Catalytic asymmetric vinylogous Mannich-type (AVM) reaction of nonactivated α-angelica lactone

Article abstract of DOI:10.1021/ol200939t

A direct highly diastereo- and enantioselective asymmetric vinylogous Mannich-type (AVM) reaction of aldimines with nonactivated natural α-angelica lactone has been successfully developed. It was demonstrated that the nonactivated natural α-angelica lacto

Full text of DOI:10.1021/ol200939t

ORGANIC
LETTERS
2011
Vol. 13, No. 12
3056–3059
Catalytic Asymmetric Vinylogous
Mannich-type (AVM) Reaction of
Nonactivated r-Angelica Lactone
Lin Zhou, Lili Lin, Jie Ji, Mingsheng Xie, Xiaohua Liu, and Xiaoming Feng*
Key Laboratory of Green Chemistry & Technology, Ministry of Education,
College of Chemistry, Sichuan University, Chengdu 610064, P. R. China
xmfeng@scu.edu.cn
Received April 10, 2011
ABSTRACT
A direct highly diastereo- and enantioselective asymmetric vinylogous Mannich-type (AVM) reaction of aldimines with nonactivated natural
R-angelica lactone has been successfully developed. It was demonstrated that the nonactivated natural R-angelica lactone is a useful vinylogous
nucleophile to give the chiral δ-amino γ,γ-disubstituted butenolide carbonyl derivatives. The N,N0-dioxide L2ꢀScIII complex is efficient toward the
obtention of a range of corresponding products with adjacent quaternary and tertiary stereocenters in excellent dr and ee values.
The butenolide unit plays an important role in organic
synthesis because of its widespread occurrence in biologi-
cally active natural products and pharmaceutically useful
molecules.1 In the past two decades, several kinds of
butenolides and analogues, such as simple γ-butenolides2
and activated silyloxyfurans,3 have been employed as
donors in asymmetric synthesis for accessing such chiral
butenolide skeleton derivatives. The natural nonactivated
R-angelica lactone, which is a cheap industrial material,
has attracted some attention as a butenolide variant
recently because of its potential in the construction of
γ,γ-disubstituted butenolides. In 2010, the Chen group
reported a highly enantioselective allylic alkylation reac-
tion with β,γ-butenolides.4 Recently, it was successfully
applied to the asymmetric Michael addition by the Alex-
akis group.5 In addition, R-angelica lactone also acted
as an enol ester for the Mannich-type reaction to afford
N-aryl 5-membered lactam under Sc(OTf)3 catalysis
(Scheme 1, path b, PG = protective group).6 However,
to the best of our knowledge, the direct catalytic asymmetric
(1) For a review on natural products containing the butenolide unit,
see: (a) Alali, F. Q.; Liu, X.-X.; McLaughlin, J. L. J. Nat. Prod. 1999, 62,
504. For reviews on the synthesis of butenolides, see: (b) Negishi, E.;
Kotora, M. Tetrahedron 1997, 53, 6707. (c) Montagnon, T.; Tofi, M.;
Vassilikogiannakis, G. Acc. Chem. Res. 2008, 41, 1001.
(4) Cui, H. L.; Huang, J. R.; Lei, J.; Wang, Z. F.; Chen, S.; Wu, L.;
Chen, Y. C. Org. Lett. 2010, 12, 720.
(5) Quintard, A.; Lefranc, A.; Alexakis, A. Org. Lett. 2011, 13, 1540.
(2) For direct catalytic asymmetric vinylogous reactions of γ-bute-
nolides, see: (a) Yamaguchi, A.; Matsunaga, S.; Shibasaki, M. Org. Lett.
2008, 10, 2319. (b) Trost, B. M.; Hitce, J. J. Am. Chem. Soc. 2009, 131,
4572. (c) Zhang, Y.; Yu, C.; Ji, Y.; Wang, W. Chem.;Asian J. 2010, 5,
1303. (d) Wang, J.; Qi, C.; Ge, Z.; Cheng, T.; Li, R. Chem. Commun.
2010, 46, 2124. (e) Ube, H.; Shimada, N.; Terada, M. Angew. Chem., Int.
Ed. 2010, 49, 1858.
(3) For selected examples on vinylogous Mannich-type reaction with
the activated siloxyfurans as donors, see: (a) Martin, S. F.; Lopez, O. D.
Tetrahedron Lett. 1999, 40, 8949. (b) Carswell, E. L.; Snapper, M. L.;
Hoveyda, A. H. Angew. Chem., Int. Ed. 2006, 45, 7230. (c) Akiyama, T.;
Honma, Y.; Itoh, J.; Fuchibe, K. Adv. Synth. Catal. 2008, 350, 399. (d)
Mandai, H.; Mandai, K.; Snapper, M. L.; Hoveyda, A. H. J. Am. Chem.
ꢀ
ꢀ
(6) Isambert, N.; Cruz, M.; Arevalo, M. J.; Gomez, E.; Lavilla, R.
Org. Lett. 2007, 9, 4199.
(7) For reviews of the Mannich and vinylogous Mannich-type reac-
tions including synthetic applications, see: (a) Arend, M.; Westermann,
B.; Risch, N. Angew. Chem., Int. Ed. 1998, 37, 1044. (b) Kobayashi, S.;
Ishitani, H. Chem. Rev. 1999, 99, 1069. (c) Casiraghi, G.; Zanardi, F.;
Appendino, G.; Rassu, G. Chem. Rev. 2000, 100, 1929. (d) Rassu, G.;
Zanardi, F.; Battistini, L.; Casiraghi, G. Chem. Soc. Rev. 2000, 29, 109.
(e) Martin, S. F. Acc. Chem. Res. 2002, 35, 895. (f) Taggi, A. E.; Hafez,
ꢀ
A. M.; Lectka, T. Acc. Chem. Res. 2003, 36, 10. (g) Cordova, A. Acc.
Chem. Res. 2004, 37, 102. (h) Marques, M. M. B. Angew. Chem., Int. Ed.
2006, 45, 348. (i) Ting, A.; Schaus, S. E. Eur. J. Org. Chem. 2007, 5797. (j)
Verkade, J. M. M.; van Hemert, L. J. C.; Quaedflieg, P. J. L. M.; Rutjes,
F. P. J. T. Chem. Soc. Rev. 2008, 37, 29. (k) Casiraghi, G.; Zanardi, F.;
Battistini, L.; Rassu, G. Synlett 2009, 1525.
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Soc. 2008, 130, 17961. (e) Gonzalez, A. S.; Arrayas, R. G.; Rivero, M. R.;
Carretero, J. C. Org. Lett. 2008, 10, 4335. (f) Yuan, Z. L.; Jiang, J. J.; Shi,
M. Tetrahedron 2009, 65, 6001.
r
10.1021/ol200939t
Published on Web 05/19/2011
2011 American Chemical Society

Scheme 1. Proposed Approach of R-Angelica Lactone with
Aldimine
Figure 1. Chiral ligands used in this study.
Table 1. Optimization of the Reaction Conditionsa
vinylogous Mannich-type (AVM) reaction7ꢀ9 of this
deconjugated butenolide to afford γ,γ-disubstituted bute-
nolides (Scheme 1, path c) has not been achieved. Herein,
we describe a N,N0-dioxideꢀScIII complex10 catalyzed
direct AVM reaction of R-angelica lactone to provide the
δ-amino butenolide blocks bearing adjacent quaternary
and tertiary stereocenters.11,12
MS (3 A) yieldb (%)
drc
eec (%)
˚
entry
L/metal ratio
1
L1/Cu(OTf)2 1/1
L1/Mg(OTf)2 1/1
L1/Ni(acac)2 1/1
L1/In(OTf)3 1/1
L1/Sc(OTf)3 1/1
L1/Y(OTf)3 1/1
L1/La(OTf)3 1/1
L2/Sc(OTf)3 1/1
L2/Sc(OTf)3 1/1
none
none
none
none
none
none
none
none
30 mg
NR
NR
NR
NR
22
2
3
4
5
85/15
90/10
85/15
93/7
68
23
20
90
82
94
95
6d
7d
8
13
(8) For selected recent reports of catalytic asymmetric Mannich
reactions involving aldimines, see: (a) Wenzel, A. G.; Jacobsen, E. N.
J. Am. Chem. Soc. 2002, 124, 12964. (b) Uraguchi, D.; Sorimachi, K.;
Terada, M. J. Am. Chem. Soc. 2004, 126, 11804. (c) Hamashima, Y.;
Sasamoto, N.; Hotta, D.; Somei, H.; Umebayashi, N.; Sodeoka, M.
Angew. Chem., Int. Ed. 2005, 44, 1525. (d) Cozzi, P. G.; Rivalta, E.
Angew. Chem., Int. Ed. 2005, 44, 3600. (e) Song, J.; Wang, Y.; Deng, L. J.
Am. Chem. Soc. 2006, 128, 6048. (f) Chi, Y.; Gellman, S. H. J. Am. Chem.
Soc. 2006, 128, 6804. (g) Hasegawa, A.; Naganawa, Y.; Fushimi, M.;
Ishihara, K.; Yamamoto, H. Org. Lett. 2006, 8, 3175. (h) Giera, D. S.;
Sickert, M.; Schneider, C. Org. Lett. 2008, 10, 4259.
(9) (a) Josephsohn, N. S.; Snapper, M. L.; Hoveyda, A. H. J. Am.
Chem. Soc. 2004, 126, 3734. (b) Suto, Y.; Kanai, M.; Shibasaki, M. J.
Am. Chem. Soc. 2007, 129, 500. (c) Yamanaka, M.; Itoh, J.; Fuchibe, K.;
Akiyama, T. J. Am. Chem. Soc. 2007, 129, 6756. (d) Hatano, M.; Horibe,
T.; Ishihara, K. J. Am. Chem. Soc. 2010, 132, 56. (e) Shepherd, N. E.;
Tanabe, H.; Xu, Y.; Matsunaga, S.; Shibasaki, M. J. Am. Chem. Soc.
2010, 132, 3666. (f) Liu, T. Y.; Cui, H. L.; Long, J.; Li, B. J.; Wu, Y.;
Ding, L. S.; Chen, Y. C. J. Am. Chem. Soc. 2007, 129, 1878.
19
43
9
10e
68
91/9
L2/Sc(OTf)3 1.2/1 30 mg
74
95/5
11e,f L2/Sc(OTf)3 1.2/1 30 mg
81
95/5
a Unless otherwise noted, the reactions were performed with 1a (0.10
mmol), metal (0.005 mmol), and N,N0-dioxide under nitrogen in THF
(0.5 mL) at 30 °C for 15 min, and then 2a (0.12 mmol) was added at 0 °C.
The reaction mixture was stirred at 0 °C for 18 h. b Isolated yield, NR =
no reaction. c Determined by chiral HPLC analysis (Chiralcel IC).
d Reaction was performed at 30 °C. e 2-Me-THF as solvent. f Using 0.3
mmol of 1a, adding 2a two times and preparing catalyst beforehand.
In the previous studies using R-angelica lactone as viny-
logous nucleophile,4 chiral amine catalysts were used that
might aid in the R-deprotonation to form activated enolate
(Scheme 1, A). We envisioned that this donor could also be
activatedthroughinsitu generated O-bond metalenolate in
the presence of Lewis acids (Scheme 1, B). The model
reaction was initiated with R-angelica lactone 2a and N-
arylaldimine 1a. Various Lewis acids coordinated with
chiral N,N0-dioxide ligand L1 (Figure 1) were surveyed
(Table 1, entries 1ꢀ5), and only Sc(OTf)3 could afford the
γ-regioselective product 3a in 22% yield with moderate dr
and ee values at 0 °C (Table 1, entry 5). At higher
temperature (30 °C), other lanthanide metals could per-
form the reaction with worse yields and ee values (Table 1,
entries 6 and 7). Comparatively, the conjugated furanone
2b (Scheme 2) failed to undergo the AVM reaction, and no
product was observed under L1ꢀSc(OTf)3 catalysis. All of
these implied that the approach of R-enolization would be
responsible for the occurrence of nucleophilic addition.
(10) For our work with the N,N0-dioxideꢀmetal complexes, see: (a)
Xie, M. S.; Chen, X. H.; Zhu, Y.; Gao, B.; Lin, L. L.; Liu, X. H.; Feng,
X. M. Angew. Chem., Int. Ed. 2010, 49, 3799. (b) Cai, Y. F.; Liu, X. H.;
Hui, Y. H.; Jiang, J.; Wang, W. T.; Chen, W. L.; Lin, L. L.; Feng, X. M.
Angew. Chem., Int. Ed. 2010, 49, 6160. (c) Wang, F.; Liu, X. H.; Zhang,
Y. L.; Lin, L. L.; Feng, X. M. Chem. Commun 2009, 7297. (d) Zhou, X.;
Shang, D. J.; Zhang, Q.; Lin, L. L.; Liu, X. H.; Feng, X. M. Org. Lett.
2009, 11, 1401.
(11) For reviews of catalytic enantioselective construction of qua-
ternary stereocenters, see: (a) Christoffers, J.; Baro, A. Angew. Chem.,
Int. Ed. 2003, 42, 1688. (b) Peterson, E. A.; Overman, L. E. Proc. Natl.
Acad. Sci. U.S.A. 2004, 101, 11943. (c) Ramon, D. J.; Yus, M. Curr. Org.
Chem. 2004, 8, 149. (d) Christoffers, J.; Baro, A. Adv. Synth. Catal. 2005,
347, 1473.
(12) For selected examples of catalytic construction of adjacent
quaternary and tertiary stereocenters, see: (a) Taylor, M. S.; Jacobsen,
E. N. J. Am. Chem. Soc. 2003, 125, 11204. (b) Austin, J. F.; Kim, S.-G.;
Sinz, C. J.; Xiao, W.-J.; MacMillan, D. W. C. Proc. Natl. Acad. Sci. U.S.
A. 2004, 101, 5482. (c) Li, H.; Wang, Y.; Tang, L.; Wu, F.; Liu, X.; Guo,
C.; Foxman, B. M.; Deng, L. Angew. Chem., Int. Ed. 2005, 44, 105. (d)
Poulsen, T. B.; Alemparte, C.; Saaby, S.; Bella, M.; Jørgensen, K. A.
Angew. Chem., Int. Ed. 2005, 44, 2896. (e) Lalonde, M. P.; Chen, Y.;
Jacobsen, E. N. Angew. Chem., Int. Ed. 2006, 45, 6366. (f) van Steenis, D.
J. V. C.; Marcelli, T.; Lutz, M.; Spek, A. L.; van Maarseveen, J. H.;
Hiemstra, H. Adv. Synth. Catal. 2007, 349, 281.
Org. Lett., Vol. 13, No. 12, 2011
3057

Further optimization of the reaction conditions was
then aimed at exploring the efficiency of Sc(OTf)3 with
other N,N0-dioxide ligands (for details: see the Supporting
Information). Fortunately, when the ligand L2 containing
bulkier isopropyl groups at the ortho position of aniline
was employed, good diastereo- and enantioselectivity (93:7
dr and 90% ee) with 43% yield were achieved (Table 1,
Table 2. Substrate Scope for the Direct AVM Reactiona
˚
entry 8). The addition of 3 A molecular sieves (MS) as
additive benefited the yield while the enantiomeric excess
had an obvious decrease (Table 1, entry 9). To our delight,
changing the ratio of the ligand L2 to Sc(OTf)3 to 1.2/1,
meanwhile using 2-Me-THF as the solvent, could greatly
improve the enantiomeric excess to 94% (Table 1, entry
10). Increasing the amount of aldimine 1a and adding R-
angelica lactone 2a two times could further enhance the
yield to 81% with the dr and ee maintained. In addition,
the catalyst could be prepared beforehand and did not
affect the results at all (Table 1, entry 11; for details, see the
Supporting Information). This operation made the proce-
dure more convenient. In these cases, no R- or β-regiose-
lective byproduct was observed (Scheme 1).
Under the optimal conditions (Table 1, entry 11), var-
ious aldimines 113 were evaluated, affording the γ,γ-dis-
ubstituted butenolide derivatives in excellent diastereo-
and enantioselectivities (up to 99/1 dr and 98% ee). As
showen in Table 2, the electronic effects of the phenol
protective group of imines were investigated. The intro-
duction of an electron-donating methyl group to N-aryli-
mine decreased the enantioselectivity slightly with good
yield, while electron-withdrawing chloric group gave the
corresponding adduct with higher diastereo- and enantios-
electivity in moderate yield (Table 2, entries 1ꢀ3). The
enantioselectivity of the reaction was sensitive to the
electronic property rather than to the steric hindrance of
substituents on the phenyl ring of aromatic aldimines. The
substrates with electron-withdrawing substituents gave
higher ee values than those with electron-donating ones
(Table 2, entries 12ꢀ15 vs 4ꢀ9). Generally, the desired γ-
methyl-γ-phenylmethanamino butenolides 3 were isolated
in excellent diastereomeric and good enantiomeric excesses
with moderate to good yields (Table 2, entries 4ꢀ15).
Moreover, fused ring and heteroaromatic aldimines were
also tolerable, affording the desired products with 93% to
97% ee (Table 2, entries 16ꢀ19). In addition, the absolute
configuration of 3s was determined to be 1S,2R by X-ray
analysis.14 Notably, by treatment of 1.0 mmol of R-angel-
ica lactone 2a under the optimal reaction conditions, γ,γ-
disubstituted butenolide 3a was produced smoothly in
71% yield with 94% ee (Table 2, entry 20).
entry
R1
R2
yieldb (%)
drc
eec (%)
1
Ph
Ph
Ph
H
Me
Cl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
3a: 81
3b: 82
3c: 67
3d: 78
3e: 77
3f: 83
3g: 77
3h: 82
3i: 90
3j: 75
3k: 82
3l: 76
3m: 74
3n: 71
3o: 58
3p: 75
3q: 83
3r: 62
3s: 82
3a: 71
95/5
93/7
96/4
99/1
95/5
95/5
95/5
96/4
97/3
95/5
95/5
96/4
96/4
99/1
96/4
97/3
95/5
86/14
96/4
94/6
95
90
97
93
92
92
90
94
90
94
91
98
96
95
97
95
93
95
97d
94
2
3
4
2-MeC6H4
3-MeC6H4
4-MeC6H4
3-MeOC6H4
4-MeOC6H4
2,3-(MeO) 2C6H3
4-PhC6H4
3-PhOC6H4
4-FC6H4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20e
4-ClC6H4
2,6-Cl2C6H3
4-BrC6H4
1-naphthyl
2-naphthyl
2-furyl
2-thienyl
Ph
a Unless otherwise noted, the reactions were performed with 1 (0.30
mmol), 36.4 mg of chiral catalyst: N,N0-dioxide (3.9 mg, 0.006 mmol),
˚
metal (2.5 mg, 0.005 mmol), 30 mg of 3 A molecular sieves (MS), 2a (0.05
mmol) in a dry reaction tube, then 2-Me-THF (0.5 mL) was added at
0 °C. After the reaction mixture was stirred for 6 h at 0 °C, the remaining
2a (0.05 mmol) was added, and then the reaction mixture was stirred at
0 °C for an additional 12 h. b Isolated yield. c Determined by HPLC
analysis. d The absolute configuration was determined to be 1S,2R by
X-ray analysis. e 1.0 mmol substrate was used.
the optimal reaction conditions, which suggested that the
R-enolization of unconjugated R-angelica lactone 2a was
easier than γ-enolization of conjugated furanones. More-
over, in the presence of triethylamine as additive, the AVM
product 3ac from simple γ-butenolide 2c was isolated in
37% yield with 62/38 dr and 85% ee (Scheme 2, eq 3),
which demonstrated that γ-deprotonation of 2c could be
promoted by amine base. On the other hand, the electron-
donating property and steric hindrance of methyl group of
5-methylfuranone 2b might impede the γ-deprotonation
and result in no product (Scheme 2, eq 1). It indicates that
R-angelica lactone would be a good candidate as a vinylo-
gous nucleophile compared with the related furanone. In
contrast to the chiral amine promoted nucleophilic addi-
tion of β,γ-butenolides in previous study,4 the addition of
amine reduced the yield to 27% with the dr and ee value
basically maintained in this scandium complex catalyzed
AVM reaction (Scheme 2, eq 4). The generation of only a
trace amount of inert 5-methylfuranone 2b from R-angel-
ica lactone 2a accelerated by Et3N would not be the main
To have a better insight into the mechanism of this
process, several control experiments were performed.
Using conjugated furanone 2b and 2c as donors, no
products were observed (Scheme 2, eqs 1 and 2) under
(13) Only trace amounts of products were obtained from aliphatic
imines. See the Supporting Information for details.
(14) CCDC 815001 (3s) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
3058
Org. Lett., Vol. 13, No. 12, 2011

Scheme 2. Comparison Experiments
Figure 2. Proposed catalytic cycle.
cause for the loss of reactivity. It should be considered that
the introduction of amine to the system would probably
restrain the catalytic recycle, which overestimated its role
in accelerating the R-enolization of R-angelica lactone.
The relationship between the ee value of ligand L2 and
the product 3a showed poor nonlinear effects15 (see the
Supporting Information), suggesting that minor oligo-
meric aggregates might exist in the reaction system. Ac-
cording to our previous study on the X-ray crystal
structure of N,N0-dioxideꢀScIII 16 and the oxygen-affinity
property of scandium,17 a catalytic cycle is proposed in
Figure 2. Itsuggested that the use of L2 and Sc(OTf)3 in the
direct AVM reaction is likely to generate a hexacoordinate
Sc(OTf)3-derived intermediate, in which not only the oxy-
gens of N-oxide but also carbonyl oxygens coordinated
with Sc(III) in a tetradentate manner. First, aldimines 118
and the four oxygen atoms of the ligand L2 were coordi-
nated to the Sc(III) center, giving the intermediate T1.
After R-angelica lactone 2a was added, chiral scandium
intermediate T2 containing ligand, R-enolized 2a, and
imine was generated, in which the attack of 5-methylfur-
an-2-ol to the Si face of the aldimine provided the access to
1R,2R-configured γ,γ-disubstituted butenolides. The ne-
gative effect of Et3N in the comparison experiments
(Scheme 2) could be rationalized that the interaction
between the phenol group of aldimine and the base wea-
kened the coordination of the substrate. The existence of
base was also unfavorable for the final protonation step.
The competition coordination between imines and R-
angelica lactone was responsible for the improved yield
by partial feeding of R-angelica lactone.
In summary, we have successfully developed a direct
highly diastereo- and enantioselective asymmetric vinylo-
gous Mannich-type (AVM) reaction of aldimines with R-
angelica lactone. Nonactivated natural R-angelica lactone
was demonstrated to be a useful vinylogous nucleophile to
afford the chiral δ-amino γ,γ-disubstituted butenolide
carbonyl derivatives. The N,N0-dioxide L2ꢀSc(OTf)3
complex is efficient for affording a range of the corre-
sponding products with adjacent quaternary and tertiary
stereocenters in excellent dr and ee values. Further me-
chanisticstudies of thiscatalyticsystemare still inprogress.
Acknowledgment. We appreciate the National Natural
Science Foundation of China (Nos. 20732003 and
21021001) and the Basic Research Program of China
(973 Program: 2010CB833300) for financial support. We
alsothank Sichuan UniversityAnalytical & Testing Center
for NMR and X-ray analysis.
(15) (a) Guillaneux, D.; Zhao, S. H.; Samuel, O.; Rainford, D.;
Kagan, H. B. J. Am. Chem. Soc. 1994, 116, 9430. (b) Girard, C.; Kagan,
H. B. Angew. Chem., Int. Ed. 1998, 37, 2922. (c) Satyanarayana, T.;
Abraham, S.; Kagan, H. B. Angew. Chem., Int. Ed. 2009, 48, 456.
(16) X-ray single crystal structure of N,N0-dioxideꢀScIII: Liu, Y. L.;
Shang, D. J.; Zhou, X.; Liu, X. H.; Feng, X. M. Chem.;Eur. J. 2009, 15,
2055.
(17) (a) Shibasaki, M.; Yoshikawa, N. Chem. Rev. 2002, 102, 2187.
(b) Kobayashi, S.; Sugiura, M.; Kitagawa, H.; Lam, W. W.-L. Chem.
Rev. 2002, 102, 2227.
(18) The hydroxyl group on the imines 1 was crucial in the catalysis.
No corresponding products were observed with imines derived from
aniline or 2-methoxyaniline. See the Supporting Information for details.
Supporting Information Available. Experimental pro-
cedures and spectral and analytical data for the products.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Org. Lett., Vol. 13, No. 12, 2011
3059