Convenient Synthesis of tert‐Butyl Esters of Indole‐5‐carboxylic Acid and Related Heterocyclic Carboxylic Acids

The tert‐butyl esters of indole‐5‐carboxylic acid and related compounds such as benzofuran‐ and benzothiophene‐5‐carboxylic acid were readily accessed by reacting the appropriate carboxylic acids with tert‐butyl trichloroacetimidate. To obtain the tert‐butyl esters of the 5‐carboxylic acids of 1H‐benzotriazole and 1H‐benzimidazole, position 1 of these heterocycles had to be protected by acetylation prior to reaction with tert‐butyl trichloroacetimidate. Cleavage of the acetyl residue of the obtained intermediates by dilute aqueous NaOH in ethanol led to the desired tert‐butyl 1H‐benzotriazole‐and 1H‐benzimidazole‐5‐carboxylates.     

Polymer Supported Synthesis of 2,3,4,6-Tetra-O-Acetyl-β-D-Glucopyranosyl Esters of Aromatic Carboxylic Acids

Aromatic carboxylic acids bound to Amberlyst A-26 react with α-acetobromoglucose to form 2,3,4,6-tetra-O-acetyl-1-0-aroyl-β-D-glucopy ranose derivatives in good yield. Glucosylation occurs satisfactorily with carboxylic acids and nitrophenols (pKa 7–4), but not with phenols whose pKa values are higher (pka ～ 10). Selective glucosylation at the carboxylic group is easily achieved in the case of phenolic acids.     

Synthesis and Hydrophosphorylation of π-Complexes of Esters of Unsaturated Carboxylic Acids with Chromium Subgroup Metals

Photochemical and thermochemical activation were used to prepare new -complexes of chromium, molybdenum and tungsten containing ²- and ⁴-coordinated methyl acrylate, methyl cynnamate, and dimethyl fumarate molecules. Geometric, electronic, and energetic parameters of the coordinated ester molecules were found and factors governing ²- and ⁴-coordination of the oxodiene system were revealed by nonempirical calculations. Monocarboxylic acid esters incorporated in the -complexes react with dialkyl hydrogen phosphites to give dialkyl acyl phosphites coordinated with the metal center and susceptible to oxidation the corresponding phosphates. In this case, the phosphorylation involves the OH-tautomer of dialkyl hydrogen phosphite. Coordinated dimethyl fumarate undergoes phosphorylation by two concurrent pathways, viz. transesterification or Pudovik reaction. In the latter case, fragmentation of the organometallic compound takes place.     

Beyond Kolbe and Hofer–Moest: Electrochemical Synthesis of Carboxylic Anhydrides from Carboxylic Acids

Herein we report a conceptually new non-decarboxylative electrolysis of carboxylic acids to obtain their corresponding anhydrides as highly valuable reagents in organic synthesis. All carbon atoms of the starting material are preserved in the product in an overall redox-neutral reaction. In a broad substrate scope of carboxylic acids the anhydrides are generated with high selectivity, which demonstrates the versatility of the developed method. Beneficially, no dehydrating reagents are required in comparison to conventional methods and the synthesis is based on uncritical starting materials using graphite and stainless steel as very inexpensive and eco-friendly electrode materials.     

Design of Supported Organocatalysts from Carboxylic Acids for the Mannich-Type Synthesis of β-Amino Carbonyl Compounds

New supported acidic organocatalysts were prepared by the impregnation of three carboxylic acids (CF₃COOH, CCl₃COOH, and CH₃COOH) on silica support at room temperature in diethyl ether. The catalysts were characterized by scanning electron microscopy, energy dispersion X-ray analysis (EDX), Brunauer-Emmett-Teller-surface-area-analysis (BET), thermogravitational analysis, Fourier transform infrared, and powder X-ray diffractometry analysis. These solid acids were observed as highly efficient reusable catalysts at room temperature for the selective synthesis of β-amino carbonyl compounds via Mannich-type reactions of acetophenone, arylamine and arylaldehydes using two different conditions in CH₂Cl₂ solution and solvent-free grinding within a short time. The more acidic two catalysts could be recycled for up to five cycles with a small loss in catalytic activity.     

Oxidation of Aldehydes and Ketones into Carboxylic Acids and Esters Using 4‐Amino‐2‐Chloroperbenzoic Acid Supported on Silica Gel

Abstract

4‐Amino‐2‐chloroperbenzoic acid supported on silica gel was found to be a versatile and efficient oxidant for the oxidation of aldehydes and ketones to the corresponding carboxylic acids and esters.     

Selective Esterification of Aliphatic Carboxylic Acids in the Presence of Aromatic Carboxylic Acids Over Monoammonium Salt of 12‐Tungstophosphoric Acid

Monoammonium salt of 12‐tungstophosphoric acid [(NH₄)H₂PW₁₂O₄₀] was found to be a practical and useful heterogeneous catalyst for an efficient and selective esterification of aliphatic carboxylic acids with alcohols in the presence of aromatic carboxylic acids. The heteropoly acid–based heterogeneous catalyst has the advantages of a simple workup procedure, water insolubility, and good activity.     

Polyenolates of Unsaturated Carboxylic Acids in Synthesis. Synthesis of Unsaturated α-Amino Acids and β-Hydrazing Acids

Regioselective reaction of lithium diene-and triene-diolates 1 and 2 with O-diphenylphosphinyl hydroxylamine affords unsaturated α-amino acids 3 and 4. Addition to DEAD leads selectively to γ-hydrazino unsaturated acids 5 and 6.     

Synthesis of Functionalized 1‐Azadienes by Reaction of 2,6‐Dimethylphenyl Isocyanide and Acetylenic Esters in the Presence of CH Acids

The adducts produced in the reaction between 2,6‐dimethylphenyl isocyanide and acetylenic esters were trapped by 3‐chloroacetylacetone, dialkyl 2‐chloromalonates, or dimethoxy methoxymalonate to produce highly functionalized 1‐azadienes in good yields.     

Synthesis and Thermal Behavior of Polyesters Derived from 1,3‐Propanediol and Various Aromatic Dicarboxylic Acids

Abstract

Seven aromatic dicarboxylic acids were esterified by melt polycondensation in two steps with 1,3‐propanediol (1,3‐PDO) in the presence of tetrabutoxytitanium as catalyst. The acids used were: terephthalic (TPA), isophthalic (IPA), naphthalene‐2,6‐dicarboxylic (2,6‐NDA), naphthalene‐1,4‐dicarboxylic (1,4‐NDA), biphenyl‐4,4^′‐dicarboxylic (4,4^′‐BPDA), diphenylsulfone‐4,4^′‐dicarboxylic (4,4^′‐DPSDA), and pyridine‐2,6‐dicarboxylic acid (2,6‐PDA). In the first step, the esterification reaction was monitored, by measuring the distilled water. The prepared oligomers were polycondensated in a second step under high vacuum using the same catalyst as before. The received poly(propylene dicarboxylate)s were characterized by viscometry, carboxyl end‐group content (CC), color measurement, and were studied by differential scanning calorimetry (DSC). From this study, the above polyesters could be classified to three classes: (a) easily crystallizing polyesters derived from TPA and 2,6‐PDA, (b) slow crystallizing polyesters derived from IPA and 2,6‐NDA, and (c) amorphous polyesters derived from 1,4‐NDA, 4,4^′‐BPDA, and 4,4^′‐DPSDA.     

Racemization-Free Recovery of α-Hydroxyphosphonates from Their Carboxylic Esters

Ammonolysis (25% aqueous NH₃ - alcohols or THF) of carboxylic esters obtained from diastereoisomerically pure α-hydroxyphosphonates leads to recovery of the phosphonates without racemization in good to excellent yields.     

Intelligence Way from Eco-friendly Synthesis Strategy of New Heterocyclic Pyrazolic Carboxylic α-Amino Esters

The α-amino acid derivatives constitute a class of compounds of particular medicinal and synthetic attention and considerable interest has been devoted to their synthesis in recent years. In the present work, we develop the computational study of the synthesis reaction of new pyrazolyl α-amino esters derivatives using the Gaussian 09 based on the DFT/B3LYP density functional theory method, with the base 6-31G(d, p) to ensure the possibility of carrying out these reactions within the laboratory of synthesis. Indeed, this research has encouraged us to establish an economical synthesis strategy of these products in overall yields of 73.5% to 87% to have access to new active biomolecule through the O-alkylation reaction between methyl α-azidoglycinate N-benzoylated and primary pyrazole alcohols[(3,5-dimethyl-1H-pyrazol-1-yl)methanol, (1H-pyrazol-1-yl)methanol and (3-ethoxy-5-methyl-1H-pyrazol-1-yl)methanol] under different operating conditions. The structure of the prepared heterocyclic systems was characterized by conventional spectroscopic techniques, like ¹H NMR, ¹³C NMR, and MS. The results revealed that the experimental study is in good correlation with the computational one.     

A Novel Method for the Synthesis of Carboxylic Esters Catalyzed by Expandable Graphite

Esterification reaction of carboxylic acid and alcohol has been carried out in excellent yield with expandable graphite as a catalyst.     

Effect of Temperature on the Solubility of Short-Chain Carboxylic Acids in Water

The aqueous solubilities of pentanoic and hexanoic acids were measured between 298.15 and 333.15 K at intervals of 5.00 K. Nonlinear dependences were found for the variation of solubility with temperature. The temperature dependences of the solubility of the acids in water are described by nonlinear van’t Hoff plots. Experimental data were fitted by the method of least-squares to a second-order polynomial equation, which was then used to determine the differential solution enthalpies at selected temperatures. The values for the apparent Gibbs energy and the apparent entropy of solution are calculated.     

New Method for the Synthesis of 2‐Aza‐1,3‐Butadienes

2‐Aza‐1,3‐butadienes have been synthesized from carbonyl compounds and 1,1,1,3,3,3‐hexamethyl‐disilazane in the presence of cobalt‐containing catalysts. The best yields (up to 95%) were achieved in the case of aldehydes branched in the α-position and 2-methylcyclohexanone. In the case of two α,β‐unsaturated ketones, pyridine derivatives were found as the main products.     

Improved Yields in the Synthesis of Spin‐Labeled Fatty Acids

Abstract

Paramagnetic amide side products (6a–g) have been isolated from the reaction mixture in the synthesis of spin‐labeled fatty acids of the doxyl type. After their hydrolysis to the corresponding acid, 7, the overall yield of spin‐labeled fatty acids is significantly increased compared with published procedures.     

Synthesis of Heterobicycles of δ-Lactam Fused with 1,3-Diazaheterocycles by the Reaction of Heterocyclic Ketene Aminals with α,β-Unsaturated Carboxylic Esters

Heterobicycles of δ-lactam fused with imidazolidine (4, 7), hexahydropyrimidine (5, 8), or hexahydro-1, 3-diazepine (6, 9) were synthesized by the reaction of heterocyclic ketene aminals 1, 2 or 3 with ester of α,β-unsaturated carboxylic acids.     

Synthesis of Chiral Nitrones from N‐Fmoc Amino Acids and N‐Fmoc Dipeptides

Abstract

In this work is presented a synthetic procedure for the preparation of chiral nitrones from N‐Fmoc protected amino acids and dipeptides. The nitrone functional group can replace the carboxyl unit of amino acid and peptide systems and can be inserted into the peptide chain. The introduction of the 1,3‐dipole in peptide segments can improve the solubility and the stability toward enzymatic degradation.     

Synthesis of Novel 2‐Vinylcyclopropane Phosphonic Acids

2‐Vinylcyclopropane‐1‐phosphonic acid diesters 1a–d were synthesized by the reaction of trans‐1,4‐dibromo‐2‐butene with α‐substituted phosphonic acid diesters. Esterification of 1‐ethoxycarbonyl‐2‐vinylcyclopropane‐1‐carboxylic acid with dimethyl 2‐hydroxyethyl‐phosphonate gave the 2‐vinylcyclopropane phosphonic acid dimethylester 1e. The silylation of phosphonic acid diesters 1a–e by halotrimethylsilanes followed by solvolysis with methanol or water resulted in the formation of phosphonic acids 2a–e. In the case of steric hinderance of the phosphoryl group, monoesters 3c,d were also formed. Furthermore, ethyl carboxylate 1b could be chemoselectively cleaved by aqueous potassium hydroxide to carboxylic acid 4.     

Two New Catalysts for the Dehydrogenative Coupling Reaction of Carboxylic Acids with Silanes—Convenient Methods for an Atom‐Economical Preparation of Silyl Esters

Tris(triphenylphosphine)cuprous chloride [Cu(PPh₃)₃Cl] has been found to be an efficient catalyst for the dehydrosilylation of carboxylic acids with silanes. In the presence of 4 mol% Cu(PPh₃)₃Cl, dehydrosilylation reactions in acetonitrile afforded the corresponding silyl esters at 80°C in good yields. It was noted that triphenylphosphine itself also functions as an adequate catalyst for the reaction.