Beckmann reaction mechanism

Oximes are also good substrates for allylsamarium bromide addition.25 The Beckmann rearrangement product 44 was produced from oxime 43 in good yields when the ratio of allysamarium bromide to oximes was more than 3 1 (Equation (8)). This type of product was also obtained when the other allylic organometallic compounds were used. The reaction mechanism was proposed as shown in Scheme 13. 

The focus of the next four chapters (Chapters 14-17) is mainly on the theoretical/computational aspects. Chapter 14 by T. S. Sorensen and E. C. F. Yang examines the involvement of p-hydrido cation intermediates in the context of the industrially important heptane to toluene dehydrocyclization process. Chapter 15 by P. M. Esteves et al. is devoted to theoretical studies of carbonium ions. Chapter 16 by G. L. Borosky and K. K. Laali presents a computational study on aza-PAH carbocations as models for the oxidized metabolites of Aza-PAHs. Chapter 17 by S. C. Ammal and H. Yamataka examines the borderline Beckmann rearrangement-fragmentation mechanism and explores the influence of carbocation stability on the reaction mechanism. 

An interesting reaction is the Beckmann rearrangement of the j8-phenyl-a,j8-unsaturated ketoxime ester 4 to form the 1-phenylisoquinoline 5. A reaction mechanism involving azacyclobutenium intermediates has been invoked ... 

Treatment of ketones with azide derivatives affords amides by a Schmidt reaction [389]. Its mechanism is similar to that of the Beckmann rearrangement The key intermediate is an iminodiazonium ion [390]. In transformations of bridged bicycHc ketones both the Schmidt and the Beckmann reaction are complementary [391] since inverse selectivities have been observed [392]. 

The intermediates (7) have been independently generated in aqueous solution. Note the similarity of this mechanism to those of insertion of CH2 (18-9) and of O (18-19). The three reactions are essentially analogous, both in products and in mechanism. Also note the similarity of the latter part of this mechanism to that of the Beckmann rearrangement (18-17). 

C. Beckmann fission of 2-methoxycyclooctanone oxime. In a 500-ml., three-necked, round-bottomed flask equipped with a mechanical stirrer, a dropping funnel, and a calcium chloride tube is placed a suspension of 62.5 g. (0.30 mole) of phosphorus pentachloride (Note 4) in 150 ml. of absolute ether, and the reaction vessel is cooled with ice. A solution of 42.8 g. of crude 2-methoxycyclooctanone oxime (0.25 mole) in 100 ml. of absolute ether is added over 30 minutes with vigorous stirring and the reaction is continued for 50 minutes at 5°. The reaction mixture, which becomes a transparent reddish brown solution (Note 5), is poured with mechanical stirring into 500 g. of ice in a 2-1. beaker. Stirring is continued for 1.5 hours at 5° (Note 6). I he ether layer is separated and the aciueous layer is extracted with... 

Triazines 347 were obtained from amidoximes 346 and ethyl orthoacetate (equation 151). The mechanism of formation of products 347 includes Beckmann rearrangement of amidoximes to carbodiimides, followed by reaction with amidoxime and orthoester. ... 

A simplified mechanism for the Beckmann rearrangements and important related reactions is shown hi Scheme 9. Summarizing the mechanism section, the key step of the reaction is the migration of an a-carbon group to the electronically deficient nitrogen atom of the oxime. A nitrilium ion in some cases or an imidate in others are key intermediates in the reaction. Their destiny determines the course of the transformation. Basically, three different pathways may be possible and can be synthetically exploited ... 

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