Direct enantioselective three-component synthesis of optically active propargylamines in water

Article abstract of DOI:10.1002/chem.201402384

An enantioselective three-component reaction of aldehydes, amines, and alkynes in water by using a bis(imidazoline)-Cu^I catalysts having a hydrophobic substituent and sodium dodecyl sulfate as a surfactant was developed. The reaction was applie

Full text of DOI:10.1002/chem.201402384

DOI: 10.1002/chem.201402384
Communication
&
Asymmetric Catalysis
Direct Enantioselective Three-Component Synthesis of Optically
Active Propargylamines in Water
Mutsuyo Ohara, Yoshichika Hara, Tohru Ohnuki, and Shuichi Nakamura*[a]
We expect that the highly tunable bis(imidazoline) structure
Abstract: An enantioselective three-component reaction
can be applied to an enantioselective reaction in water. Herein,
of aldehydes, amines, and alkynes in water by using a bis(i-
we report a highly enantioselective direct three-component re-
midazoline)–CuI catalysts having a hydrophobic substitu-
action of aldehydes, amines, and aliphatic alkynes by using
ent and sodium dodecyl sulfate as a surfactant was devel-
a chiral bis(imidazoline)–CuI catalyst in water.
oped. The reaction was applied to a broad range of alde-
We first examined the reaction of benzaldehyde, p-anisidine
hydes and alkynes to give optically active propargyla-
(1.2 equiv) and 4-phenylbutyne (1.5 equiv) by using chiral bis(i-
mines with excellent yields (up to 99%) and enantiomeric
midazoline)s 1a–f and a metal salt. The results are shown in
excesses (up to 99% ee).
Table 1.
Optically active propargylamines and their derivatives have
been proven to be useful building blocks for the preparation
of various natural products[1] and biologically active com-
pounds.[2] Their broad utility has prompted considerable inter-
est in developing asymmetric methods for their preparation
under environmentally friendly conditions. In this context, the
enantioselective three-component reaction of a carbonyl com-
pound, an amine, and an alkyne is one of the most straightfor-
ward approaches for the synthesis of chiral propargyla-
mines.[3,4] Water is a desirable solvent for organic synthesis due
to its safety, low cost, and environmentally benign character.[5]
To date, only little attention has been paid to performing enan-
tioselective three-component reactions of carbonyl com-
pounds, amines, and alkynes in water.[6,7] The reaction includes
an equilibrium to produce the product and water as a by-prod-
uct; therefore, it is difficult to carry out the propargylamine
synthesis in water by using the three-component reaction. The
best results for this reaction were described by Li and co-work-
ers who reported that the conversion of preprepared imines
and phenylacetylene by using a pybox–CuI catalyst and stearic
acid as a surfactant in water gave the desired products with
moderate to high enantioselectivities (35–97% ee).[6c] Despite
this impressive progress, the alkyne substrate was restricted to
aryl-substituted alkynes. Therefore, it is desirable to extend the
scope of the reaction to aliphatic alkynes in water. Recently,
we developed a copper–bis(imidazoline)-catalyzed three-com-
ponent synthesis of optically active propargylamines from al-
dehydes, amines and aliphatic alkynes in organic solvents.[8,9]
Table 1. Enantioselective three-component reaction of benzaldehyde, p-
anisidine, and 4-phenylbutyne by using various chiral ligands.
Entry
1
Metal salt Surfactant
Time [h] Yield [%] ee [%]
1
2
3
4
5
6
7
8
9
10
11
12[b]
13
14[d]
1a CuOTf[a]
1a CuOTf[a]
1b CuOTf[a]
1c CuOTf[a]
1d CuOTf[a]
1e CuOTf[a]
1 f CuOTf[a]
1 f CuOTf[a]
1 f CuOTf[a]
1 f CuOTf[a]
1 f Cu(OTf)2
1 f CuOTf[a]
1 f CuDS[c]
1 f CuOTf[a]
–
SDS
SDS
SDS
SDS
SDS
SDS
CTAB
Triton X-100
sodium laurate
SDS
SDS
–
84
48
48
48
48
48
18
18
18
18
18
156
18
72
1
41
12
63
37
89
99
0
17
0
96
94
91
29
45
88
43
95
93
94
98
–
98
–
98
98
98
98
–
[a]CuOTf·1/2toluene was used. [b] 1 f (5 mol%) and CuOTf·1/2toluene
(5 mol%) was used. [c] SDS=sodium dodecyl sulfate. [d] Reaction per-
formed in CH2Cl2.
The reaction in water by using 10 mol% of a N-benzoyl 1,3-
bis(imidazolin-2-ly)pyridine (N-Bz-pybim, 1a)–CuOTf·1/2toluene
complex gave product 2 in a low yield with moderate enantio-
selectivity (entry 1). During the reaction process, the reactants
were insoluble in water. Therefore, we assumed that the reac-
tion could be accelerated by using a surfactant, which forms
a colloidal dispersion with the substrates and the catalyst. Ini-
[a] M. Ohara, Y. Hara, Prof. Dr. T. Ohnuki, Prof. Dr. S. Nakamura
Department of Frontier Materials, Graduate School of Engineering
Nagoya Institute of Technology
Gokiso, Showa-ku, Nagoya 466-8555 (Japan)
Fax: (+81)52-735-5245
E-mail: snakamur@nitech.ac.jp
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201402384.
Chem. Eur. J. 2014, 20, 8848 – 8851
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
tially, sodium dodecyl sulfate (SDS) was used as a surfactant
for the reaction, and after its addition the reaction mixture was
homogenized (Figure 1).
Table 2. Enantioselective three-component reaction of various aldehydes
and alkynes by using 1 f–CuI.
Entry Aldehyde [R1] Alkyne [R2] Product Time [h] Yield [%] ee [%]
1
2
3
4
5
Ph
Ph
Ph
Ph
Ph
CH2CH2Ph
CH2CH2CH3
(CH2)3CH3
(CH2)5CH3
(CH2)7CH3
cyclopropyl
cyclopentyl
cyclohexyl
CH2CH2Br
2
3
4
5
6
7
8
9
10
18
36
48
24
48
96
66
66
66
72
72
48
24
24
24
48
72
48
96
48
99
80
93
87
93
90
91
76
62
77
60
99
85
95
86
80
67
80
91
66
98
97
97
99
97
95
95
98
98
96
90
98
90
98
99
99
86
98
92
98
6[a] Ph
7
8
9
Ph
Ph
Ph
Ph
Ph
Ph
10
11
12
13
14
15
16
17
CH2CH2OH 11
C(CH2)2OH 12
Ph
13
14
15
16
17
18
19
20
21
2-MeOC6H4
2-ClC6H4
3-MeOC6H4
3-ClC6H4
4-MeOC6H4
CH2CH2Ph
CH2CH2Ph
CH2CH2Ph
CH2CH2Ph
CH2CH2Ph
CH2CH2Ph
CH2CH2Ph
CH2CH2Ph
Figure 1. Homogenized reaction mixture after the addition of SDS.
18[b] 4-ClC6H4
19
20
Using SDS improved the chemical yield and enantioselectivi-
ty of the product (entry 1 vs. 2). When the reaction was com-
plete, the addition of NaCl to the reaction mixture easily
caused a phase separation to the aqueous and organic phase
by a salting-out effect. Next, optimization experiments for the
fine-tuning of the N-substituents of the imidazoline ligands
were carried out, and a pivaloyl group was found to be the
best substituent to give product 2 in a high yield with high
enantioselectivity (entries 2–7). In the presence of ligand 1 f,
other cationic, neutral, or anionic surfactants, such as cetyltri-
methylammonium bromide (CTAB), polyoxyethylene p-(1,1,3,3-
tetramethylbutyl)phenyl ether (Triton-X100), and sodium lau-
rate, did not give good results (entries 7–10). Although the re-
action by using Cu(OTf)2 instead of the CuOTf·1/2toluene com-
plex afforded 2 in a good yield with high enantioselectivity, p-
methoxylnitrobenzene was formed as a by-product as well,
which was obtained from the oxidation of p-anisidine by
Cu(OTf)2, which then in turn was reduced to the copper(I) spe-
cies (entry 11).[10] The catalyst loading was successfully reduced
to 5 mol% without any loss in enantioselectivity (entry 12).
When using Cu(OSO3C12H25) as a copper species without SDS,
the reaction mixture formed a colloidal dispersion to afford the
desired product 2 in high yield with high enantioselectivity
(entry 13). On the other hand, performing the reaction in
CH2Cl2 by using 1 f–CuI gave 2 with the same enantiomeric
excess but in a low yield (entry 14).
1-naphthyl
cyclohexyl
[a] Alkyne (3.0 equiv) was used. [b] Reaction was carried out at 408C.
well, giving the desired products 14–20 with 86–99% ee (en-
tries 13–19). A maximum of 99% ee was obtained in the reac-
tion with m-methoxy- or m-chlorobenzaldehyde (Table 2, en-
tries 15 and 16). The chemical yield was excellent in most
cases. With cyclohexanecarboxaldehyde, the desired product
21 was obtained in a good yield with high enantioselectivity
(entry 20), whereas the reaction in CH2Cl2 by using 1a–CuOTf
gave 21 in 13% yield with 72% ee.
Tap water and seawater are attractive and environmentally
friendly reaction media for organic synthesis.[11] Therefore, we
also examined the reaction in tap water or seawater that was
taken directly from the Pacific Ocean (Scheme 1). In these
aqueous solutions, the reaction proceeded well, affording
product 2 in high yield with high enantioselectivity.
After the reaction, most of catalyst 1 f could be recovered
by column chromatography and reused without further purifi-
Encouraged by these results, we then studied the scope and
limitations of the bis(imidazoline) 1 f-catalyzed three-compo-
nent reaction of various aldehydes and alkynes by using SDS
in aqueous micellar solutions. The results are summarized in
Table 2. The reaction of various substituted alkynes with ben-
zaldehyde afforded products 2–13 in high yields with high
enantioselectivity (entries 1–12). In the reaction with phenyla-
cetylene, both electron-rich and -poor aldehydes performed
Scheme 1. Enantioselective three-component reaction in tap water and sea-
water.
Chem. Eur. J. 2014, 20, 8848 – 8851
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
cation. The reaction by using recovered 1 f afforded product 2
in 83% yield with 98% ee.
this process and potential applications of the bis(imidazoline)
catalyst in other reactions are in progress.
The reaction of benzaldehyde, p-anisidine, and 4-phenylbu-
tyne by using Cu(OSO3C12H25) afforded almost the same result
as the reaction by using CuOTf and SDS (Table 1, entry 7 vs.
13). Therefore, the three-component reaction could be activat-
ed by 1 f–Cu(OSO3C12H25) complexes.[12] Furthermore, the sub-
stituent on the nitrogen atom of the imidazoline ligand dra-
matically influenced the yield of the product and the reactivity
of the reaction. These results show that the hydrophobic ef-
fects of the substituent on the imidazoline ligand and the
copper salt are important for the formation of a colloidal dis-
persion and the enhancement of their reactivity (Figure 2).
Experimental Section
General procedure for the enantioselective three-compo-
nent reaction of aldehydes, amines, and alkynes by using
1 f–CuI
A solution of bis(imidazoline) 1 f (0.025 mmol, 10 mol%), CuOTf·1/
2toluene (0.025 mmol, 10 mol%) and SDS (0.05 mmol, 20 mol%) in
ultra-pure water (0.6 mL) was stirred for 1 h at room temperature
(23–258C). Ultra-pure water (0.8 mL), an aldehyde (0.25 mmol), p-
anisidine (0.30 mmol) and an alkyne (0.37 mmol) were added, and
the whole reaction mixture was stirred at room temperature. After
completion of the reaction monitored by TLC, NaCl (100 mg) was
added. Water was removed by decantation then the organic phase
was purified over silica gel by column chromatography (CH2Cl2/
hexane) to give propargylamines.
Acknowledgements
This work was partly supported by the Kurata Memorial Hitachi
Science and Technology Foundation and the Hori Science and
Arts Foundation. We thank Prof. Norio Shibata at Nagoya Insti-
tute of Technology for unrestricted access to analytical facili-
ties.
Figure 2. Three-component reaction in water by using a hydrophobic chiral
catalyst.
There are several reports on the reaction mechanism for the
enantioselective alkynylation of imines by using a copper(I)
salt[13] in which the copper salt forms a pentacoordinated (dis-
torted trigonal bipyramid) complex. On the basis of these con-
siderations, the assumed transition states for the enantioselec-
tive alkynylation of imines by using 1 f–CuI are shown in
Figure 3. The copper–acetylide attacks the imine from the Si
face of the imine to provide the (R)-propargylamine. Further
studies are required to fully elucidate the mechanistic details
of the alkynylation.
Keywords: alkynylation · enantioselectivity · propargylamines ·
three-component reaction · water
[1] a) M. Konishi, H. Ohkuma, T. Tsuno, T. Oki, G. D. VanDuyne, J. Clardy, J.
Am. Chem. Soc. 1990, 112, 3715–3716; b) B. M. Trost, C. K. Chung, A. B.
Pinkerton, Angew. Chem. 2004, 116, 4427–4429; Angew. Chem. Int. Ed.
2004, 43, 4327–4329; c) M. H. Davidson, F. E. McDonald, Org. Lett. 2004,
6, 1601–1603.
[2] a) M. A. Huffman, N. Yasuda, A. E. DeCamp, E. J. J. Grabowski, J. Org.
Chem. 1995, 60, 1590–1594; b) G. S. Kauffman, G. D. Harris, R. L. Dorow,
B. P. R. Stone, R. L. Parsons, Jr., J. A. Pesti, N. A. Magnus, J. M. Fortunak,
P. N. Confalone, W. A. Nugent, Org. Lett. 2000, 2, 3119–3121; c) A. Mon-
leꢁn, G. Blay, L. R. Domingo, M. C. MuÇoz, J. R. Pedro, Chem. Eur. J.
2013, 19, 14852–14860.
[3] For reviews on the enantioselective synthesis of propargylamines, see:
a) B. M. Trost, A. H. Weiss, Adv. Synth. Catal. 2009, 351, 963–983; b) L.
Zani, C. Bolm, Chem. Commun. 2006, 4263–4275; c) C. Wei, G. Li, C.-J.
Li, Synlett 2004, 1472–1483; d) P. G. Cozzi, R. Hilgraf, N. Zimmermann,
Eur. J. Org. Chem. 2004, 4095–4105; e) W.-J. Yoo, L. Zhao, C.-J. Li, Aldri-
chimica Acta 2011, 44, 43–51.
[4] For reviews on multicomponent reactions, see: a) D. J. Ramꢁn, M. Yus,
Angew. Chem. 2005, 117, 1628–1661; Angew. Chem. Int. Ed. 2005, 44,
1602–1634; b) G. Guillena, G. D. J. Ramꢁn, M. Yus, Tetrahedron: Asym-
metry 2007, 18, 693–700; c) D. Enders, M. R. M. Hꢂttl, C. Grondal, G.
Raabe, Nature 2006, 441, 861–863; d) A. Dondoni, A. Massi, Acc. Chem.
Res. 2006, 39, 451–463; see also: e) L. Zani, T. Eichhorn, C. Bolm, Chem.
Eur. J. 2007, 13, 2587–2600.
[5] For reviews, see: a) Organic Synthesis in Water (Ed.: P. A. Grieco), Blackie
Academic & Professional, London, 1998; b) U. M. Lindstrçm, Chem. Rev.
2002, 102, 2751–2772; c) S. Kobayashi, K. Manabe, Acc. Chem. Res.
2002, 35, 209–217; d) C.-J. Li, Chem. Rev. 2005, 105, 3095–3166; e) J.
Mlynarski, J. Paradowska, Chem. Soc. Rev. 2008, 37, 1502–1511; f) J. Par-
adowska, M. Stodulski, J. Mlynarski, Angew. Chem. 2009, 121, 4352–
4362; Angew. Chem. Int. Ed. 2009, 48, 4288–4297; g) M. Raj, V. K. Singh,
Chem. Commun. 2009, 6687–6703; h) S. Bhowmick, K. C. Bhowmick, Tet-
Figure 3. Proposed transition state for the alkynylation of an imine by using
1 f–CuI.
In conclusion, we have developed an enantioselective three-
component reaction of aldehydes, amines, and alkynes by
using a bis(imidazoline)–CuI catalysts having a hydrophobic
substituent and SDS as a surfactant. The reaction was screened
for a broad range of aldehydes and alkynes. This process offers
a simple and environmentally friendly route to optically active
propargylamines. Further experiments to study the scope of
Chem. Eur. J. 2014, 20, 8848 – 8851
www.chemeurj.org
8850
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Communication
rahedron: Asymmetry 2011, 22, 1945–1979; i) T. Kitanosono, S. Kobaya-
shi, Adv. Synth. Catal. 2013, 355, 3095–3118.
2919; j) S.-m. Kim, K. Choi, Eur. J. Org. Chem. 2011, 4747–4750; k) X. Du,
H. Liu, D.-M. Du, Eur. J. Org. Chem. 2011, 786–793; l) T. Wang, X.-Q. Hao,
J.-J. Huang, J.-L. Niu, J.-F. Gong, M.-P. Song, J. Org. Chem. 2013, 78,
8712–8721; for tris(imdazorine)s, see: m) K. Murai, S. Fukushima, S. Hay-
ashi, Y. Takahara, H. Fujioka, Org. Lett. 2010, 12, 964–966; n) K. Murai, T.
Matsushita, A. Nakamura, S. Fukushima, M. Shimura, H. Fujioka, Angew.
Chem. 2010, 122, 9360–9363; Angew. Chem. Int. Ed. 2010, 49, 9174–
9177; o) K. Murai, S. Fukushima, A. Nakamura, M. Shimura, H. Fujioka,
Tetrahedron 2011, 67, 4862–4868; p) T. Arai, K. Sakagami, Eur. J. Org.
Chem. 2012, 1097–1100; q) K. Murai, A. Nakamura, T. Matsushita, M.
Shimura, H. Fujioka, Chem. Eur. J. 2012, 18, 8448–8453; r) K. Murai, T.
Matsushita, A. Nakamura, N. Hyogo, J. Nakajima, H. Fujioka, Org. Lett.
2013, 15, 2526–2529; for recent reviews on pincer-type transition-
metal catalysts including bis(oxazolyl)phenyl ligands (Phebox), see: s) H.
Nishiyama, Chem. Soc. Rev. 2007, 36, 1133–1141; t) H. Nishiyama, J. Ito,
Chem. Rec. 2007, 7, 159–166; u) H. Nishiyama, J. Ito, Chem. Commun.
2010, 46, 203–212.
[6] a) C. Wei, C.-J. Li, J. Am. Chem. Soc. 2002, 124, 5638–5639; b) C. Wei,
J. T. Mague, C.-J. Li, Proc. Natl. Acad. Sci. USA 2004, 101, 5749–5754;
c) J. Liu, B. Liu, X. Jia, X. Li, A. S. C. Chan, Tetrahedron: Asymmetry 2007,
18, 396–399; for the racemic synthesis of propargylamines by a three-
component synthesis in water, see: d) C. Wei, C.-J. Li, J. Am. Chem. Soc.
2003, 125, 9584–9585; e) C. Wei, Z. Li, C.-J. Li, Org. Lett. 2003, 5, 4473–
4475; f) L. Shi, Y.-Q. Tu, M. Wang, F.-M. Zhang, C.-A. Fan, Org. Lett. 2004,
6, 1001–1003; g) B. Sreedhar, P. S. Reddy, C. S. V. Krishna, P. V. Babu, Tet-
rahedron Lett. 2007, 48, 7882–7886; h) B. Huang, X. Yao, C.-J. Li, Adv.
Synth. Catal. 2006, 348, 1528–1532; i) V. K.-Y. Lo, Y. Liu, M.-K. Wong, C.-
M. Che, Org. Lett. 2006, 8, 1529–1532; j) C.-J. Li, C. Wei, Chem. Commun.
2002, 268–269; k) B. Sreedhar, P. S. Reddy, B. V. Prakash, A. Ravindra,
Tetrahedron Lett. 2005, 46, 7019–7022.
[7] For selected examples of enantioselective multicomponent reactions in
water, see: a) L. Cheng, X. Wu, Y. Lu, Org. Biomol. Chem. 2007, 5, 1018–
1020; b) Y. Hayashi, T. Urushima, S. Aratake, T. Okano, K. Obi, Org. Lett.
2008, 10, 21–24; c) Y.-C. Teo, J.-J. Lau, M.-C. Wu, Tetrahedron: Asymmetry
2008, 19, 186–190; d) F. Cruz-Acosta, P. de Armas, F. Garcꢃa-Tellado,
Chem. Eur. J. 2013, 19, 16550–16554; e) P. B. Thorat, S. V. Goswami, R. L.
Magar, B. R. Patil, S. R. Bhusare, Eur. J. Org. Chem. 2013, 5509–5516; see
also a review on enantioselective multicomponent reactions: f) C. M.
Marson, Chem. Soc. Rev. 2012, 41, 7712–7722; g) C. de Graaff, E. Ruijter,
R. V. A. Orru, Chem. Soc. Rev. 2012, 41, 3969–4009.
[8] a) S. Nakamura, M. Ohara, Y. Nakamura, N. Shibata, T. Toru, Chem. Eur. J.
2010, 16, 2360–2362; for related recent studies on bis(imidazoline)s
from our group, see: b) S. Nakamura, K. Hyodo, Y. Nakamura, N. Shibata,
T. Toru, Adv. Synth. Catal. 2008, 350, 1443–1448; c) M. Ohara, S. Naka-
mura, N. Shibata, Adv. Synth. Catal. 2011, 353, 3285–3289; d) K. Hyodo,
S. Nakamura, K. Tsuji, T. Ogawa, Y. Funahashi, N. Shibata, Adv. Synth.
Catal. 2011, 353, 3385–3390; e) K. Hyodo, S. Nakamura, N. Shibata,
Angew. Chem. 2012, 124, 10483–10487; Angew. Chem. Int. Ed. 2012, 51,
10337–10341; f) K. Hyodo, M. Kondo, Y. Funahashi, S. Nakamura, Chem.
Eur. J. 2013, 19, 4128–4134; g) S. Nakamura, K. Hyodo, M. Nakamura, D.
Nakane, H. Masuda, Chem. Eur. J. 2013, 19, 7304–7309.
[9] For bis(imidazoline) ligands, see the following review: a) H. Liu, D.-M.
Du, Adv. Synth. Catal. 2009, 351, 489–519, and references therein; for
selected examples, see: b) T. Arai, T. Mizukami, A. Yanagisawa, Org. Lett.
2007, 9, 1145–1147; c) S. Jautze, P. Seiler, R. Peters, Chem. Eur. J. 2008,
14, 1430–1444; d) H. Huang, R. Peters, Angew. Chem. 2009, 121, 612–
615; Angew. Chem. Int. Ed. 2009, 48, 604–606; e) S. Jautze, S. Diethelm,
W. Frey, R. Peters, Organometallics 2009, 28, 2001–2004; f) L. Cheng, J.
Dong, J. You, G. Gao, J. Lan, Chem. Eur. J. 2010, 16, 6761–6765; g) M.
Weber, S. Jautze, W. Frey, R. Peters, J. Am. Chem. Soc. 2010, 132, 12222–
12225; h) H. Liu, D.-M. Du, Adv. Synth. Catal. 2010, 352, 1113 – 1118 ;
i) D. C. Braddock, T. Cailleau, G. Cansell, S. A. Hermitage, R. H. Pouwer,
J. M. Redmond, A. J. P. White, Tetrahedron: Asymmetry 2010, 21, 2911–
[10] Catalytically active copper(I) species could be generated in situ upon
the reaction of copper(II) with alkynes, see: a) M.-C. Ye, J. Zhou, Y. Tang,
J. Org. Chem. 2006, 71, 3576–3582; b) Z. Chen, L. Lin, M. Wang, X. Liu,
X. Feng, Chem. Eur. J. 2013, 19, 7561–7567; for the reduction of cop-
per(II) to copper(I) species in the presence of sodium ascorbate; see:
c) T. F. Knçpfel, E. M. Carreira, J. Am. Chem. Soc. 2003, 125, 6054–6055;
for enantioselective alkynylations using copper(II) salts, see: d) K. Balara-
man, R. Vasanthan, V. Kesavan, Tetrahedron Lett. 2013, 54, 3613–3616;
e) A. Bisai, V. K. Singh, Org. Lett. 2006, 8, 2405–2408; f) Z. Shao, X. Pu, X.
Li, B. Fan, A. S. C. Chan, Tetrahedron: Asymmetry 2009, 20, 225–229.
[11] Selected examples for enantioselective reaction in seawater, see: a) N.
Mase, K. Watanabe, H. Yoda, K. Takabe, F. Tanaka, C. F. Barbas III, J. Am.
Chem. Soc. 2006, 128, 4966–4967; b) D.-Q. Xu, A.-B. Xia, S.-P. Luo, J.
Tang, S. Zhang, J.-R. Jiang, Z.-Y. Xu, Angew. Chem. 2009, 121, 3879–
3882; Angew. Chem. Int. Ed. 2009, 48, 3821–3824.
[12] Selected examples for chiral Lewis acids-surfactant combination cata-
lysts, see: a) S. Azoulay, K. Manabe, S. Kobayashi, Org. Lett. 2005, 7,
4593–4595; b) C. Ogawa, N. Wang, M. Boudou, S. Azoulay, K. Manabe,
S. Kobayashi, Heterocycles 2007, 72, 589–598; c) S. Bonollo, F. Fringuelli,
F. Pizzo, L. Vaccaro, Synlett 2008, 1574–1578.
[13] a) C. Koradin, K. Polborn, P. Knochel, Angew. Chem. 2002, 114, 2651–
2654; Angew. Chem. Int. Ed. 2002, 41, 2535–2538; b) J.-X. Ji, J. Wu,
A. S. C. Chan, Proc. Natl. Acad. Sci. USA 2005, 102, 11196–11200; c) A.
Bisai, V. K. Singh, Tetrahedron 2012, 68, 3480–3486; d) N. Gommermann,
C. Koradin, K. Polborn, P. Knochel, Angew. Chem. 2003, 115, 5941–5944;
Angew. Chem. Int. Ed. 2003, 42, 5763–5766. See also ref. 11e.
Received: February 26, 2014
Published online on June 12, 2014
Chem. Eur. J. 2014, 20, 8848 – 8851
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