Remarkable Reaction Rate and Excellent Enantioselective Direct α-Amination of Aldehydes with Azodicarboxylates Catalyzed by Pyrrolidinylcamphor-Derived Organocatalysts
Remarkable reaction rate and excellent enantioselective direct α-amination of unmodified aldehydes with various azodicarboxylates was catalyzed by pyrrolidinylcamphor organo-catalyst 2a (5 mol-%) to provide the desired aminated products with excellent chemical yields and high to excellent levels of enantioselectivity (up to >99%ee) at 0 °C in CH 2 Cl 2 .
Pyrrolidine-derived organocatalysts were tested in two types of α-heterofunctionalization reactions in aqueousmedia or under solvent-free ball-milling conditions. The best results in terms both activity and enantioselectivity were obtained with O-silylated 4-hydroxyproline derivatives in the α-aminoxylation reaction between n-butyraldehyde and nitrosobenzene (83% yield for water, 86% yield for ball
The asymmetricα-amination of aldehydes was performed using a resin-supportedpeptidecatalyst. A tri- or tetrapeptide with an N-terminal D-Pro-Aib sequence efficiently catalyzed the reaction in a highly enantioselective manner. The supported catalyst could be easily recovered by filtration and reused at least ten times.