LETTER
Erbium Triflate as Catalyst for Epoxide Rearrangement
2635
(3) (a) Bartoli, G.; Dalpozzo, R.; De Nino, A.; Maiuolo, L.;
Nardi, M.; Procopio, A.; Tagarelli, A. Green Chem. 2004, in
press. (b) Bartoli, G.; Dalpozzo, R.; De Nino, A.; Maiuolo,
L.; Nardi, M.; Procopio, A.; Tagarelli, A. Eur. J. Org. Chem.
2004, in press. (c) Bartoli, G.; Dalpozzo, R.; De Nino, A.;
Maiuolo, L.; Nardi, M.; Procopio, A.; Tagarelli, A. Synthesis
2004, 496. (d) Dalpozzo, R.; De Nino, A.; Maiuolo, L.;
Nardi, M.; Procopio, A.; Romeo, R.; Bartoli, G. Tetrahedron
Lett. 2003, 44, 5621. (e) Dalpozzo, R.; De Nino, A.;
Maiuolo, L.; Procopio, A.; Tagarelli, A.; Sindona, G.;
Bartoli, G. J. Org. Chem. 2002, 67, 9093. (f) Bartoli, G.;
Cupone, G.; Dalpozzo, R.; De Nino, A.; Maiuolo, L.;
Procopio, A.; Sambri, L.; Tagarelli, A. Tetrahedron Lett.
2002, 43, 5945.
The formation of a carbocation intermediate is also sup-
ported by the rearrangement of limonene oxide. Both iso-
mers led to similar mixtures of the rearranged products.
Moreover, both 13C NMR and 1H NMR spectra of the ke-
tones arising from the two reactions are super-imposable
and in agreement with formation of trans-3f.13 If the
rearrangement is a concerted process, two isomers should
be obtained (Scheme 1).
Er2+
O
O
O
H
(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%).
OEr2+
trans–3f
(5) Typical Procedure: A solution of the epoxide (1 mmol) in
CH2Cl2 (3 mL) was stirred at r.t. as Er(OTf)3 (1 mmol) 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 a-pinene oxides required
purification by preparative TLC (eluent CHCl3–MeOH,
9:1).
trans–3f
trans–1f
Er2+
H
O
O
O
cis–3f
cis–1f
Scheme 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%.
(7) Russel, P. B.; Csendes, E. J. J. Am. Chem. Soc. 1954, 76,
5714.
(8) Settine, R. L.; Parks, G. L.; Hunter, L. K. J. Org. Chem.
1964, 29, 616.
(9) (a) Cis and trans: Maestro, M. A.; Castedo, L.; Mourino, A.
J. Org. Chem. 1992, 57, 5208. (b) See also: Hua, D. H.;
Venkataraman, S. J. Org. Chem. 1988, 53, 1095. (c) Trans
only: Gabriels, S.; van Haver, D.; Vandewalle, M.; de
Clercq, P.; Viterbo, D. Eur. J. Org. Chem. 1999, 1803.
(d) See further: Ohba, M.; Iizuka, K.; Ishibashi, H.; Fujii, T.
Tetrahedron 1997, 53, 16977.
The rearrangement a-pinene oxide leads to campholenic
aldehyde 2g (Table 2, entry 8), the key intermediate in the
synthesis of naturanol,14 in very high yields (only less than
10% of carveol was detected by GC/MS).
In conclusion, erbium triflate is a very useful catalyst for
the rearrangement of epoxides to carbonyl compounds.
The advantages of this catalyst include the observed
regioselectivity, the broad applicability and easy recover-
ability.
References
(1) For reviews see: (a) Smith, J. G. Synthesis 1984, 629.
(b) Rao, A. S.; Paknikar, S. K.; Kirtane, J. G. Tetrahedron
1983, 39, 2323. (c) Parker, R. E.; Issacs, N. S. Chem. Rev.
1959, 59, 737.
(10) (a) Menwald, J.; Chapman, R. A. J. Am. Chem. Soc. 1968,
90, 3218. (b) Lopez, L.; Mele, G.; Fiandanese, V.;
Cardellicchio, C.; Nacci, R. Tetrahedron 1994, 50, 9097.
(11) Juric, S.; Kronja, O. J. Phys. Org. Chem. 2002, 15, 556.
(12) Meyer, C.; Marck, J.; Courtemanche, G.; Normant, J. F.
Tetrahedron 1994, 50, 11665.
(2) See, for example: (a) Bi(OTf)3: Bhatia, K. A.; Eash, K. J.;
Leonard, N. M.; Oswald, M. C.; Mohan, R. S. Tetrahedron
Lett. 2001, 42, 8129. (b) BiOCl4·H2O: Anderson, A. A.;
Blazek, J. M.; Garg, P.; Payne, B. J.; Mohan, R. S.
Tetrahedron Lett. 2000, 41, 1527. (c) Nafion-H: Surya
Prakash, G. K.; Mathew, T.; Krishnaraj, S.; Marinez, E. R.;
Olah, G. A. Appl. Catal. A 1999, 181, 283. (d) Fe(tpp)OTf:
Suda, K.; Baba, K.; Nakajima, S.; Takanami, T. Tetrahedron
Lett. 1999, 40, 7243. (e) [(h5-C5H5)Fe(CO)2(THF)]BF4:
Picione, J.; Mahmood, S. J.; Gill, A.; Hilliard, M.; Hossain,
M. M. Tetrahedron Lett. 1998, 39, 2681. (f) Lithium
dialkylamides: Yanagisawa, A.; Yasue, K.; Yamamoto, H.
J. Chem. Soc., Chem. Commun. 1994, 2103. (g) SbF5:
Maruoka, K.; Murase, N.; Bureau, R.; Ooi, T. O.;
Yamamoto, H. Tetrahedron 1994, 50, 3663. (h) R3SiOTf:
Jung, M. E.; Marquez, R. Tetrahedron Lett. 1999, 40, 3129.
(i) Jung, M. E.; van den Heuvel, A. Tetrahedron Lett. 2002,
43, 8169.
(13) Spectra of both 3f isomers are known9 and they are slightly
different (e.g. double-bond carbons are found at d = 147.6,
109.6 ppm and d = 146.75, 111.42 ppm and the vinyl protons
at d = 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.
Synlett 2004, No. 14, 2633–2635 © Thieme Stuttgart · New York