Phosphoramidite-Cu(OTf)2 Complexes as Chiral Catalysts for 1,3-Dipolar Cycloaddition of lminoesters and Nitroalkenes

Chiral complexes formed by phosphoramidites such as (S-a,R,R)-9 and Cu(OTf)(2) are excellent catalysts for the general 1,3-dipolar cycloaddition between azomethine ylides and nitroalkenes affording the corresponding tetrasubstituted proline esters mainly as exo-cycloadducts in high er at room temperature. The exo-cycloadducts can be obtained in enantiomerically pure form just after simple recrystallization. DFT calculations support the stereochemical results.