Additions to A-Acyl Iminium Ions

Even more reactive C=N bonds are present in N-acyliminium ions.202 

Gas phase reactivity toward allyltrimethylsilane was used to compare the reactivity of several cyclic A-acyliminium ions and related iminium ions.203 Compounds with endocyclic acyl groups were found to be more reactive than compounds with exocyclic acyl substituents. Five-membered ring compounds are somewhat more reactive than six-membered ones. The higher reactivity of the endocyclic acyl derivatives is believed to be due to geometric constraints that maximize the polar effect of the carbonyl group. 

A-Acyliminium ions are usually prepared in situ in the presence of a potential nucleophile. There are several ways of generating acyliminium ions. Cyclic examples can be generated by partial reduction of imides.204 

Various oxidations of amides or carbamates can also generate acyliminium ions. An electrochemical oxidation forms a-alkoxy amides and lactams, which then generate 

Reactions of Carbon Nucleophiles with Carbonyl Compounds 

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