Bifunctional Thio/Squaramide Catalyzed Stereoselective Michael Additions of Aldehydes to Nitroalkenes towards Synthesis of Chiral Pyrrolidines

Abstract Bifunctional squaramide and thiosquaramide organocatalysts were assessed in a stereoselective Michael addition of aldehydes to nitroalkenes. Organocatalysts feature pyrrolidine unit for enamine activation of aldehydes and hydrogen bond donating fragment for nitroalkene activation. The corresponding Michael adducts were obtained in good yields and good to high enantiomeric purities. Solvent‐free conditions were also tested but did not provide any significant improvement. Michael adducts were transformed into chiral pyrrolidines via reductive cyclization.