A secondary amine by reductive amination

N-Benzylcyclohexylamine could be disconnected into cyclohexylamine and benzyl bromide, but the alkylation of amines usually continues to the tertiary amine and the ammonium salt. An FGI mentally converts it into the imine, whose C=N bond disconnects into cyclohexanone and benzylamine.

In the synthesis, the ketone and the amine form the imine in methanol at slightly acidic pH, and sodium cyanoborohydride, which reduces the iminium ion much faster than the ketone, converts it into the amine in the same vessel. Sodium triacetoxyborohydride is a cyanide-free alternative.