87384-76-7Relevant academic research and scientific papers
Transition Metal-Free Direct Hydrogenation of Esters via a Frustrated Lewis Pair
Sapsford, Joshua S.,Csókás, Dániel,Turnell-Ritson, Roland C.,Parkin, Liam A.,Crawford, Andrew D.,Pápai, Imre,Ashley, Andrew E.
, p. 9143 - 9150 (2021/07/31)
"Frustrated Lewis pairs"(FLPs) continue to exhibit unique reactivity for the reduction of organic substrates, yet to date, the catalytic hydrogenation of an ester functionality has not been demonstrated. Here, we report that iPr3SnNTf2 (1-NTf2; Tf = SO2CF3) is a more potent Lewis acid than the previously studied iPr3SnOTf; in an FLP with 2,4,6-collidine/2,6-lutidine (col/lut), this translates to faster H2 activation and the catalytic hydrogenolysis of an ester bond by a main-group compound, furnishing alcohol and ether (minor) products. The reaction outcome is sensitive to the steric and electronic properties of the substrate; CF3CO2Et and simple formates (HCO2Me and HCO2Et) are catalytically reduced, whereas related esters CF3CO2nBu and CH3CO2Et show only stoichiometric reactivity. A computational case study on the hydrogenation of CF3CO2Et and CH3CO2Et reveals that both share a common mechanistic pathway; however, key differences in the energies of a Sn-acetal intermediate and transition states emerge, favoring CF3CO2Et reduction. The alcohol products reversibly inhibit 1-NTf2/lut via formation of resting-state species 1-OR/[1·(1-OR)]+[NTf2]- however, the extra energy required to regenerate 1-NTf2/lut exacerbates the unfavorable reduction energy profile for CH3CO2Et, ultimately preventing turnover. These findings will assist the design of future main-group catalysts for ester hydrogenation, with improved performance.
Exploiting Continuous Processing for Challenging Diazo Transfer and Telescoped Copper-Catalyzed Asymmetric Transformations
Crowley, Daniel C.,Brouder, Thomas A.,Kearney, Aoife M.,Lynch, Denis,Ford, Alan,Collins, Stuart G.,Maguire, Anita R.
, p. 13955 - 13982 (2021/09/02)
Generation and use of triflyl azide in flow enables efficient synthesis of a range of α-diazocarbonyl compounds, including α-diazoketones, α-diazoamides, and an α-diazosulfonyl ester, via both Regitz-type diazo transfer and deacylative/debenzoylative diazo-transfer processes with excellent yields and offers versatility in the solvent employed, in addition to addressing the hazards associated with handling of this highly reactive sulfonyl azide. Telescoping the generation of triflyl azide and diazo-transfer process with highly enantioselective copper-mediated intramolecular aromatic addition and C-H insertion processes demonstrates that the reaction stream containing the α-diazocarbonyl compound can be obtained in sufficient purity to pass directly over the immobilized copper bis(oxazoline) catalyst without detrimentally impacting the catalyst enantioselectivity.
REACTIONS OF STANNYL CATIONS
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Page/Page column 18; 19, (2018/01/17)
The present invention relates to a method of reducing, cleaving and/or coupling at least one C=O, C-O, C=C or C=N bond of a compound, using a reagent comprising a stannyl cation.
Improved Buchner reaction selectivity in the copper-catalyzed reactions of ethyl 3-arylmethylamino-2-diazo-3-oxopropanoates
Liu, Jing,Tu, Jianzhuo,Yang, Zhanhui,Pak, Chol-Ung,Xu, Jiaxi
, p. 4616 - 4626 (2017/07/11)
Ethyl 3-alkyl(arylmethyl)amino-2-diazo-3-oxopropanoates (diazo amidoacetates) generate generally both cyclohepta[c]pyrrolones (Buchner products) and β-lactams (1,4-insertion products), and show obvious N-substituent-controlled chemoselectivity between the intramolecular Buchner reaction and aliphatic 1,4-C-H insertion under the catalysis of copper salts. The less steric N-alkyl substituents in the amide moiety generally favor the aliphatic 1,4-C-H insertion, while the more steric N-alkyl substituents generally favor the Buchner reaction. Compared with rhodium and ruthenium-catalyzed conditions, the current copper-catalyzed conditions improved the Buchner reaction selectivity of ethyl 3-alkyl(arylmethyl)amino-2-diazo-3-oxopropanoates.
Zirconium-Catalyzed Imine Hydrogenation via a Frustrated Lewis Pair Mechanism
Flynn, Stephanie R.,Metters, Owen J.,Manners, Ian,Wass, Duncan F.
, p. 847 - 850 (2016/04/19)
Zirconium-based frustrated Lewis pairs (FLPs) are active imine hydrogenation catalysts under mild conditions. Complexes of the type [CpR2ZrOMes][B(C6F5)4] utilize the imine substrate itself as the Lewis base component of the FLP. Catalyst performance is a function of ligand structure; in general more bulky, more electron rich cyclopentadienyl derivatives give the best results. However, Cp? derivatives are not catalytically active, being stable after initial heterolytic cleavage of H2; this allows experimental verification of the competence of the zirconocene-imine pair in FLP-type heterolytic H2 cleavage. Enamines and protected nitriles are also hydrogenated if an additional internal phosphine base is used.
Structure-Reactivity Relationship in the Frustrated Lewis Pair (FLP)-Catalyzed Hydrogenation of Imines
Tussing, Sebastian,Kaupmees, Karl,Paradies, Jan
supporting information, p. 7422 - 7426 (2016/05/24)
The autoinduced, frustrated Lewis pair (FLP)-catalyzed hydrogenation of 16-benzene-ring substituted N-benzylidene-tert-butylamines with B(2,6-F2C6H3)3 and molecular hydrogen was investigated by kinetic analysis. The pKa values for imines and for the corresponding amines were determined by quantum-mechanical methods and provided a direct proportional relationship. The correlation of the two rate constants k1 (simple catalytic cycle) and k2 (autoinduced catalytic cycle) with pKa difference between imine and amine pairs (ΔpKa) or Hammett's σ parameter served as useful parameters to establish a structure-reactivity relationship for the FLP-catalyzed hydrogenation of imines.
Versatile Catalytic Hydrogenation Using A Simple Tin(IV) Lewis Acid
Scott, Daniel J.,Phillips, Nicholas A.,Sapsford, Joshua S.,Deacy, Arron C.,Fuchter, Matthew J.,Ashley, Andrew E.
supporting information, p. 14738 - 14742 (2016/11/23)
Despite the rapid development of frustrated Lewis pair (FLP) chemistry over the last ten years, its application in catalytic hydrogenations remains dependent on a narrow family of structurally similar early main-group Lewis acids (LAs), inevitably placing limitations on reactivity, sensitivity and substrate scope. Herein we describe the FLP-mediated H2activation and catalytic hydrogenation activity of the alternative LA iPr3SnOTf, which acts as a surrogate for the trialkylstannylium ion iPr3Sn+, and is rapidly and easily prepared from simple, inexpensive starting materials. This highly thermally robust LA is found to be competent in the hydrogenation of a number of different unsaturated functional groups (which is unique to date for main-group FLP LAs not based on boron), and also displays a remarkable tolerance to moisture.
Imine hydrogenation by alkylaluminum catalysts
Hatnean, Jillian A.,Thomson, Jordan W.,Chase, Preston A.,Stephan, Douglas W.
supporting information, p. 301 - 303 (2014/01/06)
Di-isobutylaluminum hydride and tri-iso-butylaluminum (DIBAL 1, TIBAL 2) are shown to be efficient hydrogenation catalysts for a variety of imines at 100 °C and 100 atm of H2, operating via a hydroalumination/ hydrogenolysis mechanism.
Zincocene and dizincocene N-heterocyclic carbene complexes and catalytic hydrogenation of imines and ketones
Jochmann, Phillip,Stephan, Douglas W.
supporting information, p. 8370 - 8378 (2014/07/08)
The N-heterocyclic carbene (NHC) adducts Zn(CpR) 2(NHC)] (CpR=C5HMe4, C 5H4SiMe3; NHC=ItBu, IDipp (Dipp=2,6- diisopropylphenyl), IMes (Mes=mesityl), SIMes) were prepared and shown to be active catalysts for the hydrogenation of imines, whereas decamethylzincocene [ZnCp*2] is highly active for the hydrogenation of ketones in the presence of noncoordinating NHCs. The abnormal carbene complex [Zn(OCHPh2)2(aItBu)]2 was formed from spontaneous rearrangement of the ItBu ligand during incomplete hydrogenation of benzophenone. Two isolated ZnI adducts [Zn2Cp* 2(NHC)] (NHC=ItBu, SIMes) are presented and characterized as weak adducts on the basis of 13C NMR spectroscopic and X-ray diffraction experiments. A mechanistic proposal for the reduction of [ZnCp* 2] with H2 to give [Zn2Cp*2] is discussed.
H2 cleavage, hydride formation, and catalytic hydrogenation of imines with zinc complexes of C5Me5 and N-heterocyclic carbenes
Jochmann, Phillip,Stephan, Douglas W.
supporting information, p. 9831 - 9835 (2013/09/23)
Decamethylzincocene, [ZnCp2], reacts with H2 to give the reduced ZnI compound [Zn2Cp2]. In the presence of coordinating and (more efficiently) of non-coordinating N-heterocyclic carbenes (NHCs), the catalytic hydrogenation of imines with H2 is achieved. The monomeric hydride [Zn(Cp)(H)(SIMes)] is presented and its mechanistic implications are considered. Copyright
