Unexpected results from the re-investigation of the Beckmann rearrangement of ketoximes into amides by using TsCl

TsCl (p-toluenesulfonyl chloride), a commercially available organosulfonyl chloride, has been widely used as a stoichiometric dehydrogenation reagent in the transformation of ketoximes into corresponding amides via the Beckmann rearrangement. It has been now found to catalyze the Beckmann rearrangement with high catalytic efficiency, converting a wide range of ketoximes into their corresponding amides under mild condition with good to excellent yields (up to 99% of yield with 1-5 mol % of catalyst loading).     

A Simple and Highly Efficient One-Pot Procedure for the Synthesis of Amides via Beckmann Rearrangements Using 1-Tosylimidazole (TsIm)

A facile and highly efficient method for one-pot Beckmann rearrangement of ketoximes into N-substituted amides using N-(p-toluenesulfonyl)imidazole (TsIm) is described. In this method, ketoximes are refluxed with TsIm and Cs₂CO₃ in the presence of SiO₂ as a recyclable catalyst in DMF affording the corresponding amides in high yields. This methodology is highly efficient and regioselective for various structurally diverse ketoximes including symmetrical and unsymmetrical as well as cyclic oximes. The results of quantum mechanical studies used to rationalize the experimental outcomes are discussed.     

A RAPID AND FACILE CONVERSION OF PRIMARY AMIDES AND ALDOXIMES TO NITRILES AND KETOXIMES TO AMIDES WITH TRIPHENYLPHOSPHINE AND N-CHLOROSUCCINIMIDE

ABSTRACT

Primary amides and aldoximes are easily converted to their corresponding nitriles using a mixture of triphenylphosphine and N-chlorosuccinimide in dichloromethane at room temperature. The reaction of aldoximes occurs almost immediately and primary amides in 0.5?h by this method. By this procedure secondary amides are produced by Beckmann rearrangement of ketoximes.     

A mild and efficient catalyst for the Beckmann rearrangement, BOP-Cl

BOP-Cl (bis(2-oxo-3-oxazolidinyl)phosphinic chloride) was found to be very active as the first organophosphorus catalyst (1-5 mol % loading) for the Beckmann rearrangement of various ketoximes to the corresponding amides in anhydrous acetonitrile at refluxing temperature.     

Concerning the Beckmann rearrangement of aryl heteryl ketoxime ions

The possible Beckmann rearrangement of aryl heteryl ketoxime ions has been investigated by studies on the 70 eV mass spectra, metastable ion spectra and collision induced dissociation spectra of pairs of isomeric ketoximes and corresponding amides. Aryl cycloalkyl ketoximes were also studied, and the molecular ions of these and the corresponding amides showed no evidence of interconversion. The introduction of the heterocyclic moieties made little change to this situation although some novel rearrangements were observed.     

Beckmann reaction of oximes catalysed by chloral: mild and neutral procedures

A variety of ketoximes undergo the Beckmann rearrangement when heated with 0.5 molar equiv. of chloral (neat melt/∼130°C), to furnish the corresponding amides in excellent yields (generally 80-95%) after simple work-up. (Aromatic aldoximes dehydrated to the corresponding nitriles in excellent yields under similar conditions.) The absence of solvent, Brønsted acids, strong Lewis acids and by-products, and a simple work-up characterise the procedures.     

Mercury-catalyzed rearrangement of ketoximes into amides and lactams in acetonitrile

An acetonitrile solution of mercury(II) chloride has been found to catalyze efficiently the conversion of a diverse range of ketoximes into their corresponding amides/lactams.     

A Mild and Highly Efficient Catalyst for Beckmann Rearrangement, BF3·OEt2

BF₃·OEt₂ (Boron trifluoride etherate), an inexpensive and commercially easily available Lewis acid stoichiometrically employed for Beckamann rearrangement in general, was now found to efficiently catalyze Beckmann rearrangement of ketoximes into their corresponding amides (up to 99% yield) in anhydrous acetonitrile under reflux temperature.     

Efficient Beckmann rearrangement and dehydration of oximes via phosphonate intermediates

Under mild conditions, conversion of a variety of ketoximes and aldoximes to their corresponding amides and nitriles proceeded in the presence of diethyl chlorophosphate with excellent yields.     

PEG-SO_3H as catalyst for the Beckmann rearrangement and dehydration of oximes

Under mild conditions, conversion of a variety of ketoximes and aldoximes to their corresponding amides and nitriles proceeded in the presence of PEG-SO3H with high yields.     

Cyanuric chloride as a mild and active Beckmann rearrangement catalyst

The first general organocatalytic Beckmann rearrangement of ketoximes into amides has been realized by the catalytic use of cyanuric chloride. Furthermore, acids such as HCl and ZnCl2 are effective as cocatalysts with cyanuric chloride. For example, azacyclotridecan-2-one, which is synthetically useful as a starting material for nylon-12, was prepared in quantitative yield by the Beckmann rearrangement of cyclododecanone oxime (100 mmol scale) catalyzed by cyanuric chloride (0.5 mol %) and ZnCl2 (1 mol %).     

Efficient Procedure for Beckmann Rearrangement of Ketoximes Catalyzed by Sulfamic Acid/Zinc Chloride

The Beckmann rearrangement of a variety of ketoximes to corresponding amides catalyzed by sulfamic acid and zinc chloride was carried out in good yields at refluxing temperature in acetonitrile.     

p-Toluenesulfonic acid mediated zinc chloride: highly effective catalyst for the Beckmann rearrangement

PTSA-ZnCl₂ has been proved to be an excellent catalyst for liquid-phase Beckmann rearrangement of ketoximes in acetonitrile. The satisfactory yields of amides were obtained in the present of this catalyst system.     

Synthesis of oximes,conversion to nitrile oxides and their subsequent 1,3-dipolar cycloaddition reactions under microwave irradiation and solvent-free reaction conditions

Aldoximes and ketoximes were readily synthesized from aldehydes and hydroxylamine hydrochloride on Al₂O₃ without solvent under microwave irradiation. At higher irradiation power, aldoximes dehydrated to nitriles and ketoximes rearranged to amides. Aldoximes reacted in a one-pot reaction with N-chlorosuccinimide and alkenes or alkynes over alumina under microwave irradiation to give isoxazolines or isoxazoles. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:351–354, 1998     

An efficient catalytic method for the Beckmann rearrangement of ketoximes to amides and aldoximes to nitriles mediated by propylphosphonic anhydride (T3P®)

An efficient method for the Beckmann rearrangement of ketoximes to amides mediated by a catalytic amount (15 mol %) of propylphosphonic anhydride (T3P®) is described. Aldoximes underwent second order Beckmann rearrangement to provide the corresponding nitriles in excellent yields on reacting with T3P (15 mol %) at room temperature. The main advantages of this environmentally friendly protocol include procedural simplicity, and particularly ease of isolation of the products.     

Beckmann rearrangement of oximes using pivaloyl chloride/DMF complex

A new complex of pivaloyl chloride and DMF was found to be very effective for converting ketoximes into their corresponding amides or lactams with excellent conversion via the Beckmann rearrangement. This method offers significant advantages such as efficiency and mild reaction conditions with shorter reaction time.     

Cover Picture

Regioselective Csp³–H and Csp²–H alkynylation under Ir(III) and Ag(I) catalytic system was developed by judicious choice of readily available and structurally modifiable ketoximes and amides as the key substrates. Key features of this transformation included: 1) For ketoxime substrates, only primary Csp³–H at γ position to the nitrogen atom of ketoximes could readily undergo this Csp³–H alkynylation under Ir(III) catalysis. Notably, by slight modification of the structure of substrates, alcohols and ketones derived ketoximes could well participate in this transformation. 2) For amide substrates, primary phenylacetamides, which are challenging substrates due to the tautomerization of the distal O‐coordinating acetamides, could well serve as suitable substrates for the Csp²–H alkynylation. Significantly, when using oxidizing amides as the directing groups, α,β‐dehydrogenative C—H alkynylation was achieved. More details are discussed in the article by Shi et al. on page 929—934.

     

Carbon Tetrabromide/Triphenylphosphine‐Activated Beckmann Rearrangement of Ketoximes for Synthesis of Amides

An efficient Beckmann rearrangement of ketoximes was developed using carbon tetrabromide/triphenylphosphine as an organocatalyst without addition of any acids or metals. The reaction showed good functional group tolerance and gave various amides in moderate to good yields.     

Keggin-type Bronsted dodecatungstophosphoric acid: a quasi homogenous and reusable catalyst system for liquid phase Beckmann rearrangement

A variety of ketoximes, prepared from corresponding ketones, undergo Beckmann rearrangement using H₃PW₁₂O₄₀ (DTPA) in acetonitrile under reflux to yield N-substituted amides and lactams in good to excellent yields (72–96%). The present method provides an efficient, clean, eco-friendly, and simple synthesis. The catalyst is cheap, moisture tolerant, recoverable, and reusable without much loss of its activity.     

SOCl2/β-Cyclodextrin: A New and Efficient Catalytic System for Beckmann Rearrangement and Dehydration of Aldoximes Under Aqueous Condition

A rapid and efficient synthesis of amides via Beckmann rearrangement of ketoximes and dehydration of aldoximes to corresponding nitriles with good to excellent yields has been carried out in the presence of SOCl₂/β-cyclodextrin under aqueous conditions. The β-cyclodextrin has been recovered and reused.