The formation of peroxides from vinyl ethers in the presence of silica-gel

Article abstract of DOI:10.1016/S0040-4039(01)00968-6

Silica-gel containing H₂O₂ or ROOH transforms vinyl alkyl or vinyl aryl ethers into the corresponding α-alkoxy hydroperoxides and dialkyl peroxides under very mild reaction conditions.

Full text of DOI:10.1016/S0040-4039(01)00968-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 5313–5314
The formation of peroxides from vinyl ethers in the
presence of silica-gel
F. Kovacˇ*
University of Ljubljana, Faculty for Chemistry and Chemical Technology, 1000 Ljubljana, Slovenia
Received 26 January 2001; revised 25 May 2001; accepted 1 June 2001
Abstract—Silica-gel containing H2O2 or ROOH transforms vinyl alkyl or vinyl aryl ethers into the corresponding a-alkoxy
hydroperoxides and dialkyl peroxides under very mild reaction conditions. © 2001 Elsevier Science Ltd. All rights reserved.
Supported reagents are very important because of their
high efficiency and very mild reaction conditions.1 The
use of heterogeneous reactions on solid support is
interesting because such reactions can be more selective
and milder than ordinary homogeneous reactions. Sil-
ica-gel and alumina are among the most important and
useful supports for a variety of transformations of
functional groups. Some reactions can occur even with-
out solvent.2 Silica-gel shows catalytic activity and it is
known that water present on silica-gel forms silylic acid
and so it shows weak acidic character (pH 5.5–7.5).3,4
For some reactions silica-gel and/or alumina supports
are prepared by the sol–gel method because of better
surface properties and homogeneity.5 The amount of
water on the surface of solid silica-gel or alumina6
depends on the activation temperature.
a dessicator (with phosphorus pentoxide) or in a dry
box and then poured into the ethereal solution of
hydrogen peroxide or alkyl peroxide. The ether was
then completely removed under vacuum at room
temperature.
Table 1. The yields of the corresponding peroxides
Compound
Product yield (%)a
Vinyl ether
R2
t-Bu
Cumyl
1a
1b
1c
1d
1e
1f
30
45
42
40
35
36
20
32
30
28
26
35
18
30
25
22
20
32
Vinyl alkyl or vinyl aryl ethers, either commercially
available or prepared by a known procedure,7 were
transformed into the corresponding a-alkoxy hydroper-
oxides and a-alkoxy dialkyl peroxides at room tempera-
ture (Table 1). For this purpose we first deactivated the
silica-gel by heating it to a high temperature. Hot
silica-gel must be cooled down to room temperature in
a The yields were determined by NMR integration and iodometry (the
purity of isolated peroxides was 95–97%).
1a: R=Et, R1=H
R
O
CH CH2R1
1b: R=Et, R1=Me
H2O2
1c: R=Ph(Me)CH, R1=H
1d: R=Ph(Me)CH, R1=Me
1e: R-R1=CH2CH2CH2
1f: R-R1=CH2(CH2)2CH2
OOH
2a-f
silica-gel
RT
R
O
CH
CHR1
1a-f
R
O
CH CH2R1
R2OOH
OOR2
R2= t-Bu, cumyl
3a-f
* Corresponding author.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00968-6

5314
F. Ko6acˇ / Tetrahedron Letters 42 (2001) 5313–5314
Acknowledgements
Vinyl ethers were dissolved in an appropriate dry non-
polar solvent (e.g. n-hexane, n-pentane, toluene, ben-
zene) and applied to the top of a column filled with the
silica-gel and the same non-polar solvent. Elution was
carried out using the same solvent. The products were
immediately adsorbed on silica-gel and desorpted with
more polar solvents (e.g. diethyl ether, methyl acetate,
ethyl acetate). When we dissolved the starting com-
pounds in polar solvents no transformations of the
vinyl ethers was observed. In the case of bad deactiva-
tion of the silica-gel we isolated the corresponding
alcohols and carbonyl compounds. Water present on
the silica-gel was being added to the vinylic double
bond under the mildly acidic conditions caused by the
silylic acid. It is known that transformations of ethers
and acetals are catalyzed by acids (pKa<3), which are
much stronger than the silylic acid formed on the
silica-gel.8–10
Acknowledgement is made to the Ministry of Science of
Slovenia for financial support.
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For characterization of the peroxides we prepared
authentic samples by known procedures from the corres-
ponding ketals11 or by conventional acid-catalyzed
transformation of vinyl ethers into hydroperoxides.12
All products were characterized by NMR Brucker
Avance DPX300 and GC–MS Hewlett Packard 6890
(with library of MS spectra – NBS75).
.