Enantioselective Synthesis of Chiral Ferrocenyl Aminoalcohols: Simultaneous Induction of Multiple Types of Chirality by a Rhodium-Catalyzed Asymmetric Ring-Opening Strategy

Abstract

Chiral ferrocenyl aminoalcohols were enantioselectively synthesized via the rhodium-catalyzed asymmetric aminative ring-opening of 1,4-epoxy-1,4-dihydronaphthalenylferrocenes. A planar chiral phosphine-olefin ligand consisting of a cyclopentadienyl (Cp) manganese scaffold provided excellent catalytic performance, furnishing the ring-opening products in high yield and enantioselctivity (up to 99 : 1 enantiomeric ratio (e.r.)). The enantioselectivity could be further improved by changing the steric congestion in the cyclopentadienyl unit of the ferrocenyl fragment of the starting 1,4-epoxy-1,4-dihydronaphthalenylferrocene. Density functional theory (DFT) calculations confirmed the high enantioselective induction in the ring-opening reaction, estimating an e.r. of 99 : 1, which is in excellent agreement with the experimental results. The application of the thus obtained chiral ferrocenyl aminoalcohols as ligands in asymmetric reactions was also investigated.