Asymmetric Construction of 3,4-Diamino Pyrrolidines via Chiral N,O-Ligand/Cu(I) Catalyzed 1,3-Dipolar Cycloaddition of Azomethine Ylides with β-Phthalimidonitroethene.

A series of chiral N,O-ligands derived from a 1,2-dihydroimidazo[1,2-a]quinolone motif have been evaluated for the asymmetric 1,3-dipolar cycloaddition of azomethine ylides with a novel dipolarophile β-phthalimidonitroethene. A newly designed DHIPOH ligand 7c bearing 1-methyl and 4-iodo substituents was found to have significant "synergistic steric effects" and consequently afforded the corresponding 4-nitro-3-aminopyrrolidines with excellent diastereo- (dr up to 98:2) and enantio selectivities (ee up to 99%). Subsequent Raney Ni-catalyzed reduction and deprotection of phthalyl led to the structurally and biologically important 3,4-diaminopyrrolidines in a straightforward and efficient pathway.