(Table 1, entries 2 and 3) and the use of TfOH led to a 65%
yield of 2a (Table 1, entry 3). To our delight, the yield of
2a was improved up to 81% in the presence of 0.3 equiv of
TfOH (Table 1, entry 5). Other solvents such as toluene,
DCE, and DMF retarded this transformation (Table 1,
entries 7ꢀ9). It should be noted that the yields of phenol
3a were higher than the yields of the furan 2a in all cases,
indicating that the migration of the phenyl group is prior
to the formation of 2a.
Scheme 1. Rearrangements of Organic Peroxides
Table 1. Optimization of the Reaction Conditions for
Acid-Promoted Rearrangement of 1aa
products8 but also their usefulness as building blocks in
synthetic chemistry.9 For these reasons, the exploration of
new methods for the synthesis of polysubstituted furans
continues to attract the interest of chemists.10 Herein, we
would like to disclose a novel method to construct 2,3-
disubstituted furans throughanefficient and selective acid-
catalyzed 1,2-aryl migration of tert-butylperoxides. Base-
catalyzed KornblumꢀDelaMare rearrangement followed
by acid-promoted PaalꢀKnorr furan formation for the
synthesis of 2,3,5-trisubstituted or 2,5-disubstituted furans
was also investigated.
To continue our exploration on the synthesis and appli-
cations of functionalized organic peroxides,11 a series of
γ-carbonyl peroxides were prepared by the Co-catalyzed
three-component reactions of alkenes, tert-butyl hydro-
peroxide (TBHP), and diones or β-ketone esters.12 Initi-
ally, the tert-butylperoxyl compound 1a was selected as a
model substrate to investigate the transformation. The
furan product 2a was obtained in 21% yield together with
a 54% yield of phenol 3a by the use of 1.0 equiv of
entry
acid (x equiv)
solvent
2a (%)b
3a (%)b
1
2
3
4
5
6
7
8
9
TsOH H2O (1.0)
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
toluene
DCE
21
54
56
84
90
87
74
70
63
<5
3
H2SO4 (1.0)
TfOH (1.0)
TfOH (0.5)
TfOH (0.3)
TfOH (0.1)
TfOH (0.3)
TfOH (0.3)
TfOH (0.3)
49
65
70
81(80)
62
56
47
DMF
trace
a Conditions: 1a (0.2 mmol), solvent (2.0 mL), 85 °C, 1 h. b NMR
yields were determined by 1H NMR using an internal standard; isolated
yield was given in parentheses.
Subsequently, the different migration groups were ex-
plored for this transformation in the presence of 0.3 equiv
of TfOH (Scheme 2). To our delight, we found that a vari-
ety of aryl groups could migrate smoothly, and the furan
product 2a and the corresponding phenolic compounds 3
were obtained in good to excellent yields. Substrates with
electron-donating (1b and 1c) or electron-withdrawing (1d
and 1e) groups on the aryl ring all proceeded well under the
optimized reaction conditions. Notably, bulky phenol 3f
could also be obtained in 83% yield through this TfOH
catalyzed 1,2-aryl migration reaction. Moreover, 2-naphthyl
substituted peroxide 1g also gave the furan 2a and
2-naphthol 3g in good yields.
TsOH H2O in CH3CN at 85 °C for 1 h (Table 1, entry 1).
Further investigations showed that the efficiency of the
furan formation is affected by the acidity of the acids
3
(8) (a) Corma, A.; Iborra, S.; Velty, A. Chem. Rev. 2007, 107, 2411.
(b) Lipshutz, B. H. Chem. Rev. 1986, 86, 795.
(9) (a) Katritzky, A. R. Comprehensive Heterocyclic Chemistry III;
Elsevier: Amsterdam; New York, 2008. (b) Kirsch, S. F. Org. Biomol. Chem.
2006, 4, 2076. (c) Maier, M. In Organic Synthesis Highlights II; Waldmann,
H., Ed.; VCH: Weinheim, 1995; p 231.
(10) (a) Yang, Y.; Yao, J.; Zhang, Y. Org. Lett. 2013, 15, 3206. (b) He,
C.; Guo, S.; Ke, J.; Hao, J.; Xu, H.; Chen, H.; Lei, A. J. Am. Chem. Soc.
2012, 134, 5766. (c) Lenden, P.; Entwistle, D. A.; Willis, M. C. Angew.
Chem., Int. Ed. 2011, 50, 10657. (d) Zhang, M.; Jiang, H.-F.; Neumann,
H.; Beller, M.; Dixneuf, P. H. Angew. Chem., Int. Ed. 2009, 48, 1681. (e)
Dudnik, A. S.; Sromek, A. W.; Rubina, M.; Kim, J. T.; Kel’in, A. V.;
Gevorgyan, V. J. Am. Chem. Soc. 2008, 130, 1440. (f) Xiao, Y.; Zhang, J.
Angew. Chem., Int. Ed. 2008, 47, 1903. (g) Brown, R. C. D. Angew.
Chem., Int. Ed. 2005, 44, 850. (h) Xiao, T.; Zhang, X.; Larock, R. C. J.
Am. Chem. Soc. 2004, 126, 11164. (i) Jung, C.-K.; Wang, J.-C.; Krische,
M. J. J. Am. Chem. Soc. 2004, 126, 4118. (j) Sromek, A. W.; Kel’in, A. V.;
Gevorgyan, V. Angew. Chem., Int. Ed. 2004, 43, 2280. (k) Ma, S.; Zhang,
J. J. Am. Chem. Soc. 2003, 125, 12386. (l) Hashmi, A. S. K.; Schwarz, L.;
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(11) (a) Liu, K.; Li, Y.; Liu, W.; Zheng, X.; Zong, Z.; Li, Z. Chem.;
Asian J. 2013, 8, 359. (b) Liu, K.; Li, Y.; Zheng, X.; Liu, W.; Li, Z.
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Encouraged by the successful transformation of 1a to
furan 2a, we then extended the reaction to a range of
substituted γ-carbonyl peroxides, and a variety of 2,3-
disubstituted furans 2 were obtained in moderate to good
yields (Table 2). Methyl-substituted tert-butylperoxide 1h
gave the corresponding furan 2b in moderate yield
(Table 2, entry 1). Both isomers of the expected furans,
2c and 2c0, were obtained when the unsymmetric substate
1i was used (Table2, entry 2). β-Benzoyl ester derived tert-
butylperoxides 1jꢀ1m all proceeded well and gave the 2-aryl-
3-ester furans 2dꢀ2g in good yields (Table 2, entries 3ꢀ6).
To our satisfaction, 2-alkyl-3-ester furans 2hꢀ2k could
also be synthesized smoothly from the corresponding
(12) See the details of the preparation in the Supporting Information.
Org. Lett., Vol. 15, No. 21, 2013
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