Organocatalytic Baylis-Hillman Reaction in Non-conventional Solvents

4 Organocatalytic Baylis-Hillman Reaction in Non-conventional Solvents 

A more elaborate molecular design is at the basis of a solvent-less reaction protocol. The ionic-tagging strategy, combined with the installation of a 

One arm of the imidazolium scaffold contains the catalytic centre, a bridgehead nitrogen atom that possesses the required nucleophilicity, and the second arm contains a primary alcohol capable of speeding up the critical proton transfer step that leads to the P-ammonium enolate intermediate, the direct precursor of the final Baylis-Hillman product. The reaction of aliphatic and aromatic aldehydes with acrylates is carried out under solvent free conditions at room temperature, affording 80-95% yields of adducts after 8-12 h at rt. Moreover, catalyst 34 can be readily recovered from the reaction mixture and reused at least six times without significant loss of catalytic activity. 

In an important achievement Vo-Thanh and co-workers realized that chiral ionic liquids such as 35 can act as chiral inducers for the asymmetric MBH reaction.The V-octyl-V-methylephedrinium trifluoromethanesulfonate salt 35, used as solvent in the DABCO-mediated reaction of methyl acrylate and benzaldehyde, produced the corresponding allylic alcohol in 60% yield and 44% ee after 7 days at 30 °C. 

---