Enantioselective Morita-Baylis-Hillman reaction promoted by L-threonine-derived phosphine-thiourea catalysts

A series of bifunctional phosphine-thiourea organic catalysts based on natural amino acid scaffolds were designed and prepared. L-threonine-derived bifunctional phosphine catalysts were found to be very efficient in promoting asymmetric Morita-Baylis-Hillman (MBH) reaction of acrylates with aromatic aldehydes, affording the desired MBH adducts with up to 90% ee. To gain mechanistic insights into the reaction, the effects of adding various additives on the MBH reaction were investigated. We propose that the hydrogen bonding interactions between the thiourea moiety of the catalyst and the enolate intermediate are crucial for the stereochemical outcome of the reaction. The method described in this report may provide a practical solution to the enantioselective MBH reaction of simple acrylates.