Erbium(III) Triflate: A Valuable Catalyst for the Rearrangement of Epoxides to Aldehydes and Ketones

Abstract

Rearrangement of epoxides is performed with erbium ­triflate as catalyst. In contrast to most proposed catalysts for this reaction, erbium triflate works well with both aromatic and aliphatic epoxides.

catalysis - epoxides - Erbium triflate - Lewis acid - rearrangements

References

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<A NAME="RG13704ST-5">5</A>

Typical Procedure: A solution of the epoxide (1 mmol) in CH₂Cl₂ (3 mL) was stirred at r.t. as Er(OTf)₃ (1 µmol) was added. Rearrangements of aliphatic epoxides were carried out under reflux conditions. The reaction was monitored by GC/MS. At the time reported in Table [2] , the starting material was completely consumed. The reaction was poured into H₂O, extracted twice with CH₂Cl₂, dried over Na₂SO₄ and evaporated under reduced pressure. Both NMR and elemental analyses of the residue showed the products to be >98% pure. Only limonene and α-pinene oxides required purification by preparative TLC (eluent CHCl₃-MeOH, 9:1).

<A NAME="RG13704ST-6">6</A>

After reaction workup, the aqueous phase can be evaporated under reduced pressure to furnish the erbium salt in 90% recovered yield, as a pale pink solid. After drying over P₂O₅ overnight, the recovered catalyst was reused five times in the rearrangement of 1a, with recovered yields of 2a always over 90%.

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Spectra of both 3f isomers are known [9] and they are slightly different (e.g. double-bond carbons are found at δ = 147.6, 109.6 ppm and δ = 146.75, 111.42 ppm and the vinyl protons at δ = 4.76, 4.73 and 4.83, 4.70 ppm in trans-3f and cis-3f, respectively).

<A NAME="RG13704ST-14">14</A>

Naturanol is a natural product of great importance in the perfume industry.