Chiral <i>cis</i>-iron(<scp>ii</scp>) complexes with metal- and ligand-centered chirality for highly regio- and enantioselective alkylation of N-heteroaromatics

Abstract

Iron-catalyzed highly regio- and enantioselective organic transformations with generality and broad substrate scope have profound applications in modern synthetic chemistry; an example is herein described based on <i>cis</i>-Fe^II complexes having metal- and ligand-centered chirality. The <i>cis</i>-β Fe^II(N₄) complex [Fe^II(L)(OTf)₂] (L = <i>N</i>,<i>N</i>'-bis(2,3-dihydro-1<i>H</i>-cyclopenta-[<i>b</i>]quinoline-5-yl)-<i>N</i>,<i>N</i>'-dimethylcyclohexane-1,2-diamine) is an effective chiral catalyst for highly regio- and enantioselective alkylation of N-heteroaromatics with α,β-unsaturated 2-acyl imidazoles, including asymmetric N1, C2, C3 alkylations of a broad range of indoles (34 examples) and alkylation of pyrroles and anilines (14 examples), all with high product yields (up to 98%), high enantioselectivity (up to >99% ee) and high regioselectivity. DFT calculations revealed that the "chiral-at-metal" <i>cis</i>-β configuration of the iron complex and a secondary π-π interaction are responsible for the high enantioselectivity.