Palladium-catalyzed Hiyama cross-coupling of aryltrifluorosilanes with aryl and heteroaryl chlorides

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.

Eucalyptol, an All-Purpose Product

Eucalyptus plants have attracted the attention of researchers and environmentalists worldwide because they are a rapidly growing source of wood and a source of oil used for multiple purposes. The main and the most important oil component is 1,8-cineole (eucalyptol: 60–85%). This review summarizes the literature reported to date involving the use of 1,8-cineole for the treatment of disorders. Additionally, we describe our efforts in the use of eucalyptol as a solvent for the synthesis of O,S,N-heterocycles. Solvents used in chemistry are a fundamental element of the environmental performance of processes in corporate and academic laboratories. Their influence on costs, safety and health cannot be neglected. Green solvents such as bio-based systems hold considerable additional promise to reduce the environmental impact of organic chemistry. The first section outlines the process leading to our discovery of an unprecedented solvent and its validation in the first coupling reactions. This section continues with the description of its properties and characteristics and its reuse as reported in the various studies conducted. The second section highlights the use of eucalyptol in a series of coupling reactions (i.e., Suzuki–Miyaura, Sonogashira–Hagihara, Buchwald–Hartwig, Migita–Kosugi–Stille, Hiyama and cyanation) that form O,S,N-heterocycles. We describe the optimization process applied to reach the ideal conditions. We also show that eucalyptol can be a good alternative to build heterocycles that contain oxygen, sulfur and nitrogen. These studies allowed us to demonstrate the viability and potential that bio solvents can have in synthesis laboratories.

Eucalyptol: A Bio-Based Solvent for the Synthesis of O,S,N-Heterocycles. Application to Hiyama Coupling, Cyanation, and Multicomponent Reactions

We report here the use of eucalyptol as a bio-based solvent for Hiyama coupling, cyanation, and multicomponent reactions on O,S,N-heterocycles. These heterocycles were chosen as targets or as starting materials given their biological potential; they play an important role in therapeutically active compounds. Once again, eucalyptol proved to be a credible and sustainable alternative to common solvents.

Greener Biogenic Approach for the Synthesis of Palladium Nanoparticles Using Papaya Peel: An Eco-Friendly Catalyst for C-C Coupling Reaction

The development of a green and sustainable synthetic methodology still remains a challenge across the globe. Encouraging the prevailing challenge, herein, we have synthesized Pd nanoparticles (Pd NPs) in a green and environmentally viable route, using the extract of waste papaya peel without the assistance of any reducing agents, high-temperature calcination, and reduction procedures. The biomolecules present in the waste papaya peel extract reduced Pd(II) to nanosize Pd(0) in a one-pot green and sustainable process. As a catalyst, the new Pd NPs offer a simple and efficient methodology in direct Suzuki-Miyaura and Sonogashira coupling with excellent yields under mild reaction conditions.

Diversity-oriented stereoselective synthesis of β,γ-disubstituted tert-homoallylic alcohols

The successive treatment of β-(trimethylsilyl)allyl phenyl sulfides with titanocene(II)-1-butene complex and ketones produced tertiary γ-(trimethylsilyl)homoallylic alcohols with good anti-selectivity, which reacted with a variety of organic halides in the presence of copper(I) tert-butoxide to afford the cross-coupling products, γ-substituted homoallylic alcohols.

Synthesis of benzochromenes and dihydrophenanthridines with helical motifs using Garratt–Braverman and Buchwald–Hartwig reactions

X-ray structures of dihydrophenanthiridine (a) and benzochromene (b) showing greater helicity in (a).

An efficient continuous flow approach to furnish furan-based biaryls

Suzuki cross-couplings of 5-formyl-2-furanylboronic acid with activated or neutral aryl bromides were performed under continuous flow conditions in the presence of (Bu)4N(+)F(-) and the immobilised t-butyl based palladium catalyst CatCart™ FC1032™. Deactivated aryl bromides and activated aryl chlorides were cross-coupled with 5-formyl-2-furanylboronic in the presence of (Bu)4N(+)OAc(-) using the bis-triphenylphosphine CatCart™ PdCl2(PPh3)2-DVB. Initial evidence indicates the latter method may serve as a universal approach to conduct Suzuki cross-couplings with the protocol successfully employed in the synthesis of the current gold standard Hedgehog pathway inhibitor LDE225.

Three roles for the fluoride ion in palladium-catalyzed Hiyama reactions: transmetalation of [ArPdFL₂] by Ar'Si(OR)₃

From the kinetic data on the transmetalation/reductive elimination in fluoride-promoted Hiyama reactions, obtained using electrochemical techniques, it has been established that fluoride ions play three roles. F(-) reacts with trans-[ArPdBrL2] (L=PPh3) to form trans-[ArPdFL2], which reacts with Ar'Si(OMe)3 in the rate-determining transmetalation, whereas trans-[ArPdBrL2] does not react with Ar'Si(OMe)3. F(-) reacts with Ar'Si(OMe)3 to deliver the unreactive silicate Ar'SiF(OMe)3(-), thus leading to two antagonistic kinetic effects. In addition, F(-) catalyzes the reductive elimination from intermediate trans-[ArPdAr'L2].

Upgrading malic acid to bio-based benzoates via a Diels–Alder-initiated sequence with the methyl coumalate platform

Malic acid dimerization was optimized to methyl coumalate from which a Diels–Alder strategy produced a variety of bio-based benzoates.

Activation of Si-Si Bonds for Copper(I)-Catalyzed Conjugate Silylation

Several alkyl- and vinylsilanes were prepared through the copper(I)-catalyzed conjugate silylation of α,β-unsaturated compounds. Optimal reaction conditions were first investigated to realize the conjugate addition of a nucleophilic silicon species to poorly electrophilic acceptors such as phenylvinyl sulfone by cleavage of the Si-Si bond of a disilane reagent. The scope of this reaction was extended to various electrophiles bearing different electron-withdrawing groups and afforded the desired substituted alkyl- and vinylsilanes. Among the wide range of commercially available disilanes, the reactivities of alkyl-, aryl-, and ethoxydisilane were also examined.