Beckmann reaction

In addition to the Beckmann reaction, the Schmidt rearrangement is used to generate M-alkylated lactams, too. Alkyl azides 231 react with the cyclic ketones (and aldehydes) in the presence of proton or Lewis acids. On running the inter-molecular reactions, in most cases symmetric ketals 230 have been converted... 

Finally, the TMSOTf 20-catalyzed Beckmann reaction of cyclohexanone with N,N-dimethoxyamine HN(OMe)2 1148 [176] affords, via 1149, N-methoxycaprolac-... 

The most widely used route to l-benzazepin-2-ones involves the Beckmann or Schmidt reaction of the easily accessible 1-tetralones. Many biologically active compounds described in this review have been prepared on the basis of these reactions they have been fully reviewed [2], In the Beckmann reaction of 1-tetralone oximes, polyphosphoric acid is used as a catalyst-solvent in most instances. Aryl migration generally takes precedence over alkyl migration under these reaction conditions, and various 1-tetralone oximes substituted on the aromatic and/or aliphatic rings can be converted to the appropriate 2,3,4,5-tetrahydro-l//-l-benzazepin-2-ones (51) [5, 20-23, 36, 59, 65, 80, 107-112]. Both courses of the rearrangement occur in some instances, yielding l-benzazepin-2-ones (51) and the isomeric 2-benzazepine-l-ones, probably due to electronic effects of the substituents [90, 113, 114]. 

In the Beckmann reaction alternative ionic intermediates, two nitrilium ions (225, via route a or b and 237, via route c) or one iminium ion (235, via route b or c), may be formed from the activated oximes (Scheme 7). 

As mentioned previously, the Beckmann reaction remains one of the most reliable transformations to incorporate efficiently a nitrogen atom in acyclic or cyclic systems, providing a powerful synthetic method (Scheme 8). 

Krow and colleagues investigated the migratory preferences of the Schmidt and Beckmann rearrangements in norcamphors. Two isomeric lactams are usually formed in the Schmidt reaction but one lactam is obtained almost exclusively in a Beckmann reaction (equation 178). 

Benzodiazocines 429 were prepared to be tested as calcium-sensitizing agents (equation 181). A mixture of isomeric lactams was obtained when the Schmidt rearrangement was applied to 427, but only one product 428 was produced using the Beckmann reaction. 

R. E. Gawley, The Beckmann reactions Rearrangements, elimination-additions, fragmentations, and rearrangement-cyclizations , in Organic Reactions, Vol. 35 (Ed. A. S. Kende), Wdey-Intersdence, London, 1988, pp. 1-415. 

R. E. Gawley, The Beckmann Reactions Rearrangements, Elimination-Additions, Fragmentations, and Rearrangement-Cyclizations, Org. React. 1988, 35, 1-420. 

The Beckmann Reactions Rearrangements, Elimination-Additions, Fragmentations, and Rearrangement-Cydizations... 

Another general method for the introduction of a nitrogen atom into a macrocyclic skeleton is via the Beckmann reaction. Rearrangement of cyclotridecanone oxime led to cyclic lactam, which was reduced to amine by lithium aluminium hydride (LAH). Further substitution yielded 14-membered mutuporamine <1999TL5401>. Dieckmann condensation was used for the preparation of 14-membered aza ketone 15 <1999JA2919>, but no experimental details were given. 

The Schmidt and Beckmann reactions have been useful in the synthesis of homopiperazinones through ring expansion. In this... 

One of the most useful variants of the Beckmann reaction is that in which the intermediate is trapped with a nucleophile other than water. Both carbon and heteroatomic nucleophiles have been used in this context. Intramolecular interception gives cyclized products. 

Azide ion has been shown to be an effective trap for a Beckmann intermediate. Treatment of acetophenone oxime with thionyl cloride in the presence of hydrazoic acid gave tetrazole (37), as shown in equation (23). Thiolates participate efficiendy in Beckmann reactions, and the sulW nucleophile may be incorporated into a Lewis acidic reagent, as demonstrated in equation (24). ... 

Lewis acid induced Beckmann reaction in the presence of silyl enol ethers has been used to prepare vinylogous amides (equation 27). ... 

The use of internal nucleophiles in the Beckmann reaction has be i demonstrated to be an effective method for the synthesis of N>heterocycles. Substituted pynolines are readily available via diis qiproach, as exemplifled in equation (28). ... 

Benzoxazoles have been prepared by intramolecular reaction of a phenolic —OH groiq) with a Beckmann intermediate (equation 30). A cyclic imidate was isolated in high yield from tosylation and in situ Beckmann reaction of the erythromycin-derived oxime (4[Pg.698]

Into this group fall the named oxidation rearrangement reactions which proceed with carbon-carbon bond cleavage and 1,2-transfer of an alkyl group to a heteroatom, such as the Baeyer-Villiger reaction (discussed in Chapter 5.1, this volume) and the Beckmann reaction (found in Chapter 5.2, this volume) of ketones, as well as the Hofmann reaction/Schmidt reaction/Curtius reanangement of carboxylic acid derivatives. The two examples discussed here involve related reactions of alcohols. 

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