Diphenylammonium triflate (DPAT): efficient catalyst for esterification of carboxylic acids and for transesterification of carboxylic esters with nearly equimolar amounts of alcohols

Atom-Economical Synthesis of N-Arylamides Utilizing Isopropenyl Esters with Heterogeneous Acid Catalysts

Existing methods for the catalytic synthesis of N-arylamides are limited by a narrow substrate scope, high catalyst costs, and complicated purification processes of products. To overcome these limitations, this study developed an ecofriendly method for the synthesis of N-arylamides using isopropenyl esters. Isopropenyl esters activated using heterogeneous acid catalysts reacted smoothly even with less reactive arylamines to afford N-arylamides in high yields. This method exhibits a wide substrate scope and is applicable for the synthesis of various N-arylamides (33 examples, 46-99% yield). The developed method enabled the obtainment of high-purity products with a facile workup procedure and showed excellent process mass intensity values due to the reduction of chemical waste.

An Electrochemical Design for Catalytic Dehydration: Direct, Room-Temperature Esterification without Acid or Base Additives

An electrochemical approach has been leveraged to underpin a new conceptual platform for dehydration reactions, which has been demonstrated in the context of esterification. Esters were prepared from the corresponding acid and alcohol partners at room temperature without acid or base additives and without consuming stoichiometric reagents. This methodology therefore addresses key complications that plague esterification and dehydration reactions more broadly and that represent a leading challenge in synthetic chemistry.

Harnessing Protonated 2,2'-Bipyridinium Salts as Powerful Brønsted Acid Catalysts in Organic Reactions

It is the first time that the readily available protonated 2,2'-bipyridinium salts are used as Brønsted acid catalysts to accelerate a series of organic transformations that included the hydration of aromatic alkynes, etherification of alcohols, cyclotrimerization of aliphatic aldehydes, Ritter reaction, Mannich reaction, Biginelli reaction, preparation of substituted alkenes from alcohols, synthesis of spirooxindole, bisindolylmethane, and noncyclized tetraketone with good to excellent yields. These results strongly suggest that there exists enormous potentiality in the development of the protonated 2,2'-bipyridinium catalytic system.

Insight into the Mechanism of the Acylation of Alcohols with Acid Anhydrides Catalyzed by Phosphoric Acid Derivatives

Insight into the mechanism of a safe, simple, and inexpensive phosphoric acid (H₃PO₄)-catalyzed acylation of alcohols with acid anhydrides is described. The corresponding in situ-generated diacylated mixed anhydrides, unlike traditionally proposed monoacylated mixed anhydrides, are proposed as the active species. In particular, the diacylated mixed anhydrides act as efficient catalytic acyl transfer reagents rather than as Brønsted acid catalysts simply activating acid anhydrides. Remarkably, highly efficient phosphoric acid (1-3 mol %)-catalyzed acylation of alcohols with acid anhydrides was achieved and a 23 g scale synthesis of an ester was demonstrated. Also, phosphoric acid catalyst was effective for synthetically useful esterification from carboxylic acids, alcohols, and acid anhydride. Moreover, with regard to recent developments in chiral 1,1'-bi-2-naphthol (BINOL)-derived phosphoric acid diester catalysts toward asymmetric kinetic resolution of alcohols by acylation, some phosphate diesters were examined. As a result, a ³¹P NMR study and a kinetics study strongly supported not only the acid-base cooperative mechanism as previously proposed by other researchers but also the mixed anhydride mechanism as presently proposed by us.

Iron (III) chloride hexahydrate as a highly efficient catalyst for acetylation of protic nucleophiles with acetic anhydride under solvent-free conditions

Background:

Acetylation of protic nucleophiles is used to protect these functional groups. Most of the methods described in the literature use solvents, one equivalent or more of toxic bases or expensive and toxic catalysts. Therefore, new methodologies are still in demand, above all, greener and more economical procedures.

Objective:

An eco-efficient method developed for acetylation of alcohols, phenols, thiols, amines and carbohydrates, using acetic anhydride and a catalytic amount of the environmentally benign and inexpensive FeCl3.6H2O under solvent free conditions.

Methods:

Acetylation of a variety of protic nucleophiles was performed using 0.2 mol % of FeCl3.6H2O as the catalyst, and 1.2 equiv. as the acetylating agent at room temperature and under solvent free conditions.

Results:

Our procedure appears to be highly efficient and promoted rapid and quantitative acetylation under simple and minimum manipulation. Chromatography or recrystallization were generally not necessary for the purification of products.

Conclusion:

This eco-friendly protocol appears to be potentially universally applicable in organic design to protect protic nucleophiles and potentially scalable for industrial fields.

Direct Dehydrative Glycosylation Catalyzed by Diphenylammonium Triflate

Methods for direct dehydrative glycosylations of carbohydrate hemiacetals catalyzed by diphenylammonium triflate under microwave irradiation are described. Both armed and disarmed glycosyl-C1-hemiacetal donors were efficiently glycosylated in moderate to excellent yields without the need for any drying agents and stoichiometric additives. This method has been successfully applied to a solid-phase glycosylation.

P2O5 / SiO2 as a mild and efficient reagent for acylation of alcohols, phenols and amines under solvent-free conditions

P2O5 / SiO2 is a highly efficient reagent for the acetylations of a variety of alcohols, phenols and amines with acetic anhydride under solvent-free conditions. Primary, secondary, allylic and benzylic alcohols, diols and phenols with electron-donating or withdrawing substituents can be easily acetylated in good to excellent yield.

Esterification of Carboxylic Acids with Alcohols under Microwave Irradiation in the presence of Zinc Triflate

The esterification of aliphatic and aromatic carboxylic acids with various alcohols (1°, 2°, 3°, benzylic) was studied under microwave irradiation in the presence of zinc triflate as catalyst; the reaction times were short and the yield of reactions was good to excellent.

Synthesis of Caffeic Acid Esters

A new method for the preparation of caffeic acid esters was investigated. Ten caffeic acid esters were prepared by condensation of protocatechualdehyde with malonic acid mono-esters in moderate yield. Malonic acid mono-esters were prepared from the corresponding malonate di-esters. The conformations of compounds are trans (E) form.

Alumina Sulfuric Acid as a Novel Heterogeneous System for Esterification of Carboxylic Acids in Solvent Free Conditions

Neat chlorosulfonic acid reacts with alumina to give alumina sulfuric acid (ASA) in which sulfuric acid is immobilised on the surface of alumina via a covalent bond. Carboxylic acids can be readily converted to their corresponding esters with a combination of ASA and alcohols in solvent free conditions.

4-(Nitro)-diphenylammonium triflate(NDPAT) catalysed esterification of carboxylic acids with alcohols

4-(Nitro)-diphenylammonium triflate(NDPAT) efficiently catalysed the esterification between equimolar amounts of carboxylic acids and alcohols in good yield under mild reaction conditions.

Nano CuFe2O4: an efficient, magnetically separable catalyst for transesterification of β-ketoesters

The preparation of a variety of β-ketoesters was achieved in high yields from methyl acetoacetate under neutral conditions through the utilization of magnetic CuFe₂O₄ nanoparticles as catalyst.

Polystyrene-based superacidic solid acid catalyst: synthesis and its application in biodiesel production

A novel polystyrene-based superacidic solid acid catalyst was developed. It showed high efficiency for biodiesel production with low catalyst loading and excellent recyclability.

Synthesis of 1H-indazolo[2,1-b]phthalazine-triones catalysed by proline triflate under solvent-free conditions

An efficient procedure has been developed for the synthesis of 1 H-indazolo[2,1-b]phthalazine-triones by the one-pot condensation of cyclohexane-1,3-dione, aromatic aldehydes and phthalhydrazides catalysed by proline triflate under solvent-free conditions. The reaction proceeds in good to excellent yields.