A convenient synthesis of sulfonylureas from carboxylic acids and sulfonamides via an in situ Curtius rearrangement

A one-pot reaction of carboxylic acids with sulfonamides to afford sulfonylureas is described.     

Polymer-supported O-alkylisoureas: useful reagents for the O-alkylation of carboxylic acids

Polymer-supported O-alkylisoureas were prepared by reaction of an alcohol with a polymer-supported carbodiimide under copper(II) catalysis. These reagents were used to transform carboxylic acids into the corresponding methyl, benzyl, allyl, and p-nitrobenzyl esters in a highly chemoselective manner in high yields and in very high purity after simple resin filtration and solvent evaporation. The reactions could be carried out using both conventional or microwave heating, with reaction times as short as 3-5 min in the latter case, without compromising yield, purity, or chemoselectivity. Unfortunately, the corresponding solid-supported tert-butyl isoureas could not be prepared.     

Polymer-supported O-methylisourea: a new reagent for the O-methylation of carboxylic acids

[reaction: see text] A solid-supported O-methylisourea reagent has been prepared in one step starting from commercially available solid-supported carbodiimide. The isourea reagent has been successfully used for the preparation of methyl esters from the corresponding carboxylic acids. The crude products obtained after resin filtration and solvent evaporation are generally obtained in >98% purity.     

-trifluoroacylation - a convenient route to carboxylic acids

Trifluoroacetic anhydride will trifluoroacylate reactive aromatic and heterocylic nuclei without the aid of a Friedel-Crafts catalyst. The resulting trifluoromethyl ketone undergoes hydrolysis to yield the corresponding carboxylic acid. This provides a very simple route to aromatic and heterocyclic carboxylic acids.     

Polymer-supported triazenes as smart reagents for the alkylation of carboxylic acids

Starting from polystyrene, a simple four-step synthesis of polymer-supported alkyltriazenes (alkyl=Me, Et, benzyl) is described. With this synthesis, a loading capacity of 2.2 mmol g(-1) can be reached. The most prominent application of these polymer-supported reagents is the rapid, highly selective and high-yielding esterification of carboxylic acids, which involves a simple "mix and filter off" procedure at room temperature. If stored in a refrigerator, these reagents are stable for many months and they can be recycled several times.     

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.     

Novel ester linked glycosyl amino acids: convenient building blocks for the synthesis of glycopeptide libraries

The completely orthogonally protected aspartic acid derivative FmocAsp(OBn)O^tBu is readily synthesized on a large scale. Deprotection of the β-carboxylic acid allows coupling to various sugar derivatives via free hydroxyl groups to produce novel glycosyl amino acids. Subsequent deprotection of either the α-acid or nitrogen is achieved cleanly to allow elaboration into an oligopeptide, whilst selective deprotection of PMB protected sugar hydroxyls is also readily achievable. Such novel glycosyl amino acid building blocks may be useful for the combinatorial synthesis of novel glycopeptide libraries.     

Copper-catalyzed synthesis of aromatic carboxylic acids from arylboronic acids and acetyl acetate

A simple and efficient copper-catalyzed method for the synthesis of aromatic carboxylic acids in moderate to high yields with great functional-group compatibility in the substrates has been developed. The new method uses readily available arylboronic acids and acetyl acetate as the starting materials and inexpensive CuI as the catalyst.     

Efficient and one-pot synthesis of novel sulfamates from carboxylic acids

Effective synthesis of novel sulfamates from various carboxylic acids has been developed in the presence of chlorosulfonyl isocyanate (CSI) in mild conditions. Several acids, bases and solvents effects were investigated for one-pot synthesis sulfamates as a catalyst. Finally, triflic acid was found to possess efficiently under optimized conditions in acetonitrile. This method is easy, fair price and practical. It can be synthesized on grams and milligrams scale.     

3-butenyl esters as convenient protecting groups for carboxylic acids

Carboxylic acids were protected as their corresponding 3-butenyl esters. Deprotection was carried out via ozonolysis and β-elimination of the resultant 3-acyloxypropanal.     

A convenient synthesis of phosphonothioic acids

A method for the convenient synthesis of phosphonothioates, or phosphonothioic acids, is reported. A significant advantage of the method is the alleviation of the need for purification of intermediates, other than washing with water. No chromatography is needed and the only purification step is the crystallization of the final product. The method uses standard reagents and should be applicable to the synthesis of phosphonothioic acids bearing a range of functional groups.     

Stereoselective synthesis of C-glycosides from carboxylic acids: the tandem Tebbe-Claisen approach

A variety of beta- or alpha-C-glycosides may be readily accessed in an entirely stereoselective fashion from esters derived from the reaction of carboxylic acids and 3-hydroxy glycals, by way of a tandem reaction sequence of Tebbe methylenation and Claisen rearrangement. Though of wide scope, for example allowing the synthesis of 1-6 linked C-disaccharides, the methodology does not currently allow the synthesis of C-glycosyl alpha-amino acids.     

Thioimides: new reagents for effective synthesis of thiolesters from carboxylic acids

Thioimides and carboxylic acids are used as the precursors for the convenient synthesis of thiolesters in the phosphine mediated process. Cyclic and acyclic thioimides show equal efficiency, furnishing the desired thiolesters in good to excellent yields. The general, highly efficient transformation tolerates various functional groups and the resulting thiolesters are obtained in high purity after a simple separation. The reaction scope has been demonstrated on the preparation of several highly functionalized target molecules.     

Triphenyl borate catalyzed synthesis of amides from carboxylic acids and amines

Herein we report triphenyl borate as a new catalyst for synthesis of amides by catalytic condensation of carboxylic acids and amines. Our protocol is applicable for synthesis of wide range of amides furnishing excellent yields up to 92%. In addition developed method requires low catalyst loading, short time, less amount of solvent, works under air atmosphere and notably no need of azeotropic reflux using special Dean Stark apparatus or molecular sieves.     

Metal-free synthesis of aryl esters from carboxylic acids and diaryliodonium salts

An efficient arylation of carboxylic acids with diaryliodonium salts has been developed, giving aryl esters in high yields within short reaction times for both aromatic and aliphatic substrates. The transition-metal-free conditions are compatible with a range of functional groups, and good chemoselectivity is observed with unsymmetric diaryliodonium salts. Furthermore, steric hindrance in the ortho positions is well tolerated both in the carboxylic acid and in the diaryliodonium salt, yielding aryl esters that cannot be obtained via other esterification protocols.     

羧酸直接酰胺化的一个新方法

N, N-二甲基取代酰胺可以方便地由脂肪族或芳香羧酸与四(二甲氨基)硅烷在无水溶剂中反应制得。     

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.     

Rearrangement of epoxynitriles: a convenient homologation of acyclic and cyclic ketones to carboxylic acids

A convenient two-step homologation of both aliphatic and aromatic ketones to the corresponding carboxylic acid has been developed. First ketones were converted to epoxynitriles with the Darzens reaction. Second, a Lewis acid mediated rearrangement of these epoxynitriles with lithium bromide was achieved to give homologated secondary alkanoic acids (as well as aryl-alkanoic) in good yields. The mechanism and the scope of the rearrangement reaction were investigated. This strategy constitutes a two-step homologation of ketones to secondary carboxylic acids.