Copper-catalyzed activation of dioxygen: Oxidative cyclization of 2-arylindoles

Article abstract of DOI:10.1002/adsc.201200162

A series of unusual six-ring-fused heterocycles containing indole and quinoline skeletons was successfully synthesized by a copper-catalyzed reaction from 2-arylated indoles. Two new bonds were regioselectively formed from C-H and C-H coupling. ¹⁸O-Labelled experiments revealed that the dioxygen is not only the oxidant but also the reactant. Copyright

Full text of DOI:10.1002/adsc.201200162

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DOI: 10.1002/adsc.201200162
Copper-Catalyzed Activation of Dioxygen: Oxidative Cyclization
of 2-Arylindoles
Peng Sang,a Yongju Xie,a Jianwei Zou,a,b,* and Yuhong Zhanga,c,*
a
Department of Chemistry, Zhejiang University, Hangzhou 310027, Peopleꢀs Republic of China
Fax : (+86)-571-8795-3244; e-mail: yhzhang@zju.edu.cn
Ningbo Institute of Technology, Zhejiang University, Ningbo 315104, Peopleꢀs Republic of China
b
Fax : (+86)-574-8822-9516; e-mail: jwzou@nit.zju.edu.cn
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, Peopleꢀs Republic of China
c
Received: February 27, 2012; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201200162.
Abstract: A series of unusual six-ring-fused hetero-
cycles containing indole and quinoline skeletons
was successfully synthesized by a copper-catalyzed
reaction from 2-arylated indoles. Two new bonds
were regioselectively formed from C H and C H
coupling. 18O-Labelled experiments revealed that
the dioxygen is not only the oxidant but also the re-
actant.
rence in many natural products and biologically active
molecules and the fact that they play important roles
in the pharmaceutical and agrochemical industries.[6]
Indole[7] and quinoline[8] nuclei are privileged scaf-
folds that occupy a central role in many medicinally
relevant compounds. Indole derivatives are known to
exert antitubercular,[9] anticancer,[10] antiviral,[11] and
antioxidant activities.[12] Some of them are used to
lower cholesterol and prevent cardiovascular disease;
for example, fluvastatin, which includes an indole
moiety, is a synthetic member of the statin class of
drugs. The indole pharmacophore is even found in
a variety of antiobesity agents.[13] The quinoline ring
system is also prevalent in numerous marketed drugs
such as antibacterials, antimalarial agents, HIV-1 inte-
À
À
Keywords: copper; heterocycles; oxidative cycliza-
tion; oxygen
Oxidative C H bond functionalization is one of the grase inhibitors,[14] and other compounds of pharma-
most important and attractive strategies in organic ceutical interest.[15] Molecules containing a combina-
synthesis.[1] In most of these transformations, it is nec- tion of indole and quinoline frameworks (Figure 1)
essary to reoxidize the reduced catalyst to its oxidized are interesting synthetic target owing to their various
state.[2] For these transformations, molecular oxygen biological activities including antimalarial, anticancer,
(O2) is an ideal oxidant, since it is inexpensive and en- DNA binding and cytostatic activities.[16] Herein, we
vironmentally friendly. The use of dioxygen activation report the efficient cyclization of 2-arylindoles to the
for functionalization reactions represents one of the six-ring-fused heterocycles in the presence of
most ideal processes in organic synthesis.[3] Activation 20 mol% Cu(OH)2·CuCO3 catalyst under an oxygen
of O2 by copper enzymes has been observed in some atmosphere without the use of ligands and additional
biological oxygenase systems, such as monooxygenase bases or acids. The synthesized new motif has the po-
À
tyrosinase and dopamine b-monooxygenase that tential to exhibit biological activity. The mechanistic
[4]
À
effect the hydroxylation of C H bonds. Recently,
copper-catalyzed reactions that involve dioxygen acti-
vation and use rather simple models to realize bio-
mimetic syntheses have been intensively studied.[5] Al-
though remarkable success has been achieved, to the
best of our knowledge, it is still challenging to devel-
op aerobic oxidation systems employing low-cost
copper as catalyst to convert commercially available
or readily accessible materials in one step to target
compounds.
The construction of nitrogen heterocycles is an im-
portant goal in organic synthesis due to their occur- quinoline frameworks.
Figure 1. Structure of a conjugate containing indole and
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studies on the formation of these fused heterocycles product was found when the reaction was carried out
have been performed to provide valuable mechanistic under an N2 atmosphere (Table 1, entry 10). Oxidants
insights into the cyclization.
such as tert-butyl hydroperoxide (TBHP), t-BuOO-t-
Our initial attempt started with the reaction of 2- Bu, DDQ and Oxone showed poor efficiency
phenyl-1H-indole (1a) at 1308C in DMSO under O2 (Table 1, entries 11–14). The yield decreased when the
atmosphere by the use of CuBr as the catalyst which reaction temperature was decreased (Table 1, en-
afforded the fused heterocyclic product 2a in 18% tries 15 and 16). Other solvents such as DMF, toluene,
yield (Table 1, entry 1). Screening of the copper cata- and dioxane furnished the product in poor yields
lysts
Cu(OH)2·CuCO3
revealed
that
were
both
Cu
G
and (Table 1, entries 17 and 18).
that With the optimal reaction conditions in hand, we
active
Cu(OH)2·CuCO3 was the best to give the product 2a next examined the scope of various 2-arylindoles as
in 79% yield (Table 1, entries 1–7). No reaction was summarized in Table 2. It is found that a variety of
observed in the absence of copper catalyst (Table 1, substituted 2-arylindoles can be converted to the de-
entry 8). A 77% yield was obtained when the reaction sired products in modest to good yields, showing good
was carried out in air (Table 1, entry 9). However, no functional group tolerance. 2-Arylindoles with both
electron-withdrawing substituents (F, Cl, Br, I and
CF3) and electron-donating substituents (OMe and
Table 1. Screening for optimal conditions.[a]
Me) participated in the reaction smoothly to give the
fused heterocycles in good yields (2c, 2d, 2g–2l and
2n–2r). It should be noted that 2-o-tolyl-1H-indole
gave no product, indicating that the steric hindrance
played a role (2b). Two products were obtained when
2-m-tolyl-1H-indole was introduced as substrate (2c
and 2c’), and again the less hindered product 2c was
favored. The tolerance of halogen substituents pro-
vides this process with potential for further synthetic
transformations. The structure of the product was fur-
ther confirmed by an X-ray crystallographic study of
2a (Figure 2).[20] It was seen that the fused rings were
not in the same plane.
Entry
Catalyst
Oxidant
Yield [%][b]
1
2
CuBr
CuI
O2
O2
18
22
39
42
77
55
79
n.r.
77
n.r.
n.d.[c]
n.d.[d]
n.d.[d]
n.d.[d]
77[e]
11[f]
67 g]
n.r.[h]
3
4
CuCl
CuO
O2
O2
To gain insight into the reaction features, 2-phenyl-
indole and 2-p-tolyl-1H-indole were treated in one-
pot under the reaction conditions. A cross-over prod-
uct was indeed detected by HR-MS, supporting an in-
termolecular process [Eq. (1)]. Moreover, when 1a
5
Cu
G
O2
6
Cu(OAc)2·H2O
N
O2
7
8
Cu(OH)2·CuCO3
–
O2
O2
9
Cu(OH)2·CuCO3
Cu(OH)2·CuCO3
Cu(OH)2·CuCO3
Cu(OH)2·CuCO3
Cu(OH)2·CuCO3
Cu(OH)2·CuCO3
Cu(OH)2·CuCO3
Cu(OH)2·CuCO3
Cu(OH)2·CuCO3
Cu(OH)2·CuCO3
air
N2
10
11
12
13
14
15
16
17
18
t-BuOOH
t-BuOO-t-Bu
DDQ
Oxone
O2
O2
O2
O2
[a]
Reaction conditions: 1a (0.3 mmol), catalyst (0.06 mmol),
solvent (DMSO, 2 mL), air and O2 (1 atm) for 48 h.
Yield of isolated product.
t-BuOOH (1.5 equiv., 0.45 mmol) 0.30 mL, 5–6M in
decane, under a nitrogen atmosphere.
Oxidant (1.5 equiv., 0.45 mmol) under a nitrogen atmos-
phere.
The reaction was carried out at 1108C.
[b]
[c]
[d]
[e]
[f]
The reaction was carried out at 908C.
[g]
The reaction was carried out in DMF.[h] The reaction was
carried out in toluene or dioxane. t-BuOOH=tert-butyl
hydroperoxide, t-BuOO-t-Bu=di-tert-butyl peroxide,
DDQ=2,3-dichloro-5,6-dicyanobenzoquinone, Oxone=
potassium peroxomonosulfate.
Figure 2. The X-ray single crystal structure of product 2a.
2
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Copper-Catalyzed Activation of Dioxygen: Oxidative Cyclization of 2-Arylindoles
Table 2. Copper-catalyzed oxidative cyclization of various 2-arylindoles.[a,b]
[a]
Reaction conditions: 1a (0.3 mmol), Cu(OH)2·CuCO3 (0.06 mmol), DMSO (2 mL), O2 (1 atm), 1308C, 48 h.
Isolated yield.
[b]
was subjected to the reaction conditions employing tron transfer process. The subsequent deprotonating
a nitrogen rather than an oxygen atmosphere, forma- equilibrium gives the indolyl radical B, which is oxi-
tion of 2a did not take place (Table 1, entry 10). In dized by the oxygen/copper system to afford inter-
addition, a labelling experiment was performed using mediate C. The combination of intermediate C and D
an 18O2 atmosphere in anhydrous DMSO. About 78% delivers the oxidized dimer of 2-phenylindole E,
of the product had O18 incorporated, thus indicating which is indeed detected in the reaction solution by
that the carbonyl oxygen in the product derives from HR-MS. The subsequent cyclization might occur via
dioxygen [Eq. (2)]. On the basis of these experimen- the oxidative addition and reductive elimination pro-
tal results and a previous report,[17] a plausible reac- cess of a Cu(I)/Cu
ACTHNUTRGNEU(GN III) cycle, where the oxygen drives
tion mechanism was proposed as shown in Scheme 1. the process forward.[18] The electrophilic metallation
First, the indole radical cation A is formed in the and reductive elimination pathway is another possible
presence of copper catalyst and oxygen via the elec- route.[19]
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Scheme 1. Plausible reaction mechanism.
In summary, we have developed a copper-catalyzed were added to the cooled reaction mixture successively. The
organic phase was separated, and the aqueous phase was
further extracted with EtOAc (2ꢂ10 mL). The combined or-
ganic layers were dried over anhydrous MgSO4 and concen-
trated. The residue was subjected to flash column chroma-
tography (sila gel, petroleum ether/ethyl acetate=5:1, v/v)
to obtain the desired products in 79% yield.
method for the dimerization of 2-arylindoles. This
transformation provides a novel route for accessing
fused nitrogen-containing heterocycles. The use of an
inexpensive copper catalyst and O2 or air as the oxi-
dant is a practical advantage. The incorporation of an
oxygen atom into the organic frameworks from at-
mospheric molecular oxygen (O2) offers the most
ideal oxidation process. Further studies to elucidate
the detailed reaction mechanism and the synthetic ap-
plications are ongoing in our group.
Acknowledgements
We gratefully acknowledge the National Basic Research Pro-
gram of China (No. 2011CB936003) and NSFC (No.
21072169) for their financial support
Experimental Section
Typical Procedure for the Preparation of 2a
To an oven-dried Schlenk tube under an O2 atmosphere References
were sequentially added Cu(OH)2·CuCO3 (13.3 mg,
À
0.06 mmol) and the 2-phenylindole (57.9 mg, 0.3 mmol), fol-
lowed by DMSO (2 mL). The reaction vessel was immersed
in an oil bath preheated to 1308C and allowed to stir for
48 h. Saturated aqueous NaCl (10 mL), and EtOAc (10 mL)
[1] For some reviews on C H bond activation, see: a) L.
Ackermann, Chem. Rev. 2011, 111, 1315–1345; b) J.
Le Bras, J. Muzart, Chem. Rev. 2011, 111, 1170–1214;
c) C. S. Yeung, V. M. Dong, Chem. Rev. 2011, 111,
4
asc.wiley-vch.de
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Copper-Catalyzed Activation of Dioxygen: Oxidative Cyclization of 2-Arylindoles
1215–1292; d) C.-L. Sun, B.-J. Li, Z.-J. Shi, Chem. Rev.
2010, 110, 1293–1314; e) F. Bellina, R. Rossi, Chem.
Rev. 2010, 110, 1082–1146; f) D. Balcells, E. Colt, O. Ei-
senstein, Chem. Rev. 2010, 110, 749–823; g) T. W.
Lyons, M. S. Sanford, Chem. Rev. 2010, 110, 1147–1169.
[2] For some recent examples, see: a) W. Wei, X.-Y. Hu,
X.-W. Yan, Q. Zhang, M. Cheng, J.-X. Ji, Chem.
Commun. 2012, 48, 305–307; b) F. Yang, Z. Xu, Z.
Wang, Z. Yu, R. Wang, Chem. Eur. J. 2011, 17, 6321–
6325; c) B.-X. Tang, R.-J. Song, C.-Y. Wu, Y. Liu, M.-B.
Zhou, W.-T. Wei, G.-B. Deng, D.-L. Yin, J.-H. Li, J.
Am. Chem. Soc. 2010, 132, 8900–8902; d) A. John,
K. M. Nicholas, J. Org. Chem. 2011, 76, 4158–4162;
e) E. Boess, D. Sureshkumar, A. Sud, C. Wirtz, C.
Fareꢃs, M. Klussmann, J. Am. Chem. Soc. 2011, 133,
8106–8109.
[9] V. S. Velezheva, P. J. Brennan, V. Y. Marshakov, D. V.
Gusev, I. N. Lisichkina, A. S. Peregudov, L. N. Tcher-
nousova, T. G. Smirnova, S. N. Andreevskaya, A. E.
Medvedev, J. Med. Chem. 2004, 47, 3455–3461.
[10] a) A. Andreani, S. Burnelli, M. Granaiola, A. Leoni, A.
Locatelli, R. Morigi, M. Rambaldi, L. Varoli, L. Landi,
C. Prata, M. V. Berridge, C. Grasso, H.-H. Fiebig, G.
Kelter, A. M. Burger, M. W. Kunkel, J. Med. Chem.
2008, 51, 4563–4570; b) S. Routier, P. Peixoto, J.-Y.
Mꢅrour, G. Coudert, N. Dias, C. Bailly, A. Pierrꢅ, S.
Lꢅonce, D.-H. Caignard, J. Med. Chem. 2005, 48, 1401–
1413.
[11] G. La Regina, A. Coluccia, F. Piscitelli, A. Bergamini,
A. Sinistro, A. Cavazza, G. Maga, A. Samuele, S.
Zanoli, E. Novellino, M. Artico, R. Silvestri, J. Med.
Chem. 2007, 50, 5034–5038.
[3] Dioxygen has been used as an ideal oxidant, for some
reviews, see: a) K. M. Gligorich, M. S. Sigman, Chem.
Commun. 2009, 26, 3854–3867; b) J. Piera, J.-E. Bꢄck-
vall, Angew. Chem. 2008, 120, 3558–3576; Angew.
Chem. Int. Ed. 2008, 47, 3506–3523; c) M. S. Sigman,
D. R. Jensen, Acc. Chem. Res. 2006, 39, 221–229; d) T.
Punniyamurthy, S. Velusamy, J. Iqbal, Chem. Rev. 2005,
105, 2329–2364; e) S. S. Stahl, Angew. Chem. 2004, 116,
3480–3501; Angew. Chem. Int. Ed. 2004, 43, 3400–3420.
[4] For reviews, see: a) E. I. Solomon, P. Chen, M. Metz,
S.-K. Lee, A. E. Palmer, Angew. Chem. 2001, 113,
4702–4724; Angew. Chem. Int. Ed. 2001, 40, 4570–4590;
b) E. I. Solomon, U. M. Sundaram, T. E. Machonkin,
Chem. Rev. 1996, 96, 2563–2606.
[5] For some copper-catalyzed reactions involving dioxy-
gen activation, see: a) C. Zhang, Z. Xu, L. Zhang, N.
Jiao, Angew. Chem. 2011, 123, 11284–11288; Angew.
Chem. Int. Ed. 2011, 50, 11088–11092; b) H. Wang, Y.
Wang, D. Liang, L. Liu, J. Zhang, Q. Zhu, Angew.
Chem. 2011, 123, 5796–5799; Angew. Chem. Int. Ed.
2011, 50, 5678–5681; c) L. Zhang, G. Y. Ang, S. Chiba,
Org. Lett. 2011, 13, 1622–1635; d) A. E. King, L. M.
Huffman, A. Casitas, M. Costas, X. Ribas, S. S. Stahl, J.
Am. Chem. Soc. 2010, 132, 12068–12073; e) C. Zhang,
N. Jiao, J. Am. Chem. Soc. 2010, 132, 28–29; f) R.-J.
Song, Y. Liu, R.-X. Hu, Y.-Y. Liu, J.-C. Wu, X.-H.
Yang, J.-H. Li, Adv. Synth. Catal. 2011, 353, 1467–1473;
g) F.-T. Du, J.-X. Ji, Chem. Sci. 2012, 3, 460–465.
[12] K. E. Knott, S. Auschill, A. Jager, H.-J. Knolker, Chem.
Commun. 2009, 12, 1467–1469.
[13] a) P. M. Cowley, J. Baker, D. R. Barn, K. I. Buchanan,
I. Carlyle, J. K. Clark, T. R. Clarkson, M. Deehan, D.
Edwards, R. R. Goodwin, D. Jaap, Y. Kiyoi, C. Mort,
R. Palin, A. Prosser, G. Walker, N. Ward, G. Wishart,
T. Young, Bioorg. Med. Chem. Lett. 2011, 21, 497–501;
b) A. J. Morrison, J. M. Adam, J. A. Baker, R. A.
Campbell, J. K. Clark, J. E. Cottney, M. Deehan, A.-M.
Easson, R. Fields, S. Francis, F. Jeremiah, N. Keddie, T.
Kiyoi, D. R. McArthur, K. Meyer, P. D. Ratcliffe, J.
Schulz, G. Wishart, K. Yoshiizumi, Bioorg. Med. Chem.
Lett. 2011, 21, 506–509; c) P. D. Pierson, A. Fettes, C.
Freichel, S. Gatti-McArthur, C. H. Huwyler Jr, P.
Mohr, T. Nakagawa, M. Nettekoven, J.-M. Plancher, S.
Raab, H. Richter, O. Roche, R. M. A. Rodriꢀguez Sar-
miento, M. Schmitt, F. Schuler, T. Takahashi, S. Taylor,
C. Ullmer, R. Wiegand, J. Med. Chem. 2009, 52, 3855–
3868.
[14] a) J. E. Charris, J. N. Domꢆnguez, N. Gamboa, J. R. Ro-
drigues, J. E. Angel, Eur. J. Med. Chem. 2005, 40, 875–
881; b) R. Dayam, L. Q. Al-Mawsawi, Z. Zawahir, M.
Witvrouw, Z. Debyser, N. Neamati, J. Med. Chem.
2008, 51, 1136–1144.
[15] a) G. Roma, M. Di Braccio, G. Grossi, F. Mattioli, M.
Ghia, Eur. J. Med. Chem. 2000, 35, 1021–1035; b) M. P.
Maguire, K. R. Sheets, K. McVety, A. P. Spada, A. Zil-
berstein, J. Med. Chem. 1994, 37, 2129–2137.
[6] a) J. K. Landquist, in: Comprehensive Heterocyclic
Chemistry, (Eds.: A. R. Katritzky, C. W. Rees), Perga-
mon, New York, 1984; b) P. J. Crowley, in: Comprehen-
sive Heterocyclic Chemistry, (Eds.: A. R. Katritzky,
C. W. Rees), Pergamon, New York, 1984; c) see, for ex-
ample: The Alkaloids: Chemistry and Biology, Vol. 54,
(Ed. G. A. Cordell), Academic Press, San Diego, 2000,
and other volumes in this series.
[7] a) S. Hibino, T. Choshi, Nat. Prod. Rep. 2002, 19, 148–
180; b) R. R. Gupta, Heterocyclic Chemistry, Vol. 2,
Springer, New York, 1999, pp 193; c) A. Rahman, A.
Basha, Indole Alkaloids, Harwood Academic Publish-
ers, Amsterdam, 1998, pp 141; d) R. C. Larock, in:
Acetylene Chemistry – Chemistry, Biology, and Material
Science, (Eds.: F. Diederich, P. J. Stang, R. R. Tykwin-
ski), Wiley-VCH, New York, 2005, chapter 2, pp 51–99.
[8] J. S. Carey, D. Laffan, C. Thomson, M. T. Williams,
Org. Biomol. Chem. 2006, 4, 2337–2347.
[16] a) D. G. Hingane, R. S. Kusurkar, Tetrahedron Lett.
2011, 52, 3686–3688; b) L. R. Whittell, K. T. Batty,
R. P. M. Wong, E. M. Bolitho, S. A. Fox, T. M. E. Davis,
P. E. Murray, Bioorg. Med. Chem. 2011, 19, 7519–7525.
[17] P. Astolfi, L. Greci, C. Rizzoli, P. Sgarabotto, G. Marro-
su, J. Chem. Soc. Perkin Trans. 2 2001, 1634–1640.
[18] For selected papers, see: a) Z.-Q. Wang, W.-W. Zhang,
L.-B. Gong, R.-Y. Tang, X.-H. Yang, Y. Liu, J.-H. Li,
Angew. Chem. 2011, 123, 9130–9135; Angew. Chem.
Int. Ed. 2011, 50, 8968–8973; b) S. Chiba, L. Zhang, J.-
Y. Lee, J. Am. Chem. Soc. 2010, 132, 7266–7267; c) H.
Prokopcovꢇ, C. O. Kappe, Angew. Chem. 2008, 120,
3732–3734; Angew. Chem. Int. Ed. 2008, 47, 3674–3676;
d) Q. Shuai, G. Deng, Z. Chua, D. S. Bohle, C.-J. Li,
Adv. Synth. Catal. 2010, 352, 632–636.
[19] For selected examples, see: a) Y. Li, Y. Xie, R. Zhang,
K. Jin, X. Wang, C. Duan, J. Org. Chem. 2011, 76,
5444–5449; b) M. M. Guru, M. A. Ali, T. Punniyamur-
Adv. Synth. Catal. 0000, 000, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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thy, Org.Lett. 2011, 13, 1194–1197; c) S. Guo, B. Qian,
Y. Xie, C. Xia, H. Huang, Org.Lett. 2010, 13, 522–525;
d) H.-F. He, Z.-J. Wang, W. Bao, Adv. Synth. Catal.
2010, 352, 2905–2912; e) L. Menini, J. C. da Cruz San-
tos, E. V. Gusevskaya, Adv. Synth. Catal. 2008, 350,
2052–2058.
[20] CCDC 862203 contains the supplementary crystallo-
graphic data for this paper (compound 2a). These data
can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
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Copper-Catalyzed Activation of Dioxygen: Oxidative
Cyclization of 2-Arylindoles
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Peng Sang, Yongju Xie, Jianwei Zou,* Yuhong Zhang*
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