Bottom-Up Synthesis of Supported Thioureas and Their Use in Enantioselective Solvent-Free Aza-Henry and Michael Additions

Two sets of supported chiral thioureas, which differ in the length of the tether that connects the chiral appendage to the polymer structure and the effective functionalization, have been prepared by copolymerization of styrene, novel styryl thioureas derived from l-valine, and divinylbenzene. The efficiency of these polymeric thioureas has been tested in two different enantioselective transformations, namely, aza-Henry and nitro-Michael reactions, in neat reaction conditions. The obtained results show that it is possible to recycle the thiourea, and they are able to promote the reactions with good enantioselectivity at a low catalyst loading.