Microwave-assisted Palladium-catalyzed C-H bond Functionalizations Towards the Synthesis of Bio-inspired Heterocycles

2021 ◽  
Vol 08 ◽  
Author(s):  
Moumita Saha ◽  
Asish R. Das
Keyword(s):  
Bond Activation ◽  
Deep Understanding ◽  
Optimization Procedure ◽  
Conventional Heating ◽  
Side Reactions ◽  
Reaction Conditions ◽  
Heterocyclic Molecules ◽  
Percentage Yield ◽  
Palladium Catalyzed ◽  
Catalytic Role

: C-C or C-heteroatom bond formation from direct C-H bond activation of several heteroarenes containing suitable directing groups has now emerged as an efficient and straightforward strategy for the design of complex heterocyclic molecules as well as their late-stage functionalization. The most common problem of several C-H bond activation reactions is high temperature, long reaction time and unwanted side reactions where recent examples of MW assisted C-H bond activation showed the requirements of low temperature and short completion time and thus proved its efficacy in terms of heating effect and conversion rate of conventional heating methods. The schemes discussed in the present review depict the reaction conditions along with a look into the mechanism involved to render a deep understanding of the catalytic role of palladium-catalysis. In some examples, the optimization procedure of the corresponding strategy has been illustrated through tables, i.e., choice of catalyst, solvent screening, loading of the catalyst and percentage yield with different substrates. Each of the described illustrations has been analyzed considering a wide variety of reactants, reaction conditions, and transition metals employed as the catalyst. This review definitely allows to introduce the synthetic chemists in understanding the challenges associated with the previous methods as well as their drawbacks and future opportunities in choosing substrates, catalyst and reaction conditions. This review would be alluring to a wider range of synthetic chemists in academia and industrial R&D sectors working with heterocyclic chemistry. In this short perspective, an outline of recent eloquent examples of a variety of palladium-catalyzed C-H bond activation involving bio-oriented heterocycles achieved in the past ten years is nicely presented and the pros and cons of each strategy are highlighted so that the researchers could get enough scope for further designing and modification of developed protocols.

scholarly journals Access to N-Heterocyclic Molecules via Ru(II)-Catalyzed Oxidative Alkyne Annulation Reactions

2021 ◽  
Author(s):  
Bhisma K. Patel ◽  
Amitava Rakshit
Keyword(s):  
Transition Metal ◽  
Oxidative Coupling ◽  
Bond Activation ◽  
Reaction Conditions ◽  
Available Nitrogen ◽  
Heterocyclic Molecules ◽  
Internal Alkynes ◽  
Transition Metal Catalyzed ◽  
Metal Catalyzed

In last few decades, the transition metal-catalyzed C-H bond activation and alkyne annulation reactions have turned out to be effective methods for the construction of highly important heterocycles. In particular, the Ru(II) catalysts have been used for the oxidative coupling between an internal alkynes and readily available nitrogen directed compounds in a rapid and sustainable manner. The Ru(II) catalysts are very much beneficial due to their stability in both air and water, ease of preparation, inexpensive than those of Rh(III) and designer Co(III) catalysts usually used for alkyne annulation reactions, requirement of mild reaction conditions, and compatible with various oxidants. Owing to these advantages of Ru(II) catalysts herein, we attempt to highlight the recent development in C-H activation and annulation reactions, which lead to the formation of several important N-heterocycles.

C–O Bond Activation as a Strategy in Palladium-Catalyzed Cross-Coupling

Synlett ◽  
2020 ◽  
Author(s):  
David C. Leitch ◽  
Joseph Becica
Keyword(s):  
Bond Activation ◽  
Complex Molecule ◽  
Cross Coupling ◽  
Building Blocks ◽  
Alternative Mechanism ◽  
Major Focus ◽  
Reaction Conditions ◽  
Mild Conditions ◽  
Oxidative Additions ◽  
Palladium Catalyzed

AbstractThe activation of strong C–O bonds in cross-coupling catalysis can open up new oxygenate-based feedstocks and building blocks for complex-molecule synthesis. Although Ni catalysis has been the major focus for cross-coupling of carboxylate-based electrophiles, we recently demonstrated that palladium catalyzes not only difficult C–O oxidative additions but also Suzuki-type cross-couplings of alkenyl carboxylates under mild conditions. We propose that, depending on the reaction conditions, either a typical Pd(0)/(II) mechanism or a redox-neutral Pd(II)-only mechanism can operate. In the latter pathway, C–C bond formation occurs through carbopalladation of the alkene, and C–O cleavage by β-carboxyl elimination.1 Introduction2 A Mechanistic Challenge: Activating Strong C–O Bonds3 Exploiting Vinylogy for C–Cl and C–O Oxidative Additions4 An Alternative Mechanism for Efficient Cross-Coupling Catalysis5 Conclusions and Outlook

Suzuki–Miyaura cross-coupling for chemoproteomic applications

2020 ◽  
Author(s):  
Jian Cao ◽  
Ernest Armenta ◽  
Lisa Boatner ◽  
Heta Desai ◽  
Neil Chan ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Cross Coupling ◽  
Protein Profiling ◽  
Protein Labeling ◽  
Caspase 8 ◽  
Complex Cell ◽  
Bioorthogonal Chemistry ◽  
Reaction Conditions ◽  
Target Deconvolution ◽  
Palladium Catalyzed

Bioorthogonal chemistry is a mainstay of chemoproteomic sample preparation workflows. While numerous transformations are now available, chemoproteomic studies still rely overwhelmingly on copper-catalyzed azide –alkyne cycloaddition (CuAAC) or 'click' chemistry. Here we demonstrate that gel-based activity-based protein profiling (ABPP) and mass-spectrometry-based chemoproteomic profiling can be conducted using Suzuki–Miyaura cross-coupling. We identify reaction conditions that proceed in complex cell lysates and find that Suzuki –Miyaura cross-coupling and CuAAC yield comparable chemoproteomic coverage. Importantly, Suzuki–Miyaura is also compatible with chemoproteomic target deconvolution, as demonstrated using structurally matched probes tailored to react with the cysteine protease caspase-8. Uniquely enabled by the observed orthogonality of palladium-catalyzed cross-coupling and CuAAC, we combine both reactions to achieve dual protein labeling.

Theoretical and experimental studies of palladium-catalyzed site-selective C(sp3)−H bond functionalization enabled by transient ligands

2017 ◽  
Author(s):  
Haibo Ge ◽  
Lei Pan ◽  
Piaoping Tang ◽  
Ke Yang ◽  
Mian Wang ◽  
...  
Keyword(s):  
Bond Activation ◽  
Theoretical Calculations ◽  
Experimental Studies ◽  
Bond Functionalization ◽  
Aliphatic Ketones ◽  
Site Selectivity ◽  
Mechanistic Investigation ◽  
Palladium Catalyzed ◽  
Metal Catalyzed ◽  
Site Selective

Transition metal-catalyzed selective C–H bond functionalization enabled by transient ligands has become an extremely attractive topic due to its economical and greener characteristics. However, catalytic pathways of this reaction process on unactivated sp<sup>3</sup> carbons of reactants have not been well studied yet. Herein, detailed mechanistic investigation on Pd-catalyzed C(sp<sup>3</sup>)–H bond activation with amino acids as transient ligands has been systematically conducted. The theoretical calculations showed that higher angle distortion of C(sp2)-H bond over C(sp3)-H bond and stronger nucleophilicity of benzylic anion over its aromatic counterpart, leading to higher reactivity of corresponding C(sp<sup>3</sup>)–H bonds; the angle strain of the directing rings of key intermediates determines the site-selectivity of aliphatic ketone substrates; replacement of glycine with β-alanine as the transient ligand can decrease the angle tension of the directing rings. Synthetic experiments have confirmed that β-alanine is indeed a more efficient transient ligand for arylation of β-secondary carbons of linear aliphatic ketones than its glycine counterpart.<br><br>

A Facile, Efficient and Selective Deprotection of P - Methoxy Benzyl Ethers Using Zinc (II) Trifluoromethanesulfonate

2019 ◽  
Vol 16 (12) ◽  
pp. 955-958
Author(s):  
Reddymasu Sireesha ◽  
Reddymasu Sreenivasulu ◽  
Choragudi Chandrasekhar ◽  
Mannam Subba Rao
Keyword(s):  
Room Temperature ◽  
Protecting Groups ◽  
Side Reactions ◽  
Reaction Conditions ◽  
Acid Sensitivity ◽  
Time Period ◽  
Protective Groups ◽  
Benzyl Ethers ◽  
Last Stage ◽  
Zinc Triflate

: Deprotection is significant and conducted over mild reaction conditions, in order to restrict any more side reactions with sensitive functional groups as well as racemization or epimerization of stereo center because the protective groups are often cleaved at last stage in the synthesis. P - Methoxy benzyl (PMB) ether appears unique due to its easy introduction and removal than the other benzyl ether protecting groups. A facile, efficient and highly selective cleavage of P - methoxy benzyl ethers was reported by using 20 mole% Zinc (II) Trifluoromethanesulfonate at room temperature in acetonitrile solvent over 15-120 min. time period. To study the generality of this methodology, several PMB ethers were prepared from a variety of substrates having different protecting groups and subjected to deprotection of PMB ethers using Zn(OTf)2 in acetonitrile. In this methodology, zinc triflate cleaves only PMB ethers without affecting acid sensitivity, base sensitivity and also chiral epoxide groups.

Palladium-Catalyzed C–C Bond Activation of Cyclopropenone: Modular Access to Trisubstituted α,β-Unsaturated Esters and Amides

2021 ◽  
Vol 86 (3) ◽  
pp. 2682-2695
Author(s):  
Tanmayee Nanda ◽  
Pragati Biswal ◽  
Bedadyuti Vedvyas Pati ◽  
Shyam Kumar Banjare ◽  
Ponneri Chandrababu Ravikumar
Keyword(s):  
Bond Activation ◽  
Unsaturated Esters ◽  
Palladium Catalyzed

TBAI Catalyzed Electrochemical C-H Bond Activation of 2-arylated-N-methoxyamides for the Synthesis of Phenanthridinones

Synlett ◽  
2021 ◽  
Author(s):  
Kripa Subramanian ◽  
Subhash L. Yedage ◽  
Kashish Sethi ◽  
Bhalchandra M. Bhanage
Keyword(s):  
Electrochemical Method ◽  
Bond Activation ◽  
Supporting Electrolyte ◽  
Bioactive Compound ◽  
Reaction Conditions ◽  
Redox Catalyst ◽  
Synthetic Utility ◽  
One Step ◽  
Constant Potential

An electrochemical method for the synthesis of phenanthridinones via constant potential electrolysis (CPE) mediated by <i>n</i>-Bu<sub>4</sub>NI (TBAI) has been reported. The protocol is metal and oxidant free and proceeds with 100% current efficiency. Here TBAI plays the dual role of the redox catalyst as well as supporting electrolyte. The intramolecular C-H activation proceeds under mild reaction conditions and short reaction time via electrochemically generated amidyl radicals. The reaction has been scaled up to gram level showing its practicability and the synthetic utility and applicability of the protocol has been demonstrated by the direct one-step synthesis of the bioactive compound Phenaglaydon.

Palladium‐Catalyzed C‐C Bond Activation/Suzuki Reaction of Methylenecyclobutanes †

2021 ◽  
Author(s):  
Xiao‐Bing Chen ◽  
Li Li ◽  
Wan‐Chun Yang ◽  
Kun‐Long Song ◽  
Bin Wu ◽  
...  
Keyword(s):  
Bond Activation ◽  
Suzuki Reaction ◽  
Palladium Catalyzed
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