Asymmetric Friedel-Crafts alkylation of electron-rich N-heterocycles with nitroalkenes catalyzed by diphenylamine-tethered bis(oxazoline) and bis(thiazoline) Zn(II) complexes.
The asymmetric Friedel-Crafts alkylation of electron-rich N-containing heterocycles with nitroalkenes under catalysis of diphenylamine-tethered bis(oxazoline) and bis(thiazoline)-Zn(II) complexes was investigated. In the reaction of indole derivatives, the complex of ligand 4 f with trans-diphenyl substitutions afforded better results than previously published ligand 4 e with cis-diphenyl substitutions. Excellent yields (up to greater than 99 %) and enantioselectivities (up to 97 %) were achieved in most cases. The complex of ligand 4 d bearing tert-butyl groups gave the best results in the reactions of pyrrole. Moderate to good yields (up to 91 %) and enantioselectivities (up to 91 %) were achieved in most cases. The origin of the enantioselectivity was attributed to the NH-pi interaction between the catalyst and the incoming aromatic system in the transition state. Such an interaction was confirmed through comparison of the enantioselectivity and the absolute configuration of the products in the reactions catalyzed by designed ligands.
Liu
Han
H
Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
Lu
Shao-Feng
SF
Xu
Jiaxi
J
Du
Da-Ming
DM
D000475:Alkenes / Q000737:chemistry*; D000478:Alkylation; D002384:Catalysis; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008024:Ligands; D009574:Nitro Compounds / Q000737:chemistry*; D010080:Oxazoles; D013237:Stereoisomerism; D013844:Thiazoles
D000475:Alkenes; D006571:Heterocyclic Compounds; D008024:Ligands; D009574:Nitro Compounds; D010080:Oxazoles; D013844:Thiazoles