On the Mechanism of Bifunctional Squaramide- Catalyzed Organocatalytic Michael Addition: A Protonated Catalyst as an Oxyanion Hole

作者：Kotai Bianka; Kardos Gyoergy; Hamza Andrea; Farkas Viktor; Papai Imre^*; Soos Tibor

来源：Chemistry - A European Journal, 2014, 20(19): 5631-5639.

DOI：10.1002/chem.201304553

• density functional calculations
• Michael addition
• organocatalysis
• reaction mechanisms
• reaction intermediates

A joint experimental-theoretical study of a bifunctional squaramide-amine-catalyzed Michael addition reaction between 1,3-dioxo nucleophiles and nitrostyrene has been undertaken to gain insight into the nature of bifunctional organocatalytic activation. For this highly stereoselective reaction, three previously proposed mechanistic scenarios for the critical CC bond-formation step were examined. Accordingly, the formation of the major stereoisomeric products is most plausible by one of the bifunctional pathways that involve electrophile activation by the protonated amine group of the catalyst. However, some of the minor product isomers are also accessible through alternative reaction routes. Structural analysis of transition states points to the structural invariance of certain fragments of the transition state, such as the protonated catalyst and the anionic fragment of approaching reactants. Our topological analysis provides deeper insight and a more general understanding of bifunctional noncovalent organocatalysis.

• 出版日期2014-5-5