Facile oxidative conversion of hydrazides of carboxylic acids to corresponding acids,esters and amides using copper compounds

Oxidative conversion of hydrazides of carboxylic acids to acids, esters and amides using Cu salts was studied. Acids were obtained in high yields by using a catalytic amount of Cu(OAc)₂ at room temperature by bubbling oxygen. Hydrazides were converted to esters by the treatment with Cu(OR)Cl or Cu(OR)₂ formed in situ from CuCl₂ and sodium alkoxide. Amides were obtained in high yields by the oxidation of hydrazides with CuCl₂ in the presence of amines.     

Lewis acid-controlled reactions of zirconacyclopentadienes with isocyanates and isothiocyanates. One-pot three- or four-component synthesis of multiply substituted iminocyclopentadienes and butadiene-tethered 1,6-bisamides and electrophilic cyclization

Multiply substituted zirconacyclopentadienes including bicyclic zirconacyclopentadienes and zirconaindenes reacted with isocyanates and isothiocyanates in the presence of Lewis acids to afford iminocyclopentadienes and conjugated 1,6-bisamides, depending on the nature of Lewis acids, isocyanates, and isothiocyanates used. Only in the presence of BF₃ could iminocyclopentadienes be obtained in high isolated yields when zirconacyclopentadienes were treated with isocyanates. On the contrary, BF₃ could not mediate the reaction of zirconacyclopentadienes with isothiocyanates. For the reactions of zirconacyclopentadienes with isothiocyanates, EtAlCl₂ was found effective to generate iminocyclopentadienes as the products. Interestingly, however, for the reactions of zirconacyclopentadienes with isocyanates, EtAlCl₂ was found to work very differently from BF₃. Instead of iminocyclopentadienes, conjugated 1,6-bisamides and conjugated mono-amides were obtained as products in high isolated yields from the reactions of zirconacyclopentadienes with isocyanates, depending on the substituents of isocyanates. The reaction path and products could be controlled by Lewis acids. As a demonstration of the usefulness of thus obtained unsaturated bisamides, electrophilic cyclization using acids, NBS, and I₂ was carried out. Electrophilic cyclization of multisubstituted conjugated 1,6-bisamide derivatives afforded cyclic iminoethers in excellent yields with perfect selectivity. Only one of the amide groups took part in the electrophilic cyclization.     

Selective oxidation reactions of diaryl- and dialkyldisulfides to sulfonic acids by CH3ReO3/hydrogen peroxide

Diaryl- and dialkyl disulfides were oxidized in acetonitrile at 20 °C by CH₃ReO₃/H₂O₂ oxidant system to yield selectively the corresponding sulfonic acids in short reaction times and in high yields.     

Microwave-assisted Michael addition of sulfonamides to α,β-unsaturated esters: A rapid entry to protected β-amino acid synthesis

An efficient, clean and very simple procedure for the synthesis of protected β-amino acids is described. Michael addition of sulfonamides to α,β-unsaturated esters in the presence of K₂CO₃ and tetrabutylammonium bromide (TBAB) under microwave irradiation affords the title compounds in good to high yields and short reaction times. This new method affords protected β-amino acids in high yields and short reaction times.     

A high-yielding low-cost facile synthesis of 2-oxazolidinones chiral auxiliaries

The chiral aminol alcohols from reduction of amino acids with NaBH₄/H₂SO₄ were directly treated with EtO₂CCl to give the carbamates, which cyclized in the presence of traces of K₂CO₃ at 100–130°C under vacuum to afford chiral 2-oxazolidinones in high yields.     

Ceric Ammonium Nitrate Catalyzed Oxidation of Aldehydes and Alcohols

A variety of aromatic, aliphatic and conjugated aldehydes and alcohols were transformed to the corresponding carboxylic acids and ketones with a quantitative conversion in high yields with 70% t‐BuOOH solution in water in the presence of catalytic amounts of ceric ammonium nitrate [Ce(NH₄)₂(NO₃)₆] (CAN) under room temperature conditions. The scope of our catalytic system is applicable for a wide range of aromatic, conjugated and aliphatic substrates. These aldehydes were converted to the corresponding carboxylic acids in good isolated yields in reasonable times. This method possesses a wide range of capabilities since it can be used with other functional groups which may not tolerate oxidative conditions, involves fairly simple method for work‐up, exhibits chemoselectivity and proceeds under ambient conditions. The resulting products are obtained in good yields within reasonable time.     

Synthesis of coumarins by Pt-catalyzed hydroarylation of propiolic acids with phenols

Synthesis of coumarins from phenols and propiolic acids was examined by using a Pt catalyst such as PtCl₂/AgOTf, K₂PtCl₄/AgOTf, and K₂PtCl₄/AgOAc. Propiolic acid reacted even with less reactive phenols in trifluoroacetic acid to give coumarins and dihydrocoumarins. In the case of substituted propiolic acids, phenylpropiolic acid and 2-octynoic acid, the reactions proceeded selectively to afford coumarins in good to high yields.     

Glycidyl Esters of Aromatic Acids

Abstract

The reaction of substituted benzoic acids, dicarboxylic acids such as phthalic, terephthalic, and isophthalic acids, and the sodium or potassium salts of these acids with equimolar or excess epichlorohydrin in the presence of benzyltrimethylammonium chloride has been studied using various solvents such as toluene, dioxane, monochlorobenzene, and tetrachloroethylene. Use of the free carboxylic acids gave only fair to low yields of glycidyl esters, while sodium or potassium salts of the carboxylic acids gave excellent yields of materials of high oxirane content. The epoxidation of chlorohydrin esters of these acids by the dehydrochlorination was also studied using various dehydrochlorinating reagents such as NaOH, KOH, Na₂CO₃, and NaAlO₂ in such solvents as water, dichloromethane, dioxane, and monochlorobenzene at various temperatures. Reaction time, reaction temperature, and water content were found to influence the yield of glycidyl esters. It is suggested that the reaction path involves nucleophilic attack upon the terminal position of the epoxide or epichlorohydrin. The resulting alkoxide then reacts further to give either a glycidyl ester or a chlorine-containing by-product, the predominant course depending upon reaction conditions.     

A Novel Method for the Synthesis of Newfangled Asymmetric Schiff Bases from α‐amino Acids under Ultrasonic Conditions and in Aqueous Medium

Chiral Schiff bases were obtained at high yields via a novel technique. Aryl aldehydes and chiral α‐amino acids were treated (1) in the presence of H₃PO₄ in ethanol at 80°C for 24 h, and (2) in the presence of K₂CO₃ under ultrasonic conditions in an aqueous ethanol medium within 5 min with yields reaching up to 96%. The results showed that the presented methodology under ultrasonic conditions was effective, practical, and eco‐friendly compared to that using an acidic medium. The corresponding asymmetric Schiff bases were synthesized for the first time, and were characterized by ¹H and ¹³C nuclear magnetic resonance and infrared spectroscopy and high‐resolution mass spectrometry.     

Efficient and selective oxidative decarboxylation of arylcarboxylic acids into the corresponding aldehydes and ketones using K5CoIIIW12O40 as a green oxidant under microwave and conventional heating

The oxidative decarboxylation of various ??-aryl- and ??,??-arylcarboxylic acids having electron-donating and electron-withdrawing groups by using a stoichiometric amount of potassium 12-tungstocobaltate(III), K₅Co^IIIW₁₂O₄₀, in 50% aqueous acetonitrile solution resulted in the corresponding aldehydes and ketones in high yields within short reaction times under microwave irradiation. This transformation was also carried out under the conventional heating conditions which produced the corresponding aldehydes and ketones in relatively longer reaction times. The arylacetic acids with electron-withdrawing substituents required longer reaction times and produced lower yields. In contrast to arylacetic esters which were inert toward decarboxylation, the sodium arylacetates were decarboxylated in shorter times with yields better than those of the parent acids.     

Acylaminoacetyl derivatives of active methylene compounds. 4

Meldrum's acid has been found to be effectively acylated using the imidazolides of N-protected glycines, X-NHCH₂COOH (X = -COPh, -COMe, -Z, -Boc, -COOMe and -COOEt). The corresponding C-acylation compounds were isolated in high yields and were readily converted to the N-protected tetramic acids. It was shown by pmr spectroscopy that these acids exist as the enol tautomers in DMSO-d₆ solution, whereas in deuteriochloroform solution both the enol and keto tautomers can be observed.     

A convenient synthesis of activated enantiomerically pure 2-ethynylaziridines

2,3-cis- and 2,3-trans-N-Arylsulfonyl-2-ethynylaziridines with high enantiomeric purity have been synthesized. N-Protected amino aldehydes synthesized from natural α-amino acids were successively treated with Ph₃PC(Br)CO₂Me, DIBAL, MsCl–Et₃N, NaH in DMSO, and tert-BuOK in THF to yield 2-ethynylaziridines in good to high yields.     

Synthesis of new 3-arylindole-2-carboxylates using β,β-diaryldehydroamino acids as building blocks. Fluorescence studies

Several new methyl 3-arylindole-2-carboxylates were synthesized in high yields using a metal assisted [Pd(OAc)₂/Cu(OAc)₂, DMF, 130 °C] intramolecular C-N cyclization of β,β-diaryldehydroamino acids, developed by us, thus extending the scope of this reaction. The latter were obtained by a bis-Suzuki coupling of a β,β-dibromodehydroalanine with arylboronic acids bearing either electron-donating groups (EDGs) or electron-withdrawing groups (EWGs). We were able to establish general conditions for this coupling reaction [PdCl₂dppf·CH₂Cl₂ 1:1 (20 mol %), boronic acid (5 equiv), Cs₂CO₃ (1.4 equiv), THF/H₂O 1:1, 80 °C]. This strategy constitutes a novel, general and unprecedented approach to the synthesis of 3-arylindole-2-carboxylates. The fluorescence of the differently substituted indoles prepared was studied in several polar and non-polar solvents. In general the new indoles exhibit a solvent sensitive emission. The indoles with EDGs (OCH₃ and SCH₃) have reasonable fluorescence quantum yields in all solvents except in water. The indole with the cyano groups shows high fluorescent quantum yields in all solvents studied, despite the lower solvent sensitivity of its emission. The indole with the acetyl groups only exhibits reasonable fluorescence quantum yields in protic solvents. These studies show that the new 3-arylindole-2-carboxylates are good candidates to be used as fluorescent probes.     

Copper(II) triflate-catalyzed reduction of carboxylic acids to alcohols and reductive etherification of carbonyl compounds

A protocol is described for the reduction of carboxylic acids to primary alcohols using 1,1,3,3-tetramethyldisiloxane (TMDS) and a catalytic amount of Cu(OTf)₂. Aliphatic as well as aromatic carboxylic acids are reduced in high selectivity and good yields. TMDS/Cu(OTf)₂ has also been found to be an efficient catalytic reducing system for the preparation of symmetrical ethers from carbonyl compounds under mild conditions.     

Efficient and selective hydroarylation of propiolic acids and their esters with arenes catalyzed by a PtCl2/AgOTf system

PtCl₂/AgOTf-catalyzed hydroarylation of ethyl propiolate proceeded effectively to give ethyl (2Z)-cinnamate derivatives in good to high yields, without the formation of diethyl (1E,3Z)-4-arylbuta-1,3-diene-1,3-dicarboxylates that was observed in Pd(OAc)₂-catalyzed reaction. Especially, PtCl₂/AgOTf-catalyzed hydroarylation of propiolic acids proceeded effectively to give (2Z)-cinnamic acids exclusively.     

Efficient synthesis of racemic and chiral alkenyl sulfoxides by palladium-catalyzed Suzuki coupling

Alkenyl sulfoxide derivatives are obtained in high yields through a palladium-catalyzed Suzuki/Miyaura cross-coupling reaction of racemic and chiral 1-halo sulfoxides with aryl and alkenyl boronic acids. Chiral substrates react with no loss of optical purity and high optical yields. The reaction takes place with different palladium catalysts, such as Pd(PPh₃)₄ or Pd(OAc)₂/DABCO. Although nitrogen ligands like DABCO lead to an active palladium catalyst, they are less effective than the phosphine ones.     

Selective and Efficient Oxidation of Aldehydes to Their Corresponding Carboxylic Acids Using H2O2/HCl in the Presence of Hydroxylamine Hydrochloride

A wide variety of aldehydes were efficiently converted to their corresponding carboxylic acids in high yields using H₂O₂/HCl in the presence of hydroxylamine hydrochloride. In addition, selective oxidation of aldehydes in the presence of other functional groups such as hydroxyl group, carbon‐carbon double bond and other heteroatoms can be considered a noteworthy advantage of this method.     

Acid-catalyzed reactions of thiocyanates with camphene

The reactions of thiocyanates with camphene catalyzed by the heteropoly acids H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀ were studied. The optimal reaction conditions were found, and the formation of N-substituted thiocarbamates in comparatively high yields was established. It was shown that the heteropoly acids exhibit a higher catalytic activity than sulfuric acid.     

Palladium-catalyzed coupling reaction of amino acids (esters) with aryl bromides and chlorides

The bulky and electron-rich MOP type ligands and Pd(dba)₂ combinations showed high efficiency for the coupling reactions of amino acids and inactive aryl halides to give N-aryl amino acids. Under the catalytic conditions, not only α-amino acids, but also β-, γ-, and δ-amino acids have been coupled with aryl chlorides in moderate to high yields; in the case of optically pure β-amino acids as substrates, the optical purities of the coupling products retained.     

Epoxidation of phosphinoyl alkenes with hydrogen peroxide

The epoxidation of alkenylphosphorus compounds with hydrogen peroxide was systematically studied, revealing that while alkenylphosphine oxides failed to produce the corresponding epoxides, alkenylphosphonates, or phosphinates having a phenyl group at α-position reacted with H₂O₂/K₂CO₃ or alkenylphosphonic acids or phosphinic acids having an aliphatic group at α- or β-positions reacted with H₂O₂/Na₂WO₄/Et₃N to produce high yields of the corresponding epoxides.