Bifunctional organocatalysts based on a carbazole scaffold for the synthesis of the Hajos–Wiechert and Wieland–Miescher ketones
摘要:
Several bifunctional organocatalysts based on a carbazole scaffold containing a chiral amine and a synthetic oxyanion-hole have been synthesized and successfully applied to the synthesis of the Hajos-Wiechert and Wieland-Miescher ketones (up to 99% ee). Both enamine activation and H-bonding donor ability of these catalysts were evaluated by preparing catalysts differing in the nature of the amine [(R,R)-cyclohexanediamine or L-proline], the H-bond donor functional group (sulfonamide or amide) and the number of NH bonds. Modeling studies and an X-ray structure fully support the obtained results. (C) 2015 Elsevier Ltd. All rights reserved.