Copper(I) iodide-catalysed arylation of acetoacetate to yield 2-arylacetic acid esters

The C-C coupling reaction between ethyl acetoacetate and aryl halides in the presence of CuI is described. The effects of solvent, ligands such as vicinal diamines and amino acids, base and temperature are reported. The arylated acetoacetate ester is deacylated under the reaction conditions resulting in the generation of 2-arylacetic acid esters, constituting a mild alternative to direct arylation of carboxylate esters.     

Solvent-modulated chemoselective deprotections of trialkylsilyl esters and chemoselective esterifications

A series of trialkylsilyl esters were deprotected or transesterificated into their corresponding carboxylic acids or methyl esters under a catalytic amount of CBr₄ in alcohol reaction system. This method enables to desilylate secondary sp³-carbon, sp²-carbon, sp-carbon and aryl tethered trialkylsilyl esters to carboxylic acids, whereas primary sp³-carbon tethered trialkylsilyl esters were further converted into their methyl esters under CBr₄/MeOH reaction conditions. The highly chemoselective deprotections can be modulated and achieved by the introduced protecting trialkylsilyl groups and the used alcohols such as MeOH and EtOH under this photochemically-induced reaction conditions.     

Easy access to β-halo amino esters and aziridine 2-carboxylic esters from halohydrins

The halohydrins prepared from epoxide esters, were treated with hydroxylamine derivatives. In subsequent reaction with NaOH/K₂CO₃/Bu₄NHSO₄ the N-protected β-halo α-aminoesters thus obtained were converted into N-hydroxy ariridine 2-carboxylic esters in good yields.     

Convenient preparation of tert-butyl esters

A general method is presented for the preparation of tert-butyl esters by the gentle warming of the carboxylic acid in the presence of excess of tert-butyl acetoacetate and a catalytic amount of acid. This method generates only low pressures, and is therefore suitable for laboratory scale pressure glassware.     

Ruthenium-catalyzed oxidation of silyl ethers to silyl esters

Direct oxidation of silyl ethers to silyl esters, using RuO₄ formed in situ, is reported. The reaction was optimized to minimize formation of the corresponding carboxylic acid product whose formation pathway appears to be solvent dependent. The reaction is tolerant of halides, nitriles, nitro groups, esters, epoxides, and ketones.     

A novel synthesis of vinyl esters from vinylversatate-10

Vinylversatate-10 (VV10)¹ has successfully been used to synthesise a large number of lower vinyl esters by transvinylation in presence of mercuric acetate and sulfuric acid. The synthesis of vinylhalo esters proceeds with more difficulty. It has been observed that neither Hg(OAc)₂ nor H₂SO₄ alone is capable of initiating the transvinylation. Furthermore, it has been found that a molar ratio 2:1 of VV10 to carboxylic acid is sufficient to drive the reaction to the right by continuous distillation of the vinyl ester formed, and as a result a high yield of vinyl ester is obtained. A mechanism for this reaction and for the formation of side products has been proposed.     

Carbonylation of diols and their ethers and esters with ruthenium catalysts: synthesis of lactones and hydroxyacids ethers and esters

Diols and their formic or acetic esters can be carbonylated to give lactones or the corresponding hydroxyacid esters of ethers in the presence of carbonylruthenium iodide systems, [Ru(CO)₃I₃]⁻/alkyl or metal iodide, at a temperature of 200°C and CO pressure of 10-20 MPa. The reaction in the case of 1,3-propanediol gives γ-butyrolactone, with a selectivity of 60-% . Side reactions of homologation to 1,4-butanediol derivatives and hydrogenolysis to n-propyl derivatives by H₂ produced by the water gas shift reaction (WGSR) also occur, together with acid-catalyzed dehydration to give linear polypropylene glycols, α,ω-diols with more than 3 carbon atoms in the chain preferentially give hydroxyacid esters and ethers.The cyclic ether by-products and linear polyether by-products can be further activated and carbonylated under the reaction conditions to give lactones or hydroxy-acid derivatives thus increasing the total yield of carbonylation products. The formation of H₂ by WGSR involving water produced by the acid-catalyzed dehydration reactions, and the subsequent hydrogenolysis and homologation reactions cannot be avoided.     

Synthesis of enol and vinyl esters catalyzed by an iridium complex

Enol and vinyl esters were successfully synthesized by the use of an iridium complex as a catalyst. The reaction of carboxylic acids with terminal alkynes in the presence of catalytic amounts of [Ir(cod)Cl]₂ and Na₂CO₃ gave the corresponding 1-alkenyl esters. The addition of carboxylic acids to alkynes principally took place in the Markovnikov fashion. In addition, by the use of an Ir complex combined with NaOAc various vinyl esters were prepared through the transvinylation between carboxylic acids and vinyl acetate.     

Efficient preparation method of 4-hydroxybenzoic esters – Oxidation of substituted Hagemman’s ester

A practical two-step synthetic method of diversely R-substituted 4-hydroxybenzoic esters, which may have wide applications in household chemicals and polymeric materials, was developed by 2:1 coupling between ethyl acetoacetate and aldehydes (RCHO) in t-BuOK/t-BuOH, followed by oxidative aromatization of the resulting Hagemman’s esters. Application of the condition using stoichiometric NBS and catalytic TMS·OTf efficiently induced oxidation of the Hagemman’s esters to produce 4-hydroxybenzoic esters.     

Synthesis of carboxylic esters from aldehydes using metal carbonyl anions,part 2. Dimerization of aldehydes to carboxylic esters catalyzed by disodium pentacarbonylchromate,na2[cr(co)5]

Na₂[Cr(CO)₅] (1) was found to be an efficient catalyst for the dimerization of aldehydes to carboxylic esters. Several aromatic aldehydes including furfural gave the corresponding esters in good yields. This reaction also proceeded intramolecularly to give phthalide from phthalaldehyde. Compared with M₂[Fe(CO)₄] (M = Na, K), 1 was found to be a more efficient catalyst for this reaction. However, aliphatic aldehydes gave aldolcondensation products instead of the corresponding esters. In the reactions of p-substituted benzaldehydes with 1, the reactivity decreased with the increase of the electron-releasing ability of the substituents. However, even p-anisaldehyde, which hardly reacted with M₂[Fe(CO)₄], reacted with 1 to give the ester in moderate yield. The reaction mechanism, including the nucleophilic attack of the pentacarbonylchromate dianion on the carbonyl carbon, is discussed.     

Basic hydrolysis of glyceryl nitrate esters. II. 1,2-glyceryl and 1, 3-glyceryl dinitrate esters

Kinetics of the basic hydrolysis of 1,2-glyceryl dinitrate (1,2-DNG) and 1,3-glyceryl dinitrate (1,3-DNG) esters were investigated in CO₂-free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature controlled reactor vessel with provision for continuous N₂ sparging of the reaction mixture. Both glyceryl dinitrate esters hydrolyzed via second-order reaction at 25°C. 1,2-DNG in basic solutions isomerized to 1,3-DNG which subsequently hydrolyzed to yield products. The main hydrolysis product of 1,3-DNG was identified as glycidyl nitrate. Other products formed during the basic hydrolysis of DNGs were nitrites and nitrates.     

A novel synthetic method for γ-acetoxy-(E)-α,β-unsaturated esters by the palladium catalyzed regio- and stereoselective acetoxylation of β,γ-unsaturated esters

A new synthetic method for γ-acetoxy-α,β-unsaturated esters by the acetoxylation of β,γ-unsaturated esters catalyzed by PdCl₂ in the presence of KOAc and pentyl nitrite in acetic acid is presented. The reaction takes place at γ-position of the esters regioselectively with double bond migration to α,β-position. The E configuration of the double bond was confirmed by NMR analysis. Preliminary investigation to synthesize pyrenophorin and pyrenophorol using this reaction is described.     

Effect of catalysts on the reaction of allyl esters with hydrosilanes

The reaction of hydrosilylation of allyl esters XOCH₂CH=CH₂ (X = MeCO, CF₃CO, C₃F₇CO) and PhOCH₂CH=CH₂ with hydrosilanes HSiY₃ (Y = Cl, OEt) in the presence of the Speier catalyst, the Speier catalyst with additives, and of various nickel complexes was studied. The catalytic hydrosilylation reaction in the presence of the Speier catalyst is accompanied by the reduction. Additives to the Speier catalyst (vinyltriethoxysilane and some ethers) allow to suppress considerably the reduction reaction. In the presence of the studied nickel complexes mainly reduction and isomerization reactions occurred. The best nickel catalysts of hydrosilylation were the mixtures of NiCl₂ or Ni(acac)₂ with phosphine oxides. In contrast to allyl esters, the hydrosilylation of simple olefins proceeds easier, the content of the product of hydrosilylation in the reaction mixture reaches 94.3%.     

Facile preparation of aromatic esters from aromatic bromides with ethyl formate or DMF and molecular iodine via aryllithium

Various aromatic bromides were treated with n-BuLi and subsequently with ethyl formate, followed by the reaction with ethanol and molecular iodine in the presence of K₂CO₃ to provide the corresponding aromatic ethyl esters in good yields. Moreover, aromatic bromides could be transformed into the corresponding aromatic methyl esters in good yields by the treatment with n-BuLi and subsequently with DMF, followed by the reaction with methanol, molecular iodine, and K₂CO₃. Some aromatics could be also converted into the corresponding aromatic esters in good yields by the treatment with n-BuLi, and subsequently with ethyl formate or DMF, followed by the reaction with molecular iodine and K₂CO₃. The present reactions offer a novel route for the transition-metal-free, carbon-monoxide-free, and therefore environmentally benign one-pot conversion of aromatic bromides and aromatics into aromatic esters.     

A new oxidation process. Transformation of gem-bishydroperoxides into esters

A new oxidation process has been found where α,ω-dicarboxylic acid esters and ω-hydroxycarboxylic acid esters are formed on heating gem-bishydroperoxides in alcohol in the presence of BF₃·Et₂O. By addition of H₂O₂ to this reaction α,ω-dicarboxylic acid esters are formed almost selectively.     

Effect of zinc chloride on thermal decomposition of polymethacrylic and polyacrylic esters

Zinc chloride reduces the rate of thermal and thermooxidative decompositions of polymethacrylic esters and increases the thermal decomposition rate of polyacrylic esters. Mechanisms of the thermal decompositions of polymethacrylates and polyacrylates in the presence of ZnCl₂ have been suggested.For thermal decomposition polymethacrylic esters, the rate of depolymerization decreases due to the formation of cycles in a polymer chain by reaction of Zinc chloride with neighbouring ester groups. For thermooxidative decomposition of polymethacrylates, ZnCl₂ decreases also the rate of initiation of depolymerization and causes decomposition of hydroperoxide groups by a heterolytic mechanism. The increase in thermal decomposition rate of polyacrylic esters results from the high activity of complexes of ester groups and ZnCl₂ in decomposition reactions with formation of alcohol and CO₂ through Cameron mechanism.     

N-benzhydryl-glycolamide esters (OBg esters) as carboxyl protecting groups in pept1de synthesis

N-Benzhydryl-glycolamide esters (OBg esters) of various N-protected amino acids have been synthesized. In order to demonstrate their usefulness in peptide chemistry, the syntheses of For-Met-Leu-Phe-OH (chemiotactic peptide) and Pro-Leu-Gly-NH₂ (MIF) have been carried out. OBg esters are compatible with commonly used protecting groups and are cleanly and selectively removed in mild alkaline conditions without any side reaction, except for β-benzyl aspartyl containing sequences.     

Facile amidation of esters with aromatic amines promoted by lanthanide tris (amide) complexes

The development of catalysts capable of catalyzing amidation of esters with amines to construct amides under mild conditions is of great importance. Compared to aliphatic amines, the direct catalytic amidation of esters with less nucleophilic aromatic amines is rather difficult. Employing simple lanthanide tris (amide) complexes Ln[N (SiMe₃)₂]₃(μ-Cl)Li (THF)₃ as the catalysts, it was found a broad range of aromatic amines and esters were efficiently converted into various amides in good yields under mild conditions. A plausible mechanism for this transformation was experimentally supported as starting from an amide exchange reaction between the lanthanide tris (amide) complex and the substrate amine.     

Alumina-mediated dealkylative dimerization of 4-aminobenzyl esters

Treatment of 4-aminobenzyl esters with Al₂O₃ in DCM at rt afforded the dealkylative dimerized 4,4′-diamino-diphenylmethanes in satisfactory yield. The reaction may proceed via a quinone methide iminium ion intermediate, which may then undergo Michael type addition followed by retro-aldol extrusion of a formaldehyde species.     

Acids and their functionally substituted esters fromAmaranthus cruentus seed oil

The acid composition of seed oil ofAmaranthus cruentus and the synthesis of their glycidyl and pyridinecontaining esters are studied. It is demonstrated that 67% of the total acids are C₁₈-polyunsaturated linoleic and linolenic. A new method for preparing glycidyl esters of C₁₈-unsaturated carboxylic acids is developed by reacting their salts with ECG in an aprotic medium to produce the corresponding glycidyl esters. The reaction of the glycidyl esters and pyridine salts with carboxylic and phosphonic acids produces the propanolpyridine esters of the acids that combine the properties of the acids and pyridinium salts and are promising in the search for biologically active compounds.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Scientific Center, Russian Academy of Sciences. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 217–219, May–June, 2000.