Preparation of Functionalized Esters of Carboxylic Acids

The synthesis of simple esters (methyl, ethyl, etc.) of carboxylic acids is generally a trivial synthetic transformation due to the great variety of mehtods available (CH₂N₂, MeOH-H⁺,Me₂SO₄-Base, copper salts-alkylhalides¹, and CaO with alkylhalides²). However, what was sought in this laboratory were methods for preparation of functionalized esters. Specifically, Investigations are underway to develop methods for intra molecular transfer or intramolecular reaction of the functionalized (“R”) portion of the carboxylic acid ester (as illustrated below).     

Efficient Electrochemical Deprotection of Carboxylic and Amino Acids from Their 2-(Hydroxymethyl)-1,3-dithiane (Dim) Esters

Carboxylic acids and amino acids are electrochemically deprotected from their 2-(hydroxymethyl)-1,3-dithiane (Dim) esters.     

Stereoselective Synthesis of cis-2 and trans-2-(Indol-3-yl) Cyclopropyl Amines,Carboxylic Acids,and Esters

We report a general route for the synthesis of E and Z isomers of indol-3-yl cyclopropyl amines, carboylic acids, and esters. These cyclopropane containing molecules are of interest as conformationally constrained analogues of tryptamine and indole propionic acid, biologically active indoles. The route involves reaction of vinyl indole with ethyl diazoacetate, chromatographic separation of the E and Z stereoisomers of the resulting cyclopropane esters, hydrolysis to form the E and Z cyclopropane acids, and formation of amines by the Curtius reaction.     

Preparation of Esters and Amides from Carboxylic Acids by Activation with Dialkyl Phosphite-Carbon Tetrachloride Mixture

A simple one pot phase transfer catalytic method is described for the synthesis of carboxylic amides and esters from carboxylic acids and amines or alcohols, respectively. For the activation of the carboxylic acids “in situ” generated phosphoric acid diester chlorides were applied.     

Convenient Method for the Preparation of Carboxylic Esters Using (Chloromethylene)dimethylammonium Chloride

(Chloromethylene)dimethylammonium chloride (Vilsmeier reagent) works as an efficient condensation reagent in the formation of carboxylic esters from carboxylic acids and alcohols under mild conditions in a one-pot procedure. Secondary alcohols are converted successively into the corresponding esters in moderate to high yields with inversion of configurations.     

噻吩基1,2-迁移制备2-噻吩基酸类的研究

以α-卤代烷基噻吩基酮为原料,制得2-(2-噻吩基)丙酸、2-(5-溴-2-噻吩基)丙酸和2-(5-乙基-2-噻吩基)丙酸,研完了α-卤代烷基噻吩基酮的迁移基团、烷基、离去基、催化剂、温度和溶剂等对重排的影响,以及光学活性的2-(5-乙基-2-噻吩基)丙酸的制备,证明噻吩基1,2-迁移属邻基参与的S_N2缺电子重排。     

Direct Preparation of Trifluoromethyl Ketones from Carboxylic Esters: Trifluoromethylation with (Trifluoromethyl)trimethylsilane

Previously difficult to prepare , aliphatic and alicyclic trifluoromethylketones (e.g. 1 and 2 ), which are of pharmacalogic interest as potential enzyme inhibitors, can now be synthesized easily and efficiently. The one-step reaction starting with carbonic esters and trimethyl(trifluoromethyl)silane is induced by tetrabutylammonium fluoride in nonpolar, aprotic solvents and proceeds without formation of double-addition products.     

Trimethylsilyl Esters: Temporary Protection of Carboxylic Acids During Hydroboration Reactions

Carboxylic acid are readily protected during hydroboration reactions by converting them to the corresponding trimethylsilyl esters.     

Synthesis of the Ethyl Esters of 4-(3-Pyridyl)- and 4-(4-Pyridyl)-2-oxobutenoic Acids

We have developed a method for the synthesis of ethyl 4-(3-pyridyl)- and 4-(4-pyridyl)-2-oxobutenoates by condensation of 3-pyridinecarbaldehyde and 4-pyridinecarbaldehyde monohydrate respectively with ethyl pyruvate, esterifiction of the target acids, and hydrolysis of the corresponding ethyl ester ketals in the presence of FeCl₃·6H₂O.     

Enantioselective Preparation of (2R)- and (2S)-Azetidine-2-carboxylic Acids

The enantiomerically pure amino ketones 13 and 31 were prepared starting from the commercially available amino diol 9 and D -serine ( 21 ), respectively. Irradiation afforded highly functionalized azetidinols 15 and 33 in a fully stereoselective manner and in high yields, whereas N-phenacylglycine 5 gave only the secondary products of a Norrish-Type-II cleavage. Compounds 15 and 33 were converted into (2R)- and (2S)-azetidine-2-carboxylic acids 20 and 37 , respectively, in several steps. The influence of H-bonds on efficiency, chemo-, and stereoselectivity of the photochemical cyclization of 5 , 13 , and 31 was discussed. It was shown that conformational analysis of corresponding triplet biradicals is often valuable in understanding the photochemistry of amino ketones.     

The Facile and Efficient Preparation of Phenolic and Thiol Esters

Phenolic and thiol esters are prepared efficiently in a facile process which involves heating the desired acyl halide and thiol or phenol as a neat mixture. Distillation after HX (X = Cl or Br) gas evolution ceases provides the title compounds in 75–96% yields.     

Determination of the Content of Bound Carboxylic Acids in Mixed Cellulose Esters

A method was proposed for differential determination of bound carboxylic acids in mixed cellulose esters containing residues of acetic and higher carboxylic (capric, lauric, myristic, palmitic) acids.     

Oxidation of Alkynyl Boronates to Carboxylic Acids,Esters, and Amides

A general efficient protocol was developed for the synthesis of carboxylic acids, esters, and amides through oxidation of alkynyl boronates, generated directly from terminal alkynes. This protocol represents the first example of C(sp)?B bond oxidation. This approach displays a broad substrate scope, including aryl and alkyl alkynes, and exhibits excellent functional group tolerance. Water, primary and secondary alcohols, and amines are suitable nucleophiles for this transformation. Notably, amino acids and peptides can be used as nucleophiles, providing an efficient method for the synthesis and modification of peptides. The practicability of this methodology was further highlighted by the preparation of pharmaceutical molecules.