Selective Oxidation of Aryl Ketones to α-Diketones with 4-Aminoperoxybenzoic Acid Supported on Silica Gel in Presence of Air

Summary. 4-Aminoperoxybenzoic acid supported on silica gel in presence of air was found to be a selective and convenient oxidant for the oxidation of methylene groups in aryl ketones to convert them to -diketones.     

Convenient Synthesis of tert‐Butyl Esters of Indole‐5‐carboxylic Acid and Related Heterocyclic Carboxylic Acids

The tert‐butyl esters of indole‐5‐carboxylic acid and related compounds such as benzofuran‐ and benzothiophene‐5‐carboxylic acid were readily accessed by reacting the appropriate carboxylic acids with tert‐butyl trichloroacetimidate. To obtain the tert‐butyl esters of the 5‐carboxylic acids of 1H‐benzotriazole and 1H‐benzimidazole, position 1 of these heterocycles had to be protected by acetylation prior to reaction with tert‐butyl trichloroacetimidate. Cleavage of the acetyl residue of the obtained intermediates by dilute aqueous NaOH in ethanol led to the desired tert‐butyl 1H‐benzotriazole‐and 1H‐benzimidazole‐5‐carboxylates.     

α‐Chlorination of Carboxylic Acids Using Trichloroisocyanuric Acid

Abstract

Carboxylic acids are chlorinated in the α position by heating with trichloroisocyanuric acid after formation of a small amount of the acid chloride using phosphorus trichloride.     

Oxidative Cleavage of Oximes with Silica‐Gel‐Supported Chromic Acid in Nonaqueous Media

A simple procedure for a clean and high‐yielding oxidative deoximation of benzaldoximes and ketoximes using a silica‐gel‐supported chromic acid reagent has been developed. This solid‐supported reagent allows us to carry out this reaction in nonaqueous dichloromethane reaction media.     

Efficient and Rapid Method for the Oxidation of Electron‐Rich Aromatic Aldehydes to Carboxylic Acids Using Improved Basic Hydrogen Peroxide

An efficient and rapid method for oxidation of electron‐rich aromatic aldehydes to their corresponding carboxylic acids in excellent yields was developed. It is based on the oxidation of methoxy‐substituted benzaldehydes in methanol with an improved aqueous basic hydrogen peroxide system. Benzaldehydes with electron‐withdrawing substituents are oxidized to the corresponding carboxylic acid in excellent yields under mild reaction conditions.     

Reductive Amination of Aldehydes and Ketones Under Heterogeneous and Solvent-Free Conditions Using Sodium-Borohydride and Silica-Gel–Supported Sulfuric Acid

A regioselective and convenient procedure for preparation of amines by reductive amination of aldehydes and ketones using sodium borohydride in the presence of sulfuric acid supported on silica gel as an active, inexpensive, and recoverable catalyst under heterogeneous and solvent-free conditions at room temperature is described.     

Polymer Supported Synthesis of 2,3,4,6-Tetra-O-Acetyl-β-D-Glucopyranosyl Esters of Aromatic Carboxylic Acids

Aromatic carboxylic acids bound to Amberlyst A-26 react with α-acetobromoglucose to form 2,3,4,6-tetra-O-acetyl-1-0-aroyl-β-D-glucopy ranose derivatives in good yield. Glucosylation occurs satisfactorily with carboxylic acids and nitrophenols (pKa 7–4), but not with phenols whose pKa values are higher (pka ～ 10). Selective glucosylation at the carboxylic group is easily achieved in the case of phenolic acids.     

Influence of Carboxylic Acids on the Synthesis of Chlorohydrin Esters from 1,3‐Butanediol

The influence of diverse carboxylic acid on the preparation of chlorohydrin esters using a one‐pot esterification–chlorination reaction, in which one of the reagents (chlorotrimethylsilane) acts as solvent, is described. Whereas the acid with low pKa provided higher amounts of the 2‐chloro regioisomer, the ones with higher pKa rendered the 1‐chloro regioisomer in 80% yield. These results are in accordance with the mechanism proposed in a previous article.     

Perchloric Acid Supported on Silica Catalyzed Efficient Synthesis of 1,5‐Benzodiazepines

Perchloric acid adsorbed on silica gel efficiently catalyzed the condensation of o‐phenylenediamines (OPDA) with cyclic and acyclic ketones at ambient temperature to afford 1,5‐benzodiazepines in good yields under solvent‐free conditions.     

Fibrous Silica Composites Fabricated Via Sol–Gel Processing Using Amino Acid Surfactant Templating

Fibrils covered by a silica shell have been fabricated by using fibrous aggregates of amino acid surfactant, N-dodecanoyl--alanine, as a template for silicate generated in situ by sol–gel processing in an aqueous solution at pH around 6 and ambient temperature. It was shown that these conditions were inappropriate for tetraethoxysilane to generate silica. The synthesis was performed only when a new water-soluble precursor, tetrakis (2-hydroxy ethyl) orthosilicate, was applied. It is suggested that silica nucleation on the surfactant fibrils takes place via the formation of hydrogen bonds with corresponding functional groups of the amino acid residues.     

Silica Gel–Supported bis(Trimethylsilyl) Chromate: Oxidation of 1,4‐Dihydropyridines to Pyridines

An efficient and convenient method for the oxidation of 1,4‐dihydropyridines mediated by silica gel–supported bis(trimethylsilyl) chromate in refluxing CH₂Cl₂ is reported.     

Direct Oxidation of N‐Benzylamides to Aldehydes or Ketones by N‐Bromosuccinimide

A simple and efficient approach for the one‐pot transformation of N‐benzylamides to aldehydes or ketones under mild conditions was reported. All the 20 substrates gave moderate to excellent oxidative yields under the optimized conditions. Our study may provide a new approach for the one‐pot synthesis of aldehydes or ketones from the corresponding amides.     

Silica‐Gel‐Supported Ceric Ammonium Nitrate (CAN): A Simple and Efficient Solid‐Supported Reagent for Oxidation of Oxygenated Aromatic Compounds to Quinones

A silica‐gel‐supported heterogeneous ceric ammonium nitrate (CAN) reagent has been developed for oxidizing oxygenated aromatics to quinones in nonaqueous media. The advantages of this procedure include excellent yields, mild reaction conditions, nonaqueous media, short reaction times, and easy product isolation.     

General and Facial Synthesis of 2‐Amino‐5‐halogenpyrimidine‐4‐carboxylic Acids and Their Derivatives

A facile synthetic approach to 2‐amino‐5‐halogen‐pyrimidine‐4‐carboxylic acids from 5‐halogen‐2‐methylsulfonylpyrimidine‐4‐carboxylic acid by nucleophilic displacement of the methylsulfonyl group with primary and secondary aliphatic amines has been developed. The titled amino acids underwent decarboxylation, yielding 2‐amino‐5‐halogenpyrimidines. Starting from 2‐amino‐5‐chloropyrimidine‐4‐carboxylic acid chlorides, 2‐[5‐chloro‐2‐(amino)‐4‐pyrimidinyl]‐2‐oxo‐1‐(2‐pyridyl)‐ethyl cyanides were obtained in excellent yields.     

Barium Manganate Oxidation in Organic Synthesis: Part—IV: Oxidation of Aldehydes to Carboxylic Acids

The oxidation of aldehydes to corresponding carboxylic acids by barium manganate under heterogeneous conditions is described. Aromatic aldehydes were smoothly converted to carboxylic acids while aliphatic aldehydes underwent polymerisation.     

Convenient Preparation of N‐Maleoyl Amino Acid Succinimido Esters using N‐Trifluoroacetoxysuccinimide

One‐pot cyclization and esterification of readily available maleamic acid derivatives using N‐trifluoroacetoxysuccinimide provide a convenient and cost‐effective route to a variety of useful N‐maleoyl amino acid N‐hydroxysuccinimido esters.     

Reductions of Carboxylic Acids and Esters with NaBH4 in Diglyme at 162°C

Abstract

Aromatic esters, including the extremely sterically hindered ester: t-amyl 2-chlorobenzoate, are readily reduced to the corresponding benzyl alcohols in high yield with NaBH₄ in refluxing diglyme (162°C). In sharp contrast, aliphatic esters usually gave only low yields of alcohols. Instead, diglyme fragmentation products are formed which undergo transesterification reactions, producing complex product mixtures including products such as RCOOCH₂CH₂OCH₃. The mechanism of this process involves sodium borohydride-induced S_N2 cleavage of diglyme (hydride attack) at high temperatures. However, when the extremely electron rich, 3,4,5-trimethoxybenzoic acid is treated with NaBH₄/diglyme at 162°C (with or without an equivalent of LiCl), no 3,4,5-trimethyoxybenzyl alcohol is formed. The electron rich and hindered ester, t-amyl-3,4,5-trimethoxybenzoate, also does not reduce under these conditions (with or without LiCl). However, both methyl and isopropyl 3,4,5-trimethoxybenzoate esters were converted into 3,4,5-trimethyoxybenzyl alcohol in good yields in NaBH₄/diglyme/LiCl at 162°C. These reductions did not occur unless LiCl was present, illustrating the electron releasing effect of the three methoxy functions which reduce the carbonyl group's reactivity.     

Facile Solid‐Phase Synthesis of Aliphatic Aldehydes Using Novel Polymer‐Supported Phenylselenomethyltrimethylsilane

Treatment of a novel polymer‐supported phenylselenomethyltrimethylsilane reagent with LDA followed by alkylation and oxidative deselenation efficiently afforded aliphatic aldehydes in moderate to good yields with excellent purities.     

Effect of Concentration of Structurally-Different Carboxylic Acids on Growth and Aggregation of Calcium Oxalate in Gel Systems

The effect of concentration of structurally-different carboxylic acids such as ethylene diamine tetraacetic acid （H4edta）, citric acid （H3cit）, tartaric acid （H2tart）, and acetic acid （HOAc） on growth and aggregation of calcium oxalate （CaOxa） in gel systems was comparatively investigated. H2tart and H3cit could change the morphology of cal- cium oxalate monohydrate （COM） and induce the formation of calcium oxalate dihydrate （COD）. H4edta could induce the formation of COD at a lower concentration of 0.33 mmol/L and have the strongest ability to inhibit aggregation of COM. HOAc inhibited COM aggregation only at a higher concentration than 500 mmol/L. With increasing the number of carboxylic groups in an acid or increasing the concentration of carboxylic acid, the capacity of this acid to induce COD formation and to inhibit growth and aggregation of COM crystals increased. That is, this capacity followed the order： H4edta〉H3cit〉H2tart〉 〉HOAc. The result in this work suggested that the presence of H3cit and H2tart in urine played a role in the natural defense against stone formation.     

Exceptionally Simple Homologation of Protected α‐ to β‐Amino Acids in the Presence of Silica Gel

The Wolff rearrangement of α‐amino acid–derived diazoketones is simply achieved by gentle warming in a ethyl acetate/silica gel slurry containing catalytic amounts of silver trifluoroacetate. Without workup (not counting filtration and evaporation) the protected β‐amino acids are obtained in high yields (92–97%) without significant impurities. This variation avoids the laborious workup after a conventional silver‐catalyzed Wolff rearrangement. This method can be similarly applied to the synthesis of β‐amino acid methyl esters when methanol is used as solvent. No reaction occurs without silica gel.