Iron-catalyzed cross-coupling of aryltrimethylammonium triflates and alkyl Grignard reagents

Strategies for Using Quaternary Ammonium Salts as Alternative Reagents in Alkylations

Alkylation reactions are pivotal in organic chemistry, with wide-ranging utilization across various fields of applied synthetic chemistry. However, conventional reagents employed in alkylations often pose substantial health and exposure risks. Quaternary ammonium salts (QAS) present a promising alternative for these transformations offering significantly reduced hazards as they are non-cancerogenic, non-mutagenic, non-flammable, and non-corrosive. Despite their potential, their use in direct organic transformations remains relatively unexplored. This review outlines strategies for utilizing QAS as alternative reagents in alkylation reactions, providing researchers with safer approaches to chemical synthesis.

Electrochemically Driven para-Selective C(sp2)-H Alkylation Enabled by Activation of Alkyl Halides without Sacrificial Anodes

With alkyl halides (I, Br, Cl) as a coupling partner, an electrochemically driven strategy for para-selective C(sp2)-H alkylation of electron-deficient arenes (aryl esters, aldehydes, nitriles, and ketones) has been achieved to access diverse alkylated arenes in one step. The reaction enables the activation of alkyl halides in the absence of sacrificial anodes, achieving the formation of C(sp2)-C(sp3) bonds under mild electrolytic conditions. The utility of this protocol is reflected in high site selectivity, broad substrate scope, and scalable.

Palladium-Catalyzed Asymmetric Hydrogenolysis of Aryl Triflates for Construction of Axially Chiral Biaryls

Here we report the first palladium-catalyzed asymmetric hydrogenolysis of readily available aryl triflates via desymmetrization and kinetic resolution for facile construction of axially chiral biaryl scaffolds with excellent enantioselectivities and s selectivity factors. The axially chiral monophosphine ligands could be prepared from these chiral biaryl compounds and were further applied to palladium-catalyzed asymmetric allylic alkylation with excellent ee values and high branched and linear ratio, which demonstrated the potential utility of this methodology.

Dialkylamino and trialkylammonium groups in close proximity: intra- and intermolecular ways of formation, structural consequences, and properties. A case of metal-free directed ortho alkylation

All principal approaches to get to quaternised 1,8-bis(dialkylamino)naphthalenes along with their unusual properties are reported for the first time.

Transition-metal-free and base promoted C-C bond formation via C-N bond cleavage of organoammonium salts

A transition-metal-free and base promoted C-C bond forming reaction of benzyl C(sp³)-H bond with organoammonium salts via C-N bond cleavage has been reported. Benzyl ammonium salts as well as cinnamyl ammonium salt could couple readily with various benzyl C(sp³)-H species, producing the corresponding products in moderate to excellent yields with good functional group tolerance. Late stage chemical manipulation enabled the specific 1,2-diarylethane structure of products transformed into useful olefin compounds via dehydrogenation, which further demonstrated the utility of this reaction.

Ruthenium-Catalyzed Isomerization of ortho-Silylanilines to Their para Isomers

The catalytic ortho to para transposition of a silyl group in aniline derivatives is described. [RuCl₂(p-cymene)]₂/BINAP in conjunction with a Cu(OAc)₂ additive serves as a potent catalytic system. This method is also applicable to the isomerization of 2-silylpyrrole derivatives to the corresponding 3-silyl isomers.

Palladium-catalyzed direct reductive cross-coupling of aryltrimethylammonium salts with aryl bromides

Palladium-catalyzed direct reductive cross-coupling of aryltrimethylammonium salts with aryl bromides proceeded efficiently in a one-pot manner in the presence of Mg turnings, LiCl, and TMEDA in THF to afford the corresponding biaryl compounds.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

Chemical transformations of quaternary ammonium salts via C–N bond cleavage

The reaction of quaternary ammonium salts via C–N bond cleavage to construct C–C, C–H and C–heteroatom bonds is summarized.

Double C-N bond cleavages of N-alkyl 4-oxopiperidinium salts: access to unsymmetrical tertiary sulfonamides

In this paper, regiospecific, double intraannular C-N bond cleavages of N-alkyl 4-oxopiperidinium salts are presented. The reaction sequence involves a charge-transfer complex, in situ formed between sulfonyl chloride and N-methylmorpholine, which induces S-Cl bond homolysis of sulfonyl chloride, yielding a reactive sulfonyl radical that further induces the double C-N bond cleavages of N-alkyl 4-oxopiperidinium salt. The secondary amine thus produced was trapped by sulfonyl chloride to yield the desired sulfonamide product. The key feature of this protocol is that two intraannular C-N bonds of the 4-oxopiperidine ring are cleaved in one step under metal- and oxidant-free conditions.

Catalytic reduction of aryl trialkylammonium salts to aryl silanes and arenes

Aryl trialkylammonium salts serve as versatile substrates for nickel-catalyzed reductions, allowing access to functionalized arenes and aryl silanes.

A new approach for the reduction of aryl ammonium salts to arenes or aryl silanes using nickel catalysis is reported. This method displays excellent ligand-controlled selectivity based on the N-heterocyclic carbene (NHC) ligand employed. Utilizing a large NHC in non-polar solvents generates aryl silanes, while small NHCs in polar solvents promote reduction to arenes. Several classes of aryl silanes can be accessed from simple aniline building blocks, including those useful for cross-couplings, oxidations, and halogenations. The reaction conditions are mild, functional group tolerant, and provide efficient access to a variety of benzene derivatives.

Gram-Scale, Cheap, and Eco-Friendly Iron-Catalyzed Cross-Coupling between Alkyl Grignard Reagents and Alkenyl or Aryl Halides

A new robust methodology for gram-scale iron-catalyzed cross-coupling between alkyl Grignard reagents and alkenyl or aryl halides is developed. This method does not require toxic additives such as NMP or expensive ligands. Its efficiency relies on the use of simple alkoxide magnesium salts as additives. On the basis of these results, a new procedure for one-pot synthesis of substituted benzamides from chloroesters is also proposed.

Asymmetric synthesis via stereospecific C-N and C-O bond activation of alkyl amine and alcohol derivatives

This perspective showcases our development of benzylic and allylic amine and alcohol derivatives as electrophiles for stereospecific, nickel-catalyzed cross-coupling reactions, as well as the prior art that inspired our efforts. The success of our effort has relied on the use of benzyl ammonium triflates as electrophiles for cross-couplings via C-N bond activation and benzylic and allylic carboxylates for cross-couplings via C-O bond activation. Our work, along with others' exciting discoveries, has demonstrated the potential of stereospecific, nickel-catalyzed cross-couplings of alkyl electrophiles in asymmetric synthesis, and enables efficient generation of both tertiary and quaternary stereocenters.

Palladium-catalyzed carbonylation of benzylic ammonium salts to amides and esters via C–N bond activation

An efficient palladium-catalyzed carbonylation reaction of readily available quaternary ammonium salts with CO is reported for the first time to afford arylacetamides and arylacetic acid esters via benzylic C–N bond cleavage.

Organozinc-Mediated Direct C-C Bond Formation via C-N Bond Cleavage of Ammonium Salts

We report a direct cross-coupling reaction between diarylzinc (Ar₂ Zn) and aryltrimethylammonium salts (ArNMe₃⁺ ⋅^- OTf) in the presence of LiCl, via C-N bond cleavage. The reaction takes place smoothly upon heating in THF without any external catalyst, enabling an efficient and chemoselective formation of biaryl products. Mechanistic studies indicate that the reaction proceeds through a single electron transfer route.

Palladium-catalyzed coupling of azoles with 1-aryltriazenes via C–H/C–N cleavage

Arylation of azoles was performed via C–H functionalization with 1-aryltriazenes in the presence of PdCl₂, dppe, CuCl and Bu^tOLi.

Palladium catalyzed Suzuki cross-coupling of benzyltrimethylammonium salts via C–N bond cleavage

A Pd catalyzed Suzuki cross-coupling of a benzyltrimethylammonium salt is described. This reaction offers a highly efficient approach to diarylmethanes and also paves the way for the application of benzyltrimethylammonium salts in Pd catalyzed cross-coupling reactions.

Stille coupling via C-N bond cleavage

Cross-coupling is a fundamental reaction in the synthesis of functional molecules, and has been widely applied, for example, to phenols, anilines, alcohols, amines and their derivatives. Here we report the Ni-catalysed Stille cross-coupling reaction of quaternary ammonium salts via C–N bond cleavage. Aryl/alkyl-trimethylammonium salts [Ar/R–NMe₃]⁺ react smoothly with arylstannanes in 1:1 molar ratio in the presence of a catalytic amount of commercially available Ni(cod)₂ and imidazole ligand together with 3.0 equivalents of CsF, affording the corresponding biaryl with broad functional group compatibility. The reaction pathway, including C–N bond cleavage step, is proposed based on the experimental and computational findings, as well as isolation and single-crystal X-ray diffraction analysis of Ni-containing intermediates. This reaction should be widely applicable for transformation of amines/quaternary ammonium salts into multi-aromatics.

The Stille reaction is a long-standing method for the construction of carbon-carbon bonds by coupling aryl halides with organotin compounds. Here the authors report a Stille coupling between aryl ammonium salts and arylstannanes catalysed by nickel.

Iron-Catalyzed C-C Cross-Couplings Using Organometallics

Over the last decades, iron-catalyzed cross-couplings have emerged as an important tool for the formation of C-C bonds. A wide variety of alkenyl, aryl, and alkyl (pseudo)halides have been coupled to organometallic reagents, the most currently used being Grignard reagents. Particular attention has been devoted to the development of iron catalysts for the functionalization of alkyl halides that are generally challenging substrates in classical cross-couplings. The high functional group tolerance of iron-catalyzed cross-couplings has encouraged organic chemists to use them in the synthesis of bioactive compounds. Even if some points remain obscure, numerous studies have been carried out to investigate the mechanism of iron-catalyzed cross-coupling and several hypotheses have been proposed.

Palladium-Catalyzed C-H Arylation of (Benzo)oxazoles or (Benzo)thiazoles with Aryltrimethylammonium Triflates

The C-H arylation of (benzo)oxazoles or (benzo)thiazoles with aryltrimethylammonium triflates was carried out via Pd-catalyzed C-H/C-N cleavage. Oxazoles, thiazoles, benzoxazole, and benzothiazole were arylated using activated and deactivated aryltrimethylammonium triflates to give 2-aryl(benzo)oxazoles or 2-aryl(benzo)thiazoles in reasonable to excellent yields.

Nickel catalyzed α-arylation of ketones with aryltrimethylammonium triflates

C(sp³)–C(sp²) coupling of aromatic ketones with a variety of aryltrimethylammonium triflates was performed in the presence of Ni(COD)₂, IPr·HCl, and LiOBu^t to yield α-arylated ketones in reasonable to excellent yields.

Recent advances in iron-catalysed cross coupling reactions and their mechanistic underpinning

Advances in iron-catalysed cross coupling from 2010–2015 are critically reviewed.