Dehydrations aldoximes, acetic anhydride

Oximes derived from aldehydes (aldoximes) can be dehydrated to nitriles by many different dehydrating reagents acetic anhydride is one of the most common reagents used ... 

Aldoximes can be dehydrated to nitriles by many dehydrating agents, of which acetic anhydride is the most common. Among reagents that are effective under mild... 

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). 

Some reviews on the preparation of cyanides from aldoximes [1045, 1046] and from carboxamides [1047,1048] are available. Often used dehydration reagents are acetic anhydride for aldoximes and phosphorus pentoxide for carboxamides. In the following sections, dehydration reactions affording cyanides are described with various dehydration reagents, classified into acidic and basic reagents. 

The cyanides 1408-1412 have all been synthesized by dehydrating their carbox-aldoximes with acetic anhydride [1070-1074]. A pteridine synthesis yielded 75% of 6-cyano-l,3-dimethyUumazine 1408 [1070]. N-Acetyl (3-phenyl-l,2,4-triazolo-5-yl)-thiolacetonitrile 1409 was obtained as the condensation product from a triazole derivative and chloro acetaldehyde, followed by oximation and dehydration, in 79% yield [1071]. endo-l-Cyano-3-acetoxy-8-oxabicyclo[3.2.1]oct-6-ene 1410 (89%) is an intermediate in the synthesis of ll-oxatricyclo[5.3.1.0 Jundecane [1072]. A synthesis of loi,25-dihydroxY-18-norvitamin Dj and la,25-dihydroxy-18,19-dinorvitamin Dj requires the 8j8-acetoxy-des-A,B-cholestane-18-nitrile 1411 (86%) [1073]. A new route to spirooxindoles, a tricyclic system found in a number of interesting natural products, requires the cyanide 1412 (72%) as a key intermediate [1074]. 

PROBLEM 18.47 In Section 18.12c, we saw that primary amides could be dehydrated to nitriles (cyanides) with P2O5. Nitriles can also be prepared by treating aldoximes (1) with dehydrating agents such as acetic anhydride. Propose a mechanism for the formation of benzonitrile from the reaction of 1 with acetic anhydride. How are oximes prepared ... 

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