From nitrilium salts and nitriles under

C—C—O+N—C. a-Hydroxy ketones react with monosubstituted cyanamides under the influence of sodium hydroxide to yield derivatives of 2-aminooxazole (equation 125) (76S591). Oxazoles are obtained by the action of nitriles on a-diazo carbonyl compounds in the presence of Lewis acids, such as aluminum chloride or boron trifluoride, and the reaction is thought to involve the intermediacy of nitrilium salts (equation 126). Nitrilium salts are also the effective agents in the formation of oxazoles from a-chloro ketones and nitriles in the presence of tin(IV) chloride (equation 127). 

A nitrilium ion E or an imidate derivative G is formed as an intermediate. Their hydrolysis leads either to the formation of amide H or, in the case of nitrihum ion E, to nitrile F by fragmentation and formal loss of a carbocation. Under particular conditions nitrilium salts E derived from special substrates can be isolated [356]. 

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