Ligand-Enabled γ-C(sp3)-H Hydroxylation of Free Amines with Aqueous Hydrogen Peroxide

Yb-Doped CuY modulates Cu electronic structures for efficient oxidation of anisole to guaiacol

Copper-based catalysts are widely employed in the catalytic conversion of aromatic compounds to phenolic derivatives. However, single-atom copper catalysts often exhibit limited reactivity and stability. In this study, we addressed these limitations by loading Cu onto NaY zeolite via ion exchange to synthesize a CuY catalyst, followed by Yb modification. By optimizing the Yb content, we significantly enhanced the anisole conversion rate and guaiacol yield. Catalyst characterization revealed that Yb species modulate the electronic structure of copper, favoring the formation of abundant Cu+ species. This electronic modification promotes the catalytic generation of hydroxyl radicals (˙OH) from hydrogen peroxide, thereby accelerating the reaction kinetics. Furthermore, Yb incorporation into CuY induced the formation of oxygen vacancies, which improved hydroxyl radical adsorption and facilitated the generation of metal-oxo species. These synergistic effects collectively increased the reaction's overall conversion efficiency. Under optimized reaction conditions, the Yb/CuY catalyst achieved an anisole conversion of 56.2% and an ortho-selectivity of 74.6%, clearly outperforming previous reports.

Unified approaches in transition metal catalyzed C(sp3)-H functionalization: recent advances and mechanistic aspects

In organic synthesis, C(sp3)-H functionalization is a revolutionary method that allows direct alteration of unactivated C-H bonds. It can obviate the need for pre-functionalization and provides access to streamlined and atom economical routes for the synthesis of complex molecules starting from simple starting materials. Many strategies have evolved, such as photoredox catalysis, organocatalysis, non-directed C-H activation, transiently directed C-H activation, and native functionality directed C-H activation. Together these advances have reinforced the importance of C(sp3)-H functionalization in synthetic chemistry. C(sp3)-H functionalization has direct applications in pharmacology, agrochemicals, and materials science, demonstrating its ability to transform synthetic approaches by creating new retrosynthetic disconnections and boost the efficiency of chemical processes. This review aims to provide an overview of current state of C(sp3)-H functionalization, focusing more on recent breakthroughs and associated mechanistic insights.

β-C-H bond functionalization of ketones and esters by cationic Pd complexes

C-H activation is the most direct way of functionalizing organic molecules. Many advances in this field still require specific directing groups to achieve the necessary activity and selectivity. Developing C-H activation reactions directed by native functional groups is essential for their broad application in synthesis1. Over the past decade, several generations of bifunctional ligands developed have enabled C(sp3)-H activation reactions of free carboxylic acids2, free aliphatic amines3, native amides4,5 and alcohols6. However, an effective catalyst for ketones and carboxylic esters remains to be realized. Here we report diverse methyl β-C-H functionalizations, including intermolecular arylation, hydroxylation and intramolecular C(sp3)-H/C(sp2)-H coupling of ketones and carboxylic esters with a monoprotected amino neutral amide (MPANA) ligand. The in situ generation of cationic Pd(II) complexes by the combination MPANA ligand and HBF4 is crucial for achieving the reactivity. The compatibility of these reactions with cyclic ketones and lactams provides a method to access spirocyclic and fused ring systems. Mechanistic experiments and density functional theory studies support the role of cationic Pd complexes with MPANA ligands in enhancing catalyst-substrate affinity and facilitating the C-H cleavage step.

Pd-catalyzed regioselective activation of C(sp2)-H and C(sp3)-H bonds

Differentiating between two highly similar C-H bonds in a given molecule remains a fundamental challenge in synthetic organic chemistry. Directing group assisted strategies for the functionalisation of proximal C-H bonds has been known for the last few decades. However, distal C-H bond functionalisation is strenuous and requires distinctly specialised techniques. In this review, we summarise the advancement in Pd-catalysed distal C(sp2)-H and C(sp3)-H bond activation through various redox manifolds including Pd(0)/Pd(II), Pd(II)/Pd(IV) and Pd(II)/Pd(0). Distal C-H functionalisation, where a Pd-catalyst is directly involved in the C-H activation step, either through assistance of an external directing group or directed by an inherent functionality or functional group incorporated at the site of the Pd-C bond is covered. The purpose of this review is to portray the current state of art in Pd-catalysed distal C(sp2)-H and C(sp3)-H functionalisation reactions, their mechanism and application in the late-stage functionalisation of medicinal compounds along with highlighting its limitations, thus leaving the field open for further synthetic adjustment.

Site-Selective Distal C(sp3)-H Bromination of Aliphatic Amines as a Gateway for Forging Nitrogen-Containing sp3 Architectures

Herein, we disclose a new strategy that rapidly and reliably incorporates bromine atoms at distal, secondary C(sp3)-H sites in aliphatic amines with an excellent and predictable site-selectivity pattern. The resulting halogenated building blocks serve as versatile linchpins to enable a series of carbon-carbon and carbon-heteroatom bond-formations at remote C(sp3) sites, thus offering a new modular and unified platform that expediates the access to advanced sp3 architectures possessing valuable nitrogen-containing saturated heterocycles of interest in medicinal chemistry settings.

Manganese/Enzyme Sequential Catalytic Pathway for the Production of Optically Active γ-Functionalized Alcohols

A brief, practical catalytic process for the production of optically active γ-functionalized alcohols from relevant alkenes has been developed by using a robust Mn(III)/air/(Me2SiH)2O catalytic system combined with lipase-catalyzed kinetic resolution. This approach demonstrates exceptional tolerance toward proximal functional groups present on alkenes, enabling the achievement of high yields and exclusive enantioselectivity. Under this sequential catalytic system, the chiral alkene precursors can also be converted into γ-functionalized alcohols and related acetates as separable single enantiomers.

Directed C(sp3)-H Arylation of Free α-Aminophosphonates: Dual Models Exploration via Palladium Catalysis

In this report, we present the dual activation models for transient directing group-directed and amino-self-directed Pd-catalyzed α-aminophosphonate side-chain C(sp3)-H arylation. Both strategies showed facile, efficient, and single regioselectivity in the reaction between free α-aminophosphonates and aryl iodides. Furthermore, the modification of amino and late-stage functionalization of the C(sp3)-P bond from products indicates potential applications for α-aminophosphonates.

Modular Synthesis of 1,2-Benzothiazines and 1,2-Benzothiazine 1-Imines via Palladium-Catalyzed C-H/C-C Activation Reactions

In this study, a modular approach toward cyclic sulfoximines and sulfondiimines via palladium-catalyzed intramolecular C-H/C-C activation reactions was reported. Various 1,2-benzothiazines including bicyclic, tricyclic, highly fused ones, ones of the seven-membered ring, along with 1,2-benzothiazine 1-imines were accessed in good yields. KIE experiment demonstrated that the C-H bond cleavage at the position ortho to the sulfoximine group is not the rate-determining step in the coupling reaction.