Aza-Henry Reactions on C-Alkyl Substituted Aldimines

The reactivity of C-CH₃ substituted N-protected aldimines in aza-Henry addition reactions was compared with that of the analogous trifluoromethylated compounds. C-Alkyl aldimines easily reacted with nitro alkanes under solvent-free conditions and in the absence of catalyst, despite being worse electrophiles than C-CF₃ aldimines, they gave the aza-Henry addition only when ZrCl₄ was added. The presence of a bulky group on the imine carbon deeply influenced the reactivity.