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Highly Enantioselective Catalytic Allylboration of Ketiminoesters: Practical and Scalable Synthesis of α-Fully-Substituted Amino Esters
preprintsubmitted on 23.07.2019, 16:16 and posted on 24.07.2019, 12:11 by Urmibhusan Bhakta, Padmanabha V. Kattamuri, Juha H. Siitonen, Lawrence B. Alemany, Laszlo Kurti
We report the first catalytic enantioselective allylboration of α-ketiminoesters to afford chiral α-allyl-α-aryl and α-allyl-α-trifluoromethyl amino esters in excellent isolated yields and with high optical purity. This operationally simple allylation proceeds under ambient conditions with indium(I)-iodide/BOX-type ligand (5–10 mol%) and can be performed on a gram scale. A proposed qualitative model for the high stereoselectivity indicates that the origin of selectivity is likely due to attractive interactions between the substrate and the BOX ligand. Using a different BOX-type ligand reverses the reaction’s absolute sense of enantioselectivity. The allylated products are easily converted to enantiomerically enriched α-substituted proline derivatives.