Organocatalyst Efficiency in the α-Aminoxylation and α-Hydrazination of Carbonyl Derivatives in Aqueous Media or in a Ball-Mill

Pyrrolidine-derived organocatalysts have been tested in two types of alpha-heterofunctionalization reactions in aqueous media or under solvent-free ball-milling conditions. The best results in terms of both activity and enantioselectivity were obtained with O-silylated 4-hydroxyproline derivatives in the alpha-aminoxylation reaction between n-butyraldehyde and nitrosobenzene (83 % yield in water, 86 % yield by ball milling and ee > 99 %). A very good yield (82 %) and excellent optical purity (ee > 99 %) were also achieved in the alpha-hydrazination reaction of 3-phenylpropanal with dibenzyl azodicarboxylate by the ball-milling technique.