Dehydration of aldoximes

Pro-azaphosphatranes lb and Id function as mild and generally applicable catalysts for the conversion of both aliphatic and aromatic aldoximes to nitriles in good yield, Eq. (22) [136]. With aliphatic aldoximes the reaction is complete in two hours at room temperature, while the reaction with aromatic aldoximes is achieved in 3 - 4 h at 60 °C. After the reaction, [2b] OH and [2d] OH are formed. The preferred amount of lb is 0.4 equivalent in these reactions. When less catalyst was employed, the reaction was incomplete in the times employed. 

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With the phosphoric imidazolides D, E, and F, dehydration of the aldoximes can also be achieved (dioxane, room temperature, several hours). With diphenylimidazole-1-phosphonate (D) and phenyldiimidazole-l,l -phosphinate (E) the yields of nitriles are always higher than with (C6H50)2P(0)C1 and C6H50P(0)C12 however, with phosphoryl triimidazole (F) the yields are a little lower than with POCl3.[9] Spin-labeled phosphoric imidazolides of this type are also used for the dehydration of aldoximes.1103... 

Aldehyde 26 was treated with hydroxylamine hydrochloride in refluxing methanol to give a mixture of (E)- and (Z)-pyrrolotriazine 40 in 59% and 21% yield, respectively. Dehydration of aldoxime 40 with trifluoromethanesulfonic anhydride and triethylamine in dichloromethane afforded triazine 41. Conversion of the nitrile 41 to the deprotected amide 42 was accomplished in 96% yield on treatment of 41 with basic hydrogen peroxide in ethanol <2001CAR77>. 

Also, chlorosulfonic acid was demonstrated to be an efficient catalyst in the Beckmann rearrangement of a variety of ketoximes in refluxing toluene, and excellent conversion and selectivity was observed . This procedure can also be applied to the dehydration of aldoximes yielding the corresponding nitriles. 

Indium trifluoromethanesulfonate was found to be an effective high-yielding catalyst for the facile dehydration of aldoximes to nitriles and Beckmann rearrangement of ketoximes to anilides. ... 

Dehydration of Aldoximes and Similar Compounds C-Hydro-ZV-hydroxy-elimination... 

Nitriles may be prepared by dehydration of aldoximes an attempt to effect a Beckmann rearrangement on the oxime (481) of 5-methoxy-4-oxopyran-2-carboxaldehyde gives the nitrile (482) but under milder conditions only the chloride (483) and the chloronitrile (484) are obtained (75JHC219). 

When the reaction is carried out in boiling DMSO, no significant gain in the yield of benzamide (30%) is observed. Since under these conditions the primary dehydration of aldoximes is evident, the formation of benzamide is most likely to result from hydration of the intermediate benzonitrile rather than by the Beckmann rearrangement scheme. 

By analogy with the dehydration of aldoximes in the KOH/DMSO system, which certainly involves abstraction of the proton nearest to the oxime function, in the case ketoximes, one can expect 1,3-dehydration which leads to unstable intermediates such as the 1,3-dipole 82, azirine 83, vinylnitrene 84 or nitrile, or the stable rearrangement product of one of them (Scheme 42). 

The dehydration of aldoximes with 2-methylene-l,3-dioxepane has been found to proceed smoothly in the presence of a catalytic amount of scandium(III) triflate to give the corresponding nitriles. The authors608 proposed that coordination of Sc(OTf)3 to the oxygen atom of the 1,3-dioxepane ring induces C—O bond cleavage to form a cationic... 

Some of these procedures are exemplified in Expt 5.160. Dehydration of aldoximes proceeds under milder conditions, acetic anhydride being frequently used. The method is particularly applicable to the synthesis of aromatic nitriles (see Expt 6.170). 

Other related reactions of these high-valent species include cyclopropanation of alkenes, oxidation of benzyltrialkylstannanes, dehydration of aldoximes, and olefination of aldehydes and ketones. Mechanisms... 

Conversion of aldoximes to nitriles. The dehydration of aldoximes to nitriles can be effected by reaction with methyl isocyanate in DMF in the presence of triethylamine to give an O-(melhylcarbamoyl) aldoxime. The carbamate decomposes at 110-120° to give the nitrile and carbon dioxide and methylaminc. Yields of nitriles are 65 99%. 

Dehydration of aldoximes. Nitriles are obtained when aldoximes are treated with TBS-Cl and imidazole in DMF. 

Nitriles. Dehydration of aldoximes with iron(III) sulfate occurs in refluxing benzene. 

Dehydration. Dehydration of aldoximes and a-amido ketones with Burgess reagent afford nitriles and oxazoles, respectively. 

Dehydration of aldoximes to nitriles. This reaction can be carried out in 90-95% yield with the reagent of Corey and Kim in acetonitrile followed by addition of triethylamine. 

Dehydration of aldoximes to nitriles is an important transformation in organic synthesis. Most of the classical methods of dehydration required an excess of solvents and the catalyst remains as a waste (78S702, 80S659). However, zeohtes or clay are reported as reusable catalysts but they required harsh reaction conditions and longer reaction time (92S943). Recently, nitrile 201 was isolated in 60% yield when a mixture of the aldoxime 202 and tetrachloropyridine (TCP) adsorbed on alumina in a Pyrex test tube was subjected to MWI for 4.5 min (Scheme 42). TCP represented a... 

A mixture of a dialkyl hydrogen phosphonate, triethylamine, and carbon tetrachloride is very effective for dehydration of aldoximes (46). The actual reagent is formed by the deprotonation of the phosphonate (phosphite... 

Efficient methods for the synthesis of nitriles by dehydration of aldoximes and primary amides have been developed. " The reactions were performed in the presence of a Lewis acid ionic liquid, a uranium, or a copper catalyst. 

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