Functional Group Chemistry

2007 ◽  
Keyword(s):  
2020 ◽  
Author(s):  
José Tiago Menezes Correia ◽  
Gustavo Piva da Silva ◽  
Camila Menezes Kisukuri ◽  
Elias André ◽  
Bruno Pires ◽  
...  

A metal- and catalyst-free photoinduced radical cascade hydroalkylation of 1,7-enynes has been disclosed. The process is triggered by a SET event involving a photoexcited electron-donor-aceptor complex between NHPI ester and Hantzsch ester, which decomposes to afford a tertiary radical that is readily trapped by the enyne. <a>The method provides an operationally simple, robust and step-economical approach to the construction of diversely functionalized dihydroquinolinones bearing quaternary-centers. A sequential one-pot hydroalkylation-isomerization approach is also allowed giving access to a family of quinolinones. A wide substrate scope and high functional group tolerance was observed in both approaches</a>.


2020 ◽  
Author(s):  
Baojian Xiong ◽  
Yue Li ◽  
Yin Wei ◽  
Søren Kramer ◽  
Zhong Lian

Cross-coupling between substrates that can be easily derived from phenols is highly attractive due to the abundance and low cost of phenols. Here, we report a dual nickel/palladium-catalyzed reductive cross-coupling between aryl tosylates and aryl triflates; both substrates can be accessed in just one step from readily available phenols. The reaction has a broad functional group tolerance and substrate scope (>60 examples). Furthermore, it displays low sensitivity to steric effects demonstrated by the synthesis of a 2,2’disubstituted biaryl and a fully substituted aryl product. The widespread presence of phenols in natural products and pharmaceuticals allow for straightforward late-stage functionalization, illustrated with examples such as Ezetimibe and tyrosine. NMR spectroscopy and DFT calculations indicate that the nickel catalyst is responsible for activating the aryl triflate, while the palladium catalyst preferentially reacts with the aryl tosylate.


2020 ◽  
Author(s):  
Mikhail Trought ◽  
Isobel Wentworth ◽  
Timothy Leftwich ◽  
Kathryn Perrine

The knowledge of chemical functionalization for area selective deposition (ASD) is crucial for designing the next generation heterogeneous catalysis. Surface functionalization by oxidation was studied on the surface of highly oriented pyrolytic graphite (HOPG). The HOPG surface was exposed to with various concentrations of two different acids (HCl and HNO3). We show that exposure of the HOPG surface to the acid solutions produce primarily the same -OH functional group and also significant differences the surface topography. Mechanisms are suggested to explain these strikingly different surface morphologies after surface oxidation. This knowledge can be used to for ASD synthesis methods for future graphene-based technologies.


2020 ◽  
Author(s):  
Shunya Ohuchi ◽  
Hiroki Koyama ◽  
Hiroki Shigehisa

A catalytic synthesis of cyclic guanidines, which are found in many biologically active compounds and natu-ral products, was developed, wherein transition-metal hydrogen atom transfer and radical-polar crossover were employed. This mild and functional-group tolerant process enabled the cyclization of alkenyl guanidines bearing common protective groups, such as Cbz and Boc. This powerful method not only provided the common 5- and 6-membered rings but also an unusual 7-membered ring. The derivatization of the products afforded various heterocycles. We also investigated the se-lective cyclization of mono-protected or hetero-protected (TFA and Boc) alkenyl guanidines and their further derivatiza-tions.


2018 ◽  
Author(s):  
James Leighton ◽  
Linda M. Suen ◽  
Makeda A. Tekle-Smith ◽  
Kevin S. Williamson ◽  
Joshua R. Infantine ◽  
...  

With an average GI50 value against the NCI panel of 60 human cancer cell lines of 0.12 nM, spongistatin 1 is among the most potent anti-proliferative agents ever discovered rendering it an attractive candidate for development as a payload for antibody-drug conjugates and other targeted delivery approaches. It is unavailable from natural sources and its size and complex stereostructure render chemical synthesis highly time- and resource-intensive, however, and its development requires more efficient and step-economical synthetic access. Using novel and uniquely enabling direct complex fragment coupling alkallyl- and crotylsilylation reactions, we have developed a 22-step synthesis of a rationally designed D-ring modified analog of spongistatin 1 that is equipotent with the natural product, and have used that synthesis to establish that the C(15) acetate may be replaced with a linker functional group-bearing ester with only minimal reductions in potency.<br><div><br></div>


2018 ◽  
Author(s):  
Patrick Moon ◽  
Zhongyu Wie ◽  
Rylan Lundgren

The stability and wide availability of carboxylic acids make them valuable reagents in chemical synthesis. Most transition metal catalyzed processes using carboxylic acid substrates are initiated by a decarboxylation event that generates reactive carbanion or radical intermediates. Developing enantioselective methodologies relying on these principles can be challenging, as highly reactive species tend to react indiscriminately without selectivity. Furthermore, anionic or radical intermediates generated from decarboxylation can be incompatible with protic and electrophilic functionality, or groups that undergo trapping with radicals. We demonstrate that metal-catalyzed enantioselective benzylation reactions of allylic electrophiles can occur directly from aryl acetic acids. The reaction proceeds via a pathway in which decarboxylation is the terminal event, occurring after stereoselective carbon–carbon bond formation. The mechanistic features of the process enable enantioselective benzylation without the generation of a highly basic nucleophile. Thus, the process has broad functional group compatibility that would not be possible employing established protocols.<br>


2019 ◽  
Author(s):  
Tristan Delcaillau ◽  
Alessandro Bismuto ◽  
Zhong Lian ◽  
Bill Morandi

A nickel-catalyzed carbon-sulfur bond metathesis has been developed to access high-value thioethers. 1,2-bis(dicyclohexylphosphino)ethane (dcype) is essential to promote this highly functional group tolerant reaction. Further, synthetically challenging macrocycles could be obtained in good yield in an unusual example of ring-closing metathesis which does not involve alkene bonds. In-depth organometallic studies support a reversible Ni(0)-Ni(II) pathway to product formation. Overall, this work does not only disclose a more sustainable and more functional group tolerant alternative to previous catalytic systems based on Pd, but also presents new applications and mechanistic information which are highly relevant to the further development and application of unusual single bond metathesis reactions.


2019 ◽  
Author(s):  
Hang Shi ◽  
Lu Yi ◽  
Jiang Weng ◽  
Katherine Bay ◽  
Xiangyang Chen ◽  
...  

<p>Site-selective functionalizations of C–H bonds will ultimately afford chemists transformative tools for editing and constructing complex molecular architectures<sup>1-4</sup>. Towards this goal, developing strategies to activate C–H bonds that are distal from a functional group is essential<sup>4-6</sup>. In this context, distinguishing remote C–H bonds on adjacent carbon atoms is an extraordinary challenge due to the lack of electronic or steric bias between the two positions. Herein, we report the design of a catalytic system leveraging a remote directing template and a transient norbornene mediator to selectively activate a previously inaccessible remote C–H bond that is one bond further away. The generality of this approach has been demonstrated with a range of heterocycles, including a complex anti-leukemia agent, and hydrocinnamic acid substrates.</p>


2019 ◽  
Author(s):  
Caleb Karmel ◽  
Zhewei Chen ◽  
John Hartwig

We report a new system for the silylation of aryl C-H bonds. The combination of [Ir(cod)(OMe)]<sub>2</sub> and 2,9-Me<sub>2</sub>-phenanthroline (2,9-Me<sub>2</sub>phen) catalyzes the silylation of arenes at lower temperatures and with faster rates than those reported previously, when the hydrogen byproduct is removed, and with high functional group tolerance and regioselectivity. Inhibition of reactions by the H<sub>2</sub> byproduct is shown to limit the silylation of aryl C-H bonds in the presence of the most active catalysts, thereby masking their high activity. Analysis of initial rates uncovered the high reactivity of the catalyst containing the sterically hindered 2,9-Me<sub>2</sub>phen ligand but accompanying rapid inhibition by hydrogen. With this catalyst, under a flow of nitrogen to remove hydrogen, electron-rich arenes, including those containing sensitive functional groups, undergo silylation in high yield for the first time, and arenes that underwent silylation with prior catalysts react over much shorter times with lower catalyst loadings. The synthetic value of this methodology is demonstrated by the preparation of key intermediates in the synthesis of medicinally important compounds in concise sequences comprising silylation and functionalization. Mechanistic studies demonstrate that the cleavage of the aryl C-H bond is reversible and that the higher rates observed with the 2,9-Me<sub>2</sub>phen ligand is due to a more thermodynamically favorable oxidative addition of aryl C-H bonds.


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