Rapid One-Pot Synthesis of Alkane-α,ω-Diylbisphosphonic Acids from Dihalogenoalkanes Under Microwave Irradiation

A one-pot, two-step synthesis of alkylenebisphosphonic acids from dihalogenoalkanes was performed under microwave irradiation. The reaction is very rapid and convenient for the synthesis of small samples of alkylenebisphosphonic acids.     

gem-Dibromomethylarenes: a convenient substitute for noncommercial aldehydes in the knoevenagel-doebner reaction for the synthesis of alpha,beta-unsaturated carboxylic acids

A facile synthesis of alpha,beta-unsaturated carboxylic acids from gem-dibromomethylarenes is described. gem-Dibromomethylarenes are employed for the first time in the Knoevenagel-Doebner reaction as aldehyde equivalents for the efficient synthesis of alpha,beta-unsaturated carboxylic acids.     

有机硼酸类催化剂在有机合成中的应用

综述了有机硼酸类作为催化剂应用于有机合成反应中的最新研究进展, 重点介绍了所发现的各种有机硼酸催化剂在缩合反应、羧酸还原反应、Diels-Alder反应中的催化活性以及反应机理. 硼酸催化剂因具有催化效率高、反应条件温和、可重复使用等优点, 必将在有机合成催化领域中得到更广泛的应用.     

Synthesis of diazoketones derived from α-amino acids; problem of side reactions

Optimum conditions of synthesis of eight diazoketones derived from optically active N-(t-butyloxycarbonyl)- and N-benzyloxycarbonylamino acids have been described. The problem of formation of by-products during Arndt-Eistert synthesis of β-homoamino acids at the stage of reaction of mixed anhydride with a weak nucleophile-diazomethane - has been discussed.     

Solid-phase synthesis and stereochemical assignments of tenuecyclamides A-D employing heterocyclic amino acids derived from commercially available Fmoc alpha-amino acids

[reaction: see text] The solid-phase assembly of heterocyclic amino acids enabled the total synthesis of numerous diastereoisomers of tenuecyclamides A-D, establishing or correcting the stereochemistry of each natural product. This strategy provides a very efficient route to synthesize thiazole- and oxazole-containing macrolactams from heterocyclic amino acids that are readily prepared from Fmoc-alpha-amino acids. This methodology appears to be broadly applicable to the synthesis of natural product libraries incorporating unnatural heterocyclic amino acid residues for the purpose of drug discovery.     

Synthesis of Some Functionalized Peptomers via Ugi Four-Component Reaction

This article describes the synthesis of new peptomers through a simple and efficient route using a one-pot Ugi four-component reaction. The synthesis started from either carboxylic acids or protected amino acids, primary amines, aldehydes, and isocyanides in anhydrous methanol and proceeded under stirring at room temperature. The reaction produced several functionalized peptomers in good yields (67–80%). These compounds are versatile multifunctional intermediates that can be further unprotected or functionalized to generate new molecules with numerous applications in the field of biomedicine.     

Synthesis of poly(1,3,4-oxadiazole)s by direct polycondensation of dicarboxylic acids with hydrazine sulfate using phosphorus pentoxide/methanesulfonic acid as condensing agent and solvent

A convenient method for the synthesis of poly(1,3,4-oxadiazole)s of high molecular weights has been developed. These polymers were prepared readily by the direct polycondensation of dicarboxylic acids with hydrazine sulfate ( 1 ) using phosphorus pentoxide/methanesulfonic acid (PPMA) as both a condensing agent and solvent. Polycondensation of aliphatic dicarboxylic acids with 1 proceeded even at room temperature and produced poly(1,3,4-oxadiazole)s with inherent viscosities up to 1.4 dL/g. The synthesis of aromatic poly(1,3,4-oxadiazole)s from aromatic dicarboxylic acids containing phenyl ether structures was carried out by a one-pot procedure because the preactivation of dicarboxylic acids was required. The synthesis of 2,5-disubstituted-1,3,4-oxadiazoles by the reaction of carboxylic acids with 1 in PPMA was studied to demonstrate the feasibility of the reaction for polymer formation. The thermogravimetry of the aromatic poly(1,3,4-oxadiazole)s showed 10% weight loss both in air and in nitrogen at 440–490°C.     

Rhodium(III)‐Catalyzed [4+1] Annulation of Aromatic and Vinylic Carboxylic Acids with Allenes: An Efficient Method Towards Vinyl‐Substituted Phthalides and 2‐Furanones

A highly regio‐ and stereoselective synthesis of 3,3‐disubstituted phthalides from aryl carboxylic acids and allenes using a rhodium(III) catalyst has been demonstrated. The reaction features broad functional group tolerance and provides a simple and straightforward route to the synthesis of various 3‐vinyl‐substituted phthalides. Furthermore, the catalytic reaction can also be applied to the synthesis of biologically active 5‐vinyl‐substituted 2‐furanones from α,β‐unsaturated carboxylic acids and allenes. The reactions proceed through a carboxylate‐assisted ortho‐C?H activation and [4+1] annulation. The preliminary mechanistic studies suggest that a C?H cleavage is the rate‐determining step.     

Direct deprotected glycosyl-asparagine ligation

A simple and efficient synthesis of N-linked glycoamino acids and glycopeptides from deprotected sugars using the Staudinger reaction.     

The Chiral Synthesis of Thiazole Amino Acid Enantiomers

An efficient modified Hantzsch reaction is described for the synthesis of optically pure thiazole amino acid derivatives from the corresponding amino acids. The method is exemplified by the synthesis of a derivative of L-(Gln)Thz, the novel chiral thiazole amino acid moiety of dolastatin 3. The Cotton effects of thiazole amino acids correlate well with the absolute stereochemistry of these compounds.     

New stable backbone linker resins for solid-phase peptide synthesis

[reaction: see text] Two new 4-methoxybenzaldehyde backbone linker resins were developed for the solid-phase synthesis of peptides. The linkers are very stable during the cleavage of common protecting groups for amines (Fmoc, Boc) and carboxylic acids (Me, All, tBu) in peptide synthesis. Cleavage from the resin with refluxing TFA is sufficiently mild for peptides containing polar and nonpolar amino acids.     

Visible-light-promoted oxidative decarboxylation of arylacetic acids in air: Metal-free synthesis of aldehydes and ketones at room temperature

A metal-free photocatalytic oxidative decarboxylation reaction at room temperature was developed for the synthesis of aromatic aldehydes and ketones from the corresponding arylacetic acids. The reaction was realized under blue-light irradiation by adding 1 mol% of 4CzIPN as photocatalyst and air as oxidant. This reaction represents a novel decarboxylation of a sp³-hybridized carboxylic acids without traditional heating, additional oxidants, and metal reagents under mild conditions.     

Umpolung Reactivity of Aldehydes toward Carbon Dioxide

Carbon dioxide is an intrinsically stable molecule. Therefore, its activation requires extra energy input in the form of reactive reagents and/or activated catalysts and, often, harsh reaction conditions. Reported here is a direct carboxylation reaction of aromatic aldehydes with carbon dioxide to afford α‐keto acids as added‐value products. In situ generation of a reactive cyanohydrin was the key to the successful carboxylation reaction under operationally mild reaction conditions (25–40 °C, 1 atm CO₂). The resulting α‐keto acids served as a platform for α‐amino acid synthesis by reductive amination reactions, illustrating the chemical synthesis of essential bioactive molecules from carbon dioxide.     

N-heterocyclic carbene (NHC)-catalyzed direct amidation of aldehydes with nitroso compounds

NHC-catalyzed direct amidation of aldehydes with nitroso compounds is a powerful method for the synthesis of N-arylhydroxamic acids. A variety of aryl, alkyl, alkenyl, and heterocyclic aldehydes were found to give excellent yields of the corresponding N-arylhydroxamic acids. This chemistry was also extended to the synthesis of chiral N-arylhydroxamic acids by kinetic resolution of alpha-branched aldehydes, a domino amidation-redox amination reaction of acrolein, and a three-component reaction for the synthesis of N-arylaziridines.     

Controlled conversion of phenylacetic acids to phenylacetonitriles or benzonitriles using bis(2-methoxyethyl)aminosulfur trifluoride

A mild, efficient, and practical method for the one-step synthesis of benzonitriles from phenylacetic acids using bis(2-methoxyethyl)aminosulfur trifluoride is described. The reaction was easily extended to the synthesis of the corresponding phenylacetonitriles by inclusion of triethylphosphine.     

Facile synthesis of diphenylmethyl esters from 2-diphenylmethoxypyridine using catalytic boron trifluoride·diethyl etherate

A practical method for the direct preparation of diphenylmethyl (DPM) esters from 2-diphenylmethoxypyridine is described. The reaction was readily performed in the presence of a catalytic amount of boron trifluoride-diethyl etherate at room temperature. Using this reaction protocol, various carboxylic acids were converted to DPM esters with high yields. This method is highly effective for the protection of carboxylic acids and the synthesis of DPM esters, and offers a promising approach for facile esterification of a variety of carboxylic acids.     

Facile and direct synthesis of symmetrical acid anhydrides using a newly prepared powerful and efficient mixed reagent

An efficient mixed reagent for direct synthesis of symmetrical carboxylic anhydrides from carboxylic acids has been prepared. Carboxylic acids are converted to anhydrides using triphenylphosphine/trichloroisocyanuric acid under mild reaction conditions at room temperature. Short reaction time, excellent yields of products, low cost, availability of reagents, simple experimental procedure, and easy work-up of the products are the main advantages of the presented method.     

Catalytic asymmetric three-component acyl-Strecker reaction

The first organocatalytic asymmetric three-component Strecker reaction, the urea-catalyzed acylcyanation of in situ generated imines, has been developed. Different alpha-amido nitriles are formed in excellent yields and enantioslectivities from aldehydes, amines, and acyl cyanides in the presence of Jacobsen's thiourea catalyst 5. Despite its obvious use for the synthesis of alpha-amino acids and their derivatives, our reaction may find use in diversity oriented synthesis and medicinal chemistry. [reaction: see text]     

Ytterbium triflate-promoted tandem one-pot oxidation-Cannizzaro reaction of aryl methyl ketones

[reaction: see text] Ytterbium triflate was shown to be an effective catalyst in promoting the synthesis of either isopropyl esters or free alpha-hydroxy-arylacetic acids from substituted aromatic glyoxals and aryl methyl ketones, respectively. The reaction to provide acids starting from differently substituted ketones was carried out by an environmentally friendly method using an aqueous medium as a solvent and giving the adducts in 78-99% yield without any further purification after the usual workup.     

A novel three-component reaction of allenoates, isocyanides, and carboxylic acids: facile synthesis of highly substituted acryl imide derivatives

A novel synthesis of highly substituted acryl imide derivatives by the three-component reaction of allenoates, isocyanides, and carboxylic acids was reported, and the intramolecular cyclization reaction of allenoic acids with isocyanides was also described.