Primary amides, Beckmann rearrangements

Rare-earth exchanged [Ce ", La ", Sm"" and RE (RE = La/Ce/Pr/Nd)] Na-Y zeolites, K-10 montmorillonite clay and amorphous silica-alumina have also been employed as solid acid catalysts for the vapour-phase Beckmann rearrangement of salicylaldoxime 245 to benzoxazole 248 (equation 74) and of cinnamaldoxime to isoquinoline . Under appropriate reaction conditions on zeolites, salicyl aldoxime 245 undergoes E-Z isomerization followed by Beckmann rearrangement and leads to the formation of benzoxazole 248 as the major product. Fragmentation product 247 and primary amide 246 are formed as minor compounds. When catalysts with both Br0nsted and Lewis acidity were used, a correlation between the amount of Br0nsted acid sites and benzoxazole 248 yields was observed. 

The same activity is presented by an iridium complex [Ir(Cp )Cl2]2 that catalyses the Beckmann rearrangement of aromatic, aliphatic and heteroaromatic aldoximes 276 into the corresponding primary amide 277 in good to excellent yields (78-97%) (equation 85). 

Under solvent-free conditions, one-step Beckmann rearrangement of a variety of ketones and aldehydes proceeded in the presence of alumina sulfuric acid 285 (equation 93). Good selectivities were also obtained in the rearrangement of aldoximes to primary amides using zinc oxide as catalyst " (equation 93). 

Primary amides may be produced by a Beckmann rearrangement both from E or Z oximes which are commonly obtained from the corresponding carbonyl compound (aldehyde). Retrosynthetic analysis follows equation 98. 

Synthetically speaking, the Beckmann rearrangement of an aldoxime E or Z) wiU produce a primary amide (equation 99). 

Using this pulse sequence to estimate the nature of derivatization of Suwannee River fulvic acid with N-enriched hydroxylamine to leam more about the carbonyl functionality of fulvic acid, Thom et al.(76) obtained signals for the primary products as oximes. Additional signals of secondary products arising from Beckmann rearrangements of the initial oxime derivatives were identified as nitriles, secondary amides and lactams. The bands assigned to hydroxamic acid result from a reaction of esters with NH2OH and are evidence for the presence of esters in the fulvic acid. 

The solvent-free one step Beckmann rearrangement of ketones 1 and aldehydes in the presence of zinc oxide afforded the corresponding amides 3 (R = alkyl, aryl, cycloalkyl = H, cycloalky 1). Symmetrical ketones furnished the amides in good to excellent yields. In the case of unsymmetrical ketones the reaction was selective and one of the two possible amides was formed. Aromatic and aliphatic aldehydes were converted to the corresponding primary amides. 

Amides are common structures and they are important and versatile synthons to prepare pharmaceuticals, agrochemicals, materials and some specialty chemicals. Many methods have been developed to synthesize primary amides, secondary amides as well as tertiary amides. The traditional process to construct amide bond is the acylation of amines with carboxylic acid or carboxylic acid daivatives such as acid chlorides as well as anhydrides [1, 2]. Furthermore, the Schmidt reaction [3] and Beckmann rearrangement [4] also have been well developed for the amide synthesis. Recently, some reviews have been well summarized the synthesis routes of these amides [5-17]. In this chapter, we will focus on the recent progresses about amide synthesis only by N, NH, or NH2 atoms incorporation nitrogenation strategy via C-H and/or C-C bond cleavage. A series of nitrogen sources such as sodium... 

Martinez-Aseneio A, Yus M, Ramon DJ (2012) Copper(II) acetate-catalyzed one-pot conversion of aldehydes into primary amides through a Beckmann-type rearrangement. Tetrahedron 68(21) 3948-3951... 

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