Stereoselective Reducing Complexes Supported in Solid Phase: Preparation and Reactivity Study

Abstract

Twelve new chiral chelating resins have been prepared using solid phase organic synthesis with the Merrifield and Wang resins and the bidentate amine 1,2-ethylenediamine, followed by the coupling of asymmetric ketones such as 1-phenyletanone, 4-methyl-2-pentanone 4-nitroacetophenone and 4-methoxyacetophenone to form prochiral imines. The enantioselective reduction with borane and (R)-(+)-2-Methyl-CBS-oxazaborolidine leads to the chiral resins with yields greater than 86%. We used these chiral resins to prepare 24 reducing complexes with alkali tetrahydroborates in a very simple way giving yields greater than 87%. Finally, we achieved a preliminary enantioselective reduction of acetophenone employing the Merrifield's chiral chelating resins obtaining the corresponding S alcohol in a 70:30 ratio with the R analog alcohol.