scholarly journals Site-Fixed Hydroboration of Alkenes under Metal-Free Conditions: Scope and Mechanistic Studies

2021 ◽  
Author(s):  
Sida Li ◽  
Chenyang Hu ◽  
Xin Cui ◽  
Liu Leo Liu ◽  
Lipeng Wu
Keyword(s):  
Reaction Pathway ◽  
Original Position ◽  
Side Reactions ◽  
Single Electron Transfer ◽  
Mechanistic Studies ◽  
Radical Species ◽  
Metal Free ◽  
Proton Source ◽  
Alkene Oligomerization ◽  
Metal Catalyzed

An unprecedented and general metal-free hydroboration of alkenes with BBr3 as the boration reagent in the presence of iPr2NEt is reported. The addition of iPr2NEt not only suppresses alkene oligomerization and bromoboration side reactions, but also provides a proton source for hydroboration. More importantly, the site-fixed installation of a boryl group at the original position of the internal double-bond is easily achieved using our strategy as compared with traditional transition-metal-catalyzed hydroboration processes. Preliminary studies on the mechanism revealed a distinct reaction pathway that involves radical species and may operate through frustrated-Lewispair-type single-electron transfer.

scholarly journals Site-Fixed Hydroboration of Alkenes under Metal-Free Conditions: Scope and Mechanistic Studies

2021 ◽  
Author(s):  
Sida Li ◽  
Chenyang Hu ◽  
Xin Cui ◽  
Liu Leo Liu ◽  
Lipeng Wu
Keyword(s):  
Reaction Pathway ◽  
Original Position ◽  
Side Reactions ◽  
Single Electron Transfer ◽  
Mechanistic Studies ◽  
Radical Species ◽  
Metal Free ◽  
Proton Source ◽  
Alkene Oligomerization ◽  
Metal Catalyzed

An unprecedented and general metal-free hydroboration of alkenes with BBr3 as the boration reagent in the presence of iPr2NEt is reported. The addition of iPr2NEt not only suppresses alkene oligomerization and bromoboration side reactions, but also provides a proton source for hydroboration. More importantly, the site-fixed installation of a boryl group at the original position of the internal double-bond is easily achieved using our strategy as compared with traditional transition-metal-catalyzed hydroboration processes. Preliminary studies on the mechanism revealed a distinct reaction pathway that involves radical species and may operate through frustrated-Lewispair-type single-electron transfer.

scholarly journals THERMODYNAMIC AND KINETIC INVESTIGATION OF ANTIRADICAL POTENTIAL OF CYANIDIN

2020 ◽  
pp. 85-95
Author(s):  
Dejan Milenković ◽  
Jelena Đorović ◽  
Edina Avdović ◽  
Žiko Milanović ◽  
Marko Antonijević
Keyword(s):  
Electron Transfer ◽  
Antiradical Activity ◽  
Reaction Pathway ◽  
Radical Scavenging ◽  
Single Electron Transfer ◽  
Radical Species ◽  
Electron Transfer Mechanism ◽  
Favorable Reaction ◽  
Antioxidant Mechanisms ◽  
Polar Water

In the present paper, M05-2X/6-311+G(d,p) level of theory was used to investigate antiradical activity of cyanidin towards highly damaging radical species (.OH, .OCH3, .OOH and .OOCH3). The applied method successfully reproduces the values of reaction enthalpies (ΔHBDE, ΔHIP, and ΔHPA). These parameters are important to determine which of the mechanisms are preferred. Reaction enthalpies related to the antioxidant mechanisms of the investigated species were calculated in water and DMSO. The enthalpies of reactions indicate the preferred radical scavenging mechanisms in polar (water) and polar aprotic (DMSO) solvents. Single- electron transfer followed by proton transfer (SET-PT) is not a favorable reaction pathway under any conditions. Both remaining mechanisms, HAT and SPLET, are suitable for the reaction of cyanidin with •OH and •OCH3 in all solvents under investigation. On the other hand, in the reaction of cyanidin with •OOH and •OOCH3, the SPLET mechanism is possible in both solvents. Simulation of the reaction of the cyanidin anion with the hydroxy radical confirmed that position 3` of Cy‒O- is the most suitable for reaction with •OH through electron transfer mechanism (ET) in both solvents.

scholarly journals Metal‐Free Deoxygenation of Amine N–Oxides: Synthetic and Mechanistic Studies

ChemPhysChem ◽  
2021 ◽  
Author(s):  
Sami Lakhdar ◽  
William Lecroq ◽  
Jules Schleinitz ◽  
Mallaury Billoue ◽  
Anna Perfetto ◽  
...  
Keyword(s):  
Mechanistic Studies ◽  
Metal Free

scholarly journals Recent Advances in Transition-Metal-Free (4+3)-Annulations

Synthesis ◽  
2021 ◽  
Author(s):  
Heather Lam ◽  
Mark Lautens ◽  
Xavier Abel-Snape ◽  
Martin F. Köllen
Keyword(s):  
Transition Metal ◽  
Boronic Acid ◽  
Lewis Acids ◽  
Acid Catalysis ◽  
Heterocyclic Carbenes ◽  
Bronsted Acids ◽  
Metal Free ◽  
Previous Review ◽  
Dual Activation ◽  
Metal Catalyzed

Abstract(4+3)-Annulations are incredibly versatile reactions which combine a 4-atom synthon and a 3-atom synthon to form both 7-membered carbocycles as well as heterocycles. We have previously reviewed transition-metal-catalyzed (4+3)-annulations. In this review, we will cover examples involving bases, NHCs, phosphines, Lewis and Brønsted acids as well as some rare examples of boronic acid catalysis and photocatalysis. In analogy to our previous review, we exclude annulations involving cyclic dienes like furan, pyrrole, cyclohexadiene or cyclopentadiene, as Chiu, Harmata, Fernándes and others have recently published reviews encompassing such substrates. We will however discuss the recent additions (2010–2020) to the literature on (4+3)-annulations involving other types of 4-atom-synthons.1 Introduction2 Bases3 Annulations Using N-Heterocyclic Carbenes3.1 N-Heterocyclic Carbenes (NHCs)3.2 N-Heterocyclic Carbenes and Base Dual-Activation4 Phosphines5 Acids5.1 Lewis Acids5.2 Brønsted Acids6 Boronic Acid Catalysis and Photocatalysis7 Conclusion

scholarly journals Heterobiaryl synthesis by contractive C–C coupling via P(V) intermediates

Science ◽  
2018 ◽  
Vol 362 (6416) ◽  
pp. 799-804 ◽  
Author(s):  
Michael C. Hilton ◽  
Xuan Zhang ◽  
Benjamin T. Boyle ◽  
Juan V. Alegre-Requena ◽  
Robert S. Paton ◽  
...  
Keyword(s):  
Cross Coupling ◽  
The Other ◽  
Coupling Reactions ◽  
Mechanistic Studies ◽  
Alternative Approach ◽  
Metal Catalyzed ◽  
Polar Functional Groups ◽  
Pharmacological Function ◽  
Complex Drug ◽  
Acidic Alcohol

Heterobiaryls composed of pyridine and diazine rings are key components of pharmaceuticals and are often central to pharmacological function. We present an alternative approach to metal-catalyzed cross-coupling to make heterobiaryls using contractive phosphorus C–C couplings, also termed phosphorus ligand coupling reactions. The process starts by regioselective phosphorus substitution of the C–H bonds para to nitrogen in two successive heterocycles; ligand coupling is then triggered via acidic alcohol solutions to form the heterobiaryl bond. Mechanistic studies imply that ligand coupling is an asynchronous process involving migration of one heterocycle to the ipso position of the other around a central pentacoordinate P(V) atom. The strategy can be applied to complex drug-like molecules containing multiple reactive sites and polar functional groups, and also enables convergent coupling of drug fragments and late-stage heteroarylation of pharmaceuticals.

scholarly journals Oxidizing agents in metal-catalyzed and metal-free C-H functionalization of heteroarenes.

ARKIVOC ◽  
2021 ◽  
Vol 2021 (9) ◽  
Author(s):  
Irina Alexandrovna Utepova ◽  
Oleg Nikolaevich Chupakhin ◽  
Maria Alexandrovna Trestsova ◽  
Alexandra Alexandrovna Musikhina ◽  
Alexandr Alexandrovich Shchepochkin ◽  
...  
Keyword(s):  
Metal Free ◽  
Oxidizing Agents ◽  
Metal Catalyzed

scholarly journals SET activation of nitroarenes by 2-azaallyl anions as a straightforward access to 2,5-dihydro-1,2,4-oxadiazoles

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Dong Zou ◽  
Lishe Gan ◽  
Fan Yang ◽  
Huan Wang ◽  
Youge Pu ◽  
...  
Keyword(s):  
Transition Metal ◽  
Experimental Evidence ◽  
Radical Anion ◽  
Reaction Pathway ◽  
Cycloaddition Reaction ◽  
Electron Donors ◽  
Ring Closure ◽  
Computational Studies ◽  
Metal Free ◽  
Radical Coupling

AbstractThe use of nitroarenes as amino sources in synthesis is challenging. Herein is reported an unusual, straightforward, and transition metal-free method for the net [3 + 2]-cycloaddition reaction of 2-azaallyl anions with nitroarenes. The products of this reaction are diverse 2,5-dihydro-1,2,4-oxadiazoles (>40 examples, up to 95% yield). This method does not require an external reductant to reduce nitroarenes, nor does it employ nitrosoarenes, which are often used in N–O cycloadditions. Instead, it is proposed that the 2-azaallyl anions, which behave as super electron donors (SEDs), deliver an electron to the nitroarene to generate a nitroarene radical anion. A downstream 2-azaallyl radical coupling with a newly formed nitrosoarene is followed by ring closure to afford the observed products. This proposed reaction pathway is supported by computational studies and experimental evidence. Overall, this method uses readily available materials, is green, and exhibits a broad scope.

Five-Membered Hetarene N-Oxides: Recent Advances in Synthesis and Reactivity

Synthesis ◽  
2021 ◽  
Author(s):  
Leonid Fershtat ◽  
Fedor Teslenko
Keyword(s):  
Transition Metal ◽  
Medicinal Chemistry ◽  
Materials Science ◽  
State Of The Art ◽  
Short Review ◽  
Advanced Materials ◽  
Metal Free ◽  
Recent Advances ◽  
Application Potential ◽  
Metal Catalyzed

Five-membered heterocyclic N-oxides attracted special attention due to their strong application potential in medicinal chemistry and advanced materials science. In this regard, novel methods for their synthesis and functionalization are constantly required. In this short review, recent state-of-the-art achievements in the chemistry of isoxazoline N-oxides, 1,2,3-triazole 1-oxides and 1,2,5-oxadiazole 2-oxides are briefly summarized. Main routes to transition-metal-catalyzed and metal-free functionalization protocols along with mechanistic considerations are outlined. Transformation patterns of the hetarene N-oxide rings as precursors to other nitrogen heterocyclic systems are also presented.

A Formal Metal-Free γ-Arylation of 1,3-Dicarbonyl Compounds via a Sequence of Isomerization/1,4-Addition/[3,3]-Sigmatropic Rearrangement

2021 ◽  
Author(s):  
Shi-Chao Lu ◽  
Fuqiang Wen ◽  
Xidong Guan
Keyword(s):  
Sigmatropic Rearrangement ◽  
Mechanistic Studies ◽  
Dicarbonyl Compounds ◽  
Metal Free

A metal-free redox arylation of alkynes with sulfoxides has been developed to provide an unconventional access to diverse γ-arylated 1,3-dicarbonyl compounds in an atom-economical manner. Mechanistic studies suggest that a...

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