N-Heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed allyl-aryl coupling of allylic alcohols with arylboronic acids in neat water

Alcohols as Substrates in Transition-Metal-Catalyzed Arylation, Alkylation, and Related Reactions

Alcohols are abundant and attractive feedstock molecules for organic synthesis. Many methods for their functionalization require them to first be converted into a more activated derivative, while recent years have seen a vast increase in the number of complexity-building transformations that directly harness unprotected alcohols. This Review discusses how transition metal catalysis can be used toward this goal. These transformations are broadly classified into three categories. Deoxygenative functionalizations, representing derivatization of the C-O bond, enable the alcohol to act as a leaving group toward the formation of new C-C bonds. Etherifications, characterized by derivatization of the O-H bond, represent classical reactivity that has been modernized to include mild reaction conditions, diverse reaction partners, and high selectivities. Lastly, chain functionalization reactions are described, wherein the alcohol group acts as a mediator in formal C-H functionalization reactions of the alkyl backbone. Each of these three classes of transformation will be discussed in context of intermolecular arylation, alkylation, and related reactions, illustrating how catalysis can enable alcohols to be directly harnessed for organic synthesis.

Nickel-catalyzed cross-electrophile coupling of aryl chlorides with allylic alcohols

Nickel-catalyzed cross-electrophile coupling of aryl chlorides with allylic alcohols proceeds readily under mild conditions in the presence of zinc powder and MgCl₂ to produce allylarenes in 25-92% yields. The reaction shows high regioselectivity and E/Z-selectivity, giving linear allylation products with an E configurated double bond when 1- or 3-arylallyl alcohols were used as the substrates. Functional groups including F, CF₃, COOEt, NMe₂, OMe, SiMe₃, OH and vinyl groups as well as nitrogen-containing heterocycles were tolerated.

Iridium(III) Catalyzed Z-Selective Allylic Arylation of α-Fluoro But-1-enoic Acid Amides via β-F-Elimination in Water

Allylic arylation of α-fluoro but-1-enoic acid amides with arylboronic acids was carried out in water by comparing the catalytic activity of iridium(III) and rhodium(III). Ir(III) has shown a strong superiority over Rh(III) to give allyl-aryl coupling products with excellent stereoselectivity in favor of the Z-isomer. The origin of high stereoselectivity is perhaps because of the a coordination of iridium Ir-N or Ir-O.

Sustainability in Ru- and Pd-based catalytic systems using N-heterocyclic carbenes as ligands

This review is a critical presentation of catalysts based on palladium and ruthenium bearing N-heterocyclic carbene ligands that have enabled a more sustainable approach to catalysis and to catalyst uses.

Dehydration in water: frustrated Lewis pairs directly catalyzed allylization of electron-rich arenes and allyl alcohols

A frustrated Lewis pair (FLP)-catalyzed allylation of allyl alcohols with electron-rich arenes has been developed. Interestingly, in this reaction, the electron-rich arenes and allyl alcohols are dehydrated in water. What's more, water was the sole byproduct of the reaction. In this protocol, various allyl alcohols can be converted into allyl cations and attacked by the electron-rich arenes to form aryl cation intermediates. Finally, the aryl cation intermediates are deprotonated to give the 1,3-diarylpropenes. In this protocol, indole allyl alcohols can undergo a bimolecular ring closure reaction, and structurally diverse tetrahydroindolo[3,2-b]carbazoles could be smoothly obtained. The reaction is not sensitive to oxygen and has been performed on a gram-scale.

Rhodium(III) Catalyzed Regioselective and Stereospecific Allylic Arylation in Water by β-Fluorine Elimination of the Allylic Fluoride: Toward the Synthesis of Z-Alkenyl-Unsaturated Amides

A direct coupling of arylboronic acids with allylic fluorides was carried out in water without additives using a rhodium(III) catalyst (Cp*RhCl₂)₂. The transformation proceeded with excellent γ-selectivity to afford major allyl-aryl coupling products (Z) γ-substituted α,β-unsaturated amides. The reactions of α-chiral allylic fluorides took place with excellent α-to-γ chirality transfer to give allylated arenes with a stereogenic center at the benzylic and allylic position.

Mechanistic Study on Allylic Arylation in Water with Linear Polystyrene-Stabilized Pd and PdO Nanoparticles

The catalytic cycle of allylic arylation in water catalyzed by linear polystyrene-stabilized Pd or PdO nanoparticles (PS-PdNPs or PS-PdONPs) was investigated. Stoichiometric stepwise reactions indicated that the reaction did not proceed stepwise on the surface of the catalyst. In the case of the reaction with PS-PdNPs, the leached Pd species is the catalytically active species and the reaction takes place through a similar reaction pathway accepted in the case of a complex catalyst. In contrast, allylic arylation using PS-PdONPs as a catalyst occurs via a Pd(II) catalytic cycle.

Cross-Coupling Reaction of Allylic Ethers with Aryl Grignard Reagents Catalyzed by a Nickel Pincer Complex

A cross-coupling reaction of allylic aryl ethers with arylmagnesium reagents was investigated using β-aminoketonato- and β-diketiminato-based pincer-type nickel(II) complexes as catalysts. An β-aminoketonato nickel(II) complex bearing a diphenylphosphino group as a third donor effectively catalyzed the reaction to afford the target cross-coupled products, allylbenzene derivatives, in high yield. The regioselective reaction of a variety of substituted cinnamyl ethers proceeded to give the corresponding linear products. In contrast, α- and γ-alkyl substituted allylic ethers afforded a mixture of the linear and branched products. These results indicated that the coupling reaction proceeded via a π-allyl nickel intermediate.

Catalytic allylic functionalization via π-allyl palladium chemistry

This review highlights the palladium-catalyzed allylic C–H functionalizations via π-allyl palladium reported from early 2014 to present date.

Synthesis of multi-substituted dihydrofurans via palladium-catalysed coupling between 2,3-alkadienols and pronucleophiles

Multi-substituted dihydrofurans were obtained from a palladium-catalysed coupling reaction between 2,3-alkadienols and ketones bearing an electron-withdrawing group at the α-position.

The crystal structure of 1,3-bis(2,6-diiso-propylphenyl)imidazol-2-ylidene)-dibromido-(1-methyl-1H-imidazole-κ1N)palladium(II) – ethyl acetate – water (1/1/1), C31H42Br2N4Pd

C31H42Br2N4Pd, monoclinic, P21/c, a = 12.3093(14)Å, b = 15.2805(18) Å, c = 20.3205(17) Å, β = 112.213(5)°, V = 3538.5(7) Å3, Z = 4, R gt(F) = 0.0540, wR ref(F 2) = 0.1528, T = 298(2)K.

Synthesis and characterization of trinuclear N-heterocyclic carbene–palladium(ii) complexes and their applications in the Suzuki–Miyaura cross-coupling reaction

Five novel trinuclear N-heterocyclic carbene–palladium(ii) complexes 5a–e were conveniently synthesized in one step. The obtained palladium(ii) complexes were the effective catalyst precursors for the Suzuki–Miyaura coupling.

Cross-Coupling Synthesis of Methylallyl Alkenes: Scope Extension and Mechanistic Study

Cross-coupling reactions between 2-methyl-2-propen-1-ol and various boronic acids are used to obtain aromatic-(2-methylallyl) derivatives. However, deboronation or isomerization side reactions may occur for several boronic acids. We describe herein the synthesis of original alkenes with good yields under mild reaction conditions that decrease these side reactions. The scope of this environmentally benign reaction is thereby extended to a wide variety of boronic acids. A mechanistic study was conducted and suggested a plausible catalytic cycle mechanism, pointing to the importance of the Lewis acidity of the boronic acid used.

N-Heterocyclic carbene-palladium(ii)-1-methylimidazole complex-catalyzed Suzuki-Miyaura coupling of benzyl carbamates with arylboronic acids

The Suzuki-Miyaura coupling of benzyl carbamates with arylboronic acids was achieved in an environmentally benign medium. Using water as the sole solvent, such transformation took place very well to give the desired diarylmethane derivatives in good to almost quantitative yields in the presence of a well-defined NHC-Pd(ii)-Im complex under mild conditions. It is worth noting here that this is the first example of benzyl carbamates used in coupling reaction, thus affording a new method for the formation of diarylmethanes by palladium-catalyzed C-O bond activation.