Acid anhydrides and the unexpected N,N-diethylamides derived from the reaction of carboxylic acids with Ph3P/I2/Et3N

Synthesis of N-Hydroxysuccinimide Esters, N-Acylsaccharins, and Activated Esters from Carboxylic Acids Using I2/PPh3

A method for the syntheses of isolable, active esters is described in which carboxylic acids are treated with triphenylphosphine, iodine, and triethylamine. Active esters accessible in this way include N-hydroxysuccinimide esters, N-hydroxyphthalimide esters (N-(acyloxy)phthalimides), N-acylsaccharins, pentafluorophenol esters, pentachlorophenol esters, N-hydroxybenzotriazole esters, and hexafluoro-2-propanol esters. The approach can be similarly applied toward the formation of N-acylsaccharins and N-acylimidazoles. The method is suitable for the formation of isolable active esters of aromatic and aliphatic activated acids as well as α-amino acid derivatives. These products are widely used reagents in organic synthesis, peptide synthesis, medicinal chemistry, and chemical biology (e.g., for bioconjugations). The method has broad substrate scope, uses simple and inexpensive reagents, avoids the use of carbodiimides or other coupling agents, and occurs at room temperature. Additionally, the diastereomers of compound Boc-Ala-NHCHPh are demonstrated to be distinguishable by 1H NMR (in DMSO-d6), allowing for a straightforward NMR method to establish the degree of racemization of activated esters of Boc-Ala or amide bond formations using Boc-Ala.

Facile Cleavage of Activated Ketones: An Access to Thioethers via In Situ Generation of Anhydrides by Pummerer-Type Rearrangement

Herein, we report an oxygen insertion in activated ketones from simple inorganic carbonates for the synthesis of symmetric aromatic anhydrides. For the first time, Li2CO3 acts as an oxygen source and the in situ generated symmetric aromatic anhydrides undergo Pummerer-type rearrangement to access α-benzoyloxy-thioethers. Attractively, this protocol occurs under metal-, ligand-, and oxidant-free conditions and is compatible with a wide range of substrates. Control experiments reveal the reaction pathway.

A Facile Synthetic Method for Anhydride from Carboxylic Acid with the Promotion of Triphenylphosphine Oxide and Oxaloyl Chloride

A highly efficient synthesis reaction of carboxylic anhydrides catalyzed by triphenylphosphine oxide is described for the quick synthesis of a range of symmetric carboxylic anhydrides and cyclic anhydrides under mild and neutral conditions with a high yield. The system adopts the strong reactive intermediate Ph₃PCl₂ as the catalyst of carboxylic acid salt; driven by catalytic reaction, the synthesis takes a relatively short time to complete.

3,5-Dinitrobenzoate and 3,5-Dinitrobenzamide Derivatives: Mechanistic, Antifungal, and In Silico Studies

Fungal infections, including those caused by Candida spp., are recognized in immunocompromised individuals for their high rates of morbidity and mortality. Microorganism resistance to conventional drugs compromises treatment effectiveness and yet also reveals the need to develop new drugs. In many compounds, nitro groups contribute to antimicrobial activity; thus, the inhibitory activity of a collection of twenty esters and amides (derived from 3,5-dinitrobenzoic acid) against Candida spp. was elucidated using microdilution methods to determine the Minimum Inhibitory Concentration (MIC) and Minimum Fungicide Concentration (MFC), as well as probable mechanisms of action. The structures of the synthesized compounds were characterized by FTIR spectroscopy, 1H-NMR, 13C NMR, and HRMS. Of the tested derivatives, ten presented fungicidal activity against at least one of the tested strains. Ethyl 3,5-dinitrobenzoate (2) exhibited the most potent antifungal activity against Candida albicans (MIC = 125 µg/mL; 0.52 mM), Candida krusei (MIC = 100 µg/mL; 4.16 mM), and Candida tropicalis (MIC = 500 µg/ml; 2.08 mM). The structure of the second most potent derivative (propyl 3,5-dinitrobenzoate (3) reveals that esters with short alkyl side chains exhibit better biological activity profiles. Compounds 2 and 3 presented a mechanism of action involving the fungal cell membrane. Though compound 2 modeling against C. albicans revealed a multitarget antifungal mechanism of action, involving various cellular processes, interference in the synthesis of ergosterol was observed. Our results demonstrate that certain ester derivatives containing aromatic ring nitro groups may be useful in the search for new antifungal drugs.

Catalytic and non-catalytic amidation of carboxylic acid substrates

The present review offers an apt summary of amide bond formation with carboxylic acid substrates by taking advantage of several methods. Carboxamides can be regarded as a substantial part of organic and medicinal chemistry due to their utility in synthesizing peptides, lactams, and more than 25% of familiar drugs. Moreover, they play a leading role in the synthesis of bioactive products with anticancer, antifungal, and antibacterial properties. The data are arranged based on the type and amount of reagents used to conduct amidation and are also divided into the following categories: catalytic amidation of carboxylic acids, non-catalytic amidation, and transamidation.

Size-Driven Inversion of Selectivity in Esterification Reactions: Secondary Beat Primary Alcohols

Relative rates for the Lewis base-mediated acylation of secondary and primary alcohols carrying large aromatic side chains with anhydrides differing in size and electronic structure have been measured. While primary alcohols react faster than secondary ones in transformations with monosubstituted benzoic anhydride derivatives, relative reactivities are inverted in reactions with sterically biased 1-naphthyl anhydrides. Further analysis of reaction rates shows that increasing substrate size leads to an actual acceleration of the acylation process, the effect being larger for secondary as compared to primary alcohols. Computational results indicate that acylation rates are guided by noncovalent interactions (NCIs) between the catalyst ring system and the DED substituents in the alcohol and anhydride reactants. Thereby stronger NCIs are formed for secondary alcohols than for primary alcohols.

Synthesis of Biaryls via Decarbonylative Nickel-Catalyzed Suzuki-Miyaura Cross-Coupling of Aryl Anhydrides

Transition metal-catalyzed cross-couplings have been widely employed in the synthesis of many important molecules in synthetic chemistry for the construction of diverse C-C bonds. Conventional cross-coupling reactions require active electrophilic coupling partners, such as organohalides or sulfonates, which are not environmentally friendly enough. Herein, we disclose the first nickel-catalyzed Suzuki-Miyaura cross-coupling of aryl anhydrides and arylboronic acids for the synthesis of biaryls in a decarbonylation manner. The reaction tolerates a wide range of electron-withdrawing, electron-neutral, and electron-donating substituents in this process.

Anhydrides from aldehydes or alcohols via oxidative cross-coupling

A novel type of oxidative cross-coupling was developed to prepare symmetrical and mixed anhydrides from aldehydes or alcohols using trichloroisocyanuric acid (TCCA).

Metal-free amidation of carboxylic acids with tertiary amines

Combination of Ph₃P and I₂ with an appropriate reagent addition sequence could enable effective amidation of carboxylic acids with tertiary amines under mild conditions.