls through Pd‐Catalyzed Cascade Reactions

A palladium‐catalyzed cascade reaction based on the trapping of transient alkyl–Pd^II intermediates with arynes encompassing a C?H activation step has been developed. This synthetic pathway gives rise to hetero‐spirocyclic scaffolds containing a biaryl motif, and opens up new synthetic strategies in the design of cascade reactions since it gathers several aspects of Pd chemistry, i.e., intra‐ and intermolecular carbopalladation of unsaturated species, C?H activation and C?C coupling processes.