Palladium-Catalyzed Amide N–C Hiyama Cross-Coupling: Synthesis of Ketones

Palladium-Catalyzed/Copper-Mediated Decarbonylative Cross-Coupling of S-Pyrimidyl Thioesters for Biaryl Synthesis

A palladium-catalyzed/copper-mediated cross-coupling of S-pyrimidinyl thioesters with arylboronic acids to yield biaryls is described. The reaction is likely to proceed via cleavage of the S-C(O) bond and subsequent release of CO, rather than via cleavage of the S-C(pyrimidine) bond and release of SCO, as supported by the results of both experimental and computational studies. The investigation of the reaction scope with various S-pyrimidinyl thioesters and arylboronic acids showed that the reaction is significantly affected by the substituent of the thioester and the presence of a chelatable ortho substituent was found to increase reaction efficiency.

Trialkoxysilane-Induced Iridium-Catalyzed para-Selective C-H Bond Borylation of Arenes

An ideal approach for the construction of aryl boron compounds is to selectively replace a C-H bond in arenes with a C-B bond, and controlling regioselectivity is one of the most challenging aspects of these transformations. Herein, we report an iridium-catalyzed trialkoxysilane protecting group-assisted regioselective C-H borylation of arenes, including derivatives of benzaldehydes, acetophenones, benzoic acids, benzyl alcohols, phenols, aryl silanes, benzyl silanes, and multi-functionalized aromatic rings are all well tolerated and gave the para -selective C-H borylation products in a short time without the requirement of inert gases atmosphere. The site-selective C-H borylation can be adjustable by installing the developed trialkoxysilane protecting group on different functional groups on one aromatic ring. Importantly, the preparation process of the trialkoxychlorosilane is efficient and scalable. Mechanistic and computational studies reveal that the steric hindrance of the trialkoxysilane protecting group plays a key role in dictating the para-selectivity.

Ring Opening of N-Acyl Lactams Using Nickel-Catalyzed Transamidation

We successfully developed a nickel-catalyzed transamidation method for the ring opening of N-acyl lactams. The method involves a reaction between N-benzoylpyrrolidin-2-one derivatives and aniline derivatives, with Ni(PPh3)2Cl2 serving as the catalyst, 2,2'-bipyridine as the ligand, and manganese as the reducing agent. This reaction led to the formation of ring-opening-amidated products in good yields. Notably, the method exhibited excellent efficiency for producing the corresponding ring-opening transamidation products for various ring sizes, including four-, five-, six-, seven-, and eight-membered ring lactams.

Reductive cross-coupling of N-acyl pyrazole and nitroarene using tetrahydroxydiboron: synthesis of secondary amides

We report on a new method for the synthesis of amides using acyl pyrazoles and nitroarenes under reducing conditions. It was found that acyl pyrazoles react with organo-nitro compounds in the presence of B2(OH)4, giving the corresponding amides in good yields. We demonstrated that benzoyl pyrazoles having various substituents and nitroarenes with different substituents can be used to produce a range of N-substituted benzamides. The method shows good functional group tolerance and has potential application in the synthesis of a variety of organic molecules.

Classes of Amides that Undergo Selective N-C Amide Bond Activation: The Emergence of Ground-State Destabilization

Ground-state destabilization of the N-C(O) linkage represents a powerful tool to functionalize the historically inert amide bond. This burgeoning reaction manifold relies on the availability of amide bond precursors that participate in weakening of the nN → π*C=O conjugation through N-C twisting, N pyramidalization, and nN electronic delocalization. Since 2015, acyl N-C amide bond activation through ground-state destabilization of the amide bond has been achieved by transition-metal-catalyzed oxidative addition of the N-C(O) bond, generation of acyl radicals, and transition-metal-free acyl addition. This Perspective summarizes contributions of our laboratory in the development of new ground-state-destabilized amide precursors enabled by twist and electronic activation of the amide bond and synthetic utility of ground-state-destabilized amides in cross-coupling reactions and acyl addition reactions. The use of ground-state-destabilized amides as electrophiles enables a plethora of previously unknown transformations of the amide bond, such as acyl coupling, decarbonylative coupling, radical coupling, and transition-metal-free coupling to forge new C-C, C-N, C-O, C-S, C-P, and C-B bonds. Structural studies of activated amides and catalytic systems developed in the past decade enable the view of the amide bond to change from the "traditionally inert" to "readily modifiable" functional group with a continuum of reactivity dictated by ground-state destabilization.

Meerwein Arylation of Aryl(alkyl)idenemalononitriles and Diazonium Salts for the Synthesis of 2-(Aryl(alkyl)/arylmethylene)malononitrile Derivatives

A metal-free Meerwein arylation reaction from aryl(alkyl)idenemalononitriles and diazonium salts for the synthesis of 2-(aryl(alkyl)/arylmethylene)malononitrile derivatives under mild conditions was well developed. Different from the general addition reactions between alkenes and diazonium salts, this study performed the traditional coupling reaction for the formation of C(sp2)-C(sp2) bond arylation products. The radical reaction mechanism was well verified in the control experiments. The other advantages of the approach are broad-scope substrates and good group tolerance. Moreover, the obtained products can be readily converted into high-value asymmetric ketones and hydrogenation reactions.

Amide N-C Bond Activation: A Graphical Overview of Acyl and Decarbonylative Coupling

This Graphical Review provides an overview of amide bond activation achieved by selective oxidative addition of the N-C(O) acyl bond to transition metals and nucleophilic acyl addition, resulting in acyl and decarbonylative coupling together with key mechanistic details pertaining to amide bond distortion underlying this reactivity manifold.

Transition Metal Catalyzed Hiyama Cross-Coupling: Recent Methodology Developments and Synthetic Applications

Hiyama cross-coupling is a versatile reaction in synthetic organic chemistry for the construction of carbon-carbon bonds. It involves the coupling of organosilicons with organic halides using transition metal catalysts in good yields and high enantioselectivities. In recent years, hectic progress has been made by researchers toward the synthesis of diversified natural products and pharmaceutical drugs using the Hiyama coupling reaction. This review emphasizes the recent synthetic developments and applications of Hiyama cross-coupling.

Reaction of Amide and Sodium Azide for the Synthesis of Acyl Azide, Urea, and Iminophosphorane

Amides reacted with NaN₃ to give the acyl azides in DMF at 25 °C and produce the symmetrical ureas in THF/H₂O at 80 °C via the sequential reaction of acyl substitution and Curtius rearrangement. All acyl azides were also obtained from the secondary amides via sequential reaction of p-toluenesulfonyl chloride and NaN₃. In addition, keto-stabilized iminophosphoranes were prepared from a one-pot reaction of amides, NaN₃, and phosphines.

Ni-catalysed deamidative fluorination of amides with electrophilic fluorinating reagents

We describe here a Ni-catalysed deamidative fluorination of diverse amides with electrophilic fluorinating reagents. Different types of amides including aromatic amides and olefinic amides were well compatible, affording the corresponding acyl fluorides in good to excellent yields.

Copper-Promoted Hiyama Cross-Coupling of Arylsilanes With Thiuram Reagents: A Facile Synthesis of Aryl Dithiocarbamates

We report herein a facile Hiyama cross-coupling reaction of arylsilanes with thiuram reagents (tetraalkylthiuram disulfides or tetraalkylthiuram monosulfide) enabled by copper fluoride. Compared to our previous work, this protocol is an alternative protocol for the generation of S-aryl dithiocarbamates. It features low toxic and readily available substrates, cost-effective promoter, easy performance, and provides good yields.

Controlled Reduction of Activated Primary and Secondary Amides into Aldehydes with Diisobutylaluminum Hydride

A practical method is disclosed for the reduction of activated primary and secondary amides into aldehydes using diisobutylaluminum hydride (DIBAL-H) in toluene. A wide range of aryl and alkyl N-Boc,...

Transition-metal-catalyst-free reaction of amides and acetonitriles: synthesis of β-ketonitriles

The first example of the coupling reaction between amide and acetonitrile for the synthesis of β-ketonitriles was developed. Various amides provide the corresponding β-ketonitriles in good yields.

Synthesis of Flavanone and Quinazolinone Derivatives from the Ruthenium-Catalyzed Deaminative Coupling Reaction of 2'-Hydroxyaryl Ketones and 2-Aminobenzamides with Simple Amines

The cationic Ru-H complex [(C₆H₆)(PCy₃)(CO)RuH]⁺BF₄^- (1) with 3,4,5,6-tetrachloro-1,2-benzoquinone (L1) was found to be a highly effective catalyst for the deaminative coupling reaction of 2'-hydroxyaryl ketones with simple amines to form 3-substituted flavanone products. The analogous deaminative coupling reaction of 2-aminobenzamides with branched amines directly formed 3,3-disubstituted quinazolinone products. The catalytic method efficiently installs synthetically useful flavanone and quinazolinone core structures without employing any reactive reagents.

Mechanochemical Solvent-Free Suzuki-Miyaura Cross-Coupling of Amides via Highly Chemoselective N-C Cleavage

Although cross-coupling reactions of amides by selective N-C cleavage are one of the most powerful and burgeoning areas in organic synthesis due to the ubiquity of amide bonds, the development of mechanochemical, solid-state methods remains a major challenge. Herein, we report the first mechanochemical strategy for highly chemoselective, solvent-free palladium-catalyzed cross-coupling of amides by N-C bond activation. The method is conducted in the absence of external heating, for short reaction time and shows excellent chemoselectivity for σ N-C bond activation. The reaction shows excellent functional group tolerance and can be applied to late-stage functionalization of complex APIs and sequential orthogonal cross-couplings exploiting double solventless solid-state methods. The results extend mechanochemical reaction environments to advance the chemical repertoire of N-C bond interconversions to solid-state environmentally friendly mechanochemical methods.

Evaluation of Cyclic Amides as Activating Groups in N-C Bond Cross-Coupling: Discovery of N-Acyl-δ-valerolactams as Effective Twisted Amide Precursors for Cross-Coupling Reactions

The development of efficient methods for facilitating N-C(O) bond activation in amides is an important objective in organic synthesis that permits the manipulation of the traditionally unreactive amide bonds. Herein, we report a comparative evaluation of a series of cyclic amides as activating groups in amide N-C(O) bond cross-coupling. Evaluation of N-acyl-imides, N-acyl-lactams, and N-acyl-oxazolidinones bearing five- and six-membered rings using Pd(II)-NHC and Pd-phosphine systems reveals the relative reactivity order of N-activating groups in Suzuki-Miyaura cross-coupling. The reactivity of activated phenolic esters and thioesters is evaluated for comparison in O-C(O) and S-C(O) cross-coupling under the same reaction conditions. Most notably, the study reveals N-acyl-δ-valerolactams as a highly effective class of mono-N-acyl-activated amide precursors in cross-coupling. The X-ray structure of the model N-acyl-δ-valerolactam is characterized by an additive Winkler-Dunitz distortion parameter Σ(τ+χ_N) of 54.0°, placing this amide in a medium distortion range of twisted amides. Computational studies provide insight into the structural and energetic parameters of the amide bond, including amidic resonance, N/O-protonation aptitude, and the rotational barrier around the N-C(O) axis. This class of N-acyl-lactams will be a valuable addition to the growing portfolio of amide electrophiles for cross-coupling reactions by acyl-metal intermediates.

Palladium-Catalyzed Direct Arylation of 2-Pyridylmethyl Silanes with Aryl Bromides

The first palladium-catalyzed direct arylation of 2-pyridylmethyl silanes with aryl bromides to generate a diverse array of aryl(2-pyridyl)-methyl silane derivatives has been developed. This protocol facilitates access to various kinds of heterocycle-containing silanes in good to excellent yields (40 examples, 66-97% yield) with good functional group tolerance. The scalability of this transformation is demonstrated.

Chemoselective acylation of N-acylglutarimides with N-acylpyrroles and aryl esters under transition-metal-free conditions

The imide moiety is a well-known structural motif in bioactive compounds and a useful building block in a variety of processes.

Metal-free transamidation of benzoylpyrrolidin-2-one and amines under aqueous conditions

N-Acyl lactam amides, such as benzoylpyrrolidin-2-one, benzoylpiperidin-2-one, and benzoylazepan-2-one reacted with amines in the presence of DTBP and TBAI to afford the transamidated products in good yields. The reactions were conducted under aqueous conditions and good functional group tolerance was achieved. Both aliphatic and aromatic primary amines displayed good activity under metal-free conditions. A radical reaction pathway is proposed.