Selenium(IV) Oxide Catalyzed Oxidation of Aldehydes to Carboxylic Acids with Hydrogen Peroxide

A convenient method for oxidative transformation of aromatic, hetero-aromatic and aliphatic aldehydes into carboxylic acids is presented. It is based on the oxidation of aldehydes in THF using 30% hydrogen peroxide in the presence of 5 molar % of selenium(IV) oxide. The scope and limitation of the method are discussed.     

Polyvinylpyrrolidone-Supported Hydroperoxide for Selective Oxidation of Aldehydes to Carboxylic Acids and Sulfides to Sulfoxides

The facile immobilization of hydroperoxide on the cross-linked poly(vinylpyrrolidone) is described by treatment of a poly(vinylpyrrolidone)-Vilsmeier adduct with (35%) hydrogen peroxide. The in situ–generated poly(vinyl pyrrolidone)-supported hydroperoxide reagent showed very good performance in chemoselective oxidation of aldehydes to carboxylic acids as well as sulfides to sulfoxides.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Modified Pyridinium Chlorochromate Oxidation of Aldehydes to Carbamoyl Azides/Acyl Azides or Carboxylic Acids

Aldehydes are transformed into carbamoyl azides/acyl azides by pyridinium chlorochromate in the presence of sodium azide. Comparable oxidations modified with sodium cyanide generate carboxylic acids from simple aliphatic aldehydes whereas conjugated aldehydes are unreactive.     

A Facile One-Pot Transformation of Carboxylic Acids to Amides

Carboxylic acids, converted in situ into carboxylic-(p-nitrobenzene)sulfonic anhydrides using p-nitrobenzenesulfonyl chloride, Et3N, and DMAP in CH₃CN, react with primary or secondary amines, to give amides in high yields.     

The Direct Conversion of Carboxylic Acids to Carboxamides via Reaction with Unsolvated Bis(Diorganoamino) Magnesium Reagents

It has been found that unsolvated bis (diorganoamino) magnesium compounds react smoothly with carboxylic acids to give the corresponding carboxamides directly in good to excellent yields.     

An Efficient Iron(III)‐Catalyzed Aerobic Oxidation of Aldehydes in Water for the Green Preparation of Carboxylic Acids

The first example of a heterogeneous iron(III)‐catalyzed aerobic oxidation of aldehydes in water was developed. This method utilizes 1 atmosphere of oxygen as the sole oxidant, proceeds under extremely mild aqueous conditions, and covers a wide range of various functionalized aldehydes. Chromatography is generally not necessary for product purification. Its operational simplicity, gram‐scale oxidation, and the ability to successively reuse the catalyst, make this new methodology environmentally benign and cost effective. The generality of this methodology gives it the potential to be used on an industrial scale.     

Direct Oxidation of Primary tert-Butyldimethylsilyl Ethers to Carboxylic Acids with Jones Reagent

Treatment of the tert-butyldimethylsilyl ethers 1a-f with Jones reagent gave the carboxylic acids 2a-f in excellent yield in the absence of potassium fluoride.     

Mild and Efficient Synthesis of Carboxylic Acid Anhydrides from Carboxylic Acids and Triazine Coupling Reagents

Abstract

Anhydrides of carboxylic acids were obtained in 53%–95% yield by treatment of appropriate carboxylic acids with 2‐chloro‐4,6‐dimethoxy‐1,3,5‐triazine (CDMT) or 2,4‐dichloro‐6‐methoxy‐1,3,5‐triazine (DCMT) in the presence of N‐methylmorpholine. It has been proved that synthesis proceeds via triazine active esters 3a,b, which are able to acylate carboxylate anion but not less nucleophilic carboxylic acid.     

Triflylpyridinium Enables Rapid and Scalable Controlled Reduction of Carboxylic Acids to Aldehydes using Pinacolborane

Building up new and efficient methods for the controlled conversion of carboxylic acids to aldehydes is important. Herein, we report a rapid, modular and scalable method for the conversion of carboxylic acids to aldehydes using pinacolborane at ambient temperature, in which a triflylpyridinium reagent is used. The conversion of carboxylic acid to intermediate acylpyridinium by triflylpyridinium is new. A binary pyridine-coordinated boronium complex is generated after reduction. The unprecedented reduction of the acylpyridinium by HBpin opens up a practically direct synthesis of aldehydes from carboxylic acids. Theoretical studies indicate that the reduction of acylpyridinium requires a lower activation free energy than that of the product aldehyde. The synthetic advantage of this protocol is further highlighted by the scalable synthesis of aldehyde via continuous flow process. Configuration retention for chiral acids are presented in those syntheses.     

Direct Addition of Grignard Reagents to Aliphatic Carboxylic Acids Enabled by Bulky turbo-Organomagnesium Anilides

The synthesis of ketones through addition of organometallic reagents to aliphatic carboxylic acids is a straightforward strategy that is limited to organolithium reagents. More desirable Grignard reagents can be activated and controlled with a bulky aniline-derived turbo-Hauser base. This operationally simple procedure allows the straightforward preparation of a variety of aliphatic and perfluoroalkyl ketones alike from functionalized alkyl, aryl and heteroaryl Grignard reagents.     

Facile Conversion of Molecularly Complex (Hetero)aryl Carboxylic Acids into Alkynes for Accelerated SAR Exploration

1,2,3-Triazoles are well-established bioisosteres for amides, often installed as a result of structure−activity-relationship (SAR) exploration. A straightforward approach to assess the effect of the replacement of an amide by a triazole would start from the carboxylic acid and the amine used for the formation of a given amide and convert them into the corresponding alkyne and azide for cyclization by copper-catalyzed alkyne−azide cycloaddition (CuAAC). Herein, we report a functional-group-tolerant and operationally simple decarbonylative alkynylation that allows the conversion of complex (hetero)aryl carboxylic acids into alkynes. Furthermore, the utility of this method was demonstrated in the preparation of a triazolo analog of the commercial drug moclobemide. Lastly, mechanistic investigations using labeled carboxylic acid derivatives clearly show the decarbonylative nature of this transformation.     

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.     

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.     

One-Pot Direct Oxidation of Primary Amines to Carboxylic Acids through Tandem ortho-Naphthoquinone-Catalyzed and TBHP-Promoted Oxidation Sequence

Biomimetic oxidation of primary amines to carboxylic acids has been developed where the copper-containing amine oxidase (CuAO)-like o-NQ-catalyzed aerobic oxidation was combined with the aldehyde dehydrogenase (ALDH)-like TBHP-mediated imine oxidation protocol. Notably, the current tandem oxidation strategy provides a new mechanistic insight into the imine intermediate and the seemingly simple TBHP-mediated oxidation pathways of imines. The developed metal-free amine oxidation protocol allows the use of molecular oxygen and TBHP, safe forms of oxidant that may appeal to the industrial application.     

Selective and Efficient Oxidation of Aldehydes to Their Corresponding Carboxylic Acids Using H2O2/HCl in the Presence of Hydroxylamine Hydrochloride

A wide variety of aldehydes were efficiently converted to their corresponding carboxylic acids in high yields using H₂O₂/HCl in the presence of hydroxylamine hydrochloride. In addition, selective oxidation of aldehydes in the presence of other functional groups such as hydroxyl group, carbon‐carbon double bond and other heteroatoms can be considered a noteworthy advantage of this method.     

An Improved and Practical Sharpless Oxidation of Primary Alcohols to the Carboxylic Acids

An improved and practical procedure for the oxidation of primary alcohols to the carboxylic acids under Sharpless's conditions (NaIO₄/RuCl₃.H₂O/water/acetonitrile) using ethyl acetate as the solvent, in place of toxic and ecologically undesirable carbon tetrachloride, is described.