scholarly journals A metal-free approach for the hydrogenolysis of unactivated C(aryl)–C(alkyl) bonds

2021 ◽  
Author(s):  
Huadong Wang ◽  
Yuliang Xu ◽  
Yizhou Yang ◽  
Yizhen Liu ◽  
Zhen Li
Keyword(s):  
Heterogeneous Catalysts ◽  
Reaction Pathway ◽  
Petroleum Industry ◽  
Transition Metal Catalysts ◽  
Waste Plastics ◽  
Mechanistic Studies ◽  
Synergistic Activation ◽  
Synthetic Utility ◽  
Selective Hydrogenolysis ◽  
Opening Up

Abstract The hydrogenolysis of C–C bonds is among one of the most important processes in the petroleum industry which has been considered as a viable way to recycle waste polyolefins. These transformations typically rely on heterogeneous catalysts and take place at high temperature and high pressure with limited selectivity. Employing homogenous transition metal catalysts, while allowing the hydrogenolysis of C–C bonds to proceed under much milder conditions, is only suitable for substrates containing strained C–C bonds or directing groups. Here we report that a borenium complex can catalyze the selective hydrogenolysis of unstrained C(aryl)–C(alkyl) bonds of alkylarenes at ambient temperature, affording the corresponding alkanes and arenes. This method does not require the assistance of directing groups, and tolerates a range of functional groups. Mechanistic studies suggest a reaction pathway that involves a synergistic activation of dihydrogen by the borenium complex and alkylarenes, followed by retro-Friedel-Crafts reaction to cleave the C(aryl)–C(alkyl) bonds. The synthetic utility of this protocol was demonstrated by the conversion of post-consumer polystyrene into valuable benzene and phenylalkanes with mass recovery above 90%, thus opening up new avenues for the recycling of aromatic chemicals from waste plastics.

Synthetic and Mechanistic Studies of a Versatile Heteroaryl Thioether Directing Group for Pd(II) Catalysis

2019 ◽  
Author(s):  
Andrew Romine ◽  
Kin Yang ◽  
Malkanthi Karunananda ◽  
Jason Chen ◽  
Keary Engle
Keyword(s):  
Mechanistic Studies ◽  
Salvianolic Acid ◽  
Wide Range ◽  
Computational Data ◽  
Synthetic Utility ◽  
Directing Group ◽  
High Yields ◽  
Julia Olefination ◽  
Reaction Progress Kinetic Analysis

A weakly coordinating monodentate heteroaryl thioether directing group has been developed for use in Pd(II) catalysis to orchestrate key elementary steps in the catalytic cycle that require conformational flexibility in a manner that is difficult to accomplish with traditional strongly coordinating directing groups. This benzothiazole thioether, (BT)S, directing group can be used to promote oxidative Heck reactivity of internal alkenes providing a wide range of products in moderate to high yields. To demonstrate the broad applicability of this directing group, arene C–H olefination was also successfully developed. Reaction progress kinetic analysis provides insights into the role of the directing group in each reaction, which is supplemented with computational data for the oxidative Heck reaction. Furthermore, this (BT)S directing group can be transformed into a number of synthetically useful functional groups, including a sulfone for Julia olefination, allowing it to serve as a “masked olefin” directing group in synthetic planning. In order to demonstrate this synthetic utility, natural products (+)-salvianolic acid A and salvianolic acid F are formally synthesized using the (BT)S directed C–H olefination as the key step.

Arylboronic Acid-Catalyzed C-Allylation of Unprotected Oximes

2019 ◽  
Author(s):  
Juha Siitonen ◽  
Padmanabha V. Kattamuri ◽  
Muhammed Yousufuddin ◽  
Laszlo Kurti
Keyword(s):  
Total Synthesis ◽  
Acid Catalysts ◽  
Mechanistic Studies ◽  
Arylboronic Acid ◽  
Synthetic Utility ◽  
Acid Catalyzed

Unprotected keto- and aldoximes are readily <i>C</i>-allylated with allyl diisopropyl boronate in the presence of arylboronic acid catalysts to yield highly-substituted <i>N</i>-alpha-secondary (2°) and tertiary (3°) hydroxylamines. The method’s synthetic utility is demonstrated with the total synthesis of the trace alkaloid <i>N</i>-methyl-euphococcine. Preliminary experimental and computational mechanistic studies point toward the formation of a boroxine as the active allylating species.<br>

scholarly journals Transition-Metal-Free Boryl Substitution Using Silylboranes and Alkoxy Bases

Synlett ◽  
2017 ◽  
Vol 28 (11) ◽  
pp. 1258-1267 ◽  
Author(s):  
Hajime Ito ◽  
Eiji Yamamoto ◽  
Satoshi Maeda ◽  
Tetsuya Taketsugu
Keyword(s):  
Transition Metal ◽  
Functional Group ◽  
Experimental Studies ◽  
Transition Metal Catalysts ◽  
Alkyl Halides ◽  
Aryl Halides ◽  
Nucleophilic Attack ◽  
Important Class ◽  
Mechanistic Studies ◽  
Induced Reaction

Silylboranes are used as borylation reagents for organohalides in the presence of alkoxy bases without transition-metal catalysts. PhMe2Si–B(pin) reacts with a variety of aryl, alkenyl, and alkyl halides, including sterically hindered examples, to provide the corresponding organoboronates in good yields with high borylation/silylation ratios, showing good functional group compatibility. Halogenophilic attack of a silyl nucleophile on organohalides, and subsequent nucleophilic attack on the boron electrophile are identified to be crucial, based on the results of extensive theoretical and experimental studies. This boryl­ation reaction is further applied to the first direct dimesitylboryl (BMes2) substitution of aryl halides using Ph2MeSi–BMes2 and Na(O-t-Bu), affording aryldimesitylboranes, which are regarded as an important class of compounds for organic materials.1 Introduction2 Boryl Substitution of Organohalides with PhMe2Si–B(pin)/Alkoxy Bases3 Mechanistic Investigations4 DFT Mechanistic Studies Using an Artificial Force Induced Reaction (AFIR) Method5 Dimesitylboryl Substitution of Aryl Halides with Ph2MeSi–BMes2/Na(O-t-Bu)6 Conclusion

scholarly journals A combined experimental and theoretical study on the reactivity of nitrenes and nitrene radical anions

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Yujing Guo ◽  
Chao Pei ◽  
Rene M. Koenigs
Keyword(s):  
Radical Anion ◽  
Room Temperature ◽  
Theoretical Study ◽  
Transition Metal Catalysts ◽  
Transfer Reactions ◽  
Mechanistic Studies ◽  
Reaction Conditions ◽  
Nitrene Transfer ◽  
Triplet Nitrene ◽  
Nitrogen Bonds

AbstractNitrene transfer reactions represent one of the key reactions to rapidly construct new carbon-nitrogen bonds and typically require transition metal catalysts to control the reactivity of the pivotal nitrene intermediate. Herein, we report on the application of iminoiodinanes in amination reactions under visible light photochemical conditions. While a triplet nitrene can be accessed under catalyst-free conditions, the use of a suitable photosensitizer allows the access of a nitrene radical anion. Computational and mechanistic studies rationalize the access and reactivity of triplet nitrene and nitrene radical anion and allow the direct comparison of both amination reagents. We conclude with applications of both reagents in organic synthesis and showcase their reactivity in the reaction with olefins, which underline their markedly distinct reactivity. Both reagents can be accessed under mild reaction conditions at room temperature without the necessity to exclude moisture or air, which renders these metal-free, photochemical amination reactions highly practical.

scholarly journals Asymmetric Addition of Allylsilanes to Aldehydes – A Cr/Photoredox Dual Catalytic Approach Complementing the Hosomi–Sakurai Reaction

2021 ◽  
Author(s):  
Felix Schäfers ◽  
Subhabrata Dutta ◽  
Roman Kleinmans ◽  
Christian Mück-Lichtenfeld ◽  
Frank Glorius
Keyword(s):  
Organic Chemistry ◽  
Transition State ◽  
Bioactive Compound ◽  
General Strategy ◽  
Acid Activation ◽  
Mechanistic Studies ◽  
Mild Conditions ◽  
Homoallylic Alcohols ◽  
Synthetic Utility ◽  
Fundamental Transformation

The allylation of aldehydes is a fundamental transformation in synthetic organic chemistry. Among the multitude of available reagents, especially allylsilanes have been established as preferred allyl source. As initially reported by Hosomi & Sakurai, these non-toxic and highly stable reagents add to carbonyls via an open transition state upon Lewis acid activation. Herein, we report a general strategy to access a variety of valuable homoallylic alcohols in opposite chemo- and diastereoselectivity to the established Hosomi–Sakurai conditions by switching to photocatalytic activation in combination with a closed transition state (Chromium catalysis). Moreover, this dual catalytic approach displays a straightforward way to introduce excellent levels of enantioselectivity and its mild conditions allow for a broad substrate scope including chiral boron-substituted products as a highlight. To emphasize the synthetic utility, our method was applied as the key step in the synthesis of a bioactive compound and in the late-stage functionalization of steroid derivatives. Detailed mechanistic studies and DFT calculations hint towards an unprecedented photo-initiated chain being operative.

scholarly journals Cobalt-catalyzed deoxygenative triborylation of allylic ethers to access 1,1,3-triborylalkanes

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Wei Jie Teo ◽  
Xiaoxu Yang ◽  
Yeng Yeng Poon ◽  
Shaozhong Ge
Keyword(s):  
Building Blocks ◽  
Mechanistic Studies ◽  
Deuterium Labeling ◽  
Bond Forming ◽  
Carbon Carbon Bond ◽  
Synthetic Utility ◽  
Reaction Proceeds ◽  
Site Selective ◽  
And Control ◽  
Allylic Ethers

Abstract Polyborylated organic compounds have been emerging as versatile building blocks in chemical synthesis. Here we report a selective cobalt-catalyzed deoxygenative 1,1,3-triborylation reaction of allylic ethers with pinacolborane to prepare 1,1,3-triborylalkane compounds. With naturally abundant and/or synthetic cinnamic methyl ethers as starting materials, we have achieved the synthesis of a variety of 1,1,3-triborylalkanes (25 examples). The synthetic utility of these 1,1,3-triborylalkanes is demonstrated through site-selective allylation, protodeborylation, and consecutive carbon-carbon bond-forming reactions. Mechanistic studies including deuterium-labeling and control experiments suggest that this 1,1,3-triborylation reaction proceeds through initial cobalt-catalyzed deoxygenative borylation of allylic ethers to form allylic boronates followed by cobalt-catalyzed 1,1-diborylation of the resulting allylic boronates.

scholarly journals Manganese-mediated reductive functionalization of activated aliphatic acids and primary amines

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Zhan Li ◽  
Ke-Feng Wang ◽  
Xin Zhao ◽  
Huihui Ti ◽  
Xu-Ge Liu ◽  
...  
Keyword(s):  
Carboxylic Acids ◽  
Late Stage ◽  
Materials Science ◽  
Reaction Pathway ◽  
Chemical Conversion ◽  
Primary Amines ◽  
Mechanistic Studies ◽  
Reaction Conditions ◽  
Aliphatic Acids ◽  
Redox Active

Abstract Alkyl carboxylic acids as well as primary amines are ubiquitous in all facets of biological science, pharmaceutical science, chemical science and materials science. By chemical conversion to redox-active esters (RAE) and Katritzky’s N-alkylpyridinium salts, respectively, alkyl carboxylic acids and primary amines serve as ideal starting materials to forge new connections. In this work, a Mn-mediated reductive decarboxylative/deaminative functionalization of activated aliphatic acids and primary amines is disclosed. A series of C-X (X = S, Se, Te, H, P) and C-C bonds are efficiently constructed under simple and mild reaction conditions. The protocol is applicable to the late-stage modification of some structurally complex natural products or drugs. Preliminary mechanistic studies suggest the involvement of radicals in the reaction pathway.

Mechanistic Studies on Pyridoxal Phosphate Synthase:  The Reaction Pathway Leading to a Chromophoric Intermediate

2008 ◽  
Vol 130 (10) ◽  
pp. 3043-3052 ◽  
Author(s):  
Jeremiah W. Hanes ◽  
Kristin E. Burns ◽  
David G. Hilmey ◽  
Abhishek Chatterjee ◽  
Pieter C. Dorrestein ◽  
...  
Keyword(s):  
Pyridoxal Phosphate ◽  
Reaction Pathway ◽  
Mechanistic Studies ◽  
Phosphate Synthase

scholarly journals Atomically-Dispersed Iridium on Indium Tin Oxide Efficiently Catalyzes Water Splitting

2020 ◽  
Author(s):  
Dmitry Lebedev ◽  
Roman Ezhov Ezhov ◽  
Javier Heras-Domingo ◽  
Aleix Comas Vives ◽  
Nicolas Kaeffer ◽  
...  
Keyword(s):  
Oxygen Evolution ◽  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Heterogeneous Catalysts ◽  
Transition Metal Catalysts ◽  
Nucleophilic Attack ◽  
Late Transition Metals ◽  
Absorption Studies ◽  
Late Transition

Heterogeneous catalysts in the form of atomically dispersed metals on a support provide the most efficient utilization of the active component, which is especially important for scarce and expensive late transition metals. These catalysts also enable unique opportunities to understand reaction pathways through detailed spectroscopic and computational studies. Here we demonstrate that atomically dispersed iridium sites on indium tin oxide prepared via surface organometallic chemistry display exemplary catalytic activity in one of the most challenging electrochemical processes, oxygen evolution reaction (OER). In situ X-ray absorption studies revealed the formation of IrV=O intermediate under OER conditions with an Ir–O distance of 1.83 Å. Modelling of the reaction mechanism indicates that Ir(V)=O is likely a catalyst resting state, which is subsequently oxidized to Ir(VI) enabling fast water nucleophilic attack and oxygen evolution. We anticipate that the applied strategy can be instrumental in preparing and studying a broad range of atomically dispersed transition metal catalysts on conductive oxides for (photo)electrochemical applications.

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