Oximes solvent-free Beckmann rearrangement

The quest for a solvent-free deprotection procedure has led to the use of relatively benign reagent, ammonium persulfate on silica, for regeneration of carbonyl compounds (Scheme 6.10) [48]. Neat oximes are simply mixed with solid supported reagent and the contents are irradiated in a MW oven to regenerate free aldehydes or ketones in a process that is applicable to both, aldoximes and ketoximes. The critical role of surface needs to be emphasized since the same reagent supported on clay surface delivers predominantly the Beckmann rearrangement products, the amides [49]. 

A simple montmorillonite KIO clay surface is one among numerous acidic supports that have been explored for Beckmann rearrangement of oximes (Scheme 8.42) [54]. The conditions are not, ho vever, adaptable for aldoximes that are readily dehydrated to the corresponding nitriles under solvent-free conditions. 

Eshghi and Hassankhani (2007) studied the Beckmann rearrangement using sulfuric acid immobilized on the surface of silica gel (Scheme 5.57). Under these conditions, high conversion and excellent selectivity were found in the Beckmann rearrangement of cyclohexanone oxime. Treatment of carbamates and oxazolidi-nones with anhydrides in the presence of SSA under solvent-free conditions at room temperature results in the formation of V-acyl carbamates and oxazolidinones... 

Moghaddam et reported that the Beckmann rearrangement of oximes 2 (R = alkyl or aryl and = aryl) in the presence of AlCls-ZnCb mixture supported on silica gel under microwave irradiation in solvent-free conditions furnished the corresponding amides 3 in excellent yields. 

Hosseini-Sarvari M, Sharghi H (2006) Alumina sulfuric acid mediated solvent-free and one-step Beckmann rearrangement of ketones and aldehydes and a useful reagent for synthesis of keto- and ald-oximes. J Chem Res 3 205-208... 

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