Cu-Promoted Divergent Phosphination of Alkynylsulfonium Salts with Diarylphosphines

An efficient copper-promoted divergent phosphination of alkynylsulfonium salts 1 with secondary diarylphosphines 2 that tolerates a wide range of functional groups under mild conditions is reported. The use of excess alkynyl dibenzothiophenium salts (1/2 > 1, mole ratio) enables the phosphination to deliver alkynyl monophosphine products via a C(sp)-P cross-coupling in good to high yields, while the use of excess secondary diarylphosphines (1/2 < 0.5, mole ratio) leads to a type of cis-ethenyl bisphosphine products via sequential stereoselective double phosphination.

Regio- and stereoselective access to highly substituted vinylphosphine oxides via metal-free electrophilic phosphonoiodination of alkynes

In general, the P-centered ring-opening of quaternary phosphirenium salts (QPrS) predominantly leads to hydrophosphorylated products, while the C-centered ring-opening is primarily confined to intramolecular nucleophilic reactions, resulting in the formation of phosphorus-containing cyclization products instead of difunctionalized products generated through intermolecular nucleophilic processes. Here, through the promotion of ring-opening of three-member rings by iodine anions and the quenching of electronegative carbon atoms by iodine cations, we successfully synthesize β-functionalized vinylphosphine oxides by the P-addition of QPrS intermediates generated in situ. Multiple β-iodo-substituted vinylphosphine oxides can be obtained with exceptional regio- and stereo-selectivity by reacting secondary phosphine oxides with unactivated alkynes. In addition, a variety of β-functionalized vinylphosphine oxides converted from C-I bonds, especially the rapid construction of benzo[b]phospholes oxides, demonstrates the significance of this strategy.

A Green Synthesis Strategy of Binuclear Catalyst for the C-C Cross-Coupling Reactions in the Aqueous Medium: Hiyama and Suzuki-Miyaura Reactions as Case Studies

Cellulose, as a green and available phytochemical, was immobilized on the surface of magnetite nanoparticles then doped with imidazole and Co. complex (Fe3O4@CNF ∼ ImSBL ∼ Co.) and used as a water-dispersible, recyclable and efficient nano catalyst for the synthesis of C-C cross-coupling reactions including fluoride-free Hiyama and Suzuki reactions in an aqueous medium as an efficient and vital solvent, due to their high application and importance in various fields of science. Different spectroscopic and microscopic techniques were used for the catalyst characterization such XRD, FESEM, TEM, FT-IR, EDX, DLS, VSM, UV-Vis, and ICP analyses. The presence of imidazole as ionic section tags with hydrophilic character on the Co-complex supported on magnetic nanoparticles provides dispersion of the catalyst particles in water, which leads to both higher catalytic performance and also facile catalyst recovery and reuse six times by successive extraction and final magnetic separation. High catalytic activity was found for the catalyst and high to excellent efficiency was obtained for all Suzuki (80-98% yield; E factor: 1.1-1.9) and Hiyama (87-98% yield; E factor: 0.26-1.1) derivatives in short reaction times under mild reaction conditions in the absence of any hazardous or expensive materials. There is not any noticeable by-product found whether for Suzuki or Hiyama derivatives, which reflects the high selectivity and also the lower the E factor the more favorable is the process in view of green chemistry. The bi-aryls were achieved from the reaction of various aryl iodides/bromides and even chlorides as the highly challenging substrates, which are more available and cheaper, with triethoxyphenylsilane or phenylboronic acid. To prove the performance of the catalyst components (synergistic of SBL ∼ Co. and IL), its different homologs were incorporated individually and studied for a model reaction. Exclusively, this is an introductory statement on the use of Cobalt binuclear symmetric ionic liquid catalysts in Hiyama reactions.

Modification of Azobenzenes by Cross-Coupling Reactions

Azobenzenes are among the most extensively used molecular switches for many different applications. The need to tailor them to the required task often requires further functionalization. Cross-coupling reactions are ideally suited for late-stage modifications. This review provides an overview of recent developments in the modification of azobenzene and its derivatives by cross-coupling reactions.

1 Introduction

2 Azobenzenes as Formally Electrophilic Components

2.1 Palladium Catalysis

2.2 Nickel Catalysis

2.3 Copper Catalysis

2.4 Cobalt Catalysis

3 Azobenzenes as Formally Nucleophilic Components

3.1 Palladium Catalysis

3.2 Copper Catalysis

3.3 C–H Activation Reactions

4 Azobenzenes as Ligands in Catalysts

5 Diazocines

5.1 Synthesis

5.2 Cross-Coupling Reactions

6 Conclusion

Microwave-assisted Cobalt-copper Dual Catalyzed Ligand Free C-Se Cross-coupling

Background:

Organoselenides are important building blocks of several biologically important molecules and natural products. Several protocols have been developed by chemists for their synthesis. Transition metal-catalyzed cross-coupling is a powerful tool for this purpose in the last two decades. Various transition metal catalysts e.g. Pd, Ni, Cu, In etc. have been used for performing C-Se cross-coupling in the presence or absence of ligands.

Objective:

Development of a sustainable protocol for transition metal-catalyzed C-Se cross-coupling is the main objective of this research. Recently, Cobalt has been applied as a cheap and sustainable transition metal catalyst in several organic reactions. This protocol is focused on applying cobalt salt as a catalyst for performing C-Se cross-coupling for the first time.

Methods:

Co(acac)2 has been successfully employed for performing Se-arylations in the presence of CuI, which acts as a co-catalyst under microwave irradiation. NMP was used as solvent and KOH as a reductant in this reaction.

Results:

Both iodo-and bromoarenes have been used to perform C-Se cross-coupling with diaryl diselenide under this Co/Cu dual catalytic system. The reaction was successful with both electrondonating and withdrawing groups in ortho-, meta-, and para-positions in the aromatic ring of Bromo and iodoarenes.

Conclusion:

This is an effective protocol for the preparation of organoselenides, catalyzed by cobalt in the presence of copper. The mechanism has been established by several experimental techniques.

New Developments on the Hirao Reactions, Especially from "Green" Point of View

BACKGROUND

The Hirao reaction discovered ca. 35 years ago is an important P-C coupling protocol between dialkyl phosphites and aryl halides in the presence of Pd(PPh3)4 as the catalyst and a base to provide aryl phosphonates. Then, the reaction was extended to other Preagents, such as secondary phosphine oxides and H-phosphinates and to other aryl and hetaryl derivatives to afford also phosphinic esters and tertiary phosphine oxides. Instead of the Pd(PPh3)4 catalyst, Pd(OAc)2 and Ni-salts were also applied as catalyst precursors together with a number of mono- and bidentate P-ligands.

OBJECTIVE

In our review, we undertook to summarize the target reaction with a special stress on the developments attained in the last 6 years, hence this paper is an update of our earlier reviews in a similar topic.

CONCLUSIONS

"Greener" syntheses aimed at utilizing phase transfer catalytic and microwave-assisted approaches, even under "P-ligand-free. or even solvent-free conditions are the up-to date versions of the classical Hirao reaction. The mechanism of the reaction is also in the focus these days.

P-Arylation of secondary phosphine oxides catalyzed by nickel-supported nanoparticles

Nickel-supported nanoparticles were used as catalysts for ligand-free Hirao coupling between secondary phosphine oxides and aryl halides.