Asymmetric organocatalytic Michael addition/aza-cyclization coupled with sequential Michael addition for synthesizing densely polycyclic-fused dihydroquinolines

Enantioselective Synthesis of Chiral 1,4-Dihydroquinolines via Iridium-Catalyzed Asymmetric Partial Hydrogenation of Quinolines

Chiral 1,4-dihydroquinolines are frequently found in natural products and pharmaceuticals, yet a generally useful route for their synthesis remains elusive. Here, we present an asymmetric partial hydrogenation strategy to access enantioenriched 1,4-dihydroquinolines from quinolines. Our strategy involves incorporating an ester group at position 3 of the quinoline ring, thereby enhancing the electronic deficiency and polarity of the C3-C4 double bond. Employing a chiral Ir-SpiroPAP catalyst facilitated the hydrogenation of a wide variety of 4-substituted 3-ethoxycarbonylquinolines, yielding chiral 1,4-dihydroquinolines in high yields (up to 95%) with exceptional enantioselectivity and efficiency (up to 99% ee and 1840 TONs). Noteworthy for its scalability and practicality, the method provides a robust avenue for the synthesis of valuable compounds such as 9-aryl aza-podophyllotoxins and melatonin MT2 receptor modulators. Density functional theory calculations were performed to gain insights into the reaction mechanism and the origins of the enantioselectivity.

Organocatalytic Enantioselective Synthesis of Polycyclic Benzosultams from 2-Amino-β-nitrostyrenes with Cyclic N-Sulfonyl Ketimines

A highly efficient enantioselective [4 + 2] cycloaddition of 2-amino-β-nitrostyrenes with cyclic N-sulfonyl ketimines has been developed. This reaction utilizes an organocatalytic approach, employing a multiple-hydrogen-bonding bifunctional squaramide-based catalyst. The process allows for the precise synthesis of chiral polycyclic benzosultams, showcasing intricate structures that incorporate chiral quaternary centers. Noteworthy outcomes of this method include high yields with excellent enantioselectivities and diastereoselectivities (up to 97% yield, 96% ee, and >20:1 dr).

Asymmetric synthesis of 2,3-disubstituted indolines via an organocatalytic intramolecular Michael addition

An asymmetric synthesis of 2,3-disubstituted indolines has been developed via an organocatalytic intramolecular Michael addition.