Synthesis of chiral polyurethanes of cinchona alkaloids for the enantioselective synthesis in asymmetric catalysis

Synthesis of Crosslinked Chiral Polysiloxanes of Cinchona Alkaloid Derivatives and their Applications in Asymmetric Catalysis

“…With the ability of poly(methylhydrosiloxane) to function as scaffold for C6′−OH free cinchona alkaloid immobilization established in this work, it became a priority to improve its scope to the use of dimeric structures. We then used cinchona alkaloid dimers CPN2 , as crosslinking agent of poly(methylhydrosiloxane) ( KF‐99 ). Cinchona dimers CPN2 possess two vinyl group at both C3 positions in its molecule.…”

“…In all cases, regardless of insolubility of gel type catalysts, the heterogeneous reaction occurred smoothly with these catalysts to give the corresponding chiral product 5 in good yields. The C6′−OH in cinchona derived organocatalysts is an essential functionality to induce high level of enantioselectivity in the asymmetric Michael addition of anthrone and β‐nitrostyrene ,,. The crosslinked gel type chiral polysiloxane PSiBzQN having C6′−OMe showed poor enantioselectivity of 11% ee (entry 1).…”

“… [a] All reaction were performed with β‐ketoester 6 (0.50 mmol), β‐nitrostyrene 4 (0.60 mmol) in CH 2 Cl 2 (2.5 mL) at room temperature for the formation of 7 diastereomers . [b] Isolated yield of the product.…”

“…Cinchona alkaloid esters and urethanes derivatives were prepared according to experimental procedures reported in our previous works ,…”

“…Asymmetric Michael addition reactions with crosslinked gel type chiral polysiloxanes of cinchona alkaloid derivatives as catalysts were carried out according to experimental procedures in the literatures –. General detailed procedure for asymmetric reaction is available in supporting information.…”