Improved Synthesis of beta-Arninoboronate Esters via Copper-Catalyzed Diastereo- and Enantioselective Addition of 1,1-Diborylalkanes to Acyclic Arylaldimines

摘要

We describe herein an improved and scalable procedure to achieve the copper-catalyzed diastereo- and enantioselective 1,2-addition of 1,1-diborylalkanes to N-protected acyclic arylaldimines. We find that the installation of an N,N-dimethylsulfamoyl-group as N-protecting group in acyclic arylaldimines allows the 1,2-addition reaction to proceed with good-to excellent diastereoselectivity and enantioselectivity, thus providing beta-aminoboronate esters bearing vicinal chiral secondary amines and secondary boronate esters in good yields. The reaction can be easily scaled up to gram scale (3.25 g), highlighting the usefulness of the developed process. Synthetic applications whereby the obtained beta-aminoboronate ester is converted to other enantioen-riched compounds are also demonstrated.