K. Lam, I.E. Marko´ / Tetrahedron 65 (2009) 10930–10940
10939
2,00E-04
Supplementary data
0,00E+00
-3,50E+00
-3,00E+00
-2,50E+00
-2,00E+00
-1,50E+00
-1,00E+00
-5,00E-01
0,00E+00
General experimental procedures, extensive description of
spectroscopic data and copies of NMR spectra are provided as
electronic supplementary file. Supplementary data associated with
-2,00E-04
-4,00E-04
-6,00E-04
-8,00E-04
-1,00E-03
-1,20E-03
-1,40E-03
-1,60E-03
References and notes
1. Bouveault, L.; Blanc, G. Bull. Soc. Chim. Fr. 1904, 31, 666.
2. (a) Wagenknecht, J. H.; Goodin, R.; Kinlen, P.; Woodard, F. E. J. Electrochem. Soc.
1984, 131, 1559; (b) Gul’tyai, V. P.; Rubinskaya, T.; Korotaeva, L. Bull. Pol. Acad.
Sci. Chem. 1982, 1499; (c) Webster, R. D.; Bond, A. M. J. Org. Chem. 1997, 62, 1779;
(d) Kistenbruegger, L.; Mischke, P.; Voss, J.; Wiegand, G. Liebigs Ann. Chem. 1980,
3, 461.
Applied potential (/V vs Ag/AgCl in EtOH sat LiCl)
Figure 3. Cyclic voltammetry of 83: 10ꢀ2 M in analyte in degassed DMF containing
0.1 M NBu4BF4. Working electrode: Glassy carbon (7 mm diameter). Counter electrode:
Platinum rod. Sweeping rate: 150 mV/s.
3. Masnovi, J. J. Am. Chem. Soc. 1989, 111, 9081.
5. Nicholson, R. Anal. Chem. 1965, 38, 1406.
6. Baron, R.; Kershaw, N. M.; Donohoe, T. J.; Compton, R. G. J. Phys. Org. Chem.
2008, 22, 247.
7. (a) Girard, P.; Namy, J.-L.; Kagan, H. B. J. Am. Chem. Soc. 1980, 102, 2693; (b) For
excellent reviews, see: Krief, A.; Laval, A.-M. Chem. Rev. 1999, 99, 745; (c)
Molander, G. A.; Harris, C. R. Chem. Rev. 1996, 96, 307.
8. (a) Lam, K.; Marko´, I. E. Org. Lett. 2008, 10, 2773; (b) Kamochi, Y.; Kudo, T. Chem.
Lett. 1993, 9, 1495; (c) Kamochi, Y.; Kudo, T. Chem. Pharm. Bull. 1994, 42, 402; (d)
Guazzelli, G.; De Grazia, S.; Karl, D.; Matsubara, H.; Spain, M.; Procter, D. J. J. Am.
Chem. Soc. 2009, 131, 7214.
SmI2/HMPA procedure displaces all three protecting groups at
once. The selective hydrolysis of one benzoate after another
clearly highlights the power of electrosynthesis (Scheme 12).
9. Machrouhi, F.; Hamann, B.; Namy, J.-L.; Kagan, H. B. Synlett 1996, 633.
10. Dahle´n, A.; Hilmersson, G. Chem.d Eur. J. 2003, 9, 1123.
AcO
11. Miller, R. S.; Sealy, J. M.; Shabangi, M.; Kuhlman, M. L.; Fuchs, J. R.; Flowers, R. A.,
II. J. Am. Chem. Soc. 2000, 122, 7718.
AcO
OAc
86
12. Inagawa, J.; Ishikawa, M.; Yamaguchi, M. Chem. Lett. 1987, 1485.
13. Barton, D. H. R.; McCombie, S. W. J. Chem. Soc., Perkin Trans. 1 1975, 1574.
14. Radivoy, G.; Alonso, F.; Moglie, Y.; Vitale, C.; Yus, M. Tetrahedron 2005, 61, 3859.
15. Gevorgyan, V.; Rubin, M.; Liu, J.-X.; Yamamoto, Y. J. Org. Chem. 2000, 66, 1672.
16. (a) Yasuda, M.; Onishi, Y.; Ueba, M.; Miyai, T.; Baba, A. J. Org. Chem. 2001, 7741;
(b) Komano, K.; Shimamura, S.; Inoue, M.; Hirama, M. J. Am. Chem. Soc. 2007,
129, 14184.
17. Deoxygenation of adamantyl toluate: In a 100 mL flame-dried three necked flask,
maintained under argon and equipped with a condenser and a magnetic stirrer,
1.24 mL (7.1 mmol, 12 equiv) of HMPA were added to 17.8 mL (1.8 mmol,
3 equiv) of SmI2 (0.1 M in THF or THP). The solution turned immediately into
a purple colour. The solution was then heated at reflux and 160 mg (0.6 mmol,
1 equiv) of the toluate, dissolved in a minimum of THF or THP, was quickly
added. The reaction was followed by TLC (the reaction is usually finished within
10 s to 5 min). Then, the reaction was quenched by the addition of 10 mL of
a saturated aqueous NH4Cl solution. The aqueous layer was extracted three
times with 10 mL of dichloromethane and the organic phases were pooled,
washed twice with a saturated solution of sodium carbonate and then dried
over anhydrous sodium sulfate. The solvent was removed under reduced
pressure and the crude product was purified by silica gel column chromatog-
raphy using pentane as eluent.
1) Electrolysis -2.5V vs Ag/AgCl
2) Ac O / DMAP / Et N
1) SmI /HMPA in THF
2
2) Ac O / DMAP / Et N
2
3
2
3
61%
87%
CF
3
CF
3
Electrolysis-2V
vs Ag/AgCl
70%
Electrolysis -1.6V
vs Ag/AgCl
74%
HO
HO
O
O
O
O
O
O
O
O
O
O
HO
O
O
F C
CF
3
3
84
83
Scheme 12. Selective deprotection of aromatic esters.
85
3. Conclusion
18. Curran, D. P.; Fevig, T. L.; Jasperse, C. P.; Totleben, M. J. Synlett 1992, 943.
19. Allais, F.; Boivin, J.; Nguyen, V. T. Beilstein J. Org. Chem. 2007, 3, 46.
20. (a) Soupe, J.; Namy, J. L.; Kagan, H. B. Tetrahedron Lett. 1982, 23, 3497; (b) Manas,
K. B.; Bimal, K. B. Tetrahedron Lett. 2001, 8, 187.
In summary, the monoelectronic reduction mechanism of aro-
matic esters has been investigated and the toluate moiety has been
shown to be a particularly useful function in organic synthesis.
Depending upon the reaction conditions, an alkyl radical or anion
can be generated by the reduction of various toluates. These obser-
vations led to the development of several novel procedures for the
deoxygenation of alcohols and for the allylation of ketones. More-
over, by simply adding a proton source the chemoselective depro-
tection of several substituted benzoates can be smoothly conducted.
The electrochemical version of the Barbier–Toluate coupling is cur-
rently being studied. A deeper investigation of the mechanism of
these processes using high speed voltammetry in combination with
ultramicroelectrodes is presently ongoing in these laboratories.
21. Samarium Barbier procedure: In
a 100 mL flame-dried three necked flask,
maintained under argon and equipped with a condenser and a magnetic stirrer,
3.50 mL (38 mmol, 20 equiv) of HMPA are added to 95 mL (9.5 mmol, 5 equiv)
of SmI2 (0.1 M in THF). The solution turns immediately into a purple colour. The
solution is then heated at reflux and 330 mg (1.9 mmol, 1.2 equiv) of the tol-
uate, mixed with 200 mg of 2-octanone (1,5 mmol, 1 equiv) dissolved in
a minimum of THF, is quickly added. The reaction is followed by TLC (the re-
action is usually finished within 10 s to 5 min). Then, the reaction is quenched
by the addition of 10 mL of saturated aqueous NH4Cl. The aqueous layer is
extracted three times with 10 mL of dichloromethane and the organic phases
are pooled, washed twice with a saturated solution of sodium carbonate and
then dried over anhydrous sodium sulfate. The solvent is removed under
reduced pressure and the crude product is purified by silica gel column chro-
matography using Et2O/hexane (1:9) as eluent. Analytical data of the alcohol
was in good agreement with the literature.
22. Collin, J.; Bied, C.; Kagan, H. B. Tetrahedron Lett. 1991, 32, 629.
23. (a) Lam, K.; Marko´, I. E. Chem. Commum. 2009, 95.
24. Lund, H.; Hammerich, O. Organic Electrochemistry, 4th ed.; Marcel Dekker: New
York, NY, 2001.
Acknowledgements
25. Standard electrolysis procedure: An H-type cell, with two compartments of
Financial support of this work by the F.R.I.A. (Fond pour la For-
100 ml capacity, separated by a sintered glass with a porosity of 40 mm, was
dried during one night at 200 ꢁC. Then, each cell was equipped with a graphite
electrode of 6 cm2 and a magnetic stir bar. Both compartments were then
flushed with argon during 10 min. After filling them with 5 g of NBu4BF4 and
with 100 ml of NMP, freshly distilled under argon, 600 mg (0,6 mmol) of 9-
`
mation a la Recherche dans l’Industrie et l’Agriculture, studentship
´
to K.L.), the Universite catholique de Louvain, Merck Sharp and
Dohme (Merck Academic Development Program Award to I.E.M.)
and the FRFC (1.5.294.09F) is gratefully acknowledged.
fluorenyl toluate, dissolved in
a little NMP, were added to the cathodic