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Synlett 2004(14): 2633-2635  
DOI: 10.1055/s-2004-832842
LETTER
© Georg Thieme Verlag Stuttgart · New York

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

Antonio Procopio*a, Renato Dalpozzob, Antonio De Ninob, Monica Nardib, Giovanni Sindonab, Antonio Tagarellib
a Dipartimento di Scienze Farmaco-Biologiche, Università della Magna Graecia, Complesso Ninì Barbieri, 88021 Roccelletta di Borgia (Cz), Italy
Fax: +39(096)1391143; e-Mail: procopio@unicz.it;
b Dipartimento di Chimica, Università della Calabria, Ponte Bucci, cubo 15C, 87036 Arcavacata di Rende (Cs), Italy
Further Information

Publication History

Received 22 April 2004
Publication Date:
24 September 2004 (online)

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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.

Key words

catalysis - epoxides - Erbium triflate - Lewis acid - rearrangements

4

For example, in bench-top MeCN after 48 h, only 38% yield of 2a was detected with Ce(OTf)3, with phenylethanediol as the major product (57%).

5

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).

6

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%.

13

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).

14

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