The Beckmann Rearrangement. The Rearrangement of Some Substituted Acetophenone Oximes in Sulfuric Acid

Pearson, D. E.; Ball, Frances L.

doi:10.1021/jo01153a018

Cited by 25 publications

(10 citation statements)

References 12 publications

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“…The oxidation procedure (4), the 2,4-dinitrophenylhydrazine procedure (4), and a spectrophotometrio procedure (1) were thoroughly investigated. The 2,4dinitrophenylhydrazine procedure (4) gave the most satisfactory results with the following improvements. The samples of 2,4-dinitrophenylhydrazone were filtered using No.…”

Section: Experimental•7mentioning

confidence: 99%

“…The rate determination. Considerable improvement was made in the technique used previously (4). Individual samples (0.2000 g.) of the oxime were placed in 50-ml., standardtapered Erlenmeyer flasks.…”

Section: Experimental•7mentioning

confidence: 99%

“…Chapman and Fidler (7) measured the rates of rearrangement of the p-chloro, p-methyl, and unsubstituted oxime picryl ethers. 4 The use of sigma,, values pre-* The rates of rearrangement were adjusted to a common temperature of 85°. diets these rates exactly which lends credence to the assumptions made above.…”

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confidence: 99%

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Hammett's Sigma Constants in Certain Electrophilic Reactions

Pearson¹,

Baxter²,

Martin³

1952

J. Org. Chem.

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Section: Experimental•7mentioning

confidence: 99%

Section: Experimental•7mentioning

confidence: 99%

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Hammett's Sigma Constants in Certain Electrophilic Reactions

Pearson¹,

Baxter²,

Martin³

1952

J. Org. Chem.

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“…2B), to the vacant σ* N-O bond, leading to migration with simultaneous N-O bond cleavage (Fig. 5D) (6,12,24). The magnitude of the calculated activation barriers of benzene migration are slightly dependent on the halogen atoms, but the values are within the range of 24-28 kcal/mol (SI Appendix, Tables S1 and S3) despite different protonation site of the OMs (O-mesyl) group.…”

Section: Resultsmentioning

confidence: 93%

Stereochemical evidence for stabilization of a nitrogen cation by neighboring chlorine or bromine

Ohwada

Tani

Sakamaki

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Neighboring group participation is one of the fundamental interactions in organic reactions and can influence the reaction rate, stereoselectivity, and reaction pathway through transient carboncarbon or carbon-heteroatom bond formation. The latter category includes cyclic three-and five-membered bromonium ions, wherein lone-pair electrons of the monovalent bromine atom stabilize a trigonal carbocation. Although similar nucleophilic interactions of monovalent halogen atoms with non-carbon atom-centered cations have long been predicted, we know of no experimental evidence of such an interaction. Here, we demonstrate a nucleophilic interaction of neighboring monovalent halogen to stabilize an imino sp 2 nitrogen cation. This interaction has an overwhelming impact on the reaction pathway, completely altering the migratory preference under acid-catalyzed Beckmann rearrangement conditions. In sharp contrast to the general case of anti-migration, peri-chloroand peri-bromo-substituted O-tosyl oximes of 1-tetralone substructures and their derivatives undergo syn-migration under Beckmann rearrangement conditions (i.e., migration of the group on the syn side of the leaving group). The peri-chloro or peribromo neighboring group turned out to provide strong anchimeric assistance for syn-migration via transient formation of a cyclic five-membered imino-halonium cation with dissociation of tosylic acid. Thus, formation of the syn-migration products can be attributed to a reaction mechanism that is different from the conventional Beckmann rearrangement mechanism. That is, the positively charged imino nitrogen atom can be stabilized by, or interact with, a chloro or bromo group in close spatial proximity, and this interaction dramatically changes the reaction pathway, selectively affording regioisomeric lactams from closely related starting materials.halogen-nitrogen bonding | organic reaction mechanisms | stereochemistry

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“…This procedure was unsatisfactory for the determination of the lower molecular weight ketoximes because of appreciable solubility of the 2,4dinitrophenylhydrazones in water and in dilute acid. A new procedure was 1 Taken in major part from the Ph.D. thesis of Paul T. Scott, Vanderbilt University, 1954. 2 To whom correspondence should be sent. "…”

mentioning

confidence: 99%