Beckmann rearrangement, of oxime

The Beckmann rearrangement of oximes of the thiophene series has been applied (besides the preparation of 2-acetamidothiophene ) to thiophenocycloalkenones (192) which gave the cyclic amide (193) hydrolyzable to the amine (194). The Beckmann rearrangement was... 

Beckmann rearrangement of oxime is an acid catalysed reaction. The environmental problems associated with the use of sulphuric acid instigated interest to use number of solid acid catalysts [1], There are only scanty references about Lewis acid ion-exchanged MeAlPOs. Beyer et al. [2], Mihalyi et al. [3] and Mavrodinova et al. [4] already suggested the presence of Lewis acid metal ions as MO+ species in zeolites. The present study focussed the synthesis and characterisation of Fe3+, La3+ and Ce3+ ion-exchanged MAPO-36. The catalytic results of Beckmann rearrangement of cyclohexanone oxime over ion-exchanged catalysts are delineated in this article. 

A simple montmorillonite K 10 clay surface is one among numerous acidic supports that have been explored for the Beckmann rearrangement of oximes (Scheme 6.27) [54]. However, the conditions are not adaptable for the aldoximes that are readily dehydrated to the corresponding nitriles under solventless conditions. Zinc chloride has been used in the above rearrangement for benzaldehyde and 2-hydroxyacetophe-none, the later being adapted for the synthesis of benzoxazoles. 

Where Rj= CH3 or Ph and R2 = Ph or substituted phenyl Scheme 6.27 Beckmann rearrangement of oximes on clay. 

The Beckmann rearrangement of oximes to produce amides is promoted by perrhenate ions under phase-transfer catalytic conditions, in the presence of trifluoro-methanesulphonic acid in nitromethane [6]. Under these conditions, the rearrangement reaction is frequently accompanied by the solvolysis of the oxime to the ketone. This can be obviated by the addition of hydroxylamine hydrochloride. No reaction occurs in the absence of the ammonium catalyst or with the O-acetyl oximes. 

Perrhenate-catalysed Beckmann rearrangement of oximes (Table 9.8)... 

Beckmann, E. Chem. Ber. 1886, 89, 988. Ernst Otto Beckmann (1853—1923) was bom in Solingen, Germany. He studied chemistry and pharmacy at Leipzig. In addition to the Beckmann rearrangement of oximes to amides, his name is associated with the Beckmann thermometer, used to measure freezing and hoihng point depressions. Mazur, R. H. J. Org. Chem. 1961,26, 1289. 

Oximino cyanoacetate or malonate esters (Me02CC(CN)=N0Ts or (Me02C)2C= NOCOPh) reacted with diazoaUcanes (RCHN2) to give unstable 1,2,3-triazolines . Synthesis of Al-imidoylbenzotriazoles via benzotriazole-mediated Beckmann rearrangement of oximes is also described . ... 

The Beckmann rearrangement of oxime esters is catalysed by Brpnsted or Lewis acids and these conversions are usually non-stereospecific, as demonstrated by the studies of Beckmann rearrangement of 1-indanone oximes derivatives 240a with aluminium chloride as a catalyst " (equation 88). 

In fused ring systems, the Beckmann rearrangement of oximes at the carbon adjacent to a common carbon of the two rings usually proceeds by preferential migration of the ring system (the common carbon atom undergoes migration preferentially). This behaviour can be mainly attributed to the increased stability of the oxime in which the Af-hydroxyl (or derivative) is directed towards the outside of the molecule. 

Trimethylsilyl polyphosphate (PPSE),1 The reagent is prepared from P205 and [(CHj),Si]20. It is a colorless, volatile liquid, soluble in the usual organic solvents. It is comparable to polyphosphate ester for the Beckmann rearrangement of oximes to amides (3, 230 231). but it is prepared more easily. 

The reaction of ketone 243 with hydroxyamine resulted in the formation of oxime 244. Treatment of this oxime with polyphosphoric acid induced the Beckmann rearrangement of oxime 244 to form lactam 245 without detectable formation of isomeric lactam (Scheme 43) <1997JHG921>. Other examples of the Beckmann rearrangement of pyran and thiane derivatives have been reported <2004BML5907, 2004TL1051, 2005JOC10132>. 

Barium thiocyanate, 118 Base catalysis, 34 in acylations, 47, 48 of chelate formation, 95 of clevage, 128 of cydization, 127 in hydrolysis, 115 Basicity, of 2-aminothiazole, 90 of 2-imino-4-thiazolines, 124 Beckmann rearrangement, of oxime, 16 Benzaldehyde, with alkyl-acetamidothi-azole, 46... 

Thermal dehydration of o- (acylamino)phenols is the method of choice for the preparation of benzoxazoles (equation 96) and other annulated oxazoles. 0,iV-Diacyl derivatives of o-aminophenols cyclize at lower temperatures than do the monoacyl compounds. The synthesis is often carried out by heating the aminophenol with the carboxylic acid or a derivative, such as the acid chloride, anhydride, an ester, amide or nitrile. The Beckmann rearrangement of oximes of o-hydroxybenzophenones leads directly to benzoxazoles (equation 97). 

Nitrilium ions are generally indicated as discrete intermediates in the Beckmann rearrangement of oximes (equation 37, Y = OH2) and in the Schmidt rearrangement (equation 37, Y = N2) of ketones and aldehydes with hydrogen azide. The first stage of these reactions has been defined as an ionization by rearrangement process through a transition state of type 183 (Smith, 1963). 

Beckmann rearrangement of oximes, 572 Benzidine rearrangement, 682 Benzilic acid rearrangement, 435 Benzils, see a-Diketones Benzofurans, preparation, by dehydro-cyclization, 842... 

Barton reaction, 398, 446 Beckmann rearrangement of oximes, 325, 343-345 Benzaldehyde, 178 Benzoates, pyrolytic elimination,... 

The Beckmann rearrangement of oximes affords amides which may be hydrolysed or reduced to form amines. The geometry of the oxime is important in directing the course of the rearrangement and hence in defining which amide might be obtained (Scheme 2.32). 

Treatment of a wide variety of oxime sulfonates with several equivalents of alkyl-aluminum reagents in CH2CI2 resulted in formation of the imines, which were directly reduced with excess DIBAH to give the corresponding amines, as shown in Sch. 19. This organoaluminum-promoted Beckmann Rearrangement of oxime sulfonates has been successfully applied to the stereoselective synthesis of naturally occurring alkaloids, pumiliotoxin C, and solenopsin A and B, as illustrated in Sch. 20 [43]. 

Combination of silyl enol ethers with the organoaluminum-promoted Beckmann rearrangement of oxime sulfonates resulted in a novel reaction system that leads to the formation of enaminones [44]. Treatment of a mixture of anfr-2-methylcyclohexa-none oxime sulfonate (33) and 2-(trimethylsiloxy)-l-octene in dry CH2CI2 with Et2AlCl at -78 °C for 30 min, and at 20 °C for additional 1 h resulted in formation of the enaminone 34 in 90 % yield (Sch. 21). 

The Beckmann rearrangement of oximes may be induced by means of dicyclohexylcarbodi-imide and trifluoroacetic acid in dimethylsulphoxide. The oxime (256) of a 17-oxo-steroid gave the usual lactam (257) and seco-nitrile (258). The oxime of a 3a,5a-cyclo-6-ketone gives the ring-B lactam resulting from migration of C(5) (c/. p. 273). A kinetic study of the Beckmann rearrangement... 

There are a number of thermal and photochemical reactions for which oxaziridine intermediates have been proposed but never isolated. These include, among others, the photochemical Beckmann rearrangement of oximes, many photochemical reactions of aromatic A -oxides, and the thermal rearrangement of nitrones to amides. A brief discussion of the first two seems warranted in this review because they have been studied extensively and some strong inferential evidence for oxaziridine intermediates has been obtained. 

Oxaziridines have been proposed as intermediates in the photo-Beckmann rearrangement of oximes. A reinvestigation of the photochemistry of (+)-camphor oxime (60) has revealed that the... 

The synthetic uses of hydrazones and oximes for carbon-bond formation differ little from those of imines as their anions represent enolate equivalents except for certain methods that have been developed for asymmetric induction. Conversely, the formal replacement of the carbon substituent of imines by a heteroatom (nitrogen for hydrazones and oxygen for imines) opens reaction pathways such as the Beckmann rearrangement of oximes and the Wolff-Kishner and Shapiro reductions of hydrazones that have no analogy in the chemistry of imines. 

In addition to carbon-carbon bond forming reactions of derived anions, hydrazones and oximes are important derivatives of carbonyl groups for the Beckmann rearrangement (of oximes to amides, equation 55)203.204 jmd the Shapiro reaction (tosylhydrazones to alkenes, equation 56). ° Of historical... 

The reductive Beckmann rearrangement of oximes has been effected with several types of aluminum hydride reagents. Early examples exhibited only moderate regioselectivity, giving mixtures of primary amines and rearranged secondary amines. Recently, diisobutylaluminum hydride was reported to be most satisfactory for this type of transformation (equation 20). Here dichloromethane is the solvent of choice, and attempted use of ethereal solvents results in the formation of a mixture of primary and secondary amines. ... 

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