D. W. Blevins et al. / Tetrahedron Letters 52 (2011) 6534–6536
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Table 1
Iron trichloride promoted hydrolysis of potassium organotrifluoroborates
Entry
Substrate
Time (min)
Yielda (%)
Entry
9
Substrate
Me
Time (min)
30
Yielda (%)
Me
1
60
98
92
70
BF3K
O2N
BF3K
CHO
KF3B
2
60
97
10
25
Me
Me
BF3K
BF3K
OMe
BF3K
BF3K
N
N
F
F
3
4
5
60
94
11
12
13
60
30
30
80
87
85
MeO
F3C
CF3
BF3K
n-C5H11
420
30
98b
91
Br
Cl
BF3K
BF3K
BF3K
KF3B
OMe
6
7
30
30
81
86
14
15
30
25
98
86
Me
Me
Me
BF3K
BF3K
BF3K
8
30
94
a
Isolated yields of pure boronic acids. For experimental details, see Ref. 19
Refluxed at 65 °C.
b
proved to be more efficient than the previously reported methods.
For example, hydrolysis of potassium organotrifluoroborates bear-
ing electron-withdrawing groups requires only 60 min (entries
1–3) at room temperature (as compared to 24 h using either silica
gel or alumina). As expected, hydrolysis of potassium organotrifluo-
roborates bearing two strong electron-withdrawing groups (entry
4) is slower. For neutral aryltrifluoroborates and those containing
electron-donating groups, the hydrolysis is complete within 30
minutes (entries 6–10). As was observed in the previous
reports, prolonged reaction times can lead to partial protodeborona-
tion for more reactive reagents such as potassium 2,
2-dimethylpropyltrifluoroborate.
References and notes
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allylboration, see: (b) Suzuki, A. J. Organomet. Chem. 1999, 576, 147; (c) Hall, D. G.
Pure Appl. Chem. 2008, 80, 913; (d) Elford, T. G.; Hall, D. G. Synthesis 2010, 893.
2. (a) Chan, D. M. T.; Monaco, K. L.; Wang, R. P. Tetrahedron Lett. 1998, 39, 2933;
(b) Evans, D. A.; Katz, J. L.; West, T. R. Tetrahedron Lett. 1998, 39, 2937; (c)
Decicco, C. P.; Song, Y.; Evans, D. A. Org. Lett. 2001, 3, 1029; (d) Quach, T. D.;
Batey, R. A. Org. Lett. 2003, 5, 1381; (e) Ley, S. V.; Thomas, A. W. Angew. Chem.,
Int. Ed. 2003, 42, 5400.
3. (a) Lam, P. Y. S.; Clark, C. G.; Saubern, S.; Adams, J.; Winters, M. P.; Chan, D. M.
T.; Combs, A. Tetrahedron Lett. 1998, 39, 2941; (b) Collot, V.; Bovy, P. R.; Rault, S.
Tetrahedron Lett. 2000, 41, 9053.
4. (a) Kabalka, G. W.; Gooch, E. E. J. Org. Chem. 1980, 45, 3578; (b) Kabalka, G.
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15434; (e) Furuya, T.; Ritter, T. J. Am. Chem. Soc. 2008, 130, 10060; (f)
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Ishiyama, T.; Takagi, J.; Ishida, K.; Miyaura, N. J. Am. Chem. Soc. 2002, 124, 390;
(f) Boller, T. M.; Murphy, J. M.; Hapke, M.; Ishiyama, T.; Miyaura, N.; Hartwig, J.
F. J. Am. Chem. Soc. 2005, 127, 14263; (g) Boebel, T. A.; Hartwig, J. F. J. Am. Chem.
Soc. 2008, 130, 7534; (h) Kawamorita, S.; Ohmiya, H.; Hara, K.; Fukuoka, A.;
Sawamura, M. J. Am. Chem. Soc. 2009, 131, 5058.
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(b) Petasis, N. A.; Zavialov, I. A. J. Am. Chem. Soc. 1997, 119, 445.
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Suzuki, R.; Hattori, K.; Nishiyama, H. Synlett 2006, 1027.
Under optimized hydrolysis conditions, heteroaryl-, alkenyl-,
and alkyltrifluoroborates (entries 11–15) are also hydrolyzed effec-
tively within 1 h.
A detailed mechanistic study has not been carried out, but it is
thought that the iron(III) cation promotes the hydrolysis of
organotrifluoroborates because the resulting iron(III) fluoride has
a large lattice enthalpy (5,870 kj molÀ1 21
and low solubility in
)
the solvent system used. These are the same factors thought to
govern the lithium hydroxide13b and alumina18 mediated hydro-
lyses of organotrifluoroborates.
In conclusion, we have developed an efficient procedure for the
hydrolysis of organotrifluoroborates to the corresponding boronic
acids using iron trichloride.
Acknowledgments
9. (a)Hall, D. G., Ed.Boronic Acids; Wiley-VCH: Weinheim, 2005; (b) Kumar, S. K.;
Hager, E.; Pettit, C.; Gurulingappa, H.; Davidson, N. E.; Khan, S. R. J. Med. Chem.
2003, 46, 2813; (c) Winum, J.-Y.; Innocenti, A.; Scozzafava, A.; Montero, J.-L.;
Supuran, C. T. Bioorg. Med. Chem. 2009, 17, 3649.
10. (a) Gao, X.; Zhang, Y.; Wang, B. Org. Lett. 2003, 5, 4615; (b) Coskun, A.; Akkaya,
E. U. Org. Lett. 2004, 6, 3107.
We wish to thank Frontier Scientific, Inc., for generously provid-
ing a number of boron precursors and the Robert H. Cole Founda-
tion for Financial support.
11. (a) Coutts, S. J.; Adams, J.; Krolikowski, D.; Snow, R. Tetrahedron Lett. 1994, 35,
5109; (b) Pennington, T. E.; Hardiman, C.; Hutton, C. A. Tetrahedron Lett. 2004,
45, 6657.
12. Nakamura, H.; Fujiwara, M.; Yamaoto, Y. J. J. Org. Chem. 1998, 63, 7529.