Recent Progress in Transition-Metal-Catalyzed Reductive Cross-Coupling Reactions Using Diboron Reagents as Reductants

Abstract

Transition-metal-catalyzed reductive cross-coupling reactions have been developed as one of the important tools for constructing C−C bonds. These reactions involve the direct coupling of two distinct electrophiles promoted by transition metals and reductants. Notably, these methods offer advantages over conventional cross-coupling reactions because they circumvent the need for air-and moisture-sensitive organometallic reagents while being simple to operate and exhibiting good compatibility with various functional groups. In recent years, diboron reagents have gained prominence as reductants for reductive cross-coupling reactions alongside traditional metal reductants, such as Zn, Mn, and Mg. This Review aims to provide an insightful overview of nickel/copper/iron-catalyzed reductive coupling reactions using diboron reagents as reductants and illustrate their possible reaction mechanisms.

Micropores in Hollow Organic Cage Nanocapsule as a Size Exclusion Gate: Cage Entrapped Pd(II)-Catalyst for Efficient Cross-Coupling Reaction

“…Methodologies based on transition metal-catalyzed various coupling reactions have played an important role in modern synthetic organic chemistry, and the commercialization of new APIs, drugs, pharmaceuticals, and agrochemicals (mainly insecticides, fungicides, and herbicides). − For efficient and sustainable methodologies, there has been an emphasis on combining the benefits of heterogeneous catalysis while maintaining the conditions conducive to homogeneous reactions. , Optimum loading of the Pd­(II)-catalyst, along with its recovery after each catalytic reaction for recycling are linked to a sustainable process. , Heterogenization of such catalysts through anchoring on appropriate solid supports having a high surface area has been argued as one of the key processes for addressing this issue. Different research groups have explored several solid supports like fibers, metal–organic frameworks (MOFs), magnetic nanoparticles, covalent organic frameworks (COFs), dendrimers, and microporous inorganic solids like silica. − In a few instances, the confinement effect in microporous solids has helped in improving the efficiencies in terms of the stability, recovery/recycling of the catalysts. , However, the use of such solids as support has limited application potential owing to inadequate dispersibility in the reaction system.…”

Iron-Catalyzed Regioselective Reductive Fluoroalkylalkenylation of Unactivated Alkenes

“…However, employing Zn and Mn as reducing agents was unsuccessful for promoting this transformation (Table , entry 13), and the corresponding two- and three-component cross-coupling products were not observed. These results suggest that Fe/Zn and Fe/Mn systems are unable to initiate this reaction, further underscoring the unique nature of the iron/B 2 pin 2 systems . Additionally, when Togni reagent I (3,3-dimethyl-1-(trifluoromethyl)-1,2-benziodoxole) was used as the trifluoromethyl reagent, the desired product was afforded in 34% yield.…”

“…These results suggest that Fe/Zn and Fe/Mn systems are unable to initiate this reaction, further underscoring the unique nature of the iron/ B 2 pin 2 systems. 71 Additionally, when Togni reagent I (3,3dimethyl-1-(trifluoromethyl)-1,2-benziodoxole) was used as the trifluoromethyl reagent, the desired product was afforded in 34% yield.…”

Diastereo- and Enantioselective Dearomative Reductive Aryl-Fluoroalkenylation of Indoles by Nickel Catalysis

“…These possibly imply that nickel catalyst bearing single chiral ligand might be involved in the enantio-determining step. 15 Based on the experimental studies above and previous literature on B 2 Pin 2 /base as two-electron reducing reagent in nickel-catalyzed reductive coupling systems, 16 a plausible Ni(I)/Ni(III) catalytic cycle 4a,14,17 is proposed in Scheme 4. In the presence of base, transmetalation of the Ni(I)-X with B 2 Pin 2 offers a Bpin-Ni(I) species I, 14 activation.…”

“…Based on the experimental studies above and previous literature on B 2 Pin 2 /base as two-electron reducing reagent in nickel-catalyzed reductive coupling systems, a plausible Ni­(I)/Ni­(III) catalytic cycle ,, is proposed in Scheme . In the presence of base, transmetalation of the Ni­(I)-X with B 2 Pin 2 offers a Bpin-Ni­(I) species I , which undergoes oxidative addition into aryl bromide in N -(2-bromobenzoyl)­indoles 1 to generate the arylnickel­(III) intermediate II , which could undergo the intramolecular dearomatization with excellent control of diastereo- and enantioselectivities to form the chiral benzylnickel­(III) species III .…”