A novel calix[4]arene-based bifunctional squaramide organocatalyst for enantioselective Michael addition of acetylacetone to nitroolefins

Abstract

A new chiral calix[4]arene-based organocatalyst 3 bearing bis-squaramide moieties was designed and synthesized from p-tert-butylcalix[4]arene. This bifunctional organocatalyst was used in the enantioselective conjugate addition of acetyl acetone to β-nitrostyrenes. The corresponding adducts were obtained in good to excellent yields with high enantioselectivities.

Recent Advances in Asymmetric Organocatalyzed Conjugate Additions to Nitroalkenes

“…Thus, catalyst 107 , bearing a thiourea moiety was employed for the enantioselective addition of 1,3-diketones and malonates to nitroolefins, achieving moderate to high yields and enantioselectivities of the final adducts [ 125 ]. Similar results were obtained for the addition of 1,3-diketones when catalyst 108 , bearing a squaramide moiety in its structure was used [ 126 ].…”

Recent applications of chiral calixarenes in asymmetric catalysis

“…Therefore, it would be interesting to investigate the application of chiral calixarene-based squaramides in asymmetric catalysis. Recently, a novel chiral organocatalyst based on the calix[4]arene scaffold carrying squaramide and tertiary amine as catalytic functionalities has been readily developed in two steps from p-tert- butylcalix[4]arene diamine 60 in our lab [ 58 ]. Accordingly, dimethyl squarate 61 was stirred with p-tert -butylcalix[4]arene diamine 60 in CH 2 Cl 2 to give squarate 62 .…”

Recent Advances in Organocatalytic Asymmetric Michael Addition Reactions to α, β‐Unsaturated Nitroolefins

“…However, OMe-substituted nitroolefins were slowed down the reactivity of the reaction providing a lower yield and ee of 159 (Scheme 42). [90] Scheme 48. Organocatalytic asymmetric conjugate addition of 2-fluoro-1, 3-diketones to nitroalkenes.…”