A convenient, general synthesis of 1,1-dimethylallyl esters as protecting groups for carboxylic acids

[reaction: see text] Carboxylic acids were converted in high yield to their 1,1-dimethylallyl (DMA) esters in two steps. Palladium-catalyzed deprotection of DMA esters was shown to be compatible with tert-butyl, benzyl, and Fmoc protecting groups, and Fmoc deprotection could be carried out selectively in the presence of DMA esters. DMA esters were also shown to be resistant to nucleophilic attack, suggesting that they will serve as alternatives to tert-butyl esters when acidic deprotection conditions need to be avoided.     

Ketones from Nickel‐Catalyzed Decarboxylative,Non‐Symmetric Cross‐Electrophile Coupling of Carboxylic Acid Esters

Synthesis of the C?C bonds of ketones relies upon one high‐availability reagent (carboxylic acids) and one low‐availability reagent (organometallic reagents or alkyl iodides). We demonstrate here a ketone synthesis that couples two different carboxylic acid esters, N‐hydroxyphthalimide esters and S‐2‐pyridyl thioesters, to form aryl alkyl and dialkyl ketones in high yields. The keys to this approach are the use of a nickel catalyst with an electron‐poor bipyridine or terpyridine ligand, a THF/DMA mixed solvent system, and ZnCl₂ to enhance the reactivity of the NHP ester. The resulting reaction can be used to form ketones that have previously been difficult to access, such as hindered tertiary/tertiary ketones with strained rings and ketones with α‐heteroatoms. The conditions can be employed in the coupling of complex fragments, including a 20‐mer peptide fragment analog of Exendin(9–39) on solid support.     

Ketones from Nickel‐Catalyzed Decarboxylative,Non‐Symmetric Cross‐Electrophile Coupling of Carboxylic Acid Esters

Synthesis of the C?C bonds of ketones relies upon one high‐availability reagent (carboxylic acids) and one low‐availability reagent (organometallic reagents or alkyl iodides). We demonstrate here a ketone synthesis that couples two different carboxylic acid esters, N‐hydroxyphthalimide esters and S‐2‐pyridyl thioesters, to form aryl alkyl and dialkyl ketones in high yields. The keys to this approach are the use of a nickel catalyst with an electron‐poor bipyridine or terpyridine ligand, a THF/DMA mixed solvent system, and ZnCl₂ to enhance the reactivity of the NHP ester. The resulting reaction can be used to form ketones that have previously been difficult to access, such as hindered tertiary/tertiary ketones with strained rings and ketones with α‐heteroatoms. The conditions can be employed in the coupling of complex fragments, including a 20‐mer peptide fragment analog of Exendin(9–39) on solid support.     

Novel bulky esters of cellulose

Novel bulky esters of cellulose were synthesized homogeneously, applying the solvent systems DMA/LiCl or DMSO/TBAF, by conversion of the biopolymer with aryl polyester dendrons. The carboxylic acid moieties were efficiently activated in situ with CDI or the acid chloride was applied. Cellulose esters with DS values of up to 0.7 were obtained. The functionalization pattern was analyzed by different NMR spectroscopic techniques indicating that not only position 6 (primary hydroxyl group) but also the secondary one at position 2 was included in the reaction.     

Interactions of Some Amino Acids with Aqueous N,N-Dimethylacetamide Solutions at 298.15 and 308.15 K: A Volumetric Approach

The apparent molar volumes, V _φ , of glycine, L-alanine and L-serine were obtained in aqueous 0 to ∼4 mol⋅kg⁻¹ N,N-dimethylacetamide (DMA) solutions from density measurements at 298.15 and 308.15 K. The standard partial molar volume, V _φ ^o, and standard partial molar volumes of transfer, Δ_tr V _φ ^o, were determined for these amino acids. It has been shown that hydrophilic-hydrophilic interactions between charged groups of the amino acids and the —CON= group of DMA are predominant in the case of glycine and L-serine, but for L-alanine the interactions between its side group (—CH₃) and DMA are predominant. An increase in temperature increases the standard partial molar volumes but decreases the transfer volumes of the amino acids. The results have been interpreted in terms of cosphere overlap model.     

Surfactants based on fatty acids and other natural hydrophobes

In the search for environmentally safer surfactants from renewable sources, the interest has lately been focused on new fatty acids and derivatives like ethoxylated fatty acid methyl esters and α-sulfo methyl esters. For the latter more efficient production procedures have been developed opening up for new application areas. In parallel, knowledge about the physico-chemical properties of this group of products has steadily grown. Thus fatty acids and soaps have a high potential to remain the biggest surfactant type especially if their use as raw materials is included.     

Kinetics and mechanism of the hydrolysis of esters of hydroxymethylphosphonic and hydroxymethylethylphosphinic acids

Conclusions The reactivity of ethyl esters of phosphonic and phosphinic acids containing a hydroxymethyl group at the phosphorus atom in their reaction with hydroxide anion is usually high as a consequence of intramolecular catalysis of the cleavage of the ester bond involving the ionized OH group. The spontaneous hydrolysis of these esters proceeds according to a mechanism analogous to that for other alkyl esters of tetracoordinated phosphorus acids.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2139–2140, September, 1985.     

Amino acids and peptides. XXIII. Synthesis of N alpha-protected amino acid 6-chloro-2-pyridyl esters and their evaluation for peptide synthesis

6-Chloro-2-pyridyl esters (OPyCl) of N alpha-benzyloxycarbonyl and tert-butyloxycarbonylamino acids were synthesized by the N,N'-dicyclohexylcarbodiimide (DCC) method from the acids and 6-chloro-2-hydroxypyridine in dimethylformamide (DMF). The reactivity of the 6-chloro-2-pyridylester with amino group is much higher than that of the corresponding 2-pyridyl ester (OPy) and p-nitrophenyl esters (ONp) in dioxane and DMF, and a peptide bond is formed without acylation at the side chain hydroxyl group of amino acids. Z-Asp(OBzl)-OPyCl reacted with amino acid methyl esters in dioxane to give the corresponding dipeptide without any detectable aspartimide formation.     

Facile synthesis of methylthiomethyl esters through Pummerer-type rearrangement of carboxylic acids and DMSO under metal-free conditions

A green and cost-effective Pummerer-type rearrangement between readily accessible carboxylic acids and DMSO has been achieved under metal-free conditions in satisfactory to excellent yields. The transformation for the synthesis of valuable methylthiomethyl esters is shown to be a convenient strategy for various (hetero)aromatic acids, α,β-unsaturated carboxylic acids and saturated alkyl carboxylic acids with good functional group tolerance.     

Selective reductions. 59. Effective intramolecular asymmetric reductions of alpha-, beta-, and gamma-keto acids with diisopinocampheylborane and intermolecular asymmetric reductions of the corresponding esters with B-chlorodiisopinocampheylborane

A comparison of the stereochemistry of the products obtained from the intramolecular asymmetric reduction of a series of keto acids with (-)-diisopinocampheylborane and intermolecular asymmetric reduction of the corresponding series of keto esters with (-)-B-chlorodiisopinocampheylborane ((-)-DIP-Chloride) has been made. The stereochemistry of the hydroxy acids from the reduction of keto acids is dependent only on the enantiomer of the reagent used. The stereochemistry of the products from the reduction of keto esters is also consistent, except those of aliphatic alpha-keto esters. alpha-, beta-, and gamma-keto acids provide the corresponding hydroxy acids in 77-98% ee, and the alpha- and gamma- keto esters afford the hydroxy esters in 82->or=99% ee. beta-Keto esters do not undergo reduction. Although the reduction of delta-keto acids does not proceed under the same reaction conditions, the reduction of delta-keto esters is facile. All of the products from the reduction of gamma-keto acids and esters and delta-keto esters were converted to the corresponding lactones. This study revealed that DIP-Chloride is an efficient reagent for the reduction of alpha-keto esters at low temperatures.     

Chemoenzymatic synthesis of optically active 4-methyl-tetrahydro-5-oxo-2-furancarboxylic acids and esters

Enantiomerically pure 4-methyl-tetrahydro-5-oxo-2-furancarboxylic acids and esters are prepared by enzymatic resolution of the chiral racemic esters. Their stereochemistry as well as their absolute configurations have been established by chemical correlation. The influence of the alkoxycarbonyl group at C-2 and that of the methyl group at C-4 on the sign of the Cotton effect in their CD spectra have been investigated. Formation of enantiomerically pure hydroxydiesters, precursors of the above-mentioned γ-lactones, by baker’s yeast reduction of the corresponding ketodiesters was unsatisfactory.     

Synthesis of o-Carboranyl Containing Esters of Pentavalent Phosphorus Acids

Abstract

A new method for the synthesis of o-carboranyl containing phosphoric, phosphonic and phosphinic acid esters, where the o-carboranil group is in the ester group, has been developed. The propargyl esters of these acids were prapared in two ways: by the reaction of phosphorus acid salts with propargyl chlorid and by interaction of propargyl alcohol with acid chlorides in the presence of Et₃N. The propargyl esters have been converted into carboranyl containing compounds upon treatment with decaborane and dimethyl aniline     

Chemical transformations of tetracyclo[3.3.1.1.<Superscript>3,7</Superscript>.0.<Superscript>1,3</Superscript>]decane (1,3-dehydroadamantane): I. Reaction of 1,3-dehydroadamantane with carboxylic acids esters

Adamantylation of carboxylic acids esters was performed with 1,3-dehydroadamantane for the first time. The reaction proceeds under mild conditions and can be used as a convenient single stage procedure for the synthesis of esters of branched carboxylic acids having an adamantyl group in the α-position to the carbonyl group.     

Synthesis of dicarboxylic acids and diesters of the difurylmethane series

The condensation with saturated aliphatic carbonyl compounds of furan acids and esters having a functional group not conjugated with the furan nucleus has been carried out. Symmetrical bifunctional derivatives of the difurylmethane series have been synthesized.     

Free Radical Formation from Excited States of Aliphatic Carboxylic Acids and esters in solution as studied by electron spin resonance

During UV.-irradiation of aliphatic carboxylic acids and esters in aqueous and nonaqueous solutions various alkyl and acyl type radicals derived from parent compounds and solvents have been observed by ESR.-spectroscopy. The structures of the radicals point to α-cleavage, β-dehalogenation and photoreduction as major photolytic processes of carboxylic acids and esters. The relative contributions of these processes to the overall photodecompositions depend on the carboxyl substituents, on solvent and temperature. Similarities of carboxyl and carbonyl group photochemistry are discussed.     

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%).     

A fast and practical synthesis of tert-butyl esters from 2-tert-butoxypyridine using boron trifluoride·diethyl etherate under mild conditions

A practical direct preparation of tert-butyl esters from 2-tert-butoxypyridine has been developed. This system features the use of boron trifluoride·diethyl etherate in toluene solvent to rapidly achieve the reaction at room temperature. Using this reaction protocol, a variety of tert-butyl esters were synthesized from several different carboxylic acids at high yields. This practical procedure provides a promising and effective approach to the protection of carboxylic acids with a tert-butyl group.     

Zur Synthese von fungizid wirksamen Isocamphanderivaten: Synthesen in der Isocamphanreihe, 34. Mitt.

Summary Some esters of isocamphenilanic acid (4) have been prepared and tested for their fungicidal and insecticidal activity. Esters of various acids with isocamphanyl ethylalcohol (5) have also been synthesized and included in the fungicidal/acaricidal/insecticidal screening programme. All esters bear a geminal dimethyl group at C-3 of the bicyclus which is important because of its shielding effect.

     

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.     

有机磷化合物的研究 VIII. 酸性有机磷化合物的气相色谱

Acidic organophosphorus compounds may be identified by GLC via their methyl esters, usually prepared from diazomethane. The wide applications of this mthod are, however, limited by the toxicity of diazomethane. Tetramethyl ammonium hydroxide in methanol solution reacted rapidly with acidic organophosphorus compounds at room temperature to form tetramethyl ammonium salts, which were then converted to the corresponding methyl esters by pyrolysis at 300-350 deg.C. A simple and convenient method for separation and identification of various types of acidic phosphates, phosphonates and phosphinates by GLC has been developed. The GLC behaviours of phosphoric acid dialkyl esters, mono-esters of phenyl-and cyclohexyl-phosphonic acids as well as dialkylphosphinic acids can be represented by corrected retention time (t'R) which correlates linearly with the number of carbon atoms of the alkyl groups in these organophosphorus compounds. The influence of number of carbon atoms and isomerization of alkyl group on t'R values and retention index (I) calculated by Kovats equation was discussed. As shown by our experiments the change in retention index (ΔI) in the homologous series of phosphoric acid dialkyl esters is nearly a constant on lengthening the alkyl group of the esters with methylene linkages.