Al-NiCl2·6H2O: A mild and efficient system for selective reduction of functional groups in organic synthesis

Abstract

(A) Chemoselective reduction of α-enones: α,β-Unsaturated carbonyl compounds give saturated ketones upon treatment with Al-NiCl 2·6H2O. Aromatic aldehydes and ketones are smoothly reduced to the corresponding alcohols. Isolated double bonds, esters, aliphatic aldehydes, and ketones remain unaffected by this reagent.7 (Chemical Equation Presented) (B) Reduction of nitroarenes to amines: Sarmah et al. showed that aromatic nitro compounds are reduced to the corresponding amines efficiently under neutral and mild conditions. Short reaction times and a simple work-up procedure make this a versatile reagent.8 (Chemical Equation Presented) (C) Conversion of oxiranes into alcohols: Ring opening of the oxiranes takes place from the less hindered side of the epoxides, thereby giving the highest-substituted alcohols. An exception is the case of styrene oxide, where 1-phenyl-ethanol is the major product. α,β-Epoxy ketones remain unaffected under these reaction conditions.2 (Chemical Equation Presented) (D) Addition to electron-deficient alkenes: The Al-NiCl 2·6H2O redox couple promotes the addition of per(poly)fluoroalkyl iodides to per(poly)fluoroalkyl-substituted ethenes, giving the corresponding addition-elimination products in moderate yields.9 (Chemical Equation Presented) (E) Conversion of nitroolefins into carbonyl compounds: Saturated ketones can be obtained from nitroolefins in mild reaction conditions with Al-NiCl2·6H2O.10 (Chemical Equation Presented) (F) Synthesis towards pyrrolo[2,1-c][1,4] benzodiazepines (PBD): Employing Al-NiCl2·6H2O, many heterocyclic compounds like PBDs and dilactams can be synthesized via solid-phase reductive cyclization of nitro and azido compounds.11 (Chemical Equation Presented) (G) Facile reduction of sulfoxides to sulfides: Sulfoxides can be reduced to the corresponding sulfides within short periods of time in high yields. Interestingly, ketones are not reduced under these reaction conditions.12 (Chemical Equation Presented). © Georg Thieme Verlag Stuttgart.