Rearrangement of epoxides by transition metal salts in ionic liquid

Abstract

A new and efficient system for the rearrangement of aryl epoxides by nickel complexes in imidazolium ionic liquids has been developed. Types of nickel complexes, ionic liquids, reaction temperature and reaction time were optimized. The rearrangement of styrene oxide with NiBr2·3H2O and anhydrous NiBr2 in 1-hexyl-3-methylimidazolium bromide ([hmim][Br]) at 120oC for 15 min provided 76 and 84% yield of phenylacetaldehyde, respectively. Applications on the rearrangements of aryl-substituted epoxides were fruitfully achieved yielding desired products in moderate to high yield and excellent selectivity via hydride migration. The activity of the reused NiBr2.3H2O/[hmim][Br] was tested in subsequent runs without addition of fresh catalyst for five runs on α-methylstyrene oxide. However, the reuse of NiBr2.3H2O/[hmim][Br] with styrene oxide gave unsatisfactory result. Anhydrous NiBr2 could be used to solve this problem. Moreover, the aids of microwave for the rearrangement of styrene oxide with anhydrous NiBr2 in [hmim][Br] at 90 oC for 5 min provided 85% yield of the target product. Very good reusability of the recovered ionic liquid without significant loss of the activity was observed within three subsequent runs.