Beckmann rearrangements synthetic methods

Amines 297 and/or carboxylic acids 298 may be obtained by amide hydrolysis and the latter compound may be produced from a ketone by a Beckmann rearrangement (equation 103). Therefore, the Beckmann rearrangement of a ketone oxime followed by amide hydrolysis provides a synthetic method to cleave the C—C bond between the carbon... 

Although the Beckmann fragmentation may be regarded as a limitation for the application of the Beckmann rearrangement, it provides a synthetic method to produce nitrile compounds. Some examples from the recent literature are collected in the next section. 

Other classical synthetic approaches to 2-furanamine have failed, including the Curtius method and Beckmann rearrangement of 2-benzoylfuran oxime. However, hydrazinolysis of AT-(2-furyl)phthalimide, obtained from phthalimide and 2,5-dimethoxy-2,5-dihy-drofuran, gives 2-furanamine which was not isolated but detected by GLC-MS and H NMR spectroscopy. The latter reveals the absence of imino tautomers (75AP713). The chemistry of 2-dialkylamino-5-phenylfurans is typical of enamines protonation occurs on carbon to produce iminium salts. They are stable to base but afford 5-phenylfuran-2(3//)-one on hydrolysis with dilute acid. 2-Morpholino-5-phenylfuran couples with diazonium salts and affords Diels-Alder adducts with maleic anhydride and IV-phenylmaleimide (73JCS(P1)2523). 

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. 

Ganboa, i., Paiomo, C. Reagents and synthetic methods. 33. improved one-step Beckmann rearrangement from ketones and... 

The synthesis of lactams has attracted considerable attention in recent years. This is presumably because they represent versatile synthetic intermediates that are present h many biologically important molecules. Despite the wide range of methodologies that have been examined for the synthesis of lactams, the Beckmann and Schmidt rearrangements still remain by far the most convenient and general methods. The strongly acidic conditions required for the Schmidt rearrangement often lead to undesired byproducts. This is a major limitation particularly with acid-labile substrates. 

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