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.