Activation of “Inert” Alkenyl/Aryl CO Bond and Its Application in Cross-Coupling Reactions

Direct borylation of benzyl alcohol and its analogues in the absence of bases

Direct borylation of arylmethanols to synthesize important and useful benzylboronates was carried out through Pd(OAc)₂-catalyzed sp³ C–O activation.

Reductive cleavage of inert aryl C–O bonds to produce arenes

Reductive cleavage of aryl C–O bonds in phenols and aryl ethers was achieved using LiAlH₄–KOtBu, producing arenes in high yields.

Theoretical study on homolytic C(sp2)–O cleavage in ethers and phenols

The C(sp²)–O BDEs and the substituent effect of ethers/phenols were investigated in detail by the wB97 method.

Exploring the Catalytic Reactivity of Nickel Phosphine–Phosphite Complexes

In this study, we present an investigation into various nickel phosphite and phosphite–phosphine complexes for use in the Mizoroki–Heck and Suzuki–Miyaura cross-coupling reactions and the ammonia arylation reaction. In these coupling reactions, it was discovered that the Ni[P(OEt)3]4, (dppf)Ni[P(OPh)3]2, and (binap)Ni[P(OPh)3]2 catalysts were the most effective. In addition, an optimisation process for these catalytic systems as well as functional group compatibility are discussed.

Palladacycles derived from arylphosphinamides for mild Suzuki–Miyaura cross-couplings

We present the arylphosphinamide-derived palladacyclic complexes (see Scheme) which could be used as efficient and versatile precatalysts for mild Suzuki–Miyaura cross-coupling.

A divergent synthesis of 3,10-dialkylpicenes

A series of 3,10-dialkylated picenes has been synthesized through sequential Ni-catalyzed alkynylation of a C–O bond, alkylation, and hydrogenation.

Pyridynes and indolynes as building blocks for functionalized heterocycles and natural products

This feature article showcases the use of pyridynes and indolynes to construct functionalized heterocycles and complex natural products.

Efficient methods for enol phosphate synthesis using carbon-centred magnesium bases

Efficient conversion of ketones into enol phosphates under mild and accessible conditions has been realised using the developed methods with di-tert-butylmagnesium and bismesitylmagnesium. Optimisation of the quench protocol resulted in high yields of enol phosphates from a range of cyclohexanones and aryl methyl ketones.

Highly efficient pincer nickel catalyzed cross-coupling of aryltrimethylammonium triflates with arylzinc reagents

N,N,P-Pincer nickel complexes [Ni(Cl){N(2-R₂PC₆H₄)(2′-Me₂NC₆H₄)}] highly effectively catalyze the cross-coupling of aryltrimethylammonium triflates with arylzinc reagents.

Transition metal free intramolecular selective oxidative C(sp3)–N coupling: synthesis of N-aryl-isoindolinones from 2-alkylbenzamides

A transition metal-free intramolecular selective oxidative coupling reaction of C(sp³)–H and N–H bonds has been presented utilizing iodine, potassium carbonate and di-tert-butyl peroxide in acetonitrile at 110–140 °C.

[Efficient synthesis of multisubstituted aromatic compounds from phenol derivatives]

Phenols are abundant in nature and diverse phenols are readily available commercially at low cost. Thus, phenols can be used as the raw materials for the synthesis of valuable multisubstituted aromatic compounds by the direct activation of phenolic hydroxyl groups (C-O bond activation), followed by substitutions with other substituents. Although the derivatization of phenolic hydroxyl groups to sulfonates, such as triflates, nonaflates, tosylates and mesylates, followed by the transition-metal-catalyzed coupling reactions has been extensively investigated for this purpose, the direct C-O bond activation of phenols for subsequent functional group transformation has been a long-standing challenge in modern organic synthesis. In this review, I have summarized my recent studies on the formal direct C-O bond activation of phenols using nonafluorobutanesulfonyl fluoride (NfF) for the synthesis of multisubstituted aromatics. I have focused on the dual use of NfF, a less expensive commercially available reagent, including the tentative formation of highly reactive nonaflates from phenols and the use of the liberated fluoride ion as a nucleophile to promote the reactions of nonaflates. The following four topics are discussed: 1) palladium-catalyzed coupling reactions of phenols, 2) novel preparation of benzynes from 2-silylphenols, 3) synthesis of fluorinated aromatic compounds via the formation of benzynes, and 4) Hiyama coupling of (tert-butyldimethylsilyl)arenes activated by internal phenolic hydroxyl groups.

The role of aryne distortions, steric effects, and charges in regioselectivities of aryne reactions

The distortion/interaction model has been used to explain and predict reactivity in a variety of reactions where more common explanations, such as steric and electronic factors, do not suffice. This model has also provided new fundamental insight into regioselectivity trends in reactions of unsymmetrical arynes, which in turn has fueled advances in aryne methodology and natural product synthesis. This article describes a systematic experimental and computational study of one particularly important class of arynes, 3-halobenzynes. 3-Halobenzynes are useful synthetic building blocks whose regioselectivities have been explained by several different models over the past few decades. Our efforts show that aryne distortion, rather than steric factors or charge distribution, are responsible for the regioselectivities observed in 3-haloaryne trapping experiments. We also demonstrate the synthetic utility of 3-halobenzynes for the efficient synthesis of functionalized heterocycles, using a tandem aryne-trapping/cross-coupling sequence involving 3-chlorobenzyne.

1,3-Dicyclohexylimidazol-2-ylidene as a superior ligand for the nickel-catalyzed cross-couplings of aryl and benzyl methyl ethers with organoboron reagents

A new catalytic system has been developed involving the use of Ni(cod)2 in conjunction with 1,3-dicyclohexylimidazol-2-ylidene for the cross-coupling of aryl and benzyl methyl ethers with organoboron reagents. This method not only allows for the use of readily available methyl ethers as halide surrogates but also provides a functional group tolerant method for the late-stage derivatization of complex molecules.

Silver-catalyzed regio- and stereoselective addition of carboxylic acids to ynol ethers

A silver-catalyzed trans addition of carboxylic acids to ynol ethers is described. The reaction has a broad scope with respect to carboxylic acids and ynol ethers, delivering (Z)-α-alkoxy enol esters in good yields with excellent regio- and stereoselectivity. Meaningfully, the Ni-catalyzed selective coupling of alkenyl C-OPiv bonds of (Z)-α-alkoxy enol esters with boronic acids enables a convenient route to the access of (E)-enol ethers. As such, the two-step procedure, consisted of a hydrocarboxylation and a subsequent Suzuki-Miyaura coupling, offers a formal trans hydroarylation of ynol ethers, thus providing a good complementary method to our previous report.

Nickel-Catalyzed Amination of Aryl Chlorides and Sulfamates in 2-Methyl-THF

The nickel-catalyzed amination of aryl O-sulfamates and chlorides using the green solvent 2-methyl-THF is reported. This methodology employs the commercially available and air-stable precatalyst NiCl2(DME), is broad in scope, and provides access to aryl amines in synthetically useful yields. The utility of this methodology is underscored by examples of gram-scale couplings conducted with catalyst loadings as low as 1 mol % nickel. Moreover, the nickel-catalyzed amination described is tolerant of heterocycles and should prove useful in the synthesis of pharmaceutical candidates and other heteroatom-containing compounds.

Enabling the use of heterocyclic arynes in chemical synthesis

Heterocyclic arynes have long been targeted as potential tools for the synthesis of substituted heterocycles. Recent advances have led to an improved understanding of the factors that determine regioselectivity in reactions of these strained intermediates and, in turn, the aryne distortion model. This paper highlights the use of this predictive model to enable the use of heterocyclic arynes, such as indolynes and pyridynes, in chemical synthesis.

Recent advances in homogeneous nickel catalysis

Tremendous advances have been made in nickel catalysis over the past decade. Several key properties of nickel, such as facile oxidative addition and ready access to multiple oxidation states, have allowed the development of a broad range of innovative reactions. In recent years, these properties have been increasingly understood and used to perform transformations long considered exceptionally challenging. Here we discuss some of the most recent and significant developments in homogeneous nickel catalysis, with an emphasis on both synthetic outcome and mechanism.

Bismuth(III)-catalyzed dehydrative etherification and thioetherification of phenolic hydroxy groups

Use of a bismuth catalyst allowed efficient dehydrative substitution of phenolic hydroxy groups with alcohols and thiols to form C-O and C-S bonds. The reaction required equimolar amounts of two readily available substrates that generated H(2)O as the only byproduct. The relatively mild reaction conditions were compatible with the functional groups selected, and provided excellent chemoselectivity.

Palladium-Catalyzed Intra- and Intermolecular C-H Arylation Using Mesylates: Synthetic Scope and Mechanistic Studies

This paper describes the development of Pd-catalyzed inter- and intramolecular direct arylation using mesylates. Furthermore, a sequential mesylation/arylation protocol using phenols as substrates is described. These transformations are general with respect to the electronics of the C-H substrates and allow for the synthesis of diverse heterocyclic motifs in good yields. Both arenes and heteroarenes efficiently participate in these reactions. Preliminary mechanistic studies are presented for both inter- and intramolecular arylations.

The First Example of Nickel-Catalyzed Silyl-Heck Reactions: Direct Activation of Silyl Triflates Without Iodide Additives

For the first time, nickel-catalyzed silyl-Heck reactions are reported. Using simple phosphine-supported nickel catalysts, direct activation of silyl triflates has been achieved. These results contrast earlier palladium-catalyzed systems, which require iodide additives to activate silyl-triflates. These nickel-based catalysts exhibit good functional group tolerance in the preparation of vinyl silanes, and unlike earlier systems, allows for the incorporation of trialkylsilanes larger than Me₃Si.

Copper-catalyzed aerobic oxidative N-S bond functionalization for C-S bond formation: regio- and stereoselective synthesis of sulfones and thioethers

A regio- and stereoselective synthesis of sulfones and thioethers by means of Cu(I)-catalyzed aerobic oxidative N-S bond cleavage of sulfonyl hydrazides, followed by cross-coupling reactions with alkenes and aromatic compounds to form the C sp 2-S bond, is described herein. N2 and H2O are the byproducts of this transformation, thus offering an environmentally benign process with a wide range of potential applications in organic synthesis and medicinal chemistry.

Nickel-catalyzed α-arylation of ketones with phenol derivatives

The nickel-catalyzed α-arylation of ketones with readily available phenol derivatives (esters and carbamates) provides access to useful α-arylketones. For this transformation, 3,4-bis(dicyclohexylphosphino)thiophene (dcypt) was identified as a new, enabling, air-stable ligand for this transformation. The intermediate of an assumed C-O oxidative addition was isolated and characterized by X-ray crystal-structure analysis.

A mild Ni/Cu-catalyzed silylation via C-O cleavage

A Ni/Cu-catalyzed silylation of unactivated C-O electrophiles derived from phenols or benzyl alcohols is described. This transformation is characterized by its wide scope and mild conditions, providing a direct access to synthetically versatile silylated compounds. The protocol allows for the coupling of C(sp(2))-O and even C(sp(3))-O bonds with similar efficiency.