Recent contributions from the Baylis-Hillman reaction to organic chemistry

Enantioselective Morita-Baylis-Hillman reaction of isatins with acrylates: facile creation of 3-hydroxy-2-oxindoles

The first tertiary amine catalyzed enantioselective Morita-Baylis-Hillman (MBH) reaction of isatins with acrylates has been demonstrated, allowing asymmetric synthesis of biologically significant 3-substituted-3-hydroxy-2-oxindoles in good yields and with excellent enantioselectivities. The C6'-OH group of β-isocupreidine (β-ICD) is believed to facilitate the key proton transfer step in the MBH reaction, via an intramolecular proton relay process.

A unified mechanistic view on the Morita-Baylis-Hillman reaction: computational and experimental investigations

The thermodynamic properties and reaction mechanism of the Morita-Baylis-Hillman (MBH) reaction have been investigated through experimental and computational techniques. The impossibility to accelerate this synthetically valuable transformation by increasing the reaction temperature has been rationalized by variable-temperature experiments and MP2 theoretical calculations of the reaction thermodynamics. An increase in temperature results in a switching of the equilibrium to the reactants occurring at even moderate temperature levels. The complex reaction mechanism for the MBH reaction has been investigated through an in-depth analysis of the suggested alternative pathways, using the M06-2X computational method. The results provided by this theoretical approach are in agreement with all the experimental/kinetic evidence such as reaction order, acceleration by protic species (methanol, phenol), and autocatalysis. In particular, the existing controversy about the character of the key proton transfer in the MBH reaction (Aggarwal versus McQuade pathways) has been resolved. Depending on the specific reaction conditions both suggested pathways are competing mechanisms, and depending on the amount of protic species and the reaction progress (early or late stage) either of the two mechanisms will be favored.