Metal-free cross-dehydrogenative C–N coupling of azoles with xanthenes and related activated arylmethylenes

Zhang

ACS Appl. Mater. Interfaces

et al. 2021

Cross-dehydrogenative coupling (CDC) is an effective tool for carbon–carbon bond formation in chemical synthesis. Herein, we report a metal–organic framework (MOF) possessing dual Lewis acidic Cr sites and sulfonic acid sites (MIL-101(Cr)–SO3H) as an efficient catalytic material for direct cross-coupling of xanthene and different nucleophiles using O2 as the oxidant. The highly porous structure of MIL-101(Cr)–SO3H enables the free access of reactants to the catalytic active sites inside MOF pores. Kinetic studies indicated that the Cr sites of MOF accelerate the rate-limiting autoxidation reaction of xanthene, which synergistically work with the sulfonic acid group on MOF ligands in promoting the CDC reactions. Besides, the catalytic system shows excellent functional group compatibility, and a variety of valuable xanthene derivatives were synthesized with satisfactory yields. Furthermore, MIL-101(Cr)–SO3H can be reused and its catalytic activity and crystal structure remain after six consecutive runs.

Section: Introductionmentioning

confidence: 99%

Cooperative Interplay of Brønsted Acid and Lewis Acid Sites in MIL-101(Cr) for Cross-Dehydrogenative Coupling of C–H Bonds

Zhang

ACS Appl. Mater. Interfaces

et al. 2021

“…Radical C( sp 3 )−H/N−H cross‐dehydrogenative coupling of 9‐aminoxanthenes 85 with N‐heterocycles was developed employing dibenzoyl peroxide (BPO) as the oxidant (Scheme 38). [132] Besides xanthene derivatives, the reaction is also compatible with a wide scope of other activated diarylmethylenes. A broad variety of azoles 86 were tested as N‐coupling partners.…”

Section: Radical Functionalization Of Heterocyclesmentioning

confidence: 96%

CH‐Functionalization of Heterocycles with the Formation of C−O, C−N, C−S/Se, and C−P Bonds by Intermolecular Addition of Heteroatom‐Centered Radicals

et al. 2023

In the last decade, free radicals have found a wide application in functionalization of unsaturated compounds, such as alkenes, alkynes, and arenes, via the free-radical addition to carbon-carbon π-bonds. In these processes, intermolecular free-radical attack on the aromatic substrates represents a challenge due to relatively high resistance of aromatic π-system to addition reactions in comparison to alkene C=C bonds. The free-radical functionalization of heterocycles is especially interesting due to the diversity of their structures and chemical properties as well as their importance for medicinal chemistry, agrochemistry, and materials science. Addition of C-centered radicals to heterocycles is widely known as the Minisci-type reactions and well-reviewed. In this paper, we have summarized the main achievements in less explored group of processes: functionalization of heterocycles by intermolecular addition of heteroatom-centered radicals (O-, N-, S-/Se-, and P-radicals) with the emphasis on the papers published after 2010. Literature analysis revealed the strong trend towards the usage of electrochemistry and photoredox-catal-ysis for the generation of free radicals in recent years. The remaining fundamental problem in this field is the lack of strong experimental support for the proposed mechanisms and frequent existence of several plausible reaction pathways. The progress in mechanistic studies can significantly improve the prediction of optimal reaction conditions depending on the substrates structure. 1. Introduction 2. Radical Functionalization of Heterocycles 2.1. Reactions with the Formation of CÀ O Bonds 2.2. Reactions with the Formation of CÀ N Bonds 2.3. Reactions with the Formation of CÀ S and CÀ Se Bonds 2.4. Reactions with the Formation of CÀ P Bonds 3. Conclusions

“…Recently in 2019, Liang and co-workers reported a metal-free C(sp 3 )À H/NÀ H CDC reaction between azoles and arylmethylenes with the aid of benzoyl peroxide (BPO) (Scheme 129). [249] Methylene derivatives containing heteroatom-bridged bisaryl groups were reacted smoothly with different azolic NÀ H sources to provide CÀ N CDC products in moderate to excellent yields.…”

Section: Bpo-mediated C(sp 3 )à H Aminationmentioning

confidence: 99%

Cross‐Coupling of C−H and N−H Bonds: A Hydrogen Evolution Strategy for the Construction of C−N Bonds

et al. 2022

The progress in CÀ N bond construction is significant in synthetic and biological chemistry. Cross-dehydrogenative couplings of CÀ H and NÀ H motifs serve as a unique class of the most atom-economical and straightforward strategies for constructing CÀ N bonds. Herein, we enclosed the most updated methodologies developed in the assembly of CÀ N bonds via photo-catalyzed, transition-metal-catalyzed, electrochemical, and metal-free amination and amidation reactions of saturated and unsaturated CÀ H bonds. Compared with the well-established transition-metal-catalyzed protocols, electricity, or visible light-mediated amination and amidation reactions are competent and appealing. Plausible mechanistic pathways are also described in representative amidation and amination reactions to provide insights for the future development of environmentally kind processes.