Water-soluble and reusable copper catalyst for the allylic benzoyloxylation of olefins

Article abstract of DOI:10.1016/S0040-4039(01)02170-0

Simple mixing of [(HOCH₂CH₂NHCOCH₂)₂NCH ₂]₂ with Cu(MeCN)₄BF₄ in water led to an efficient and reusable catalytic system for the allylic oxidation of olefins by tert-b

Full text of DOI:10.1016/S0040-4039(01)02170-0

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 431–433
Water-soluble and reusable copper catalyst for the allylic
benzoyloxylation of olefins
Jean Le Bras and Jacques Muzart*
Unite´ Mixte de Recherche ‘Re´actions Se´lectives et Applications’, CNRS, Universite´ de Reims Champagne-Ardenne, BP 1039,
51687 Reims cedex 2, France
Received 5 November 2001; accepted 14 November 2001
Abstract—Simple mixing of [(HOCH2CH2NHCOCH2)2NCH2]2 with Cu(MeCN)4BF4 in water led to an efficient and reusable
catalytic system for the allylic oxidation of olefins by tert-butyl perbenzoate. © 2002 Elsevier Science Ltd. All rights reserved.
The Kharasch–Sosnovsky reaction involves the allylic
oxidation of olefins by an organic peroxyester in the
presence of catalytic amounts of a copper salt.1,2 This
simple and general method for the synthesis of allyl
esters which has been known for almost half a century,
has been carried out in various organic solvents; we3
and others4 have proposed enantioselective versions of
this process. Presently, there is considerable interest in
the development of water-soluble ligands,5 which allows
metal-catalyzed reactions to take place in either water6
or biphasic systems;7 these approaches frequently result
in an improvement of the productive process from both
economical and ecological points of view.8 We were
interested in the use of such ligands to carry out
Kharasch–Sosnovsky reactions in water as well as the
aim of obtaining catalyst recycling.
prepared from ethylenediaminetetraacetic acid perm-
ethyl ester10 and 2-aminoethanol (Eq. (1)),11 was able to
fulfil our objectives; thus, we report here our main
results (Eq. (2), Table 1).
The catalytic system was in situ prepared by mixing
12
Cu(MeCN)4BF4 with 1 equiv. of 1 in degassed water.
After addition of neat cyclohexene (50 equiv./Cu), tert-
butyl perbenzoate (10 equiv./Cu) and heating at 80°C,
the aqueous phase was blue-colored while the organic
phase was very lightly yellow. Stirring this mixture at
80°C for 48 h led to the disappearance of the perester;
the subsequent workup yielded 67% of 2-cyclohexenyl-
1-benzoate.13 An array of olefins was then reacted
under similar conditions (Table 1). Cycloheptene and
1,5-cyclooctadiene (entries b and d) were oxidized in
good yields in 48 h, while the reaction with cyclooctene
required several days (entry c). The benzoyloxylation of
linear 1-alkenes, allylbenzene and 1-octene, was accom-
panied by migration of the double bond, affording a
mixture of the corresponding esters, the main one being
the secondary isomer in both cases (entries e and f )
One of the most useful water-soluble ligand is TPPTS;9
this phosphine cannot however be used in an oxidizing
medium. During our research on the synthesis of new
N-donor ligands, we discovered that highly hydrophilic
[(HOCH2CH2NHCOCH2)2NCH2]2 (1), which is easily
O
O
O
O
HO
OH
MeO
MeO
OMe
OMe
N
H
H
N
N
H
H
N
80°C
20 h
(1)
(2)
+
4
H2N
N
N
N
N
OH
HO
OH
O
1
O
O
O
Keywords: catalysis; copper; perester; olefins; allylic oxidation; water.
* Corresponding author. Fax: 03 26 91 31 66; e-mail: jacques.muzart@univ-reims.fr
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)02170-0

432
J. Le Bras, J. Muzart / Tetrahedron Letters 43 (2002) 431–433
Table 1. Catalyzed allylic oxidation of olefins with Cu(MeCN)4BF4/1 in water13
and with a low yield when 1-octene was the starting
material.
to the organic phase and (ii) the oxidation proceeds
mainly in the organic phase. Comparison of the results
demonstrates the value of 1 in obtaining an effective
recycling of the catalyst.
The aqueous phase recovered from workup of such an
oxidation remains blue-colored and more interestingly,
was catalytic active. For example, the oxidation of
cyclohexene (entry a) was repeated four times in using
the recovered aqueous phase: an increase in efficiency
from 67% in the first cycle to 80% in the last cycle was
observed. The very low coloration of the organic phase
in the course of these recycling experiments and their
efficiencies show that most of the copper complex
remains thus in the aqueous phase.
In conclusion, we have described a new and recyclable
water-soluble system to efficiently catalyze the allylic
oxidation of olefins. Our future work will be concen-
trated on the nature of the active species and on the
development of this copper–salt with different additives
such as b-cyclodextrins.
Acknowledgements
To examine the role of 1, the oxidation of cyclohexene
was carried out as in entry a but in the absence of this
additive. Some differences were observed: (i) the
organic phase was blue-colored as soon as the mixture
was heated to 80°C; (ii) the perester was fully consumed
in 24 h; (iii) the yield of 2-cyclohexenyl-1-benzoate was
slightly reduced (65%) and (iv) more importantly, the
recycling of the catalyst was much less efficient, the
yield of the fourth run being less than 20% instead of
the 77% obtained under the previous recycling condi-
tions. These experiments indicate that in the absence of
1: (i) a large part of the copper complex is transferred
This work was supported by the European Community
(COST D12/0028/99) and CNRS.
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