Bismuth(III) oxide perchlorate promoted rearrangement of epoxides to aldehydes and ketones

Article abstract of DOI:10.1016/S0040-4039(99)02330-8

Aryl-substituted epoxides and aliphatic epoxides with a tertiary epoxide carbon undergo smooth rearrangement in the presence of 10-50 mol% bismuth(III) oxide perchlorate, BiOClO₄·XH₂O, to give carbonyl compounds. The rearrangement is regioselective with aryl substituted epoxides and a single carbonyl compound arising from cleavage of benzylic C-O bond is formed. BiOClO₄·XH₂O is relatively non-toxic, insensitive to air and inexpensive, making this catalyst an attractive alternative to more corrosive and toxic Lewis acids such as BF₃·Et₂O or INCl₃ currently used to effect epoxide rearrangements. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(99)02330-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 1527–1530
Bismuth(III) oxide perchlorate promoted rearrangement of
epoxides to aldehydes and ketones
Andrew M. Anderson, Jesse M. Blazek, Parie Garg, Brian J. Payne and Ram S. Mohan ∗
Department of Chemistry, Illinois Wesleyan University, Bloomington, IL 61701, USA
Received 1 December 1999; accepted 15 December 1999
Abstract
Aryl-substituted epoxides and aliphatic epoxides with a tertiary epoxide carbon undergo smooth rearrangement
in the presence of 10–50 mol% bismuth(III) oxide perchlorate, BiOClO4·×H2O, to give carbonyl compounds.
The rearrangement is regioselective with aryl substituted epoxides and a single carbonyl compound arising
from cleavage of benzylic C–O bond is formed. BiOClO4·×H2O is relatively non-toxic, insensitive to air and
inexpensive, making this catalyst an attractive alternative to more corrosive and toxic Lewis acids such as BF3·Et2O
or InCl3 currently used to effect epoxide rearrangements. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: bismuth; bismuth compounds; epoxides; rearrangements.
Epoxides are one of the most versatile functional groups in organic chemistry due to their ready
availability and ease of transformation into a wide variety of functional groups.1 The rearrangement
of epoxides to carbonyl compounds is a useful synthetic transformation and several reagents have
been utilized for this purpose. Some examples include BF3·Et2O,2a lithium salts,2b MgBr2,2a and
more recently, Pd(OAc)2 in the presence of a phosphine ligand2c and InCl3.2d The constitution of the
rearrangement product is determined by the identity of the Lewis acid, the migratory aptitude of the
epoxide substituents, and the solvent (Scheme 1).
Despite a number of methods that have been developed for this rearrangement, only a few are
both regioselective and catalytic in nature. For example, BF3·Et2O and MgBr2 are typically used
in stoichiometric or excess amounts.2a In addition, many of these reagents have some drawbacks.
Boron trifluoride etherate is corrosive and air-sensitive while indium chloride is highly toxic and
very expensive. The rearrangements promoted by these reagents also require anhydrous conditions.
With increasing environmental concerns, it is imperative that new ‘environment friendly’ reagents be
developed.3 Recently, bismuth compounds have become attractive candidates for use as reagents in
organic synthesis for several reasons. Most bismuth compounds are relatively non-toxic, readily available
at low cost and are fairly insensitive to small amounts of water.4 Bismuth has an electron configuration of
∗
Corresponding author. Fax: (309)-556-3864; e-mail: rmohan@titan.iwu.edu (R. S. Mohan)
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(99)02330-8
tetl 16258

1528
Scheme 1.
[Xe]4f145d106s26p3. Due to the weak shielding of the 4f electrons (Lanthanide contraction), bismuth(III)
compounds exhibit Lewis acidity. The Lewis acidity of bismuth(III) chloride and bismuth triflate have
been recently exploited in organic synthesis. They are catalysts for Diels–Alder,5 Michael6 and aldol
reactions.7 We wish to report that BiOClO4·×H2O is a very efficient reagent for rearrangement of
epoxides to carbonyl compounds (Eq. (1), Table 1).
(1)
BiOClO4·×H2O is commercially available and requires no special handling.8 Use of an inert atmos-
phere is not required unless the product is particularly air sensitive (entries 5–7). The reagent is insoluble
in common organic solvents and is used as a suspension. For most epoxides, the best yields were obtained
with use of 20 mol% reagent though stilbene oxides (entries 1–4) underwent smooth rearrangement with
as little as 10 mol% reagent. Dichloromethane was found to be the best solvent for the rearrangement.
The rearrangement was very slow in tetrahydrofuran and benzene while no rearrangement was observed
when diethyl ether was used as the solvent.
Rearrangement of stilbene oxides (entries 1–4) gave only the diphenylacetaldehydes. Thus, this
procedure is a good example of an epoxide rearrangement method that is both catalytic and regioselective
in nature. These cases gave very clean products, and further purification was deemed unnecessary. In all
cases, the phenyl group was found to migrate in preference to hydrogen. Thus, rearrangement of both cis-
and trans-stilbene oxides (entries 1 and 2) gave diphenylacetaldehyde as the only product. In contrast, the
rearrangement of trans-stilbene oxide by MgBr2 in benzene gave a 3:1 mixture of diphenylacetaldehyde
(phenyl migration) and deoxybenzoin (hydrogen migration).2c With BF3·Et2O, trans-stilbene oxide
gives only diphenylacetaldehyde while the cis isomer gives a mixture of both diphenylacetaldehyde and
deoxybenzoin. It was found that hydrogen migrates in preference to a methyl group: both cis- and trans-
β-methylstyrene oxides (entries 5 and 6) gave only phenylacetone upon rearrangement.
Rearrangement of styrene oxide did not give a very pure product. While starting material was
seen to disappear by TLC in 15 min, the crude product appeared to be very impure and attempted
purification gave very low yields (15%) of phenylacetaldehyde. Contrary to reports in the literature,2d
we were not able to repeat the rearrangement of styrene oxide with indium chloride in good yield.
In our hands, styrene oxide rearranged rapidly, both with InCl3 and BiOClO4·×H2O but the product
phenylacetaldehyde was found to be unstable to the reaction conditions. A significant amount of
product formed by aldol condensation of phenylacetaldehyde was detected in the crude product mixture.
Aliphatic epoxides that contained a tertiary epoxide carbon also underwent rearrangement readily. For
example, 1-methylcyclohexene oxide (entry 8) underwent ready rearrangement to give an 85:15 mixture
of 2-methylcyclohexanone (migration of methyl group) and 1-methyl-1-cyclopentanecarboxaldehyde

1529
Table 1
Rearrangement of epoxides with BiOClO4·×H2O in CH2Cl2

1530
(migration of C–C bond), respectively. In contrast, rearrangement of 1-methylcyclohexene oxide with
LiBr-HMPA in benzene gave 1-methyl-1-cyclopentanecarboxaldehyde as the major product (95%).2b
Good yields of tert-butyl methyl ketone were obtained by rearrangement of the aliphatic epoxide 2,3-
dimethylbutene oxide (entry 9).9 The rearrangement of α-pinene oxide (entry 10) occurred quite readily
at room temperature to give the expected aldehyde in good yield.10 Cyclohexene oxide did not undergo
rearrangement even when refluxed for 12 h and the starting material was recovered in good yield. This
indicates that BiOClO4·×H2O is a mild Lewis acid. When cyclohexene oxide is reacted with InCl3,
while no rearrangement occurs, the corresponding chlorohydrin is reported to form in good yield.2d
In summary, this work demonstrates a new method for high-yielding, selective rearrangement of
aromatic epoxides to carbonyl compounds using BiOClO4·×H2O. Aliphatic epoxides containing a
tertiary epoxide carbon also undergo facile rearrangement. Advantages of this method include low
toxicity and low cost of the Lewis acid catalyst, fast reaction rates and insensitivity to air and moisture. A
representative procedure is given here: A solution of trans-stilbene oxide (1.00 g, 5.10 mmol) in CH2Cl2
(20 mL) was stirred as BiOClO4·×H2O (0.331 g, 1.02 mmol) was added. After 25 min, water (10 mL)
and CH2Cl2 (10 mL) were added and the organic layer was washed with 10% NaHCO3 (10 mL) and
saturated sodium chloride (10 mL). The organic layer was dried (Na2SO4) and the solvent was removed
on a rotary evaporator to yield 0.879 g (88%) of diphenylacetaldehyde that was determined to be >98%
pure by 1H NMR.11,12
Acknowledgements
Acknowledgement is made to the donors of The Petroleum Research Fund, administered by the
American Chemical Society for partial support of this research. R.M. would also like to thank Illinois
Wesleyan University for an Artistic and Scholarly Grant awarded to develop this research project.
References
1. (a) Gorzynski Smith, J. Synthesis 1984, 8, 629. (b) Parker, R. E.; Issacs, N. S. Chem Rev. 1959, 59, 737. (c) Rao, A. S.;
Paknikar, S. K.; Kirtane, J. G. Tetrahedron 1983, 39, 2323.
2. (a) House, H. O. J. Am. Chem. Soc. 1955, 70, 3070. (b) Rickborn, B.; Gerkin, R. M. J. Am. Chem. Soc. 1971, 93, 1693. (c)
Kulasegaram, S.; Kulawiec, R. J. J. Org. Chem. 1997, 62, 6547. (d) Ranu, B. C.; Jana, U. J. Org. Chem. 1998, 63, 8212.
3. Garrett R. L. In Designing Safer Chemicals; ACS Symposium Series 640; American Chemical Society: Washington, DC,
1996; Chapter 1.
4. (a) Reglinski, J. In Chemistry of Arsenic, Antimony and Bismuth; Norman, N. C., Ed.; Blackie Academic and Professional:
New York, 1998; pp. 403–440. (b) Marshall, J. A. Chemtracts 1997, 1064–1075. (c) Suzuki, H.; Ikegami, T.; Matano, Y.
Synthesis. 1997, 249.
5. Garrigues, B.; Gonzanga, F.; Robert, H.; Dubac, J. J. Org. Chem. 1997, 62, 4880
6. Wada, M.; Takegichi, E.; Matsumoto, T. Bull. Chem. Soc. Jpn. 1991, 64, 990.
7. Ohki, H.; Wada, M.; Akiba, K. Tetrahedron Lett. 1988, 29, 4719.
8. BiOClO4·×H2O was purchased from Aldrich Chemical Company and used as received. While we did not encounter any
problems with this reagent, caution should be exercised in handling perchlorates.
9. Barry, C. N.; Evans, S. A. J. Org. Chem. 1983, 48, 2825.
10. Lewis, J. B.; Hedrick, G. W. J. Org. Chem. 1965, 30, 4271.
11. Gensler, W. J.; Koehler, W. R. J. Org. Chem. 1962, 27, 2754.
12. Halterman, R. T.; McEnvoy, M. A. J. Am. Chem. Soc. 1990, 112, 6690