Due to using (R)‐ or (S)‐α‐methylbenzylamine as a chiral auxiliary, and low‐temperature regime for reduction of the intermediate ferrocenyl‐mono‐ or 1,1′‐bis‐ketimines, the corresponding secondary mono‐ or 1,1′‐bis‐amines were prepared with high diastereoselectivity. Removal of the α‐methylbenzyl group afforded the opticallyactive primary mono‐ and bis‐ferrocenylethylamines in high yields. The absolute
efficient, metal-free highly stereoselective reduction of ketimines to chiralamines was developed. Different imines bearing a very cheap and removable chiral auxiliary were reduced simply by trichlorosilane in the presence of N,N-dimethyl-formamide, often in quantitative yield and complete control of the absolute stereochemistry, to afford highly enantiomerically enriched amines.
Highly Stereoselective Metal-Free Catalytic Reduction of Imines: An Easy Entry to Enantiomerically Pure Amines and Natural and Unnatural α-Amino Esters
A highly efficient catalytic stereoselective ketimine reduction is described. The combination of an inexpensive chiral organocatalyst, easily prepared in a single step, and of a very cheap removable chiral auxiliary allowed us to obtain enantiomerically pure amino compounds. The methodology allowed synthesis of chiral secondary and primary amines and natural and unnatural amino esters in high yields often with total control of the absolute stereochemistry.