Epoxidation of olefins with peracid at low temperature with copper catalysis

Article abstract of DOI:10.1016/S0040-4039(00)00070-8

Treatment of a wide range of olefins with m-chloroperbenzoic acid (MCPBA) at low temperature in the presence of copper(I) and (II) catalysts in methylene chloride provides epoxides in good to excellent yields. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)00070-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 1013–1014
Epoxidation of olefins with peracid at low temperature with
copper catalysis
Merritt B. Andrus ∗ and Benjamin W. Poehlein †
Brigham Young University, Department of Chemistry and Biochemistry, C100 BNSN, Provo, UT 84602, USA
Received 16 July 1999; accepted 22 July 1999
Abstract
Treatment of a wide range of olefins with m-chloroperbenzoic acid (MCPBA) at low temperature in the presence
of copper(I) and (II) catalysts in methylene chloride provides epoxides in good to excellent yields. © 2000 Elsevier
Science Ltd. All rights reserved.
Keywords: epoxidation; epoxides; catalysis; olefins.
While various transition metals have been employed with great success,1 epoxidations with copper are
rare. Iodosylbenzene with copper(II) nitrate and triflate with stilbenes,2 silylalkyl peroxybenzoate with
Cu(II) trifluoroacetate3 and binuclear trisamino complexes have been reported.4 Substrates are limited
to electron rich olefins where low yields and isomerization of cis-alkenes to trans products are typically
found. As copper has recently gained in prominence as a catalyst for numerous transformations,5 it
became useful to investigate various oxidants for low temperature epoxidation with a wide range of
substrates as a prelude to ligand identification.
Initial attempts were disappointing. Use of Cu(CH3CN)4PF66 or Cu(SbF6)2 as catalysts with stoichio-
metric oxone or iodosylbenzene at −40°C gave no product even after 2 d (Fig. 1). Yet, remarkably when
MCPBA (2 equiv., 60–80% Aldrich) was used the reaction with 5 mol% copper(I) was complete after 10
h at −78°C giving the epoxide from allylbenzene in 92% isolated yield. Without added copper, MCBPA
gave no product after 2 d at −78°C.7 The catalyst–oxidant system was then employed with a range of
electron-rich and deficient olefins to explore the scope of the process (Table 1).8
Fig. 1. Epoxidation at low temperature with copper catalysis
∗
†
Corresponding author. E-mail: mbandrus@chemgate.byu.edu (M. B. Andrus)
Work performed at Purdue University, Department of Chemistry.
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)00070-8
tetl 16350

1014
Table 1
Epoxidation of olefins with MCPBA (2 equiv.) and Cu(CH3CN)4PF6 (5 mol%) in CH2Cl2
The temperature needed to be adjusted to −20°C in some cases to ensure a reasonable rate as with
styrene, methyl cinnamate and chalcone. Bicarbonate was added in the case of the TBS silylether to
prevent protecting group removal by the benzoic acid by-product. Cinnamaldehyde was epoxidized at
−78°C for 8 h in 67% yield. Other electron deficient substrates reacted with lower yields requiring 10
mol% catalyst in the case of cinnamate. Use of Cu(SbF6)2 at −78°C for 10 h with allylbenzene also gave
epoxide in high yield (90%). Cu(II) had a similar effect with the stilbenes. The cis isomer gave trans
product predominantly suggestive of a step-wise radical or a reversible copper–oxetane process.9 With
an efficient low temperature system, efforts can now proceed to identify suitable asymmetric ligands.
Acknowledgements
Funding was provided by the NSF (CHE-9501867, Career Award to MBA).
References
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mediated decomposition.
8. Representative experimental: A dry, sealed flask with Cu(CH3CN)4PF6 (5 mol%), MCPBA (2 equiv.) and CH2Cl2 (0.2 M)
was degassed with N2, stirred for 5 min and cooled to −78°C. The olefin was added and stirring continued. Aqueous NaHCO3
quench, methylene chloride extraction, MgSO4 drying, and flash chromatography (EtOAc/hexanes) gave the pure epoxide.
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