Microwave irradiation Beckmann rearrangement

Keywords oximes, zinc chloride, microwave irradiation, Beckmann rearrangement, amide, nitrile... 

Lee, J. K., Kim, D.-C., Song, C. E., Lee, S.-g. Thermal behaviors of ionic liquids under microwave irradiation and their application on microwave-assisted catalytic Beckmann rearrangement of ketoximes. Synth. Commun. 2003, 33, 2301-2307. 

The A-Boc group is rapidly removed on reaction with AlClj under microwave irradiation. Friedel-Crafts reactions. Both alkylation and acylation of arenes can be performed without solvent, by thoroughly grinding the reagents in an agate mortar and pestle at room temperature. (This technique is also applicable to Beckmann rearrangement of oximes in nearly quantitative yields. )... 

Prolonged heating of Bi(OAc)3 wifh amines, N-substituted formamides, and alcohols affords moderate yields of amides, N-acetylformamides, and esters [203]. BiCU mediates the Beckmann rearrangement of ketoximes under microwave irradiation [204[, and Bi(NOj)3- il I,/) mediates fhe guanidylation of N-benzoylfhiour-eas (Scheme 14.100) [205]. 

The one pot synthesis of amide 18 was accomplished within 2 min. by P205/Si02 catalyzed Beckmann rearrangement of the ketone 17 under microwave irradiation." Other ketones such as cyclohexanone, benzophenone, acetophenone and benzil furnished the rearranged products in excellent yields. 

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. 

A silica sulphate (Si02-OSOjH)-supported Beckmann rearrangement of oximes 2 (R = R = H, alkyl, aryl and heterocyclyl) under microwave irradiation in acetone was reported by Li et This recyclable catalyst upon simple workup procedure furnished amides 3 rapidly with high selectivity. 

Usually, Beckmann rearrangement of oximes of ketones are converted into anilides by heating with acidic reagents like PCl, HCOOH, SOCI2 etc. However, solid-state Beckmann rearrangement has been reported. In this method oxime of a ketone is mixed with montmorillonite and irradiated for 7 min in a microwave oven to give corresponding anilide in 91% yield (Scheme 24). 

Alternatively, the Beckmann rearrangement of aldoximes affords amides (see Beckmann reaction, under Section 9.3.2.2). Recent developments along these hnes have been focused on utihzing Si02 at high temperature under microwave irradiation [230]. Furthermore, a one-pot amide synthesis using hydroxylamine in the presence of AI2O3 and sulfonic add has been introduced [231]. 

Phosphoric acid is an efficient and mild reagent for conversion of ketoximes to amide or lactam by Beckmann rearrangement (Baneijee and Mitra, 2005). The reactions are carried out in solvent-free condition under microwave irradiation. It gives good to excellent yields (73-82%). 

A new and efficient microwave induced bismuth trichloride catalyzed Beckmann rearrangement of oximes in the solid state has been achieved by Thakur et al. (2007). Beckmann rearrangement of aryl ketoximes catalyzed by In(OTf)3 gave amides in ionic liquid under microwave irradiation. These aryl ketoximes were converted to corresponding amides in good yields within very short times (10-270 sec). The catalyst and the ionic liquid were easily recovered and reused (Sugamoto et al, 2011). 

Silica supported dichlorophosphate has been found to be an efficient, recoverable and reusable catalyst for Beckmann rearrangement of a variety of ketoximes and dehydration of various aldoximes in tetrahydrofuran under microwave irradiation (Li and Lu, 2008). This protocol is also advantageous because of high conversion, high selectivity, short reaction time, no environmental pollution and simple work-up procedure. 

Potassium dihydrogen phosphate (KH2PO4) was found to be a new and efficient medium for the Beckmann rearrangement in solvent-free conditions under micro-wave irradiation (Niralwad et al, 2013). It was observed that the yield of the products increases with reduction in time as the power of microwaves was increased. The yield was 93% in 25 min for power 600 watts. 

Bagheri and Karimkoshteh (2013) used nano silica-H SO as an efficient and mild catalyst for the Beckmann rearrangement of ketoximes to amides. The reactions were carried out in solvent-free conditions under microwave irradiation (600 W) within 50-120 sec in good yields. 

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