and tetrazolyl ether, have also been reported to serve as substrates
for reductive deoxygenation. See references cited in 3b.
5 The cleavage of the C(aryl)–O bond in pincer-type ligands using a
stoichiometric amount of a rhodium complex has been reported:
M. E. van der Boom, S.-Y. Liou, Y. Ben-David, L. J. W. Shimon
and D. Milstein, J. Am. Chem. Soc., 1998, 120, 6531.
6 (a) M. Tobisu, T. Shimasaki and N. Chatani, Angew. Chem., Int.
Ed., 2008, 47, 4866; (b) M. Tobisu, T. Shimasaki and N. Chatani,
Chem. Lett., 2009, 38, 710; see also: (c) T. Shimasaki, Y. Konno,
M. Tobisu and N. Chatani, Org. Lett., 2009, 11, 4890.
7 (a) E. Wenkert, E. L. Michelotti and C. S. Swindell, J. Am. Chem.
Soc., 1979, 101, 2246; (b) E. Wenkert, E. L. Michelotti,
C. S. Swindell and M. Tingoli, J. Org. Chem., 1984, 49, 4894;
(c) J. W. Dankwardt, Angew. Chem., Int. Ed., 2004, 43, 2428;
(d) B.-T. Guan, S.-K. Xiang, T. Wu, Z.-P. Sun, B.-Q. Wang,
K.-Q. Zhao and Z.-J. Shi, Chem. Commun., 2008, 1437Ni-
catalyzed cross-coupling involving the cleavage of C(aryl)–OH
bonds in naphthols has also been reported: (e) D.-G. Yu,
B.-J. Li, S.-F. Zheng, B.-T. Guan, B.-Q. Wang and Z.-J. Shi,
Angew. Chem., Int. Ed., 2010, 49, 4566.
8 Results using other reducing agents are as follows. HB(pin): 64%
GC yield at 140 1C for 12 h. HCO2NH4: 0%. For a complete list of
hydrosilanes examined, see ESIw.
9 b-Hydride elimination of methoxo-metal to form metal-hydride
and formaldehyde is proposed in the stoichiometric C(aryl)–O
bond cleavage reaction. See ref. 5.
Scheme 2 A pivaloxy group as a removal handle for regioselective
arene functionalization.
processes,16 our deoxygenation protocol should be useful for
structure–activity relationship studies of such compounds.
A
representative synthetic application of this nickel-
catalyzed deoxygenation reaction is depicted in Scheme 2. A
pivalate group can activate a benzene ring toward electrophilic
bromination and also direct the reaction to occur at the para
position, affording 24. The robust nature of a pivalate group
made this group remain intact during the catalytic arylation
under Suzuki–Miyaura conditions, forming 25. A pivalate
group then serves as an ortho-director in a palladium-catalyzed
C–H bond activation reaction using diaryliodonium salts,17
which leads to the formation of 26. Finally, a pivaloxy group
can be removed through our catalysis to furnish 27. Thus, a
pivaloxy group can be employed as a versatile traceless
handle for regioselective functionalization reactions of aromatic
compounds.18
10 Reducing ability of alkoxysilanes is increased by forming hyper-
valent species. See: (a) S. Rendler and M. Oestreich, Synthesis,
2005, 1727; (b) Y. Orito and M. Nakajima, Synthesis, 2006,
1391.
11 A similar interaction has been indicated in the transmetalation
between Ar–Ni–OAc and PhB(OH)2 by DFT calculation: Z. Li,
S.-L. Zhang, Y. Fu, Q.-X. Guo and L. Liu, J. Am. Chem. Soc.,
2009, 131, 8815.
12 C(benzyl)–O bonds are normally cleaved preferentially over
C(aryl)–O bonds. For example, catalytic hydrogenolysis of benzyl
phenyl ether affords phenol and toluene: C. H. Hartung and
C. Simonoff, Org. React., 1953, 7, 263.
13 (a) F. Kakiuchi, M. Usui, S. Ueno, N. Chatani and S. Murai,
J. Am. Chem. Soc., 2004, 126, 2706; (b) S. Ueno, E. Mizushima,
N. Chatani and F. Kakiuchi, J. Am. Chem. Soc., 2006, 128,
16516.
14 (a) B.-T. Guan, Y. Wang, B.-J. Li, D.-G. Yu and Z.-J. Shi, J. Am.
Chem. Soc., 2008, 130, 14468; (b) K. W. Quasdorf, X. Tian and
N. K. Garg, J. Am. Chem. Soc., 2008, 130, 14422; (c) B.-J. Li,
Y.-Z. Li, X.-Y. Lu, J. Liu, B.-T. Guan and Z.-J. Shi, Angew.
Chem., Int. Ed., 2008, 47, 10124; (d) B.-J. Li, L. Xu, Z.-H. Wu,
B.-T. Guan, C.-L. Sun, B.-Q. Wang and Z.-J. Shi, J. Am. Chem.
Soc., 2009, 131, 14656; (e) T. Shimasaki, M. Tobisu and
N. Chatani, Angew. Chem., Int. Ed., 2010, 49, 2929.
15 The use of acetate and benzoate of biphenyl-4-ol resulted
in the undesired cleavage of C(acyl)–O bonds. This trend is
typically observed in other nickel-catalyzed transformation of aryl
carboxylates. See refs. 14a, b and e.
In summary, we have developed a nickel-catalyzed method
for removing oxygenated functionalities, such as alkoxy and
pivaloxy groups, on aromatic rings using hydrosilane as a mild
reducing agent.19 In addition to a fundamental significance in
terms of catalytic activation of unreactive carbon–oxygen
bonds, the present study offers a new synthetic strategy for a
regioselective functionalization of arenes by employing steric,
electronic and coordinating nature of alkoxy and pivaloxy
groups temporarily. Studies are ongoing to further develop
the nickel-catalyzed transformation of inert carbon–oxygen
bonds.
16 For a representative review, see: P. Heneberg, Curr. Med. Chem.,
2009, 16, 709.
17 B. Xiao, Y. Fu, J. Xu, T.-J. Gong, J.-J. Dai, J. Yi and L. Liu,
J. Am. Chem. Soc., 2010, 132, 468.
18 For other traceless directing groups for C–H bond functionalization
reactions: (a) V. G. Zaitsev, D. Shabashov and O. Daugulis,
J. Am. Chem. Soc., 2005, 127, 13154; (b) S. J. Pastine,
D. V. Gribkov and D. Sames, J. Am. Chem. Soc., 2006, 128,
Notes and references
1 Selected recent examples: (a) J. Cianci, J. B. Baell, B. L. Flynn,
R. W. Gable, J. A. Mould, D. Paul and A. J. Harvey, Bioorg. Med.
Chem. Lett., 2008, 18, 2055; (b) N. Z. Burns, I. N. Krylova,
R. N. Hannoush and P. S. Baran, J. Am. Chem. Soc., 2009, 131,
9172.
2 Selected recent examples: (a) G. Arnott, H. Brice, J. Clayden and
E. Blaney, Org. Lett., 2008, 10, 3089; (b) C. J. Rohbogner,
G. C. Clososki and P. Knochel, Angew. Chem., Int. Ed., 2008,
47, 1503.
3 Selected examples: (a) S. Cacchi, P. G. Ciattini, E. Morera and
G. Ortar, Tetrahedron Lett., 1986, 27, 5541; (b) A. Mori,
T. Mizusaki, T. Ikawa, T. Maegawa, Y. Monguchi and
H. Sajiki, Chem.–Eur. J., 2007, 13, 1432.
4 Although less common, leaving groups, including tosylates,
mesylates, phosphates, carbamimidates, 2,4-dinitrophenyl ether
14220; (c) A. Garcıa-Rubia, R. G. Arrayas and J. C. Carretero,
´ ´
Angew. Chem., Int. Ed., 2009, 48, 6511; (d) M. Tobisu,
R. Nakamura, Y. Kita and N. Chatani, J. Am. Chem. Soc.,
2009, 131, 3174; (e) M. Tobisu, R. Nakamura, Y. Kita and
N. Chatani, Bull. Korean Chem. Soc., 2010, 31, 582;
(f) N. Chernyak, A. S. Dudnik, C. Huang and V. Gevorgyan,
J. Am. Chem. Soc., 2010, 132, 8270.
19 (a) The studies outlined in this manuscript were first presented at
the 90th annual meeting of the Chemical Society of Japan on
March 28, 2010 (No. 3F2-01); (b) During the preparation of this
´
manuscript, an independent work appeared: P. Alvarez-Bercedo
and R. Martin, J. Am. Chem. Soc., 2010, 132, 17352.
c
2948 Chem. Commun., 2011, 47, 2946–2948
This journal is The Royal Society of Chemistry 2011