| Abstract: | Meerwein recommended nitrilium salts ( 2 ) as catalysts for the Beckmann rearrangement of oximes ( 1 ) under neutral and water-free conditions. For the first time, primary adducts (Z)–( 3 ) of oximes to nitrilium salts have been isolated. Reported are activation energies for Beckmann rearrangements of these adducts, and an X-ray structural analysis of (Z)– 3a . Rearrangement of 3 produces mixtures of up to four different N-acylamidinium salts 5 – 8 , which arise from fast reactions of primary-formed secondary amides ( 4 ) with nitrilium salts ( 2 ). Because of their ambident electrophilic character the N-acylamidinium salts react with excess of oxime not only to amides ( 4 ) but to mixtures of products. It is shown that nitrilium salts cannot be used as catalysts for the Beckmann rearrangement. |
