共查询到20条相似文献,搜索用时 15 毫秒
1.
Wen Zhang Keith L. Carpenter Song Lin 《Angewandte Chemie (International ed. in English)》2020,59(1):409-417
Riboflavin‐derived photocatalysts have been extensively studied in the context of alcohol oxidation. However, to date, the scope of this catalytic methodology has been limited to benzyl alcohols. In this work, mechanistic understanding of flavin‐catalyzed oxidation reactions, in either the absence or presence of thiourea as a cocatalyst, was obtained. The mechanistic insights enabled development of an electrochemically driven photochemical oxidation of primary and secondary aliphatic alcohols using a pair of flavin and dialkylthiourea catalysts. Electrochemistry makes it possible to avoid using O2 and an oxidant and generating H2O2 as a byproduct, both of which oxidatively degrade thiourea under the reaction conditions. This modification unlocks a new mechanistic pathway in which the oxidation of unactivated alcohols is achieved by thiyl radical mediated hydrogen‐atom abstraction. 相似文献
2.
Luca Buzzetti Giacomo E. M. Crisenza Paolo Melchiorre 《Angewandte Chemie (International ed. in English)》2019,58(12):3730-3747
The fast‐moving fields of photoredox and photocatalysis have recently provided fresh opportunities to expand the potential of synthetic organic chemistry. Advances in light‐mediated processes have mainly been guided so far by empirical findings and the quest for reaction invention. The general perception, however, is that photocatalysis is entering a more mature phase where the combination of experimental and mechanistic studies will play a dominant role in sustaining further innovation. This Review outlines the key mechanistic studies to consider when developing a photochemical process, and the best techniques available for acquiring relevant information. The discussion will use selected case studies to highlight how mechanistic investigations can be instrumental in guiding the invention and development of synthetically useful photocatalytic transformations. 相似文献
3.
The Reactivity of Dimethyl Acetylenedicarboxylate and Heterocyclization of Hydrazinecarbothioamides to 1,3‐Thiazolidin‐4‐ones
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Alaa A. Hassan Nasr K. Mohamed Kamal M. A. El‐Shaieb Hendawy N. Tawfeek Stefan Bräse Martin Nieger 《Journal of heterocyclic chemistry》2016,53(1):46-50
2‐Substituted hydrazinecarbothioamides and N,2‐disubstituted hydrazinecarbothioamides react, in high yields with dimethyl acetylenedicarboxylate to give 4‐oxo‐Z‐(thiazolidin‐5‐ylidene)acetate derivatives. Several mechanistic options involving interaction are presented. The structures of thiazolidin‐4‐ones have been unambiguously confirmed by single crystal X‐ray crystallography. 相似文献
4.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(14):4073-4077
An efficient yttrium‐catalyzed intramolecular hydroalkoxylation/Claisen rearrangement sequence has been achieved, thus enabling facile access to a diverse array of valuable medium‐sized lactams. Furthermore, a mechanistic rationale for this novel cascade reaction is well supported by a variety of control experiments. 相似文献
5.
Restriction of Intramolecular Motions: The General Mechanism behind Aggregation‐Induced Emission
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Nelson L. C. Leung Dr. Ni Xie Dr. Wangzhang Yuan Dr. Yang Liu Dr. Qunyan Wu Prof. Qian Peng Prof. Qian Miao Dr. Jacky W. Y. Lam Prof. Ben Zhong Tang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(47):15349-15353
Aggregation‐induced emission (AIE) has been harnessed in many systems through the principle of restriction of intramolecular rotations (RIR) based on mechanistic understanding from archetypal AIE molecules such as tetraphenylethene (TPE). However, as the family of AIE‐active molecules grows, the RIR model cannot fully explain some AIE phenomena. Here, we report a broadening of the AIE mechanism through analysis of 10,10′,11,11′‐tetrahydro‐5,5′‐bidibenzo[a,d][7]annulenylidene (THBDBA), and 5,5′‐bidibenzo[a,d][7]annulenylidene (BDBA). Analyses of the computational QM/MM model reveal that the novel mechanism behind the AIE of THBDBA and BDBA is the restriction of intramolecular vibration (RIV). A more generalized mechanistic understanding of AIE results by combining RIR and RIV into the principle of restriction of intramolecular motions (RIM). 相似文献
6.
Evidence of CuI/CuII Redox Process by X‐ray Absorption and EPR Spectroscopy: Direct Synthesis of Dihydrofurans from β‐Ketocarbonyl Derivatives and Olefins
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Hong Yi Zhixiong Liao Guanghui Zhang Guoting Zhang Chao Fan Xu Zhang Prof. Dr. Emilio E. Bunel Dr. Chih‐Wen Pao Prof. Dr. Jyh‐Fu Lee Prof. Dr. Aiwen Lei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(52):18925-18929
The CuI/CuII and CuI/CuIII catalytic cycles have been subject to intense debate in the field of copper‐catalyzed oxidative coupling reactions. A mechanistic study on the CuI/CuII redox process, by X‐ray absorption (XAS) and electron paramagnetic resonance (EPR) spectroscopies, has elucidated the reduction mechanism of CuII to CuI by 1,3‐diketone and detailed investigation revealed that the halide ion is important for the reduction process. The oxidative nature of the thereby‐formed CuI has also been studied by XAS and EPR spectroscopy. This mechanistic information is applicable to the copper‐catalyzed oxidative cyclization of β‐ketocarbonyl derivatives to dihydrofurans. This protocol provides an ideal route to highly substituted dihydrofuran rings from easily available 1,3‐dicarbonyls and olefins. 相似文献
7.
An intramolecular, organocatalyzed Michael addition has been developed to obtain biologically important 2,3‐disubstituted cis‐2,3‐dihydrobenzofurans. By using mandelic acid salts of primary aminocatalysts, derived from cinchona alkaloids, the intramolecular cyclization reaction has been developed to proceed in high yield, with moderate to good diastereoselectivity, and up to 99 % ee. Based on the absolute configuration of the formed 2,3‐disubstituted‐cis‐2,3‐dihydrobenzofurans and by considering the observed substrate scope restrictions, a mechanistic rationalization has been presented. 相似文献
8.
Dr. Marco Bandini Prof. Andrea Bottoni Dr. Astrid Eichholzer Dr. Gian Pietro Miscione Dr. Marco Stenta 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(41):12462-12473
Asymmetric phase‐transfer catalysis (PTC) has risen to prominence over the last decade as a straightforward synthetic methodology for the preparation of pharmacologically active compounds in enantiomerically pure form. However, the complex interplay of weak nonbonded interactions (between catalyst and substrate) that could account for the stereoselection in these processes is still unclear, with tentative pictorial mechanistic representations usually proposed. Here we present a full account dealing with the enantioselective phase‐transfer‐catalyzed intramolecular aza‐Michael reaction (IMAMR) of indolyl esters, as a valuable synthetic tool to obtain added‐value compounds, such as dihydro‐pyrazinoindolinones. A combined computational and experimental investigation has been carried out to elucidate the key mechanistic aspects of this process. 相似文献
9.
Rhodium(III)‐Catalyzed Selective ortho‐Olefinations of N‐Acyl and N‐Aroyl Sulfoximines by CH Bond Activation
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Dr. Kanniyappan Parthasarathy Prof. Dr. Carsten Bolm 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4896-4900
Two new rhodium‐catalyzed oxidative couplings between sulfoximine derivatives and alkenes by regioselective C?H activation, affording ortho‐olefinated (Heck‐type) products, are reported. A synthetic application of the ortho‐alkenylated products into the corresponding cyclic derivatives has been demonstrated, and a mechanistic rational for the rhodium catalysis is presented. 相似文献
10.
Florian Schevenels Prof. Dr. Bernard Tinant Prof. Dr. Jean‐Paul Declercq Prof. Dr. István E. Markó 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(13):4335-4343
Highly functionalised benzofurans have been prepared from ortho‐hydroxyphenones and 1,1‐dichloroethylene. The key intermediate, a chloromethylene furan, smoothly rearranged into the corresponding benzofuran carbaldehyde under acidic conditions. Some mechanistic investigations have been performed and several biologically active benzofurans have been synthesised. 相似文献
11.
Dr. Romain Ramozzi Dr. Nicolas Chéron Dr. Laurent El Kaïm Dr. Laurence Grimaud Dr. Paul Fleurat‐Lessard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(29):9094-9099
Following our previous mechanistic studies of multicomponent Ugi‐type reactions, theoretical calculations have been performed to predict the efficiency of new substrates in Ugi–Smiles couplings. First, as predicted, 2,4,6‐trichlorophenol experimentally gave the corresponding aryl‐imidate. Theoretical predictions of nitrosophenols as good acidic partners were then successfully confirmed by experiments. In the latter case, the reaction offers a new access to benzimidazoles. 相似文献
12.
《Journal of heterocyclic chemistry》2017,54(3):1995-2002
Synthesis of new 1‐hydroxyindole‐2‐carboxylates 1 and mechanistic studies on the reaction pathways were described. The substrates 2 , prepared through two‐step synthetic sequences, were treated with nucleophiles in the presence of SnCl2 · 2H2O to obtain compounds 1 . In particular, the mechanistic studies led to a significant finding that reactions with thiol nucleophiles occur through a newly proposed pathway (path B: 1,4‐addition followed by reduction/condensation) rather than through a previously assumed pathway (path A: reduction/condensation followed by 1,5‐addition). Further mechanistic investigations revealed steric effects of o‐substituents in 2 governing the ratio of products ( 1i / 7 ). 相似文献
13.
Switching Regioselectivity of β‐Ketothioamides by Means of Iodine Catalysis: Synthesis of Thiazolylidenes and 1,4‐Dithiines
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Prof. Li‐Rong Wen Lian‐Bin Men Tao He Guo‐Jing Ji Prof. Ming Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):5028-5033
An efficient I2‐catalyzed synthesis of thiazolylidenes and 1,4‐dithiines from β‐ketothioamides (KTAs) has been developed by only controlling the amount of I2 that triggers different cascade reaction sequences by means of [3+2] or [3+3] cyclocondensation in a one‐step process. A possible mechanistic proposal for these transformations is presented. 相似文献
14.
S8‐Mediated Cyclization of 2‐Aminophenols/thiophenols with Arylmethyl Chloride: Approach to Benzoxazoles and Benzothiazoles
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Dr. Haifeng Gan Dazhuang Miao Qiang Pan Renhe Hu Xiaotong Li Prof. Dr. Shiqing Han 《化学:亚洲杂志》2016,11(12):1770-1774
A metal‐free approach to benzazoles from arylmethyl chlorides and 2‐mercaptan/2‐hydroxyanilines using elemental sulfur as a traceless oxidizing agent has been developed. The reactions proceeded in good to excellent yields, exhibiting good functional groups tolerance and gram‐scale ability. A key mechanistic investigation indicated that the key intermediate trisulfide 6 , which was characterized by NMR, HRMS and crystal X‐ray crystallography, was separated in the reaction prior to the formation of the product. 相似文献
15.
Ahmed Kamal Dr. Nagula Markandeya Nagula Shankaraiah Dr. C. Ratna Reddy S. Prabhakar C. Sanjeeva Reddy Prof. Marcos N. Eberlin Prof. Leonardo Silva Santos Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(29):7215-7224
Aluminium and gadolinium triflates catalyze the chemoselective reduction of aromatic azides to the corresponding amines in combination with sodium iodide. This mild chemoselective method has been applied to the synthesis of various aryl amines, C2‐azido‐substituted pyrrolo[2,1‐c][1,4]benzodiazepines, and fused[2,1‐b]quinazolinones by an intramolecular azido reduction tandem cyclization reaction. Interestingly, this methodology selectively reduces aryl azides with enhanced yields and proceeds in shorter reaction times than previous strategies. The mechanistic aspects have been investigated and the intermediates associated with this selective transformation have been intercepted and characterized by online monitoring of the reaction by ESI‐MS. 相似文献
16.
Selective Growth and Structural Analysis of Regular MnO Nanooctapods Bearing Multiple High‐Index Surface Facets
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Although numerous morphologies of MnO nanostructures have been reported, an exact structural analysis and mechanistic study has been lacking. In the present study, the formation of regular MnO octapods was demonstrated in a simple procedure, comprising the thermal decomposition of manganese oleate. Because of their structural uniformity, an ideal three‐dimensional model was successfully constructed. The eight arms protruded from the cubic center with tip angles of 38° and surface facets of {311} and {533} with rounded edges. The concentrations of oleate and chloride ions were the determining factors for the octapod formation. Selective coordination of the oleate ions to the {100} faces led to edge growth along the <111> direction, which was then limited by the chloride ions bound to the high‐index surface facets. These structural and mechanistic analyses should be helpful for understanding the complex nanostructures and for tuning their structure‐related properties. 相似文献
17.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(35):10514-10518
Selectivity control in hydroarylation‐based C−H alkylation has been dominated by steric interactions. A conceptually distinct strategy that exploits the programmed switch in the C−H activation mechanism by means of cobalt catalysis is presented, which sets the stage for convenient C−H alkylations with unactivated alkenes. Detailed mechanistic studies provide compelling evidence for a programmable switch in the C−H activation mechanism from a linear‐selective ligand‐to‐ligand hydrogen transfer to a branched‐selective base‐assisted internal electrophilic‐type substitution. 相似文献
18.
Reaction Optimization,Scalability, and Mechanistic Insight on the Catalytic Enantioselective Desymmetrization of 1,1‐Diborylalkanes via Suzuki–Miyaura Cross‐Coupling
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Ho‐Yan Sun Koji Kubota Prof. Dennis G. Hall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(52):19186-19194
A method for enantioselective desymmetrization of 1,1‐diborylalkanes through a stereoselective Pd‐catalyzed Suzuki–Miyaura cross‐coupling has been thoroughly optimized. The most effective ligand was found to be a α,α,α,α‐tetra‐aryl‐1,3‐dioxolane‐4,5‐dimethanol (TADDOL)‐derived phosphoramidite. Results show that in order to achieve high selectivity, a suitable balance between the sterics of the aryl groups and the amino group on the ligand must be achieved. While the base has been known to facilitate transmetallation in cross‐coupling reactions, mechanistic studies on this desymmetrization process reveal that the base, in the presence of KHF2, likely plays an additional role in the hydrolysis of the pinacol boronates to the corresponding boronic acids. Through an in depth optimization of the chiral ligand and mechanistic studies, it was possible to obtain ee values over 90 % for several aryl bromides and to develop a reliably scalable process (up to one gram of 1,1‐diborylalkane substrate). 相似文献
19.
Richard A. Bunce James E. Schammerhorn Jessica Sigle 《Journal of heterocyclic chemistry》2013,50(2):373-380
A tandem imine addition‐SNAr annulation reaction has been developed as a new approach to the synthesis of 4‐oxo‐1,2,3,4‐tetrahydroquinoline‐3‐carboxylic esters. A series of these structures has been generated by reacting selected imines with tert‐butyl 2‐fluoro‐5‐nitrobenzoylacetate. Structural variations in the final products are accomplished by changing the substituents on the imine and the alkyl group of the ester. The title compounds are isolated as their enols in 55–97% yield without the need for added base or catalysts. The synthesis of the starting materials as well as mechanistic studies and further synthetic conversions of the products are presented. 相似文献
20.
Reversible Photochemical and Thermal Isomerization of Azaboratabisnorcaradiene to Azaborabenzotropilidene
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Ying‐Li Rao Dr. Christian Hörl Prof. Dr. Holger Braunschweig Prof. Dr. Suning Wang 《Angewandte Chemie (International ed. in English)》2014,53(34):9086-9089
Two new tricyclic 1,2‐azaboratabisnorcaradiene molecules ( 1 b and 2 b ) generated through the photoisomerization of N‐methyl‐2‐phenylimidazolyl‐chelated dimesitylboranes ( 1 a and 2 a ) have been found to undergo unusual photoisomerization, producing the first examples of 1,2‐azaborabenzotropilidenes ( 1 c and 2 c ), accompanied by a distinct color change, upon irradiation at 350 nm. Compounds 1 c and 2 c contain a conjugated alkylideneborane unit and can be fully reverted back to 1 b and 2 b , and subsequently to 1 a and 2 a upon heating. The mechanistic pathway of the new isomerism has been established to involve “walk” rearrangements by DFT computational studies. 相似文献