Esters In High Yields Research Articles

Pd-Catalyzed Selective Carbonylation of gem-Difluoroalkenes: A Practical Synthesis of Difluoromethylated Esters.

The first catalyst for the alkoxycarbonylation of gem-difluoroalkenes is described. This novel catalytic transformation proceeds in the presence of Pd(acac)2 /1,2-bis((di-tert-butylphosphan-yl)methyl)benzene (btbpx) (L4) and allows for an efficient and straightforward access to a range of difluoromethylated esters in high yields and regioselectivities. The synthetic utility of the protocol is showcased in the practical synthesis of a Cyclandelate analogue using this methodology as the key step.

Pd‐Catalyzed Selective Carbonylation of gem‐Difluoroalkenes: A Practical Synthesis of Difluoromethylated Esters

AbstractThe first catalyst for the alkoxycarbonylation of gem‐difluoroalkenes is described. This novel catalytic transformation proceeds in the presence of Pd(acac)2/1,2‐bis((di‐tert‐butylphosphan‐yl)methyl)benzene (btbpx) (L4) and allows for an efficient and straightforward access to a range of difluoromethylated esters in high yields and regioselectivities. The synthetic utility of the protocol is showcased in the practical synthesis of a Cyclandelate analogue using this methodology as the key step.

Developing Nickel–Zirconia Co-Precipitated Catalysts for Production of Green Diesel

The transformation of sunflower oil (SO) and waste cooking oil (WCO) into green diesel over co-precipitated nickel–zirconia catalysts was studied. Two series of catalysts were prepared. The first series included catalysts with various Ni loadings prepared using zirconium oxy-chloride, whereas the second series included catalysts with 60–80 wt % Ni loading prepared using zirconium oxy-nitrate as zirconium source. The catalysts were characterized and evaluated in the transformation of SO into green diesel. The best catalysts were also evaluated for green diesel production using waste cooking oil. The catalysts performance for green diesel production is mainly governed by the Ni surface exposed, their acidity, and the reducibility of the ZrO2. These characteristics depend on the preparation method and the Zr salt used. The presence of chlorine in the catalysts drawn from the zirconium oxy-chloride results to catalysts with relatively low Ni surface, high acidity and hardly reduced ZrO2 phase. These characteristics lead to relatively low activity for green diesel production, whereas they favor high yields of wax esters. Ni-ZrO2 catalysts with Ni loading in the range 60–80 wt %, prepared by urea hydrothermal co-precipitation method using zirconium oxy-nitrate as ZrO2 precursor salt exhibited higher Ni surface, moderate acidity, and higher reducibility of ZrO2 phase. The latter catalysts were proved to be very promising for green diesel production.

Highly Diastereo- and Enantioselective Access to syn-α-Amido β-Hydroxy Esters via Ruthenium-Catalyzed Dynamic Kinetic Resolution-Asymmetric Hydrogenation.

Dynamic kinetic resolution (DKR) of racemic aryl α-amino β-ketoesters via Ru-diphosphine-catalyzed asymmetric hydrogenation was realized at 70 °C under 50 atm of hydrogen, affording syn α-amido β-hydroxy esters in high yields (up to 96%) with high reactivity (TON up to 940) and diastereo- and enantioselectivities (up to 99:1 dr, 98% ee). These hydrogenation products provide valuable chiral synthons in many natural products and pharmaceuticals. Gram-scale DKR asymmetric hydrogenation (DKR-AH) was also performed with retained reactivity and stereoselectivity, revealing the synthetic utility of this method.

Production of esters from grease trap waste lipids under supercritical conditions: Effect of water addition on ethanol

The transesterification of the lipid fraction of grease trap waste in a catalyst-free medium, under supercritical conditions, was studied. The aim was to evaluate the effect of different concentrations of water (in ethanol) on the production of ethyl esters. Reactions were conducted in a continuous reactor applying different temperatures (275 °C, 300 °C, 325 °C) and residence times (10 min, 20 min, 30 min) using ethanol with water concentrations varying from (2.5 to 10) wt%. The addition of up to 2.5 wt% of water favored the formation of esters at low residence times. The ester yield was not affected by longer residence times (30 min) and with a water content of 5 wt% or higher the ester yield was reduced. It was found that a high temperature (325 °C) and long residence time favored the thermal degradation, which was more prominent for ethyl linoleate. The highest ester yield (92.6%) and lowest content of unreacted compounds (5.5 wt%) was obtained using ethanol with 2.5 wt% of water.

Aluminium complex-catalysed hydroboration of alkenes and alkynes

Catalytic hydroboration of terminal alkenes/alkynes with HBpin using the Al(III) catalyst, [κ2-{Ph2P(=Se)NCH2(C5H4N)}Al(CH3)2] (1), under mild and solvent-free conditions to afford corresponding alkyl/alkenyl boronate esters in high yield is reported.

A cheap metal for a challenging task: nickel-catalyzed highly diastereo- and enantioselective hydrogenation of tetrasubstituted fluorinated enamides.

Nickel-catalyzed asymmetric hydrogenation of challenging tetrasubstituted fluorinated enamides has been achieved, affording chiral α-fluoro-β-amino esters in high yields with excellent diastereo- and enantioselectivities (up to 98% yield, >99 : 1 dr, up to >99% ee). Deuterium-labeling experiments and control experiments were conducted to probe the mechanism, and the results indicated that the acidity of the solvent plays a critical role in the control of diastereoselectivity by trapping the adduct of nickel hydride to C[double bond, length as m-dash]C bonds via protonolysis, giving the hydrogenation product with stereospecific syn-selectivity. This protocol provides efficient access to chiral α-fluoro-β-amino esters which have important potential applications in organic synthesis and medicinal chemistry.

Synthesis of N-aryl β-amino acid derivatives via Cu(ii)-catalyzed asymmetric 1,4-reduction in air.

In the presence of the inexpensive and stable stoichiometric reductant polymethylhydrosiloxane (PMHS) as well as certain amounts of appropriate alcohol and base additives, the non-precious metal copper-catalyzed asymmetric 1,4-hydrosilylation of β-aryl or β-alkyl-substituted N-aryl β-enamino esters was well realized to afford a diverse range of N-aryl β-amino acid esters in high yields and excellent enantioselectivities (26 examples, 90–98% ee). This approach tolerated the handling of both catalyst and reactants in air without special precautions. The chiral products obtained have been successfully converted to the corresponding enantiomerically enriched β-lactam and unprotected β-amino acid ester, which highlighted the synthetic utility of the developed catalytic procedure.

An imidazolin-2-iminato ligand organozinc complex as a catalyst for hydroboration of organic nitriles

Catalytic hydroboration of nitriles with pinacolborane (HBpin) using the imidazolin-2-iminato zinc alkyl complex [{(ImtBuN)Zn(CH2CH3)}2] (1c) under mild and solvent-free conditions to afford corresponding diboronate esters in high yield is reported.

Organocatalytic Asymmetric Allylic Alkylations of Sulfoximines.

An enantio- and regioselective allylic alkylation of sulfoximines with Morita-Baylis-Hillman carbonates was developed. The asymmetric reaction is directed by a quinidine-derived organocatalyst providing a range of optically active α-methylene β-sulfoximidoyl esters in high yields (up to 93%) with good to excellent enantiomeric excesses (up to 95%) under mild reaction conditions.

Synthesis of Esters Via a Greener Steglich Esterification in Acetonitrile.

The Steglich esterification is a widely-used reaction for the synthesis of esters from carboxylic acids and alcohols. While efficient and mild, the reaction is commonly performed using chlorinated or amide solvent systems, which are hazardous to human health and the environment. Our methodology utilizes acetonitrile as a greener and less hazardous solvent system. This protocol exhibits rates and yields that are comparable to traditional solvent systems and employs an extraction and wash sequence that eliminates the need for the purification of the ester product via column chromatography. This general method can be used to couple a variety of carboxylic acids with 1° and 2° aliphatic alcohols, benzylic and allylic alcohols, and phenols to obtain pure esters in high yields. The goal of the protocol detailed here is to provide a greener alternative to a common esterification reaction, which could serve useful for ester synthesis in both academic and industrial applications.

Enol Ester Synthesis via Cobalt-Catalyzed Regio- and Stereoselective Addition of Carboxylic Acids to Alkynes

A cobalt-catalyzed highly regio- and stereoselective hydro-oxycarbonylation of alkynes is reported. Both terminal and internal alkynes can react with carboxylic acids to afford enol esters in high yields. The catalyst generated from Co(BF4)2, tridentate phosphine ligand L5, and zinc in situ exhibits much higher reactivity than the corresponding cobalt/diphosphine complex.

Application of an immobilized Rhizopus oryzae lipase to batch and continuous ester synthesis with a mixture of a lauric acid and fusel oil

Five commercial lipase preparations immobilized on epoxy-polysiloxane- hydroxyethylcellulose were tested as potential biocatalysts to mediate the esterification reaction of isoamyl alcohol with lauric acid. Among them, the immobilized lipase from Rhizopus oryzae was the most active biocatalyst, attained high ester yield (81.26%) in 24 h, being selected for subsequent tests using fusel oil as a source of isoamyl alcohol under batch and continuous runs. Under batch conditions, no adverse effect was found when pure isoamyl alcohol was replaced by fusel oil. However, under continuous runs, the selected biocatalyst was found to have limited performance (half-life time = 173 h) and the average ester productivity was only 277.8 ± 19.3 μmol g−1 min−1. These results can be credited to the high affinity of the hybrid matrix for the water formed as a by-product, modifying the substrate interaction with the essential water around the enzyme limiting the substrate migration to the solid phase and thereby reducing the enzyme activity. By replacing the hybrid support for a higher hydrophobic matrix such as commercial copolymer styrene-divinylbenzene it was possible to attain a stable operation, achieving an average ester productivity of 794.43 ± 66.04 μmol g−1 min−1 and increasing the half-life time to 285 h. Further productivity incremental (1598.68 ± 135.79 μmol g−1 min−1) was also attained by using higher substrate loading. This process shows to be an attractive alternative to bulk chemical routes to satisfy increasing commercial demands for isoamyl laurate an essential emollient in the cosmetic industry.

Lipase immobilization on high water adsorbing capacity bagasse: applications in bio-based plasticizer synthesis.

This study investigates the structure and water adsorbing capacity of bagasse and of sodium hydroxide pretreated bagasse. The structures of bagasse and bagasse-NaOH were compared by SEM and XRD. Candida antarctica lipase B was then immobilized on bagasse, bagasse-NaOH and DPA@bagasse-NaOH. The expressed activity and immobilization yield of lipase immobilized on bagasse-NaOH (1.0%) was 36% and 45% higher than that on bagasse. When dopamine (DPA) was used as cationic polymer monomer via self-polymerization for mediating immobilization, the protein loading amounts and activity of lipase immobilized on DPA@bagasse-NaOH were higher than that of bagasse-NaOH. When the DPA concentration was 100mg/ml, the immobilized lipase expressed activity reached its highest value (800 U/g), where the immobilization yield achieved 96.8%, which was 3.93-fold of lipase immobilized on native bagasse (24.6%). Then the immobilized lipases were used to synthesize a bio-based plasticizer. Lipase immobilized on DPA@bagasse-NaOH exhibited a significantly improved operational stability. Even after 12 batches, a high ester yield (84.2%) was maintained. Additionally, poly (vinyl chloride) PVC blends plasticized with methyl oleate as a secondary plasticizer were investigated. It was discovered that methyl oleate can be used as an effective bio-based plasticizer for PVC. These results indicate that bagasse with high water adsorbing capacity and self-polymerized DPA layer could create a favorable microenvironment for bio-based plasticizer synthesis in esterification reactions.

Regio‐ and Enantioselective Synthesis of α‐Amino‐δ‐Ketoesters Through Catalytic Umpolung Reaction of α‐Iminoesters with Enones

AbstractChiral α‐amino‐δ‐keto esters are important precursors of organocatalysts, pharmaceuticals, and biochemically interesting molecules. The organocatalytic asymmetric umpolung reaction of imines has been developed to obtain chiral amines in a highly enantioselective manner. Herein, we report the organocatalytic asymmetric umpolung synthesis of α‐amino‐δ‐keto esters in high yield (up to 95% ee, >20/1 r.r.).magnified image

Mild Esterification of Carboxylic Acids via Continuous Flow Diazotization of Amines.

A new continuous flow protocol for the diazotization of methylamine with 1,3-propanedinitrite in THF is reported. The synthesis of methyl esters was achieved in high yields from a variety of carboxylic acids in 20 min at 90 °C. Additionally, this protocol was extended to other aryl and alkyl amines, namely secondary amines, to produce various substituted esters in high yield using 2-MeTHF as a solvent. The reaction conditions were compatible with many functional groups, namely nitrogen-containing heterocycles, alkynes, alkenes, alcohols, and phenols. Mechanistic investigations reveal that the reaction appears to proceed through a transient diazonium species rather than a diazo intermediate.

Zinc‐Catalyzed Esterification of N‐β‐Hydroxyethylamides: Removal of Directing Groups under Mild Conditions

Amide transformations involving C–N bond cleavage are recognized as difficult reactions owing to the inert nature of amides resulting from resonance. Accordingly, a strong inductive effect and geometrical distortion reasonably decrease the resonance stabilization to attenuate the C–N linkage. Although the conversion of such activated amides has been studied intensively, reaction systems for “unactivated” amides are underdeveloped. We herein report that a zinc(II) trifluoromethanesulfonate [Zn(OTf)2] catalyst achieves the esterification of a wide range of unactivated tertiary amides with the assistance of intramolecular acyl rearrangement. The reaction was applied to the one‐pot removal of various amide‐based directing groups under mild reaction conditions to afford the corresponding esters in high yields.

Intermolecular Halogenation/Esterification of Alkenes with N‐Halosuccinimide and Acetic Acid Catalyzed by 1,4‐Diazabicyclo[2.2.2]octane

Abstract1,4‐Diazabicyclo[2.2.2]octane (DABCO) is a suitable Lewis base that acts as an organocatalyst in the activation of N‐chlorosuccinimide (NCS) towards the chlorination of alkenes. The chloriranium ion formed from NCS and the alkene, can be intermolecularly opened by a nucleophile, such as acetic acid, to produce highly functionalized trans‐chloro esters in high yields. The protocol is also applied to the synthesis of chlorohydrins and chloro ethers using water or methanol as nucleophiles instead of acetic acid. Brominated analogs can also be synthesized from alkenes and N‐bromosuccinimide (NBS) in the presence of various basic catalysts. However, the reaction patterns seem to be remarkably different. The catalytic performance of bases in the bromoesterification of alkenes was found to be strongly affected by their Brønsted basicity, suggesting that acetyl hypobromite, formed in situ from NBS and acetic acid, acts as a real brominating agent in these systems.magnified image

Palladium‐Catalyzed Carbonylation of sec‐ and tert‐Alcohols

A general palladium-catalyzed synthesis of linear esters directly from sec- and tert-alcohols is described. Compared to the classic Koch-Haaf reaction, which leads to branched products, this new transformation gives the corresponding linear esters in high yields and selectivity. Key for this protocol is the use of an advanced palladium catalyst system with L2 (pyt bpx) as the ligand. A variety of aliphatic and benzylic alcohols can be directly used and the catalyst efficiency for the benchmark reaction is outstanding (turnover number up to 89 000).

Palladium‐Catalyzed Carbonylation of sec‐ and tert‐Alcohols

AbstractA general palladium‐catalyzed synthesis of linear esters directly from sec‐ and tert‐alcohols is described. Compared to the classic Koch–Haaf reaction, which leads to branched products, this new transformation gives the corresponding linear esters in high yields and selectivity. Key for this protocol is the use of an advanced palladium catalyst system with L2 (pytbpx) as the ligand. A variety of aliphatic and benzylic alcohols can be directly used and the catalyst efficiency for the benchmark reaction is outstanding (turnover number up to 89 000).