Intermolecular addition of alkyl radicals to imines in the absence and in the presence of a Lewis acid

The metal-catalyzed, and metal-catalyzed enantioselective, intermolecular additions of alkyl radicals to imines have been investigated. The reaction proceeds well for imines having both activating and deactivating nitrogen substituents, and can be controlled and accelerated to a high extent by the use of Lewis acids. For imines having different carbon substituents, it has been observed that those derived from glyoxylate react much faster than those derived from 3-oxopropionate or benzaldehyde. The intermolecular radical addition can be carried out for different types of imines with alkyl and alkoxyalkyl radicals and it is demonstrated that it is possible to perform the radical addition in a catalytic enantioselective fashion with moderate yield and enantioselectivity. On the basis of the experimental results and theoretical calculations the mechanism for the radical addition to imines is discussed.