scholarly journals Migratory functionalization of unactivated alkyl bromides for construction of all-carbon quaternary centers via transposed tert-C-radicals

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Chuan Zhu ◽  
Ze-Yao Liu ◽  
Luning Tang ◽  
Heng Zhang ◽  
Yu-Feng Zhang ◽  
...  
Keyword(s):  
Alkyl Halide ◽  
Coupling Reactions ◽  
Quaternary Centers ◽  
Cross Coupling Reactions ◽  
Radical Trapping ◽  
Alkyl Bromides ◽  
Bond Homolysis ◽  
Radical Generation ◽  
Metal Catalyzed ◽  
Chain Walking

Abstract Despite remarkable recent advances in transition-metal-catalyzed C(sp3)−C cross-coupling reactions, there remain challenging bond formations. One class of such reactions include the formation of tertiary-C(sp3)−C bonds, presumably due to unfavorable steric interactions and competing isomerizations of tertiary alkyl metal intermediates. Reported herein is a Ni-catalyzed migratory 3,3-difluoroallylation of unactivated alkyl bromides at remote tertiary centers. This approach enables the facile construction of otherwise difficult to prepare all-carbon quaternary centers. Key to the success of this transformation is an unusual remote functionalization via chain walking to the most sterically hindered tertiary C(sp3) center of the substrate. Preliminary mechanistic and radical trapping studies with primary alkyl bromides suggest a unique mode of tertiary C-radical generation through chain-walking followed by Ni–C bond homolysis. This strategy is complementary to the existing coupling protocols with tert-alkyl organometallic or -alkyl halide reagents, and it enables the expedient formation of quaternary centers from easily available starting materials.

Monodentate Trialkylphosphines: Privileged Ligands in Metal-catalyzed Crosscoupling Reactions

2020 ◽  
Vol 24 (3) ◽  
pp. 231-264 ◽  
Author(s):  
Kevin H. Shaughnessy
Keyword(s):  
Transition Metal ◽  
Cross Coupling ◽  
Coupling Reactions ◽  
Cross Coupling Reactions ◽  
Aryl Bromides ◽  
Wide Range ◽  
Sterically Demanding ◽  
Transition Metal Catalyzed ◽  
Catalyzed Reactions ◽  
Metal Catalyzed

Phosphines are widely used ligands in transition metal-catalyzed reactions. Arylphosphines, such as triphenylphosphine, were among the first phosphines to show broad utility in catalysis. Beginning in the late 1990s, sterically demanding and electronrich trialkylphosphines began to receive attention as supporting ligands. These ligands were found to be particularly effective at promoting oxidative addition in cross-coupling of aryl halides. With electron-rich, sterically demanding ligands, such as tri-tertbutylphosphine, coupling of aryl bromides could be achieved at room temperature. More importantly, the less reactive, but more broadly available, aryl chlorides became accessible substrates. Tri-tert-butylphosphine has become a privileged ligand that has found application in a wide range of late transition-metal catalyzed coupling reactions. This success has led to the use of numerous monodentate trialkylphosphines in cross-coupling reactions. This review will discuss the general properties and features of monodentate trialkylphosphines and their application in cross-coupling reactions of C–X and C–H bonds.

Synthesis of Marine Polyacetylenes Callyberynes A−C by Transition-Metal-Catalyzed Cross-Coupling Reactions to sp Centers

2006 ◽  
Vol 71 (7) ◽  
pp. 2802-2810 ◽  
Author(s):  
Susana López ◽  
Francisco Fernández-Trillo ◽  
Pilar Midón ◽  
Luis Castedo ◽  
Carlos Saá
Keyword(s):  
Transition Metal ◽  
Cross Coupling ◽  
Coupling Reactions ◽  
Cross Coupling Reactions ◽  
Transition Metal Catalyzed ◽  
Metal Catalyzed

scholarly journals Protecting group-free, selective cross-coupling of alkyltrifluoroborates with borylated aryl bromides via photoredox/nickel dual catalysis

2015 ◽  
Vol 112 (39) ◽  
pp. 12026-12029 ◽  
Author(s):  
Yohei Yamashita ◽  
John C. Tellis ◽  
Gary A. Molander
Keyword(s):  
Small Molecules ◽  
Functional Group ◽  
Cross Coupling ◽  
Differential Protection ◽  
Coupling Reactions ◽  
Protecting Group ◽  
Cross Coupling Reactions ◽  
Aryl Bromides ◽  
Rapid Construction ◽  
Metal Catalyzed

Orthogonal reactivity modes offer substantial opportunities for rapid construction of complex small molecules. However, most strategies for imparting orthogonality to cross-coupling reactions rely on differential protection of reactive sites, greatly reducing both atom and step economies. Reported here is a strategy for orthogonal cross-coupling wherein a mechanistically distinct activation mode for transmetalation of sp3-hybridized organoboron reagents enables C-C bond formation in the presence of various protected and unprotected sp2-hybridized organoborons. This manifold has the potential for broad application, because orthogonality is inherent to the activation mode itself. The diversification potential of this platform is shown in the rapid elaboration of a trifunctional lynchpin through various transition metal-catalyzed processes without nonproductive deprotection or functional group manipulation steps.

scholarly journals Copper’s rapid ascent in visible-light photoredox catalysis

Science ◽  
2019 ◽  
Vol 364 (6439) ◽  
pp. eaav9713 ◽  
Author(s):  
Asik Hossain ◽  
Aditya Bhattacharyya ◽  
Oliver Reiser
Keyword(s):  
Visible Light ◽  
Organic Dyes ◽  
Low Cost ◽  
Cross Coupling ◽  
Coupling Reactions ◽  
Photoredox Catalysis ◽  
Cross Coupling Reactions ◽  
Rapid Ascent ◽  
Catalyzed Reactions ◽  
Metal Catalyzed

Visible-light photoredox catalysis offers a distinct activation mode complementary to thermal transition metal catalyzed reactions. The vast majority of photoredox processes capitalizes on precious metal ruthenium(II) or iridium(III) complexes that serve as single-electron reductants or oxidants in their photoexcited states. As a low-cost alternative, organic dyes are also frequently used but in general suffer from lower photostability. Copper-based photocatalysts are rapidly emerging, offering not only economic and ecological advantages but also otherwise inaccessible inner-sphere mechanisms, which have been successfully applied to challenging transformations. Moreover, the combination of conventional photocatalysts with copper(I) or copper(II) salts has emerged as an efficient dual catalytic system for cross-coupling reactions.

Iron-Catalyzed Cross-Coupling: Mechanistic Insight for Rational Applications in Synthesis

Synthesis ◽  
2017 ◽  
Vol 49 (15) ◽  
pp. 3269-3280 ◽  
Author(s):  
Tobias Parchomyk ◽  
Konrad Koszinowski
Keyword(s):  
Catalyst Activity ◽  
Cross Coupling ◽  
Short Review ◽  
Coupling Reactions ◽  
Cross Coupling Reactions ◽  
Open Questions ◽  
Carbon Carbon Bonds ◽  
Bond Homolysis ◽  
Molecular Complexity ◽  
Synthetic Application

Iron-catalyzed cross-coupling reactions provide a promising way to form new carbon–carbon bonds and build up molecular complexity. This short review presents recent advances in the synthetic application of these reactions as well as in the elucidation of their mechanism. It also highlights remaining problems and aims at pointing out ways toward possible remedies.1 Introduction2 Synthesis: Recent Accomplishments and Unsolved Problems2.1 Substrate Scope: Electrophiles2.2 Substrate Scope: Nucleophiles2.3 Catalyst Activity and Chemoselectivity2.4 Stereoselectivity2.5 Practical Aspects3 Mechanism: Recent Insights and Open Questions3.1 Transmetallation and Activation of the Iron Precatalyst3.2 Coupling via Oxidative Addition and Reductive Elimination3.3 Coupling via C–X Bond Homolysis and Radical Rebound3.4 Coupling via Bimolecular C–X Bond Homolysis3.5 Other Reactions of Organoiron Species with Electrophiles4 Toward Rational Reaction Improvement5 Conclusion

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