Catalytic Enantioselective Addition of Nitro Compounds to Imines-A Simple Approach for the Synthesis of Optically Active #beta#-Nitro-#alpha#-Amino Esters

摘要

The development of C-C bond-forming reactions that create two new stereogenic centers with high diastereo- and enantioselectivity in a single step can open new routes to highly valuable optically acrive compounds. The catalytic enantioselective addition to imines~[1] belongs to this class of important reactions, and recently new catalytic asymmetric processes, for example, for Mannich-type,~[2] ene,~[3] allylation and alkylation,~[4] aza-Diels-Alder,~[5] Strecker,~[6] and aromatic electrophilic substitution reactions~[7] have appeared. Another important reaction of imines is a powerful C-C bond-forming method that leads to 2-nitroamines.~[8] To the best of our knowledge there is only one other paper that describes the catalytic enantioselective version of the nitro-Mannich reaction.~[9] Although this reaction was catalyzed by a hetero-bimetallic complex, it has been described for nitromethane only and requires 60 mol% of the chiral ligand. In a very recent paper, we described the first catalytic asymmetric reaction of silyl nitronates with imines.~[10] The reaction proceeds at - 100deg C in the presence of bisoxazoline - copper catalysts to give 2-nitroamines eith high enantioselectivities.