Direct Synthesis of Chiral 3-Arylsuccinimides by Rhodium-Catalyzed Enantioselective Conjugate Addition of Arylboronic Acids to Maleimides

Chiral rhodium catalysts comprising 2,5-diaryl- substituted bicyclo[2.2.1]diene ligands L1-L10 were utilized in the enantioselective 1,4-addition reaction of arylboronic acids to N-substituted maleimides. In the presence of 2.5mol % of Rh^I/L2, enantioenriched conjugate addition adducts were isolated in 72-99 % yields with 86-98 %ee. This protocol offers a convenient method to access a variety of 3-arylsuccinimides in a highly enantioselective manner. Maleimides with readily cleavable N-protecting groups were tolerated enabling the synthesis of useful synthetic intermediates. Pyrrolidine 4, a biologically active compound, and pyrrolidine 5, an ent-precursor to an HSD-1 inhibitor, were synthesized to demonstrate the utility of this method. The road to rhodium! Enantioselective conjugate addition of a range of arylboronic acids to variously N-substituted maleimides, catalyzed by Rh^I complexes prepared in situ using chiral bicyclo[2.2.1]diene ligands, afforded the corresponding 3-arylsuccinimides with up to 98 %ee at 50 C (see scheme).