Addition to imines, iminium salts and related compounds

1 ADDITION TO IMINES, IMINIUM SALTS AND RELATED COMPOUNDS 

On the other hand, benzophenone imines undergo addition only under forcing conditions, to give products such as (1) resulting from attack at a ring [5]. 

Imines may be activated by complexation with Lewis acids, but this also increases the acidity of a-hydrogen atoms. A combination of copper(i) halide and boron trifluoride etherate is a possible solution to the problem [6, 7]. Activation by trimethylsilyl triflate is also effective with aldimines (though not with ketimines) [7, 8]. 

It should be noted that in cases where the stereochemistry of the addition is dependent on chelation control, the presence of Lewis acids may profoundly influence the selectivity, e.g. [9]. 

The above additions to activated imines presumably involve iminium salt/complex intermediates. Addition to preformed iminium salts can also be effective, as in the examples given here. 

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