CeCl3-Catalyzed Reduction of Methyl Esters of Carboxylic Acids to Corresponding Alcohols with Sodium Borohydride

A wide range of methyl esters, including esters of aromatic carboxylic acids, alkenyl carboxylic acids, aliphatic carboxylic acids, and protected amino acids, were reduced to the corresponding alcohols with NaBH₄ in ethanol in the presence of a catalytic amount of CeCl₃. The reaction was completed within 24 h at ambient temperature and showed high functional group compatibility and chemoselectivity. With esters containing nitro, methoxyl, halogen, alkenyl, and protected amino functionalities, only the ester group was reduced. The alcohols were isolated after evaporation of the solvent and routine aqueous workup in good yields (75–95%).     

Decarboxylative Conjunctive Cross‐coupling of Vinyl Boronic Esters using Metallaphotoredox Catalysis

The synthesis of complex alkyl boronic esters through conjunctive cross‐coupling of vinyl boronic esters with carboxylic acids and aryl iodides is described. The reaction proceeds under mild metallaphotoredox conditions and involves an unprecedented decarboxylative radical addition/cross‐coupling cascade of vinyl boronic esters. Excellent functional‐group tolerance is displayed, and application of a range of carboxylic acids, including secondary α‐amino acids, and aryl iodides provides efficient access to highly functionalized alkyl boronic esters. The decarboxylative conjunctive cross‐coupling was also applied to the synthesis of sedum alkaloids.     

Esterification of Carboxylic Acids and Diacids by Trialkyl Borate under Solvent- and Catalyst-Free Conditions

Esterification or transesterification reactions are usually carried out in the presence of homogeneous or heterogeneous catalysts. However, recently a new method was reported for the esterification of carboxylic acids by tributyl borate under solvent- and catalyst-free conditions. In order to show the synthetic ability of trialkyl borate esters in the esterification reactions, here, the esterification of other carboxylic acids and diacids by tributyl-, triisoamyl-, and tribenzyl borate under the same conditions were reported. Some of the prepared ester and diester products have found wide applications as plasticizers and synthetic ester base lubricants. The esterification reactions have been cleanly carried out in the absence of any solvent under catalyst-free conditions. The maximum rate belongs to isoamyl trichloroacetate （VIb） which reached about 76% within about 6.5 h. On the basis of obtained findings, it seems that electron withdrawing groups on carboxylic acid facilitate the esterification reaction.     

Visible‐Light‐Mediated Decarboxylative Radical Additions to Vinyl Boronic Esters: Rapid Access to γ‐Amino Boronic Esters

The synthesis of alkyl boronic esters by direct decarboxylative radical addition of carboxylic acids to vinyl boronic esters is described. The reaction proceeds under mild photoredox catalysis and involves an unprecedented single‐electron reduction of an α‐boryl radical intermediate to the corresponding anion. The reaction is amenable to a diverse range of substrates, including α‐amino, α‐oxy, and alkyl carboxylic acids, thus providing a novel method to rapidly access boron‐containing molecules of potential biological importance.     

Preparation of Esters and Amides from Carboxylic Acids by Activation with Dialkyl Phosphite-Carbon Tetrachloride Mixture

A simple one pot phase transfer catalytic method is described for the synthesis of carboxylic amides and esters from carboxylic acids and amines or alcohols, respectively. For the activation of the carboxylic acids “in situ” generated phosphoric acid diester chlorides were applied.     

Arsenorgano-Verbindungen. XX. Synthese und Reaktionsverhalten der Diphenylarsinocarbonsäuren

Organo-arsenic Compounds. XX. Synthesis and Reactivity of Diphenylarsino Carboxylic Acids Natrium diphenylarside reacts with chlorocarboxylic acids and their amides or esters in liquid ammonia to give the corresponding diphenylarsino carboxylic acids, amides, and esters. Their properties and some reactions are described. The synthesis of secondary ω-phenylarsino carboxylic acids from 2 and 3 has been studied.     

An improved method for the protection of carboxylic acids as 1,1-dimethylallyl esters

1,1-Dimethylallyl (DMA) esters of various N-protected amino acids have been synthesized using prenyldimethylsulfonium tetrafluroborate, a reagent that can be readily made and stored, in conjunction with catalytic CuBr. These reactions were complete within several hours and afforded DMA esters in high yields. As has been previously shown in our group, DMA esters represent a palladium-labile proctecting group for carboxylic acids that resists nucleophilic attack as a tert-butyl ester would.     

Stereoselektive synthese von D-α-hydroxycarbonsäuren bzw. D-α-hydroxycarbonsäuren enthaltenden depsipeptiden aus L-aminosäuren

Depsipeptides containing D-α-hydroxy carboxylic acids are efficiently synthesized by the reactions of L-α-halo-carboxylic acid esters (obtained from L-amino acids) with caesium salts of N-protected amino acids.     

Organo-arsenverbindungen : XXXI. Synthese und eigenschaften sekundärer arsinofunktioneller carbonsäuren und ihrer derivate

Sodium phenylarside and sodium-n-butylarside react with chloro (bromo) carboxylic acids and their sodium salts, amides or esters in liquid ammonia to give the corresponding secondary arsino carboxylic acid derivatives. Their properties and reactions are described. In some cases the derivatives of arsindiyl-di-carboxylic acids are obtained as by-products due to transmetalation reactions.     

Pyrolysis of Amino Acid Derived Stabilised Ylides as a Route to Chiral Acetylenic Amines and Amino Acids and Gaba Analogues

Abstract

We recently reported the pyrolysis of stabilised ylides as a method for overall conversion of carboxylic acids to homologous acetylenic esters and terminal alkynes.^1,2 This has now been applied successfully to amino acids. A wide range of alkoxycarbonyl protected amino acids have been converted to the stable crystalline ylides 1. These have been fully characterised, and upon FVP, eliminate Ph₃PO to afford the protected acetylenic amino acids 2 in good yield and without significant racemisation. Subsequent reactions of these extremely versatile intermediates have been used to gain access to a wide variety of chiral amine and amino acids of great interest as potential selective enzyme inhibitors and components for modified peptide structures.     

Synthesis of various acylating agents directly from carboxylic acids

Abstract

A straightforward synthesis of acylating reagents such as Weinreb and MAP amides from aromatic, aliphatic carboxylic acids, and amino acids using PPh₃/NBS combination is described. A chemo-selective modification of the carboxylic acid group into Weinreb amide in the presence of more reactive aldehydes and ketones is presented. All reactions were performed at ambient temperature under air using undried commercial grade solvent. Furthermore, the present methodology could be performed at a gram scale under inert-free reaction conditions. In addition, 7-azaindoline amide auxiliary (used for catalytic asymmetric aldol- and Mannich-type reactions), which behaves like Weinreb amide is also synthesized under similar reaction conditions.     

Improved Cs2CO3 Promoted O-Alkylation of Acids

Cesium carbonate mediated O-alkylation of carboxylic acids was efficiently carried out under mild in situ conditions to give the corresponding esters exclusively. Chiral templates including α-hydroxy and α-alkoxy acids were also converted to their corresponding esters with no observed racemization.     

Organic syntheses on an icosahedral borane surface: closomer structures with twelvefold functionality

The syntheses of a series of novel ester-linked derivatives of the icosahedral [closo-B12(OH)12]2- boron cluster (closomer esters) are described using several synthetic methods. The reaction of bis(tetrabutylammonium)-closo-dodecahydroxy-dodecaborate, [NBu4]2 1, with carboxylic acid chlorides and anhydrides, vinyl esters with a Y5(OiPr)13O catalyst and 1,1'-carbonyldiimidazole-activated carboxylic acids yields the corresponding dianionic dodeca-ester closomers. The method using 1,1'-carbonyldiimidazole-activated carboxylic acids may be employed as a general synthetic strategy. The use of elevated reaction temperatures, achievable under pressure, to expedite syntheses is described. An attractive methodology using immobilized scavenger reagents for the expeditious purification of the closomer esters was employed. The developed methodology is compatible with a variety of peripheral functional groups attached to the termini of densely packed, carboxylate ester-linked radial arms bonded to the icosahedral borane surface. A closomer ester having twelve terminal amino groups was prepared, and without isolation, fully acetylated in good yield.     

A novel and expedient synthesis of optically active fluoroalkylated amino acids via palladium-catalyzed allylic rearrangement and Ireland–Claisen rearrangement

The allylic substitution reactions of various chiral α-fluoroalkylated mesylates with carboxylic acids in the presence of a palladium catalyst proceeded smoothly to give γ-fluoroalkylated allyl esters in excellent yields. The esters were subsequently subjected to Ireland–Claisen rearrangement without isolation, leading to the corresponding homochiral α-fluoroalkylated-β,γ-unsaturated amino acids in good yields.     

Rhodium(I)-catalyzed carboxylation of aryl- and alkenylboronic esters with CO2

When the esters of arylboronic acids with 2,2-dimethylpropan-1,3-diol were treated with a catalytic amount of [Rh(OH)(cod)]2 in the presence of 1,3-bis(diphenylphosphino)propane and CsF in dioxane at 60 degrees C under carbon dioxide atmosphere, the benzoic acid derivatives were obtained in good yields. Reactions of alkenylboronic esters also proceeded under similar conditions to give alpha,beta-unsaturated carboxylic acids. As these boronic esters are now easily available through coupling or direct borylation reactions, this method would be a useful method for the preparation of various functionalized aryl- and alkenyl-carboxylic acids.     

Stereoselective Synthesis of Unsaturated and Functionalized l-NHBoc Amino Acids, Using Wittig Reaction under Mild Phase-Transfer Conditions

The stereoselective synthesis of a new amino acid phosphonium salt was described by quaternization of melting triphenylphosphine with the γ-iodo NHBoc-amino ester, derived from l-aspartic acid. The deprotection of the carboxylic acid function to afford the phosphonium salt with a free carboxylic acid group was achieved by a palladium-catalyzed desallylation reaction. This phosphonium salt was used in the Wittig reaction with aromatic or aliphatic aldehydes and trifluoroacetophenone, under solid-liquid phase-transfer conditions in chlorobenzene and in the presence of K(3)PO(4) as weak base, to afford the corresponding unsaturated amino acids without racemization. Thus, the reaction with substituted aldehydes allows to graft various functionalized groups on the lateral chain of the amino acid, such as trifluoromethyl, cyano, nitro, ferrocenyl, boronato, or azido. In addition, the reaction of the amino acid Wittig reagent with α,β-unsaturated aldehydes leads to amino acids bearing a diene on the lateral chain. Finally, this amino acid phosphonium salt appears to be a new powerful tool for the preparation of unsaturated and non-proteinogenic α-amino acids, directly usable for the synthesis of customized peptides.     

Palladium-catalyzed intramolecular alpha-arylation of alpha-amino acid esters.

The Pd-catalyzed intramolecular alpha-arylation of alpha-amino acid esters is described. Starting from readily available amino acids, the synthesis of a variety of isoindolines and tetrahydroisoquinoline carboxylic acid esters has been accomplished. Additionally, fused tricyclic systems can be efficiently prepared from cyclic amino acid esters. Reaction conditions have been found that allow the use of tert-butyl ester and N-(benzyloxycarbonyl) protecting groups.     

Light‐Driven Kinetic Resolution of α‐Functionalized Carboxylic Acids Enabled by an Engineered Fatty Acid Photodecarboxylase

Chiral α‐functionalized carboxylic acids are valuable precursors for a variety of medicines and natural products. Herein, we described an engineered fatty acid photodecarboxylase (CvFAP)‐catalyzed kinetic resolution of α‐amino acids and α‐hydroxy acids, which provides the unreacted R‐configured substrates with high yields and excellent stereoselectivity (ee up to 99 %). This efficient light‐driven process requires neither NADPH recycling nor prior preparation of esters, which were required in previous biocatalytic approaches. The structure‐guided engineering strategy is based on the scanning of large amino acids at hotspots to narrow the substrate binding tunnel. To the best of our knowledge, this is the first example of asymmetric catalysis by an engineered CvFAP.     

Esterification‐nitration of Ortho‐hydroxyphenyl Carboxylic Acids and Benzoic Acids with Cerium(IV) Ammonium Nitrate (CAN)

A convenient and useful esterification was realized, and this reaction proceeded without a dehydrating reagent or water removal equipment. A series of ortho‐hydroxyphenyl carboxylic acids and benzoic acids were transformed to their corresponding methyl esters under CAN/CH₃OH reaction conditions. Whereas in an aprotic solvent, acetonitrile, sp³‐C tethered ortho‐hydroxyphenyl carboxylic acids undergo simultaneous o,p‐dinitration and intramolecular esterification reactions in good yields. Also, 2‐((1 E)‐2‐nitrovinyl)‐4‐nitro‐phenol ( 3e ) showed selective cytotoxicities toward MCF‐7, HEP G2, and HEP 3B cell lines with IC₅₀ values of 23.50, 7.33, and 7.59 ug/mL, respectively.     

High-Energy Phosphonium Compounds and Their Application to Polymer Synthesis

High-energy phosphonium compounds, the N-phosphonium salts of pyridines, were prepared by the oxidation of phosphorous acid and its esters with mercuric salts or halogens in pyridines, or by a hydrolysis-dehydration reaction of diphenyl and triaryl phosphites or phosphonites. These salts are very reactive to nucleophiles, activating carboxyl, amino, or hydroxyl compounds via the corresponding N-phosphonium salts to yield carboxylic amides and esters in high yields on further aminolysis, alcoholysis, and acidolysis. These reactions, especially the hydrolysis-dehydration reactions with phosphites, were successfully extended to the direct polycondensation reaction of dicarboxylic acids with diamines, of free α-amino acids or dipeptides, and of carbon dioxide and disulfide with diamines under mild conditions, yielding linear polymers of high molecular weight (polyamides, polypeptides, polyureas, and polythioureas).