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ChemComm
DOI: 10.1039/C5CC03563E
COMMUNICATION
Journal Name
cleavage of C-O-C in di-4-ethyl-phenyl ether and di-4-tert- depolymerize the common aryl C-O-C linkage in lignin compounds
butylphenyl ether resulted in ethylbenzene and tert-butylbenzene, to arenes. In these reactions, the desired products are obtained in
respectively (Table 2, entries 14, 15). As for di-2-methoxyphenyl good to excellent yields and the aromatic rings are not
ether that contains two aryl methoxyl groups and an aryl C-O-C hydrogenated. Particularly, the transformation of phenols to arenes
linkage, all the three aryl C-O bonds could be cleaved, producing was achieved for the first time below 200 °C. Although the reaction
benzene in a yield of 38% under the experimental conditions. When mechanism of these interesting reactions needs to be further
the amounts of LiAlH
respectively, a benzene yield of 74% was achieved; further reductive cleavage of aromatic C-O bonds is under a radical
increasing the amounts of LiAlH and KOtBu to 15 and 7.5 equiv., mechanism. This work opens a novel and simple way to produce
4
and KOtBu were increased to 10 and 5 equiv., studied, the results from this work have demonstrated that the
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respectively, the benzene yield reached 95% (Table 2, entry 16). 2- arenes from aryl C-O containing compounds, which may have
Phenoxy-1-phenethanol was transformed to benzene and ethyl promising applications in the production of aromatics from lignin
benzene under the experimental conditions (Table 2, entry 17). The compounds.
formation of ethylbenzene suggests that the alkyl hydroxyl group
This work was financiallysupported by theNational Natural
could be removed under the experimental conditions, probably via Science Foundation of China (No. 21125314, 21321063, 21403252).
the dehydration and subsequent hydrogenation of the
corresponding intermediate. Similarly, keeping the amounts of
Notes and references
4
LiAlH and KOtBu to C-O bonds in the substrate at 5 and 2.5 equiv.,
respectively, higher products yields (benzene 94%, ethyl benzene
1
E. Furimsky, Appl. Catal. A.,2000, 199, 147; J. Zakzeski, P. C.
A. Bruijnincx, A. L. Jongerius, B. M. Weckhuysen, Chem. Rev.,
7
4%) could be achieved. 2-(2-Methoxylphenoxy)-1-phenethanol and
-phenoxy-1-phenylpropal-1,3-diol are lignin model compounds
2
Grubbs, Chem. Sci., 2013, , 1640.
010, 110, 3552; A. Fedorov, A. A. Toutov, N. A. Swisher, R. H.
4
2
with more complicated structures, which were also nearly
completely deoxygenated (Table 2, entries 18, 19). As for 1,4-
diphenoxybenzene, which is a trimmer in lignin model compounds,
the two C-O-C linkages were broken, further being deoxygenated to
benzene (64%) (Table 2, entry 20). The above findings indicate that
all the aryl C-O bonds in phenols, aryl ethers and diaryl etherscould
2
3
A. Maercker, Angew. Chem. Int. Ed., 1987, 26, 972.
P. Dabo, A. Cyr, J. Lessard, L. Brossard, H. Ménard, Can. J.
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P. Alvarez-Bercedo, R. Martin, J. Am. Chem. Soc., 2010,
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32, 17352; A. G. Sergeev, J. F. Hartwig, Science, 2011, 332,
39; M. Tobisu, K. Yamakawa, T. Shimasaki, N. Chatani, Chem.
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Commun., 2011, 47, 2946; A. G. Sergeev, J. D. Webb, J. F.
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be cleaved to form corresponding arenes via the reduction by LiAlH
4
in the presence of KOtBu.
The reaction system of LiAlH
effective for the cleavage of various aryl C-O bonds. As known,
LiAlH is a commonly used reducing agent, which can generate
active H in reaction process, and also can accelerate single electron
4
and KOtBu was simple and very
5
6
4
B. M. Rosen, K. W. Quasdorf, D. A. Wilson, N. Zhang, A. M.
Resmerita, N. K. Garg, V. Percec, Chem. Rev., 2011, 111, 1346;
1
1
transfer in C-S bond cleavage. KOtBu is a strong base, which can
B. J. Li, D. G. Yu, C. L. Sun, Z. J. Shi, Chem. Eur. J., 2011, 17
1728; D. G. Yu, B. J. Li, Z. Shi, J. Acc. Chem. Res., 2010, 43
,
,
1
2
initiate radicals.
The reactions performed in the above
1
486.
experiments might be under a radical mechanism. To get some
evidences for the reaction mechanism, TEMPO (2,2,6,6-
tetramethylpiperidine 1-oxyl) as a radical scavenger was added to
the reaction system of phenol. It was found that TEMPO influenced
the reaction significantly. For example, a very low benzene yield of
7
8
C. Zhao, Y. Kou, A. A. Lemonidou, X. Li, J. A. Lercher, Angew.
Chem. Int. Ed., 2009, 48, 3987.
H. Sievekin, W. Luttke, Angew. Chem. Int. Ed., 1969, 8, 457;
A. Song, X. S. Zhang, X. X. Song, X. B. Chen, C. G. Yu, Angew.
Chem. Int. Ed., 2014, 53, 4940; J. Wang, A. D. Ebner, J. A.
Ritter, J. Am. Chem. Soc., 2006, 128, 5949; A. G. Schultz, M.
3
.2% was obtained as 1 equiv. of TEMPO was added, and no
product was detectable as the amount of TEMPO was increased to
.5 equiv. under the comparable other conditions (see Table S2).
Moreover, the reaction mixture was EPR active (see Figure S3),
A. Holoboski, M. S. Smyth, J. Am. Chem. Soc.,1996, 118
,
6213.
C. L. Sun, H. Li, D. G. Yu, M. Yu, X. Zhou, Nat. Chem., 2010, 2
1044.
2
9
,
indicating the existence of radicals during the reactions. As TEMPO 10 T. H. Parsell, B. C. Owen, I. Klein, T. M. Jarrell, C. L. Marcum,
Chem. Sci., 2013, 4, 806; S. K. Hanson, R. Wu, L. A. “Pete”
was added to the reaction system of anisole, similar results were
obtained. In addition, in the reaction solution of anisole methane
was generated. All these findings indicate that the reduction of
anisole also proceeded through a radical mechanism. Based on the
above results, a tentative mechanism for deoxygenation of phenols
Silks, Angew. Chem. Int. Ed., 2012, 51, 3410; S. Son, F. D.
Toste, Angew. Chem. Int. Ed., 2010,49, 3791; G. Zhang, B. L.
Scott, R. Wu, L. A. “Pete” Silks, S. K. Hanson, Inorg. Chem.,
2012, 51, 7354; J. M. Nichols, L. M. Bishop, R. G. Bergman, J.
A. Ellman, J. Am. Chem. Soc. 2010, 132, 12554 .
1
1 J. J. Eisch, L. E. Hallenbeck, K. I. Han, J. Am. Chem. Soc., 1986,
1
3
and aryl ethers in the LiAlH
4
/KOtBu reaction system was proposed
08, 7763; E. C. Ashby, C. O. Welder, J. Org. Chem., 1997, 62
542; E. C. Ashby, A. B. Goel, R. N. DePriest, H. S. Prasad, J.
,
and shown in Scheme S1.
In summary, selective cleavage of various aryl C-O bonds in
aromatic compounds to arenes was achieved using LiAlH
reducing agent in the presence of KOtBu. The LiAlH /KOtBu
Am. Chem. Soc., 1981, 103, 973.
as a 12 W. Liu, H. Cao, H. Zhang, H. Zhang, K. H. Chung, J. Am. Chem.
4
Soc., 2010, 132, 16737; M. Rueping, M. Leiendecker, A. Das,
T. Poisson, L. Bui, Chem. Commun., 2011, 47, 10629; G. P.
Yong, W. L. She, Y. M. Zhang, Y. Z. Li, Chem. Commun., 2011,
4
combination system not only possesses the ability to
simultaneously deoxygenate the aryl C-O containing aromatics to
benzene analogous, but also has the powerful ability to
47, 11766.
4
| J. Name., 2012, 00, 1-3
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