Rapid and reusable copper catalytic system for allylic oxidation of olefins in hexafluoroisopropanol as solvent

Article abstract of DOI:10.1055/s-2002-35574

Cu₂O mixed with perfluorododecanoic acid C₁₁F₂₃COOH and t-butyl peroxybenzoate in hexafluoroisopropanol led to a rapid and reusable catalytic system for the Kharasch-Sosnovsky reaction.

Full text of DOI:10.1055/s-2002-35574

LETTER
2035
Rapid and Reusable Copper Catalytic System for Allylic Oxidation of Olefins
in Hexafluoroisopropanol as Solvent
C
F
opper Cataly
a
tsfor
A
llyl
b
ic
O
xidation
i
of
O
lef
e
ins nne Fache,* Olivier Piva
Laboratoire de Chimie Organique, Photochimie et Synthèse, Université Claude Bernard Lyon 1, Unité Mixte de Recherche CNRS 5622,
Bât. Raulin, 43 bd du 11 novembre 1918, 69622 Villeurbanne Cedex, France
Fax +33(4)72448136; E-mail: fache@univ-lyon1.fr
Received 13 September 2002
(
59 °C) under stirring until complete conversion (TLC
Abstract: Cu O
mixed
with
perfluorododecanoic
acid
2
control). Without the fluorinated acid or even with an ex-
cess of benzoic acid, no reaction occurred. When benzene
was used instead of HFIP, even in the presence of
C F COOH, the reaction mixture remained heteroge-
neous with some red particles of starting Cu O. The cata-
lytic system thus could not be recovered properly.
C F COOH and t-butyl peroxybenzoate in hexafluoroisopropanol
1
1 23
led to a rapid and reusable catalytic system for the Kharasch–Sos-
novsky reaction.
11 23
Key words: allylic oxidation, olefins, copper catalyst, HFIP, recy-
cling
2
HFIP could be recycled by careful distillation and the fi-
Allylic oxidation of olefins with copper catalysis and or- nal product was isolated by flash chromatography over
ganic peroxyester as oxidant is a powerful reaction, which SiO (petroleum ether/EtOAc, 95:5). The catalytic system
2
has been extensively studied since the seminal work of could be recovered very easily. When all the perester
1
Kharasch and Sosnovsky. Numerous asymmetric ver- was consumed, HFIP was evaporated and the resulting
2
–4
sions of this reaction have been also reported. Among crude product was rinsed three times with petroleum ether
the different systems published in the literature, only few (15 mL). The catalytic system was thus isolated by simple
5
of them could be recycled. Thus, Sartori et al. used cop- decanting the insoluble turquoise blue solid. It could be
6
per-exchanged zeolites, while, Le Bras and Muzart re- reused without further addition of copper and acid. All the
ported a reusable water-soluble copper catalyst. This nice results are summarised in Table 1.
system is competitive in terms of isolated yields with the
2
Table 1 Comparative Results Using New Cu O Catalyst and a Pre-
best results published in the literature but reaction times
to go to completion were quite long (few days). In a search
to improve the reactivity of the copper catalytic system for
2
treated One
Yield (%)a
En- Olefin
Reaction Product
time (h)
allylic oxidation of olefins, we took into account the great try
advantages of fluorinated alcohols in oxidation reac-
b
Cu O Cu O
2
2
7
,8
tions. We thus explored the potentiality of hexafluoro-
-propanol (HFIP) with copper catalyst and t-butyl per-
benzoate as the oxidant (Scheme 1).
(initial) (recycled)
2
1
3
30
72
O
Ph
O
O
Cu O, C11F23COOH,
2
O
Ph
t-BuOOC(O)Ph
2
3
4
15
24
20
20
33
52c
10
Ph
Ph
O
O
O
O
F3C
OH
42c
23
F3C
Scheme 1 Allylic oxidation of cyclohexene in a fluorinated medi-
um.
C H
3 7
C H
4
9
O
O
O
75
In a typical procedure, Cu O (0.05 mmol) was mixed with
the commercially available perfluorinated acid
2
Ph
C F COOH (0.1 mmol) in HFIP (1.5 mL) to ensure its
1
1
23
Ph
3 7
C H
complete solubility. The solution took rapidly a deep blue
colour. Olefin (5 mmol) and t-BuOOC(O)Ph (1 mmol)
were then added and the reaction was heated to reflux
O
25
5
18
30
50
O
Ph
Ph
O
Ph
Synlett 2002, No. 12, Print: 02 12 2002.
Art Id.1437-2096,E;2002,0,12,2035,2036,ftx,en;G27302ST.pdf.
a
b
c
Isolated yield.
Cu O recycled from a cyclohexene reaction.
2
©
Georg Thieme Verlag Stuttgart · New York
No C=C migration occurred.
ISSN 0936-5214

2
036
F. Fache, O. Piva
LETTER
Isolated yields were based on peroxyester consumption. In a typical procedure, Cu
O (7 mg, 0.05 mmol) was mixed with
C F COOH (61 mg, 0.1 mmol) in HFIP (1.5 mL) to ensure its
2
The reaction was rapid (always < 24 h) and in the case of
cyclohexene only three hours were necessary for the reac-
tion to go to completion (entry 1). The first cycle of the
catalytic system led to moderate isolated yields, irrespec-
tive of the substrate. In contrast, with cyclohexene, 72%
11 23
complete solubility. The solution rapidly became a deep blue co-
lour. Olefin (5 mmol) and 190 L (1 mmol) of t-BuOOC(O)Ph were
then added and the reaction was heated to reflux (59 °C) under stir-
ring until complete conversion (TLC control). When all the perester
was consumed, HFIP was evaporated. The solid thus obtained was
(
isolated yield) of the desired oxidation product was ob- rinsed with petroleum ether (3 15 mL). The resulting organic
tained using a recycled catalyst and the reaction was re- phase was evaporated and the desired product was purified by flash-
chromatography over silica gel (petroleum ether/EtOAc, 95:5).
peated thrice without loss of activity (70–72% isolated
yield in 4 hours). We assumed that some of the peroxyes- For recycling experiments: the solid obtained above after being
rinsed with petroleum ether was dried by simple evaporation of re-
ter was consumed in the first cycle to form the active cop-
sidual petroleum ether. Recycled catalyst (50 mg) was recovered.
per species, which should explain the lower yields. In the
Then HFIP (1.5 mL), t-BuOOC(O)Ph (190 L) and the olefin (5
mmol) were stirred under reflux until complete conversion of the
perester. The desired product was recovered according to the above
procedure.
second cycle, all the peroxyester could be used to form the
final product. Moreover, with this catalytic system recov-
ered from cyclohexene, the oxidation process occurred
nicely irrespective of the nature of the substrate with iso-
lated yields similar to those published in the literature.2
References
Thus, gram amounts of Cu O have been pre-treated with
2
cyclohexene under the reaction conditions described
above and then used successfully with other olefins
(1) Kharasch, M. S.; Sosnovsky, G. J. J. Am. Chem. Soc. 1958,
80, 756.
(
2) Malkov, A. V.; Bella, M.; Langer, V.; Kocovsky, P. Org.
(
Table 1). This new catalyst is very easy to prepare and to
Lett. 2000, 2, 3047.
handle.
(3) Levina, A.; Muzart, J. Tetrahedron: Asymmetry 1995, 6,
In the case of allylbenzene, a complete regioselective ox-
idation took place to deliver only the terminal primary al-
cohol derivative with 50% isolated yield (entry 5) whereas
147.
(4) For reviews, see: (a) Brunel, J.-M.; Legrand, O.; Buono, G.
C. R. Acad. Sci. 1999, 2, 19. (b) Eames, J.; Watkinson, M.
Angew. Chem., Int. Ed. 2001, 40, 3567. (c) Andrus, M. B.;
Lashley, J. C. Tetrahedron 2002, 58, 845.
2
reported systems usually led to a mixture of regioiso-
mers. Acyclic olefins like n-hexene gave poorer yields as
(
5) Carloni, S.; Frullanti, B.; Maggi, R.; Mazzacani, A.; Bigi, F.;
4
already observed (entry 4).
Sartori, G. Tetrahedron Lett. 2000, 41, 8947.
In conclusion, we have described a new catalytic system
for allylic oxidation of olefins, which is rapid and easily
recycled. An asymmetric version of this system is current-
ly in progress, to take advantage of the fluorous phase.
(6) Le Bras, J.; Muzart, J. Tetrahedron Lett. 2002, 43, 431.
(
7) Van Vliet, M. C. A.; Arends, I. W. C. E.; Sheldon, R. A.
Synlett 2001, 248.
(
8) Legros, J.; Crousse, B.; Bourdon, J.; Bonnet-Delpon, D.;
Bégué, J.-P. Tetrahedron Lett. 2001, 42, 4463.
Synlett 2002, No. 12, 2035–2036 ISSN 0936-5214 © Thieme Stuttgart · New York