Showing papers on "Decarboxylation published in 2014"
TL;DR: The direct decarboxylative arylation of α-amino acids has been achieved via visible light-mediated photoredox catalysis and offers rapid entry to prevalent benzylic amine architectures from an abundant biomass.
Abstract: The direct decarboxylative arylation of α-amino acids has been achieved via visible light-mediated photoredox catalysis. This method offers rapid entry to prevalent benzylic amine architectures from an abundant biomass, specifically α-amino acid precursors. Significant substrate scope is observed with respect to both the amino acid and arene components.
392 citations
TL;DR: A homogeneous iron catalyst is reported that, when used with a Lewis acid (LA) co-catalyst, gives approximately 1,000,000 turnovers for FA dehydrogenation, which is the highest turnover number reported for a first-row transition metal catalyst.
Abstract: Formic acid (FA) is an attractive compound for H2 storage. Currently, the most active catalysts for FA dehydrogenation use precious metals. Here, we report a homogeneous iron catalyst that, when used with a Lewis acid (LA) co-catalyst, gives approximately 1,000,000 turnovers for FA dehydrogenation. To date, this is the highest turnover number reported for a first-row transition metal catalyst. Preliminary studies suggest that the LA assists in the decarboxylation of a key iron formate intermediate and can also be used to enhance the reverse process of CO2 hydrogenation.
348 citations
TL;DR: A novel, simple, and efficient radical oxidative decarboxylative coupling with the assistant of the photocatalyst [Ru(phen)3 ]Cl2 is described, and various functional groups are well-tolerated in this reaction and thus provides a new approach to developing advanced methods for aerobic oxidative decarations.
Abstract: Photochemistry has ushered in a new era in the development of chemistry, and photoredox catalysis has become a hot topic, especially over the last five years, with the combination of visible-light photoredox catalysis and radical reactions. A novel, simple, and efficient radical oxidative decarboxylative coupling with the assistant of the photocatalyst [Ru(phen)3 ]Cl2 is described. Various functional groups are well-tolerated in this reaction and thus provides a new approach to developing advanced methods for aerobic oxidative decarboxylation. The preliminary mechanistic studies revealed that: 1) an SET process between [Ru(phen)3 ](2+) * and aniline play an important role; 2) O2 activation might be the rate-determining step; and 3) the decarboxylation step is an irreversible and fast process.
330 citations
TL;DR: Mechanistic studies rule out a picolinic acid intermediate, and an isolable rhodium complex sheds further light on the reaction mechanism, giving 5-substituted pyridines with very high levels of regioselectivity.
Abstract: α,β-Unsaturated carboxylic acids undergo Rh(III)-catalyzed decarboxylative coupling with α,β-unsaturated O-pivaloyl oximes to provide substituted pyridines in good yield. The carboxylic acid, which is removed by decarboxylation, serves as a traceless activating group, giving 5-substituted pyridines with very high levels of regioselectivity. Mechanistic studies rule out a picolinic acid intermediate, and an isolable rhodium complex sheds further light on the reaction mechanism.
245 citations
TL;DR: A practical and unified strategy has been described for the preparation of mono- and difluoromethylated phenanthridine derivatives using a visible-light-promoted alkylation and decarboxylation sequence from biphenyl isocyanides with ethyl bromofluoroacetate (EBFA) or ethylbromodifluoro acetate (EBDFA).
213 citations
TL;DR: A light-induced ruthenium-catalyzed N-acyl nitrene transfer to sulfides and sulfoxides by decarboxylation of 1,4,2-dioxazol-5-ones at room temperature, thus providing direct access to N-ACYl sulfimides and sulphoximines under mild reaction conditions.
Abstract: 1,4,2-Dioxazol-5-ones are five-membered heterocycles known to decarboxylate under thermal or photochemical conditions, thus yielding N-acyl nitrenes. Described herein is a light-induced ruthenium-catalyzed N-acyl nitrene transfer to sulfides and sulfoxides by decarboxylation of 1,4,2-dioxazol-5-ones at room temperature, thus providing direct access to N-acyl sulfimides and sulfoximines under mild reaction conditions. In addition, a one-pot sulfur imidation/oxidation sequence catalyzed by a single ruthenium complex is reported.
180 citations
TL;DR: A combination of photoredox and palladium catalysis has been employed to facilitate the room temperature decarboxylative allylation of recalcitrant α-amino and phenylacetic allyl esters.
Abstract: A combination of photoredox and palladium catalysis has been employed to facilitate the room temperature decarboxylative allylation of recalcitrant α-amino and phenylacetic allyl esters. This operationally simple process produces CO2 as the only byproduct and provides direct access to allylated alkanes. After photochemical oxidation, the carboxylate undergoes radical decarboxylation to site-specifically generate radical intermediates which undergo allylation. A radical dual catalysis mechanism is proposed. Free phenylacetic acids were also allylated utilizing similar reactions conditions.
167 citations
TL;DR: In this reaction the carboxy group is used as a traceless directing group, which is removed during a one-pot process, and a possible mechanism is proposed, involving a tandem sequence of Ir-mediated B-H activation, alkyne insertion, protonation, and decarboxylation.
Abstract: Iridium catalyzed alkyne hydroboration with o-carborane cage B–H has been achieved, leading to the formation of a series of 4-B-alkenylated-o-carborane derivatives in high yields with excellent regioselectivity via direct B–H bond activation. In this reaction the carboxy group is used as a traceless directing group, which is removed during a one-pot process. After the confirmation of a key intermediate, a possible mechanism is proposed, involving a tandem sequence of Ir-mediated B–H activation, alkyne insertion, protonation, and decarboxylation.
167 citations
TL;DR: It was proposed that the radical, generated from the silver-catalyzed decarboxylation in the "oil-in-water" droplets, could easily react with the trifluoromethylthiolating reagent to form the product.
Abstract: A silver-catalyzed decarboxylative trifluoromethylthiolation of secondary and tertiary carboxylic acids under mild conditions tolerates a wide range of functional groups. The reaction was dramatically accelerated by its performance in an aqueous emulsion, which was formed by the addition of sodium dodecyl sulfate to water. It was proposed that the radical, which was generated from the silver-catalyzed decarboxylation in the "oil-in-water" droplets, could easily react with the trifluoromethylthiolating reagent to form the product.
164 citations
TL;DR: A silver catalysed synthesis of 6-acyl phenanthridines by oxidative radical decarboxylation-cyclization of α-oxocar boxylates and isocyanides was developed and various functional groups were well-tolerated.
135 citations
TL;DR: In this article, the present level of understanding of the bonding modes of carboxylic acids (acetic acid in particular) on the TiO2 and ZrO2 surfaces as obtained from DFT calculations is discussed.
Abstract: Carboxylic acids play a fundamental role in the transformation of biomass into liquid fuels and other useful chemicals. In order to reduce the O/C content of biofuels, carboxylic acids need to be decomposed by decarboxylation, dehydroxylation, or decarbonylation unimolecular reactions, or they need to be converted into ketones via complex bimolecular reaction mechanisms. Ketonization, that is, the transformation of carboxylic acids into ketones, carbon dioxide, and water, is promoted by heterogeneous catalysts based on oxide materials. Among the most active catalysts are titania and zirconia surfaces. In recent years, a large body of experimental data has been complemented by specific investigations performed with first-principles electronic structure calculations based on density functional theory (DFT). In this review, I discuss the present level of understanding of the bonding modes of carboxylic acids (acetic acid in particular) on the TiO2 and ZrO2 surfaces as obtained from DFT calculations. Enolizat...
TL;DR: The application of this method to the synthesis of enantioenriched 1-aryl-2, 2,2,2-trifluoroethyl chiral amines starting from natural α-amino acids further testifies to the utility of the developed photocatalytic decarboxylative reduction protocol.
TL;DR: A series of biologically and synthetically important 3-vinyl indolines are rapidly assembled with a high reaction efficiency and stereoselectivity through the enantioselective trapping of Pd-stabilized zwitterionic intermediates by the sulphur ylides.
Abstract: Sulphur ylides are useful reagents in organic synthesis, typically reacting with highly polar reagents. Here, the authors show a catalytic asymmetric process for the addition of sulphur ylides to cyclic allylic esters with loss of CO2, giving access to chiral, highly functionalised indolines.
TL;DR: A visible-light-induced decarboxylative trifluoromethylation of α,β-unsaturated carboxylic acids, which uses the Togni reagent as the CF3 source is disclosed, and preliminary mechanistic analyses suggest a radical-type mechanism.
TL;DR: In this paper, the pyrolytic conversion of mono unsaturated free fatty acids to hydrocarbon products for use as renewable chemicals and fuels was studied, and the dominant reaction pathways were uncovered.
TL;DR: Preliminary mechanism studies support that the carbon-carbon bond formation precedes the decarboxylation and the reaction occurs in an outer-sphere mechanism.
Abstract: A rhodium-catalyzed chemo- and regioselective intermolecular decarboxylative addition of β-ketoacids to terminal allenes is reported. Using a Rh(I)/DPPF system, tertiary and quaternary carbon centers were formed with exclusively branched selectivity under mild conditions. Preliminary mechanism studies support that the carbon–carbon bond formation precedes the decarboxylation and the reaction occurs in an outer-sphere mechanism.
TL;DR: The decarboxylative coupling of aromatic diacids is a very promising tool which further enlarges the portfolio of reactions allowing for on-surface polymerizations and novel organometallic systems preparations.
Abstract: Metal-catalyzed polymerization of 2,6-naphthalenedicarboxylic acid (NDCA) to form poly-2,6-naphthalenes at various surfaces is reported. Polymerizations occur via initial formal dehydrogenation of self-assembled diacids with subsequent decarboxylation to give polymeric bisnaphthyl-Cu species at elevated temperature as intermediate structures (<160 °C). Further temperature increase eventually leads to poly-naphthalenes via reductive elimination. It is demonstrated that the Cu(111) surface works most efficiently to conduct such polymerizations as compared to the Au(111), Ag(111), Cu(100), and Cu(110) surfaces. Poly-2,6-naphthalene with a chain length of over 50 nm is obtained by using this approach. The decarboxylative coupling of aromatic diacids is a very promising tool which further enlarges the portfolio of reactions allowing for on-surface polymerizations and novel organometallic systems preparations.
TL;DR: It is shown that the wild-type halogenase SyrB2 can indeed direct aliphatic nitration and azidation reactions by the same chemical logic and suggests unrecognized or untapped versatility in ferryl-mediated enzymatic C–H-bond activation.
Abstract: Iron-dependent halogenases employ cis-halo-Fe(IV)-oxo (haloferryl) complexes to functionalize unactivated aliphatic carbon centers, a capability elusive to synthetic chemists. Halogenation requires (i) coordination of a halide anion (Cl(-) or Br(-)) to the enzyme's Fe(II) cofactor, (ii) coupled activation of O2 and decarboxylation of α-ketoglutarate to generate the haloferryl intermediate, (iii) abstraction of hydrogen (H•) from the substrate by the ferryl and (iv) transfer of the cis halogen as Cl• or Br• to the substrate radical. This enzymatic solution to an unsolved chemical challenge is potentially generalizable to installation of other functional groups, provided that the corresponding anions can support the four requisite steps. We show here that the wild-type halogenase SyrB2 can indeed direct aliphatic nitration and azidation reactions by the same chemical logic. The discovery and enhancement by mutagenesis of these previously unknown reaction types suggest unrecognized or untapped versatility in ferryl-mediated enzymatic C-H bond activation.
TL;DR: Palladium-catalyzed decarboxylative acylation of highly substituted indolines with α-keto acids via C-H bond activation is described, providing efficient access to C7-carbonylated indoles known to have diverse biological profiles.
TL;DR: This reaction represents a novel decarboxylation of an sp(3)-hybridized carbon and the use of a benzylic carboxylic acid as a source of carbonyl compounds.
Abstract: Aromatic aldehydes or ketones from copper catalyzed aerobic oxidative decarboxylation of phenylacetic acids and α-hydroxyphenylacetic acids have been synthesized. This reaction combined decarboxylation, dioxygen activation, and C–H bond oxidation steps in a one-pot protocol with molecular oxygen as the sole terminal oxidant. This reaction represents a novel decarboxylation of an sp3-hybridized carbon and the use of a benzylic carboxylic acid as a source of carbonyl compounds.
TL;DR: A silver-mediated decarboxylative C-S cross-coupling reaction of aliphatic carboxylic acid is described and provides an alternative approach for the synthesis of alkyl aryl sulfides.
TL;DR: The key finding is that the transmetalation has a comparably high barrier as the decarboxylation, which was previously believed to be solely rate-determining.
Abstract: The reaction mechanism of decarboxylative cross-couplings of benzoates with aryl halides to give biaryls, which is cooperatively catalyzed by copper/palladium systems, was investigated with DFT methods. The geometries and energies of all starting materials, products, intermediates, and transition states of the catalytic cycle were calculated for the two model reactions of potassium 2- and 4-fluorobenzoate with bromobenzene in the presence of a catalyst system consisting of copper(I)/1,10-phenanthroline and the anionic monophosphine palladium complex [Pd(PMe3)Br]−. Several neutral and anionic pathways were compared, and a reasonable catalytic cycle was identified. The key finding is that the transmetalation has a comparably high barrier as the decarboxylation, which was previously believed to be solely rate-determining. The electronic activation energy of the transmetalation is rather reasonable, but the free energy loss in the initial Cu/Pd adduct formation is high. These results suggested that research a...
TL;DR: The ring-opening polymerization (ROP) of racemic transcyclohexene carbonate (rac-CHC) and enantiopure trans-(R,R)-CHC is successfully carried out with various catalyst systems as mentioned in this paper.
Abstract: The ring-opening polymerization (ROP) of racemic trans-cyclohexene carbonate (rac-CHC) and enantiopure trans-(R,R)-CHC is successfully carried out with various catalyst systems. Poly(cyclohexene carbonate) (PCHC) with a slight isotactic bias (Pm = ca. 60–76%) is obtained by ROP of rac-CHC catalyzed by zinc diaminophenolate, zinc β-diketiminate, yttrium bis(phenolate), or 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) in combination with an alcohol as a co-initiator. Purely isotactic PCHC is synthesized for the first time via ROP of enantiopure (R,R)-CHC with a zinc/benzyl alcohol catalyst system. All reactions proceed without decarboxylation, affording well-defined PCHCs with Mn,NMR up to 17 000 g mol–1 and ĐM = ca. 1.2. Purely isotactic PCHC is semicrystalline, with Tg = 130 °C, Tc = 162 °C, and Tm = 248 °C. DFT computations further highlight the significant favorable impact of the trans-cyclohexane ring-strain to enable the ROP of CHC, as opposed to meso-CHC which is unreactive.
TL;DR: In this article, an increase of reaction time and temperature increase the selectivity to heptadecane, and a higher selectivity was observed in the presence of hydrogen, with a selectivity of 98% for oleic acid at 325°C.
Abstract: Catalytic decarboxylation and further conversion of oleic acid to branched and aromatic hydrocarbons in a single process step, over Pt–SAPO-11 and Pt/chloride Al 2 O 3 is presented. An increase of both reaction time and temperature increase the selectivity to heptadecane. Higher selectivity to heptadecane was observed in the presence of hydrogen. Decarboxylation of oleic acid was as high as ∼98 wt% (selectivity for heptadecane >30%) at 325 °C in the presence of hydrogen. Branched isomers, alkyl aromatics, like dodecyl benzene and cracked ( 17 ) paraffins were the other products.
TL;DR: A Cu2O-catalyzed aerobic oxidative decarboxylative ammoxidation to primary benzamides from phenylacetic acids and α-hydroxyphenylacetics acids is developed.
TL;DR: The catalyst-free sp(3) C-H functionalization of 2-alkylazaarenes has been achieved and this method provides facile synthesis of biologically important azaarene-substituted 3,4-dihydro(thio)coumarins in a single step in high yields.
TL;DR: In this paper, the decarbonylation and decarboxylation of heptanoic acid over carbon-supported Pt nanoparticles were studied in a continuous flow fixed bed reactor at 573 K and 37 bar for liquid phase operation and 1 bar for gas phase operation.
TL;DR: In this article, the catalytic, gas-phase hydrodeoxygenation (HDO) of propanoic acid (PAc) over supported group VIII noble metals (M = Pd, Pt, Rh, Ru, Ni) was studied at 1-atm and 200-400°C.
Abstract: The catalytic, gas-phase hydrodeoxygenation (HDO) of propanoic acid (PAc) over supported group VIII noble metals (M = Pd, Pt, Rh, Ru, Ni) was studied at 1 atm and 200-400 °C. The activity and selectivity as a function of the reaction temperature was investigated. The reaction activity based on the TOF follows the order: Pd > Ru > Pt > Rh > Ni. The reaction over Pd, Pt and Rh catalysts proceeds mainly via decarbonylation (DCN) and decarboxylation (DCX) pathways at each reaction temperature. For Ru and Ni catalysts, while decarbonylation and decarboxylation pathways were predominant at lower temperatures (e.g., 200–250 °C), at higher temperatures (>300 °C) the formation of diethyl ketone was observed. Additionally, the kinetics of Pd over different supports (carbon, SiO2 and TiO2) were examined. The activity based on the TOF decreases in the following order: Pd/SiO2 > Pd/TiO2 > Pd/C. The reaction orders in acid and H2 were found to be approximately 0.5 and zero, respectively, regardless of the support. The apparent activation energies studied in a temperature range of 200–240 °C, were 16.7 ± 0.6, 19.3 ± 1.6 and 11.7 ± 0.7 kcal/mole for Pd/C, Pd/TiO2 and Pd/SiO2 catalysts, respectively. The selectivity for Pd/C and Pd/SiO2 indicated mainly decarbonylation/decarboxylation and hydrogenation reaction pathways. In contrast, Pd/TiO2 at low temperatures (200 °C) could generate decarbonylation and esterification products.
TL;DR: In this article, Linoleic acid (cis,cis-9,12-octadecedienoic acid) was selected as a model polyunsaturated fatty acid and batch pyrolysis reactions were conducted at temperatures from 350 to 450°C for 0.5 to 8h reaction times.
TL;DR: The design, synthesis, and mechanistic studies of the half-sandwich ruthenium complex 12 are reported, which are established as the most active and practical catalyst for anti-Markovnikov reductive hydration discovered to date and define the structural parameters of 12 underlying its activity and stability and delineate design strategies for synthesis of other multifunctional catalysts.
Abstract: The conversion of terminal alkynes to functionalized products by the direct addition of heteroatom-based nucleophiles is an important aim in catalysis. We report the design, synthesis, and mechanistic studies of the half-sandwich ruthenium complex 12, which is a highly active catalyst for the anti-Markovnikov reductive hydration of alkynes. The key design element of 12 involves a tridentate nitrogen-based ligand that contains a hemilabile 3-(dimethylamino)propyl substituent. Under neutral conditions, the dimethylamino substituent coordinates to the ruthenium center to generate an air-stable, 18-electron, κ3-complex. Mechanistic studies show that the dimethylamino substituent is partially dissociated from the ruthenium center (by protonation) in the reaction media, thereby generating a vacant coordination site for catalysis. These studies also show that this substituent increases hydrogenation activity by promoting activation of the reductant. At least three catalytic cycles, involving the decarboxylation ...