30148-17-5Relevant academic research and scientific papers
Photoenzymatic Hydrogenation of Heteroaromatic Olefins Using ‘Ene’-Reductases with Photoredox Catalysts
Biegasiewicz, Kyle F.,Black, Michael J.,Chung, Megan M.,Hyster, Todd K.,Meichan, Andrew J.,Nakano, Yuji,Sandoval, Braddock A.,Zhu, Tianyu
supporting information, p. 10484 - 10488 (2020/04/29)
Flavin-dependent ‘ene’-reductases (EREDs) are highly selective catalysts for the asymmetric reduction of activated alkenes. This function is, however, limited to enones, enoates, and nitroalkenes using the native hydride transfer mechanism. Here we demonstrate that EREDs can reduce vinyl pyridines when irradiated with visible light in the presence of a photoredox catalyst. Experimental evidence suggests the reaction proceeds via a radical mechanism where the vinyl pyridine is reduced to the corresponding neutral benzylic radical in solution. DFT calculations reveal this radical to be “dynamically stable”, suggesting it is sufficiently long-lived to diffuse into the enzyme active site for stereoselective hydrogen atom transfer. This reduction mechanism is distinct from the native one, highlighting the opportunity to expand the synthetic capabilities of existing enzyme platforms by exploiting new mechanistic models.
Base-Promoted Amidation and Esterification of Imidazolium Salts via Acyl C-C bond Cleavage: Access to Aromatic Amides and Esters
Karthik, Shanmugam,Muthuvel, Karthick,Gandhi, Thirumanavelan
supporting information, p. 738 - 751 (2019/01/24)
Imidazolium salts have been effectively employed as suitable acyl transfer agents in amidation and esterification in organic synthesis. The weak acyl C(O)-C imidazolium bond was exploited to generate acyl electrophiles, which further react with amines and alcohols to afford amides and esters. The broad substrate scope of anilines and benzylic amines and base-promoted conditions are the benefits of this route. Interestingly, phenol, benzylic alcohols, and a biologically active alcohol can also be subjected to esterification under the optimized conditions.
Synthesis of 2-aroyl-1-methyl-1H-imidazoles using aryl carboxylic acids
Oyama, Kin-ichi,Watanabe, Noriyuki,Yoshida, Kumi
, p. 1177 - 1183 (2019/12/11)
A new and useful reaction for the synthesis of 2-aroyl-1-methyl-1H-imidazoles using free aryl carboxylic acids was developed. This method was applicable to naphthoic acid and benzoic acid derivatives to give each target compound with up to 80% yield.
Mechanism of the CuII-catalyzed benzylic oxygenation of (aryl)(heteroaryl)methanes with oxygen
Sterckx, Hans,De Houwer, Johan,Mensch, Carl,Caretti, Ignacio,Tehrani, Kourosch Abbaspour,Herrebout, Wouter A.,Van Doorslaer, Sabine,Maes, Bert U. W.
, p. 346 - 357 (2015/12/30)
A mechanistic study of the copper-catalyzed oxidation of the methylene group of aryl(di)azinylmethanes was performed. Initial reaction rates were measured making use of in situ IR reaction monitoring and a kinetic analysis of the reaction was executed. The reaction proved to be first order in oxygen concentration. For substrate and acid concentration, saturation kinetics due to O2 mass transfer limitation were observed. The occurrence of mass transfer limitation was further confirmed by examining the effect of the stirring rate on the initial reaction rate. Interestingly, the effect of the concentration of the catalyst on the rate shows that higher loadings result in a maximal initial rate, followed initially by a steady decrease and subsequently a rate plateau when the concentration is increased further. Mass transfer limitation and increased concentration of dinuclear catalytically active species rationalizes this hitherto unprecedented rate behavior. Continuous-wave and pulsed electron paramagnetic resonance methods were used to characterize the catalytic species present in the solution during the reaction and confirmed the presence of both mono- and dinuclear copper species. Analysis of a diverse substrate scope points towards imine-enamine tautomerization as a crucial process in the oxidation reaction. DFT calculations of these equilibrium constants (pKeq) provided us with a qualitative tool to predict whether or not a substrate is viable for oxidation under the reaction conditions developed.
Enantioselective rhodium/ruthenium photoredox catalysis: en route to chiral 1,2-aminoalcohols
Ma, Jiajia,Harms, Klaus,Meggers, Eric
supporting information, p. 10183 - 10186 (2016/08/18)
A rhodium-based chiral Lewis acid catalyst combined with [Ru(bpy)3](PF6)2 as a photoredox sensitizer allows for the visible-light-activated redox coupling of α-silylamines with 2-acyl imidazoles to afford, after desilylation, 1,2-amino-alcohols in yields of 69-88% and with high enantioselectivity (54-99% ee). The reaction is proposed to proceed via an electron exchange between the α-silylamine (electron donor) and the rhodium-chelated 2-acyl imidazole (electron acceptor), followed by a stereocontrolled radical-radical reaction. Substrate scope and control experiments reveal that the trimethylsilyl group plays a crucial role in this reductive umpolung of the carbonyl group.
N-Heterocyclic carbene (NHC) catalyzed chemoselective acylation of alcohols in the presence of amines with various acylating reagents
Samanta, Ramesh C.,De Sarkar, Suman,Froehlich, Roland,Grimme, Stefan,Studer, Armido
, p. 2177 - 2184 (2013/05/21)
This edge article reports the synthesis and full characterization including X-ray analysis of three different acylazolium ions. The reactivity of these acylazolium ions as acylating reagents of amines and alcohols is discussed. Whereas benzylamine slowly reacts with the acylazolium ions, benzyl alcohol acylation does not occur. However, upon activation of the alcohol with an N-heterocyclic carbene (NHC) as catalyst, efficient esterification is achieved. Importantly, benzylester formation is obtained in the presence of benzylamine upon selective alcohol activation by the NHC. High level DFT calculations reveal that alcohol activation occurs by strong H-bond formation between the NHC and the alcohol thereby increasing the nucleophilicity of the alcohol. For oxidatively generated acylazolium ions under NHC catalysis, the carbene has a dual role (cooperative catalysis): (a) the NHC is used for generation of the acylazolium ion and (b) the NHC is used for activation of the alcohol in the subsequent acylation step. NHC-catalyzed selective acylation of benzyl alcohol in the presence of benzylamine can also be achieved with trifluoroethyl and hexafluoroisopropylesters as acylation reagents. Moreover, an enol acetate also shows high O-selectivity as a chemoselective acetylation reagent. Kinetic and mechanistic studies are provided and some examples of the chemoselective acylation of amino alcohols are presented.
Synthesis of 2-keto-imidazoles utilizing N -arylamino-substituted N-heterocyclic carbenes
Zarganes-Tzitzikas, Tryfon,Neochoritis, Constantinos G.,Stephanidou-Stephanatou, Julia,Tsoleridis, Constantinos A.
supporting information; experimental part, p. 1468 - 1471 (2011/04/26)
A new method for the synthesis of 2-aroyl-, 2-heteroaroyl-, and 2-cinnamoyl-substituted imidazoles in very good yields has been developed. The reaction employs novel nitrogen heterocyclic carbenes (NHCs), namely, N-arylamino-substituted NHCs, formed in situ from the corresponding imidazolium salts, and subsequent reaction with aromatic, heteroaromatic, and cinnamic aldehydes without utilizing transition metals or expensive specialized catalysts.(Figure Presented)
FUNGICIDE HYDROXIMOYL-HETEROCYCLES DERIVATIVES
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Page/Page column 106-107, (2009/12/05)
The present invention relates to hydroximoyl-heterocycle derivatives, their process of preparation, intermediate compounds for their preparation, their use as fungicide active agents, particularly in the form of fungicide compositions, and methods for the control of phytopathogenic fungi, notably of plants, using these compounds or compositions.
[1,2]-rearrangement of imino-N-heterocyclic carbenes - Synthesis and structures of chelating iminoimidazole Pd and Ni complexes
Steiner, Georg,Krajete, Alexander,Kopacka, Holger,Ongania, Karl-Hans,Wurst, Klaus,Preishuber-Pfluegl, Peter,Bildstein, Benno
, p. 2827 - 2836 (2007/10/03)
Imidazolium and benzimidazolium salts with an N-iminoyl and an N′-alkyl group are potential precursors for new bidentate [N,C] ligands which are of interest as novel steering ligands for applications of their metal complexes in homogeneous catalysis. Deprotonation of these azolium salts with potassium hydride does indeed occur, however, the initially formed imino-N-heterocyclic carbenes rearrange spontaneously under migration of the N-iminoyl group from the nitrogen to the former carbene carbon with the formation of 2-iminoyl(benz)imidazoles. These rearranged compounds are new [N,N] ligand systems, which can also be synthesized by aluminum-assisted condensation of anilines with the corresponding 2-acylimidazoles. Palladium and nickel [N,N] complexes have been prepared, characterized by single-crystal X-ray analysis, and briefly evaluated for their catalytic performance in ethylene polymerizations and in Suzuki cross-coupling reactions. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
Synthesis, Characterisation, and Reactivity of 1-(1-Methylimidazol-2-yl)ethenes
Abarca-Gonzalez, Belen,Jones, R. Alan,Medio-Simon, Mercedes,Quilez-Pardo, Juan,Sepulveda-Arques, Jose,Zaballos-Garcia, Elena
, p. 321 - 331 (2007/10/02)
Thermally labile 1-(1-methylimidazol-2-yl)ethenes, synthesised using the Wittig reaction, have been characterised as stable picrate or N-phenacyl salts.The free bases can be regenerated from the picrates on treatment with triethylamine and their reactivit
