A New Catalytic Method for Producing Preceramic Polysilazanes

1986 ◽  
Vol 73 ◽  
Author(s):  
Yigal D. Blum ◽  
Richard M. Laine ◽  
Kenneth B. Schwartz ◽  
David J. Rowcliffe ◽  
Robert C. Bening ◽  
...  
Keyword(s):  
Transition Metal ◽  
Carbon Content ◽  
Low Temperatures ◽  
Bond Formation ◽  
Catalytic Method ◽  
Reaction Conditions ◽  
Preceramic Polymers

ABSTRACTA transition metal (e.g., Ru3 (CO)12, Pt/C) catalyzed process for Si-N bond formation is discussed that provides a new route to mono-, oligo-, and polysilazanes. The catalysts function by activating Si-H bonds in the pres-ence of ammonia. Polymeric silazanes can also be produced from oligomers in the presence of ammonia at low temperatures. This method allows us to control or modify the composition of the polysilazane during or after the polymeriza-tion. A variety of polysilazanes were prepared and converted to Si3 N4 with ceramic yields ranging from 55%-85%. By varying the monomers and reaction conditions, we can control the nitrogen and carbon content in the preceramic polymers, which enables us to obtain ceramic products that are primarily Si3N4and simultaneously minimizes the coproduction of SiC and C.

Ruthenium-Catalyzed Room-Temperature Coupling of α-Keto Sulfoxonium Ylides and Cyclopropanols for δ-Diketone Synthesis

2021 ◽  
Author(s):  
Lili Fang ◽  
Shuaixin Fan ◽  
Tielei Li ◽  
Weiping Wu ◽  
Jin Zhu
Keyword(s):  
Transition Metal ◽  
Room Temperature ◽  
Low Cost ◽  
Rhodium Catalyst ◽  
Catalytic Method ◽  
Reaction Conditions ◽  
Transition Metal Catalyzed ◽  
Metal Catalyzed

Previous transition metal-catalyzed synthesis of δ-diketones is plagued by high cost of rhodium catalyst and harsh reaction conditions. Herein a low-cost, room temperature ruthenium catalytic method is developed based on...

Direct Cyclization of Alkenyl Thioester via Transition Metal‐hydrogen Atom Transfer/radical‐polar Crossover Mechanism

2019 ◽  
Author(s):  
Shiori Date ◽  
Kensei Hamasaki ◽  
Karen Sunagawa ◽  
Hiroki Koyama ◽  
Chikayoshi Sebe ◽  
...  
Keyword(s):  
Natural Products ◽  
Hydrogen Atom ◽  
Transition Metal ◽  
Hydrogen Atom Transfer ◽  
Synthetic Method ◽  
Atom Transfer ◽  
Reaction Conditions ◽  
Hydride Hydrogen ◽  
Sulfur Heterocycles ◽  
One Step

<div>We report here a catalytic, Markovnikov selective, and scalable synthetic method for the synthesis of saturated sulfur heterocycles, which are found in the structures of pharmaceuticals and natural products, in one step from an alkenyl thioester. Unlike a potentially labile alkenyl thiol, an alkenyl thioester is stable and easy to prepare. The powerful Co catalysis via a cobalt hydride hydrogen atom transfer and radical-polar crossover mechanism enabled simultaneous cyclization and deprotection. The substrate scope was expanded by the extensive optimization of the reaction conditions and tuning of the thioester unit.</div>

Carbon Dioxide-Mediated C(sp2)–H Arylation of Primary and Secondary Benzylamines

2018 ◽  
Author(s):  
Mohit Kapoor ◽  
Pratibha Chand-Thakuri ◽  
Michael Young
Keyword(s):  
Carbon Dioxide ◽  
Transition Metal ◽  
Bond Activation ◽  
Bond Formation ◽  
Carbon Bond ◽  
Chelate Effect ◽  
Free Amine ◽  
Carbon Carbon Bond ◽  
New Strategy ◽  
Metal Catalyzed

Carbon-carbon bond formation by transition metal-catalyzed C–H activation has become an important strategy to fabricate new bonds in a rapid fashion. Despite the pharmacological importance of <i>ortho</i>-arylbenzylamines, however, effective <i>ortho</i>-C–C bond formation from C–H bond activation of free primary and secondary benzylamines using Pd<sup>II</sup> remains an outstanding challenge. Presented herein is a new strategy for constructing <i>ortho</i>-arylated primary and secondary benzylamines mediated by carbon dioxide (CO<sub>2</sub>). The use of CO<sub>2</sub> is critical to allowing this transformation to proceed under milder conditions than previously reported, and that are necessary to furnish free amine products that can be directly used or elaborated without the need for deprotection. In cases where diarylation is possible, a chelate effect is demonstrated to facilitate selective monoarylation.

Pd Catalyzed N1/N4 Arylation of Piperazine for Synthesis of Drugs, Biological and Pharmaceutical Targets: An Overview of Buchwald Hartwig Amination Reaction of Piperazine in Drug Synthesis

2018 ◽  
Vol 15 (2) ◽  
pp. 208-220 ◽  
Author(s):  
Vaibhav Mishra ◽  
Tejpal Singh Chundawat
Keyword(s):  
Bond Formation ◽  
Catalyst Design ◽  
Biologically Active ◽  
Reaction Conditions ◽  
Biological Targets ◽  
Amination Reaction ◽  
Drug Synthesis ◽  
Substituted Piperazine ◽  
Approved Drugs ◽  
Fda Approved Drugs

Background: Substituted piperazine heterocycles are among the most significant structural components of pharmaceuticals. N1/N4 substituted piperazine containing drugs and biological targets are ranked 3rd in the top most frequent nitrogen heterocycles in U.S. FDA approved drugs. The high demand of N1/N4 substituted piperazine containing biologically active compounds and U.S. FDA approved drugs, has prompted the development of Pd catalyzed C-N bond formation reactions for their synthesis. Buchwald-Hartwig reaction is the key tool for the synthesis of these compounds. Objective: This review provides strategies for Pd catalyzed C-N bond formation at N1/N4 of piperazine in the synthesis of drugs and biological targets with diverse use of catalyst-ligand system and reaction parameters. Conclusion: It is clear from the review that a vast amount of work has been done in the synthesis of N1/N4 substituted piperazine containing targets under the Pd catalyzed Buchwald-Hartwig amination of aryl halides by using different catalyst-ligand systems. These methods have become increasingly versatile as a result of innovation in catalyst design and improvements in reaction conditions. This review gives an overview of recent utilization of Buchwald-Hartwig amination reaction in drug/target synthesis.

Modern Organic Synthesis in the Laboratory

2008 ◽  
Author(s):  
Jie Jack Li ◽  
Chris Limberakis ◽  
Derek A. Pflum
Keyword(s):  
Organic Chemistry ◽  
Graduate Students ◽  
Organic Synthesis ◽  
Functional Group ◽  
Bond Formation ◽  
Reaction Conditions ◽  
Carbon Bond ◽  
Oxidation Reduction ◽  
Carbon Carbon Bond ◽  
Daunting Task

Searching for reaction in organic synthesis has been made much easier in the current age of computer databases. However, the dilemma now is which procedure one selects among the ocean of choices. Especially for novices in the laboratory, it becomes a daunting task to decide what reaction conditions to experiment with first in order to have the best chance of success. This collection intends to serve as an "older and wiser lab-mate" one could have by compiling many of the most commonly used experimental procedures in organic synthesis. With chapters that cover such topics as functional group manipulations, oxidation, reduction, and carbon-carbon bond formation, Modern Organic Synthesis in the Laboratory will be useful for both graduate students and professors in organic chemistry and medicinal chemists in the pharmaceutical and agrochemical industries.

scholarly journals Rate Dependence on Inductive and Resonance Effects for the Organocatalyzed Enantioselective Conjugate Addition of Alkenyl and Alkynyl Boronic Acids to β-Indolyl Enones and β-Pyrrolyl Enones

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1615
Author(s):  
Amy Boylan ◽  
Thien S. Nguyen ◽  
Brian J. Lundy ◽  
Jian-Yuan Li ◽  
Ravikrishna Vallakati ◽  
...  
Keyword(s):  
Positive Charge ◽  
Bond Formation ◽  
Conjugate Addition ◽  
Reaction Rates ◽  
Boronic Acids ◽  
Key Factors ◽  
Resonance Contribution ◽  
Reaction Conditions ◽  
Resonance Effects ◽  
Resonance Stabilization

Two key factors bear on reaction rates for the conjugate addition of alkenyl boronic acids to heteroaryl-appended enones: the proximity of inductively electron-withdrawing heteroatoms to the site of bond formation and the resonance contribution of available heteroatom lone pairs to stabilize the developing positive charge at the enone β-position. For the former, the closer the heteroatom is to the enone β-carbon, the faster the reaction. For the latter, greater resonance stabilization of the benzylic cationic charge accelerates the reaction. Thus, reaction rates are increased by the closer proximity of inductive electron-withdrawing elements, but if resonance effects are involved, then increased rates are observed with electron-donating ability. Evidence for these trends in isomeric substrates is presented, and the application of these insights has allowed for reaction conditions that provide improved reactivity with previously problematic substrates.

Soluble lanthanide-transition-metal clusters Ln36Co12 as effective molecular electrocatalysts for water oxidation

2021 ◽  
Vol 57 (29) ◽  
pp. 3611-3614
Author(s):  
Rong Chen ◽  
Chao-Long Chen ◽  
Ming-Hao Du ◽  
Xing Wang ◽  
Cheng Wang ◽  
...  
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Synergistic Effect ◽  
Water Oxidation ◽  
Metal Clusters ◽  
Bond Formation ◽  
Transition Metal Clusters ◽  
Oxidation Activity ◽  
Acidic Conditions ◽  
Effective Water

The stable 48-metal Ln36Co12 clusters show an effective water oxidation activity under weak acidic conditions because of the synergistic effect between lanthanide and transition metals in O–O bond formation.

scholarly journals Transition Metal-Catalyzed α-Position Carbon–Carbon Bond Formations of Carbonyl Derivatives

Catalysts ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 861 ◽  
Author(s):  
Ha-Eun Lee ◽  
Dopil Kim ◽  
Ahrom You ◽  
Myung Hwan Park ◽  
Min Kim ◽  
...  
Keyword(s):  
Transition Metal ◽  
Carbonyl Compounds ◽  
Bond Formation ◽  
Chiral Ligand ◽  
Catalytic Systems ◽  
Carbon Bond ◽  
Carbonyl Derivatives ◽  
Carbon Carbon Bond ◽  
Transition Metal Catalyzed ◽  
Metal Catalyzed

α-Functionalization of carbonyl compounds in organic synthesis has traditionally been accomplished via classical enolate chemistry. As α-functionalized carbonyl moieties are ubiquitous in biologically and pharmaceutically valuable molecules, catalytic α-alkylations have been extensively studied, yielding a plethora of practical and efficient methodologies. Moreover, stereoselective carbon–carbon bond formation at the α-position of achiral carbonyl compounds has been achieved by using various transition metal–chiral ligand complexes. This review describes recent advances—in the last 20 years and especially focusing on the last 10 years—in transition metal-catalyzed α-alkylations of carbonyl compounds, such as aldehydes, ketones, imines, esters, and amides and in efficient carbon–carbon bond formations. Active catalytic species and ligand design are discussed, and mechanistic insights are presented. In addition, recently developed photo-redox catalytic systems for α-alkylations are described as a versatile synthetic tool for the synthesis of chiral carbonyl-bearing molecules.

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