A. P. da Silva et al. / Tetrahedron Letters 46 (2005) 3233–3235
3235
2
e
1991, 113, 8375; Amatore, C.; Jutand, A.; Mottier, L.
J. Electroanal. Chem. 1991, 306, 125.
M
II(L)
M (L)
0
3
4
5
6
7
8
9
. Durandetti, M.; Devaud, M.; P e´ richon, J. New J. Chem.
1996, 20, 659.
. Cassol, T. M.; Demnitz, F. W. J.; Navarro, M.; Neves, E.
A. Tetrahedron Lett. 2000, 41, 8203.
. De Fran c¸ a, K. W. R.; Navarro, M.; Leonel, E.; Durand-
etti, M.; N e´ del e´ c, J.-Y. J. Org. Chem. 2002, 67, 1838.
. Caetano, V. F.; Demnitz, F. W. J.; Diniz, F. B.; Mariz, R.
M., Jr.; Navarro, M. Tetrahedron Lett. 2003, 44, 8217.
. Handique, J. G.; Purkayashtha, A.; Baruah, J. B. J.
Organomet. Chem. 2001, 620, 90.
M
II(L)
M
0
(L)
+
H
M
II(L) + H
O
2
H
M = Ni, Co, Fe
L = solvent or bipy
Scheme 3. Proposed mechanism for olefin reduction mediated by
metallic ions in aprotic solvent (DMF).
. Santana, D. S.; Lima, M. V. F.; Daniel, J. R. R.; Navarro,
M. Tetrahedron Lett. 2003, 44, 4725.
. Santana, D. S.; Lima, M. V. F.; Melo, G. O.; Daniel, J. R.
R.; Areias, M. C. C.; Navarro, M. J. Electroanal. Chem.
in the presence of 3 equiv of the ligand L . This mecha-
1
nism is supported by the constant electrochemical po-
tential which remained at the cathode (ꢀ1.1 V versus
saturated calomelane electrode (SCE)), which corre-
2
004, 569, 71.
0. Navarro, D. M. A. F.; Navarro, M. Qu ı´ m. Nova 2004, 27,
01.
1. Moutet, J. C. Org. Prep. Proced. Int. 1992, 24, 309.
1
3
2
+
+ 15
sponds to reduction of the Fe complex into Fe .
As the 2-cyclohexen-1-one indirect reduction process,
described in this work, occurs at more negative poten-
1
12. The controlled current preparative electrolyses were car-
ried out in undivided cells of 20 mL capacity. A metal rod
(Zn, Ni or Fe) of 0.8 cm diameter and nickel foam
0
tials (ꢀ1.5 V/SCE), we can propose that M (M = Co,
0
Ni and Fe) and M bipy (M = Ni, Fe) solvated species
(
(
10 cm · 4 cm, Nitech) were used as sacrificial anode
immersed >1 cm in solution) and cathode (Ni foil or
probably mediate the reduction of the olefin, as depicted
in Scheme 3.
bar can also be used), respectively. The Ni foam electrode
can be reused about 20 times, after cleaning with a 6 M
HCl solution. The anode should be polished before
Solvated metallic ions and metal complexes should be
reduced at the cell potential applied (ꢁ2.0 V), and in
the presence of the 2-cyclohexen-1-one, p-bond is re-
duced giving an intermediary complex. The protonation
of the metal–olefin complex should occur due to residual
water presence or extraction step of the products, how-
ever the extraction performed with deuterated water
gave no deuterated product.
0
electrolysis. For experiments involving Ni bipy as medi-
was prepared sepa-
II
ator, the precursor [Ni (bipy)]Br
2
1
6
rately according to the literature.
[Fe (bipy)]- (SO ) was obtained in situ, from dissolution
The complex
II
4
0
of FeSO and 2,2 -bipyridine. Other mediators were tested
4
from the following salts: ZnSO
and FeSO . The electrolytic cell was charged under
4 4 2 2
, CuSO , CoCl , NiBr
4
nitrogen with 15 mL DMF containing (4.0 mmol) NaI
and (1.4 mmol) 1,2-dibromoethane. A pre-electrolysis was
initiated under 150 mA constant current during 30 min.
The (1.5 mmol) 2-cyclohexen-1-one was mixed with
In conclusion, the results obtained from homogeneous
electromediated reduction of the 2-cyclohexen-1-one,
by transition metals, show that it is possible to control
the selectivity of the reduction process by varying
parameters like sacrificial anode, mediator and water
concentration.
(
0.3 mmol) mediator in 5mL of solvent and then added
to the cell. A 100 mA constant current was applied until
full consumption of the starting reagent, always observing
the limit cell potential of 2.0 V (when occurs overpotential
the constant current should be diminished). The product
yield was determined by taking 0.5 mL aliquot from
reaction solution. 2 mL of water were added into the
aliquot and the products were extracted with 2 mL of ethyl
acetate containing 0.067 mmol of toluene, used as internal
standard. The product yields were determined by GC
analysis using a Varian 3380 chromatograph, fitted with
a 30 m capillary CP-SPL5CB Chrompack column, using
Acknowledgements
We would like to acknowledge CNPq, FINEP/CTPE-
TRO and Petrobras for financial support.
ꢀ
1
6
0–200 ꢁC temperature range (10 ꢁC min ).
1
1
3. Durandetti, M.; Meignein, C.; P e´ richon, J. J. Org. Chem.
2003, 5, 317.
References and notes
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2003, 68, 3121.
15. Saji, T.; Aoyaghi, S. J. Electroanal. Chem. 1975, 58, 401.
16. Uchino, M.; Asagi, K.; Yamamoto, A.; Ikeda, S. J.
Organomet. Chem. 1975, 84, 93.
1
2
. N e´ del e´ c, J.-Y.; P e´ richon, J.; Troupel, M. Top. Curr. Chem.
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1