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We also met the Beckmann fragmentation at the end of the previous chapter on rearrangements. In this chapter, we will focus exclusively on fragmentations that are synthetically useful. Like rearrangements, fragmentations occur readily under strongly acidic conditions, but this leads to uncontrolled decomposition for most substrates.
- Rearrangements
Heating the tosylates yields four products. Products 1 and 2...
- Beckmann Rearrangement
The Beckmann rearrangement is a reaction discovered in the...
- Rearrangements
The Beckmann fragmentation is a reaction that frequently competes with the Beckmann rearrangement. [3] When the group α to the oxime is capable of stabilizing carbocation formation, the fragmentation becomes a viable reaction pathway.
The most prominent of these is the so-called photochemical Beckmann rearrangement, first observed by De Mayo in 1963 and discussed in a review several years ago. Worthy of mention, however, is the fact that many oximes that suffer fragmentation under acidic conditions undergo rearrangement when photolyzed.
Jan 23, 2023 · The Beckmann rearrangement is a reaction discovered in the mid-1880’s by the chemist Ernst Otto Beckmann. The reaction converts oximes into their corresponding amides 1 allowing the insertion of the nitrogen atom from the C=N bond into the carbon chain forming a C–N bond. Depending on the starting material, it could also produce nitriles ...
The Beckmann is the rearrangement of the oxime to the amide. This is generally achieved through conversion of the oxime oxygen to a good leaving group, followed by heat, which results in an alkyl (or hydride) shift, breaking the weak N-O bond. The second step involves trapping of the carbon with water (forming an amide) or, if a hydride shift ...
Jan 22, 2022 · Abnormal beckmann rearrangement. Certain oximes having quaternary carbon anti to the hydroxyl group undergo rearrangement to give nitriles instead of amides. Such reaction is termed as abnormal Beckmann rearrangement or Beckmann fragmentation. The alkyl group of the nitrilium cation intermediate detaches to give nitrile as a product instead of ...
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7.25.4.2 The Beckmann Fragmentation This mode of the Beckmann reaction (equation 1 ) accompanies the main rearrangement mode as a side reaction in several cases. However, under certain conditions, this ‘second-order’ mode can predominate to varying extents; it can either be driven by relief of strain or be assisted electronically by an α heteroatom lone pair.
