A C3‐Symmetric Diphenylethylendiamine‐Based Catalyst in the Asymmetric Michael Addition of α,β‐Unsaturated Ketones with 4‐Hydroxycoumarin and 4‐Hydroxyquinolin‐2‐One

Two C₃-symmetric organocatalysts with multiple amino groups are prepared and employed in the asymmetric addition of 4-hydroxycoumarin and quinoline-2-one to unsaturated ketones. The all-amino version of the catalyst induces the better stereoselectivity and provides the products in up to 95% yield. A successful gram-scale reaction and catalyst reuse (three-fold) attest to the potential of the C₃-symmetric catalyst.

Even though the amino-organocatalysis has been known for decades, the use of chiral C₃-symmetric multiamino catalysts in asymmetric synthesis is not widespread. Herein, the previously employed approach for the chiral 1,2-diamino-cyclohexane to the enantiopure 1,2-diphenylethylendiamine is extended. The independent activity of each catalytic subunit is also confirmed for this enantiopure motif by offline high-resolution electrospray mass spectrometry (ESI-MS) experiments. The advantages and limitations of this novel approach in the asymmetric Michael addition of α,β-unsaturated ketones to 4-hydroxycoumarin and 4-hydroxyquinolin-2-one, achieving up to 95% yield and moderate-to-good stereocontrol (enantiomeric ratio up to 80:20) are evaluated. In the pool of synthetized molecules, there are two novel compounds, and one is prepared for the first time using organocatalysis. In addition, some of these molecules show an intrinsic scavenging ability on ABTS^•+ radical.

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