Scope and mechanism of enantioselective Michael additions of 1,3-dicarbonyl compounds to nitroalkenes catalyzed by nickel(II)-diamine complexes.
Readily prepared Ni(II)-bis[(R,R)-N,N'-dibenzylcyclohexane-1,2-diamine]Br(2) was shown to catalyze the Michael addition of 1,3-dicarbonyl compounds to nitroalkenes at room temperature in good yields with high enantioselectivities. The two diamine ligands in this system each play a distinct role: one serves as a chiral ligand to provide stereoinduction in the addition step while the other functions as a base for substrate enolization. Ligand modification within the catalyst was also investigated to facilitate the reaction of aliphatic nitroalkenes, 1,3-diketones, and beta-ketoacids. Ni(II)-bis[(R,R)-N,N'-di-p-bromo-benzylcyclohexane-1,2-diamine]Br(2) was found to be an effective catalyst in these instances. Furthermore, monodiamine complex, Ni(II)-[(R,R)-N,N'-dibenzylcyclohexane-1,2-diamine]Br(2), catalyzed the addition reaction in the presence of water. The proposed model for stereochemical induction is shown to be consistent with X-ray structure analysis.
Evans
David A
DA
Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138, USA. evans@chemistry.harvard.edu
Mito
Shizue
S
Seidel
Daniel
D
D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D003959:Diamines / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D009532:Nickel / Q000737:chemistry*; D009574:Nitro Compounds / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D013237:Stereoisomerism
D000475:Alkenes; D003959:Diamines; D007659:Ketones; D008024:Ligands; D009574:Nitro Compounds; D009942:Organometallic Compounds; D009532:Nickel