978
S. Maurer et al.
LETTER
plying DMSO–H2O as solvent system was better suited, of solid starting materials (e.g., 4-iodoanisole, 1-bromo-4-
as like for 4-acetylphenyliodide (entry 15), because the iodobenzene, among others) are likely to undergo.
latter underwent some extent undesired side reactions in
t-BuOH. Hydroxymethylene and carboxyl groups are also
suitable substituents for this transformation (entries 10
and 12). Also substrates with ortho substituents gave the
Supporting Information for this article is available online at
desired phenols in excellent yields. Noticeably, when 2-
iodophenol was employed as a substrate, 5 equivalents of
KOH were needed to achieve high conversions (entry 3).
Acknowledgment
The authors are grateful to National Natural Science Foundation of
China (grant 20621062 & 20872156) for their financial support.
Then, we further tested the activity of aryl bromides under
our reaction conditions. But several cases gave low yields
(entries 18–21), it seemed that our catalytic system was
not suited for aryl bromides. Only 4-nitrophenyl bromide
provided the corresponding phenol in good yield (entry
22).
References and Notes
(1) Weber, M.; Weber, M.; Kleine-Boymann, M. Phenol, In
Ullmann's Encyclopedia of Industrial Chemistry, 7th ed.;
Elvers, B.; Hawkins, S.; Schulz, G., Eds.; Wiley: Weinheim,
2004.
(2) (a) Gerlich, O.; Pompetzki, W.; Ahrens, D. EP 980846,
2000. (b) Vlad, I.; Mercas, M.; Stratula, C.; Cheta, I.; Oprea,
F. RO 109191, 1994.
(3) (a) Tyrer, D. US 2445500, 1945. (b) Oren, J.; Adda, M.
WO 9726235, 1997. (c) Matsumoto, M.; Kyoshima, J.
JP 06211716, 1994.
When methyl 4-iodobenzoate was used, 4-hydroxybenzo-
ic acid was isolated in 90% yield, indicating that the ester
moiety could not survive under these reaction conditions.
While both hydroxylation and dehydration occurred when
1-(4-iodophenyl)ethanol was utilized, as evident from the
formation of 4-vinylphenol in 60% (Scheme 1).
(4) (a) Stepaniuk, N. J.; Lamb, B. J. US 4822927, 1989.
(b) Wu, Z.; Glaser, R. J. Am. Chem. Soc. 2004, 126, 10632.
(5) (a) Anderson, K. W.; Ikawa, T.; Tundel, R. E.; Buchwald, S.
L. J. Am. Chem. Soc. 2006, 128, 10694. (b) Clement, J.-B.;
Hayes, J. F.; Sheldrake, H. M.; Sheldrake, P. W.; Wells,
A. S. Synlett 2001, 1423.
I
MeOOC
HO
OH
HOOC
CuI(10 mol%)
E (20 mol%)
1r
2r 90%
2s 60%
KOH
t-BuOH–DMSO–H2O
100 °C, 48 h
OH
I
(6) Chen, G.; Chan, A. S. C.; Kwong, F. Y. Tetrahedron Lett.
2007, 48, 473.
1s
(7) (a) Schulz, T.; Torborg, C.; Schäffner, B.; Huang, J.; Zapf,
A.; Kadyrov, R.; Börner, A.; Beller, M. Angew. Chem. Int.
Ed. 2009, 48, 918. (b) Sergeev, A. G.; Schulz, T.; Torborg,
C.; Spannenberg, A.; Neumann, H.; Beller, M. Angew.
Chem. Int. Ed. 2009, 48, 7595.
Scheme 1
For 4-bromobenzonitrile, a mixture of 4-hydroxy benzoic
(8) For selected examples for copper-catalyzed arylation of
phenols, see: (a) Cai, Q.; He, G.; Ma, D. J. Org. Chem. 2006,
71, 5268. (b) Cai, Q.; Zou, B.; Ma, D. Angew. Chem. Int. Ed.
2006, 45, 1276. (c) Buck, E.; Song, Z. J.; Tshaen, D.;
Dormer, P. G.; Volane, R. P.; Reider, P. J. Org. Lett. 2002,
4, 1623. (d) Cristau, H.-J.; Cellier, P. P.; Hamada, S.;
Spindler, J.-F.; Taillefer, M. Org. Lett. 2004, 6, 913.
(e) Ma, D.; Cai, Q. Org. Lett. 2003, 5, 3799. (f) Ouali, A.;
Spindler, J.-F.; Cristau, H.-J.; Taillefer, M. Adv. Synth.
Catal. 2006, 348, 499.
acid (2r) and 4-bromo benzoic acid (4, the ratio is about
1:3 determined by H NMR) was obtained (Scheme 2).
This result indicates that the nitrile group was totally hy-
drolyzed under these reaction conditions.
1
CuI (10 mol%)
E (20 mol%)
OH
HOOC
Br
NC
2r 21%
4 62%
KOH, DMSO–H2O
80 °C, 48 h
3f
(9) (a) Kormos, C. M.; Leadbeater, N. E. Tetrahedron 2006, 62,
4728. (b) Ma, D.; Cai, Q.; Zhang, H. Org. Lett. 2003, 5,
2453.
Br
HOOC
(10) Zhao, D.; Wu, N.; Zhang, S.; Xi, P.; Su, X.; Lan, J.; You, J.
Angew. Chem. Int. Ed. 2009, 48, 8729.
Scheme 2
(11) Tlili, A.; Xia, N.; Monnier, F.; Taillefer, M. Angew. Chem.
Int. Ed. 2009, 48, 8725.
In conclusion, we have developed an efficient and mild
protocol for the copper-catalyzed hydroxylation of aryl
iodides which provided phenols with a wide diversity of
substitution patterns, employing the commercial available
ligand 8-hydroxyquinoline. Many functional groups such
as nitro, carbonyl, carboxyl, and hydroxy groups are tol-
erated under these reactions conditions. The unusual
solvent system DMSO–t-BuOH–H2O successfully sup-
pressed the undesirable sublimation process that a range
(12) Typical Procedure for Preparation of 2a
An oven-dried Schlenk tube was charged with CuI (19 mg,
0.1 mmol), 4-iodoanisole (1 mmol), 8-hydroxyquinoline (29
mg, 0.2 mmol), and KOH (224 mg, 4 mmol). The tube was
evacuated and backfilled with argon, and DMSO (1 mL),
t-BuOH (1 mL), and H2O (0.1 mL) were added. The reaction
mixture was stirred at 100 °C till the material was
completely converted (monitored by TLC). Then the
mixture was acidified to pH ~1 with 1 N HCl. Extract
workup followed by chromatography afford 4-methoxy-
phenol in 96% yield.
Synlett 2010, No. 6, 976–978 © Thieme Stuttgart · New York