Reusable Chiral Dicationic Chromium(III) Salen Catalysts for Aminolytic Kinetic Resolution of trans-Epoxides

A series of new recyclable chiral dicationic chromium(III) salen complexes 1-10 bearing different substituents, viz., hydrogen, methyl, tert-butyl, triphenylphosphinomethyl, triethylaminomethyl, methylimidazolium, methylpyridinium, methyl-N,N-dimethylpyridinium at the 3,3'-and 5,5'-positions of the salen unit with (1S,2S)-(+)-1,2-diaminocyclohexane, (1S,2S)-(-)-1,2-diphenyl-1,2-diaminoethane, and (S)-(-)-1,1'-binaphthyl-2,2'-diamine collars have been synthesized and characterized by various physico-chemical methods. These complexes were used as catalysts for the highly enantioselective aminolytic kinetic resolution of racemic trans-epoxides with different anilines as nucleophiles at room temperature. With the use of catalyst 3, anti-beta-amino alcohols were obtained in excellent yields (> 99% with respect to the nucleophile) and enantioselectivities (ee > 99%) with the concomitant recovery of corresponding epoxides in high optical purity (ee up to > 99%) and quantitative yields in 12 h. The catalyst 3 is recyclable in the aminolytic kinetic resolution process and worked well up to six cycles with retention of enantioselectivity.