Diastereoselective and enantioselective capture of chiral zinc enolate using nitroolefins: A rapid access to chiral γ-nitro carbonyl compounds

Article abstract of DOI:10.1039/c1ob05903c

Highly diastereoselective and enantioselective catalytic capture of chiral zinc enolates using nitroolefins as electrophiles is described. The tandem products γ-nitro ketones were obtained in good yields with high diastereoselectivities and enantioselectivities. The γ-nitro ketones were readily hydrogenated to the optically enriched and diastereomerically pure chiral pyrrolidines with four contiguous stereocentres under mild conditions.

Full text of DOI:10.1039/c1ob05903c

View Article Online / Journal Homepage / Table of Contents for this issue
Organic &
Biomolecular
Chemistry
Dynamic Article Links
Cite this: Org. Biomol. Chem., 2011, 9, 6211
www.rsc.org/obc
COMMUNICATION
Diastereoselective and enantioselective capture of chiral zinc enolate using
nitroolefins: a rapid access to chiral c-nitro carbonyl compounds†
Cheng-Yan Ni,a Sha-Sha Kan,a Quan-Zhong Liu*a and Tai-Ran Kanga,b
Received 5th June 2011, Accepted 13th July 2011
DOI: 10.1039/c1ob05903c
Highly diastereoselective and enantioselective catalytic cap-
ture of chiral zinc enolates using nitroolefins as electrophiles
is described. The tandem products c-nitro ketones were
obtained in good yields with high diastereoselectivities and
enantioselectivities. The c-nitro ketones were readily hydro-
genated to the optically enriched and diastereomerically pure
chiral pyrrolidines with four contiguous stereocentres under
mild conditions.
intermediates formed.8 The tandem reactions have been success-
fully applied in the synthesis of structurally and functionally
diverse organic compounds.9 Michael addition of nucleophiles to
a,b-unsaturated carbonyl compounds represents one of the most
important transformations in organic chemistry.10 Diethylzinc has
been employed in the enantioselective conjugate addition to a,b-
unsaturated ketones.10–11 The chiral zinc enolates formed in situ
in the process can be captured by a series of electrophiles such
as aldehydes, ketones, nitriles, oxocarbenium ions, carboxylates,
alkylhalides, imines, nitrosos andtosylates forming molecules with
complex stereochemistry and functionalities.12 Up to now, there
is no report of using a,b-unsaturated systems as electrophiles to
trap the formed chiral zinc enolate. In this regard, nitroolefins are
attractive Michael acceptors because the corresponding Michael
product can be conveniently converted to important nitrogen-
containing compounds via Nef reaction, Meyer reaction and other
transformations.13 Employment of nitroolefins as electrophiles
to trap the chiral zinc enolates formed in the copper catalyzed
Michael addition of diethylzinc to a,b-unsaturated ketones would
yield valuable g-nitro substituted carbonyl compounds.14 The g-
nitro substituted carbonyl compounds would be readily trans-
formed to the corresponding chiral pyrrolidine bearing multiple
contiguous chiral centres using the known procedures (Scheme 1).
Based on this concept, we initiated the copper catalyzed enantios-
elective addition of diethylzinc to a,b-unsaturated systems and
capture of the chiral zinc enolate using nitroolefins as electrophiles.
Herein we report our results toward the efforts.
The pyrrolidine motifs are important structural scaffolds found in
many bioactive molecules.1 Chiral pyrrolidines form the core of
numerous natural products and synthetic analogues displaying a
broad and interesting range of biological activities (Fig. 1).2 They
are also useful as synthetic intermediates as well as organocatalysts
in asymmetric catalysis.3
Fig. 1 Representative natural products containing the chiral pyrrolidine
motif.
The chiral pyrrolidine derivatives can be readily synthesized
from naturally occurring a-amino acids.4 Other approaches such
as the ring closure metathesis (namely RCM) or ring exposure,5
azomethine ylide cycloaddition,6 and asymmetric 1,3-dipolar
addition7 and other methods are also employed. Despite the great
successes achieved in the past years, highly efficient access to these
structurally complex molecules is still urgently required. In this
regard, asymmetric tandem C–C bond formations are attractive
methodologies which provide access to complex molecules with
excellent regio-, chemo-, diastereo-, and enantioselectivities by
using a single catalyst in one pot, without the isolation of the
aChemical Synthesis and Pollution Control Key Laboratory of Sichuan
Province, Nanchong, P. R. China; College of Chemistry and Chemical
Engineering, China West Normal University, Nanchong 637009, P. R. China
Scheme 1 Copper catalyzed Michael addition/Michael trapping and a
possible route to the pyrrolidine derivative.
bState Key Laboratory of Biotherapy, West China Hospital, Sichuan
University, Chengdu, China. E-mail: quanzhongliu@sohu.com
† Electronic supplementary information (ESI) available: 1H and 13C
spectra, HPLC for all compounds. CCDC reference numbers 806147 and
816318. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c1ob05903c
Initially, using the reported procedure, chalcone was exposed
to diethylzinc in the presence of 2 mol% of Cu(OTf)2 and
monodentate phosphoramidite 1a (4 mol%) which was found to
This journal is
The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 6211–6214 | 6211
©

View Article Online
Table 1 The scope of the substrates
be effective in the asymmetric Michael addition of diethylzinc to
a,b-unsaturated ketones.15 The intermediate zinc enolate formed
was captured by trans-b-nitrostyrene at -20 ◦C affording the three
component product. Only one diastereoisomer was observed in
79% yield with 85% ee. The major side product was the Michael
addition of diethylzinc to nitroolefins (<10% yield), no other
side reactions such as the polymerization of nitroolefins were
observed. This result encouraged us to further evaluate other
phosphoramidites (Fig. 2).
Entrya
R1, R2
Ar
Product
Yield%b
Eec
1
H, H
H
4a
4b
4c
4d
4e
4f
4g
4h
4i
71
76
56
60
27
81
74
89
64
42
68
25
61
72
66
76
68
78
46
53
63
56
89
91
86
90
89
88
96
90
92
90
93
79
94
90
95
80
90
78
89
76
80
87
2
3
H, H
H, H
H, H
H, H
H, H
H, H
H, H
H, H
4-ClC6H5
4-FC6H5
4-BrC6H5
2-ClC6H5
4-CH3C6H5
3-OMeC6H5
4-OMeC6H5
2-furyl
4
5d
6
7
8
9
10
11
12
13
14e
15
16
17
18
19
20
21
22
H, H
H, H
H, H
1-naphthyl
2-thienyl
cyclohexyl
4j
4k
4l
4-Cl, H
4-NO2, H
4-Br, H
4-OMe, H
4-F, H
2-CH3, H
3-OMe, H
1-Nap, H
H, 4-Cl
H, 4-OMe
H
H
H
H
H
H
H
H
H
H
4m
4n
4o
4p
4q
4r
4s
4t
4u
4v
Fig. 2 The phosphoramidites investigated in the work.
a Unless otherwise stated, 0.2 mmol of chalcone was exposed to 0.24 mmol
of diethylzinc in the presence of 3 mol% of Cu(OTf)2 and 6 mol% of chiral
phosphoramidite 1a, unless otherwise stated, the diastereomerically pure
(dr > 20 : 1, determined by the 1HNMR of the crude products) products
were obtained. b Isolated yields. c Enantioselectivities were determined by
chiral HPLC. d Diastereomerically mixed product was obtained (dr: 5 : 1,
the ee value of the major isomer was 89% ee, the configuration of major
Among the phosporamidites investigated, 1a was best for
the reaction in terms of yield and enantioselectivity. Further
optimization was thus carried out (see Supporting Information†).
When the reaction was carried out at -40 ◦C in the presence
of 3 mol% of copper triflate in combination with 6 mol% of
phosphoramidite using toluene as the reaction medium, the
corresponding three component product 4a was isolated in 71%
yield with 89% ee (see Supporting Information†).
1
isomer was deduced from HNMR); e Diastereomerically mixed product
was obtained (dr: 10 : 1).
The generality of this reaction was further investigated (Table 1).
Under the optimal conditions, various nitroolefins substituted
with electron withdrawing or donating groups at the benzene
ring uniformly provided the diastereomerically pure products with
excellent enantioselectivities. For example, the introduction of
methyl, fluoro, chloro, bromo, or methoxy group at the para
position of the benzene ring appended to the nitroolefins did
not significantly affect the reactivity and enantioselectivity of the
reaction (entries 2–4, 6 and 8, Table 1). The steric hindrance in
the nitroolefins had much effect on the reaction, for example,
2-chlorobenzaldehyde derived nitroolefin yielded the product 4e
in only 27% yield albeit with excellent ee (entry 5, Table 1).
Similarly, 42% yield was obtained with 90% ee when the 1-
naphthaldehyde derived nitroolefin was employed (entry 10, Table
1). Among the substrates investigated, only the nitroolefin derived
from 2-chlorobenzaldehyde provided a diastereomerically mixed
product (dr: 5 : 1). Generally speaking, larger steric hindrance in
the nitroolefins led to better enantioselectivities but lower yields.
It should be noted that heteroaromatic aldehydes such as furyl
and thienyl aldehyde derived nitroolefins were tolerable under
the reaction conditions affording excellent enantioselectivities
and good yields (entries 9 and 11, Table 1). The aliphatic
aldehyde derived nitroolefins were also tested and only the
nitroolefin derived from cyclohexanecarbaldehyde afforded the
corresponding diastereomerically pure product in low yield with
good enantioselectivity (entry 12, Table 1). The low yield may
result from the steric hindrance caused by the cyclohexyl group.
Other aliphatic substituted olefins were not tolerable under the
conditions investigated.
A brief survey of the scope of the reaction with respect
to the structure of a,b-unsaturated ketones was also carried
out. Varieties of a,b-unsaturated ketones reacted smoothly with
diethylzinc and were captured by trans-b-nitrostyrene affording 4
in good yields with good to excellent enantioselectivities. The steric
hindrance and electronic property of the ketones had little effect
on the reaction. All the 4, 3, and 2-substitution patterns of the
aromatic ring of the ketones afforded the corresponding product
in 46–78% yield and with good to excellent enantioselectivities
(entries 13–22, Table 1). For a specific substituent pattern, the
substituents that are helpful to the polarization of the double
bond led to better yields. For all 4-substituted enones, (entries
13–15, 17 vs. 16), electron-withdrawing groups on the phenyl
ring attached to the C C bond afforded the products in a less
satisfactory yield. This is also the case for the substitution of
phenyl ring attached to carbonyl. (Entries 21–22). The ortho and
meta substituted substrates also provided similar results (entries
18–19).
The absolute configuration of 4d was determined to be
(2R,3R,1¢S) by X-ray analysis (Fig. 3). The structure of other
6212 | Org. Biomol. Chem., 2011, 9, 6211–6214
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
tivity and diastereoselectivity were observed. Recrystallization
from the mixed solvent of hexane and ethyl acetate afforded
the enantiomerically pure 5d in 81% yield. It should be noted
that bromine containing 4d underwent dehalogenation under
the present hydrogenation conditions forming the corresponding
product 5a. The absolute configuration of 5a was determined to
be 2S,3R,4S,1¢R by X-ray diffraction (Fig. 5).
Fig. 3 The molecular structure of 4d.
products was assigned by analogy. In the 1HNMR spectrum of 4d
(Fig. 3), 2¢-H proton signals were observed as two ABC resonances
at dH 4.98 and 4.91 ppm (J = 13.6 Hz, 11.2 Hz, 4.0 Hz). 1¢-H was
observed as dt signal at dH 3.57 ppm (J = 11.2 Hz and 4.4 Hz).
2-H appeared as dd at dH 4.10 ppm (J = 10.0 Hz and 4.8 Hz). This
indicates that 1¢-H has a cis relationship in respect to 2-H with a
coupling constant J = 4.4 Hz. The 3-H signal appeared at dH 2.92
ppm as td with J = 10.6 Hz and 4.0 Hz. The coupling constant
between 3-H and 2-H should be 10.6 Hz and revealed that the two
protons are trans relationship. The 1HNMR signals unequivocally
proved the molecular structure of 4d.
The approach of the chiral zinc enolate from chalcone 3a
to trans-b-nitrostyrene 2a is possible two ways (Fig. 4). Si-face
approach provided the product 4a observed in the experiment. The
attack of enolates to Si-face of nitroolefins would be favorable for
the removal of the steric repulsion. Re-face approach would yield
the minor diastereoisomer 4a¢ which was not observed in most
cases.
Fig. 5 The crystal structure of 5a.
In summary, highly diastereoselective and enantioselective
catalytic capture of chiral enolates using nitroolefins as elec-
trophile was developed. The tandem products g-nitro ketones
were obtained in good yields with high diastereoselectivities
and enantioselectivities. The g-nitro ketones were readily hydro-
genated to optically enriched and diastereomerically pure chiral
pyrrolidines with four stereocentres under mild conditions. The
absolute configuration of both g-nitro ketones and pyrrolidines
were established by X-ray diffraction. Using other a,b-unsaturated
systems as electrophiles for trapping the chiral zinc enolates is
being investigated, and these results will be reported in due course.
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (20772097) and Sichuan Provincial
Science Foundation for the Outstanding Youth (05ZQ026-008).
Notes and references
Fig. 4 Diastereoselective capture of chiral zinc enolate with nitroolefin
2a.
1 (a) S. M. Li, Nat. Prod. Rep., 2010, 27, 57; (b) I. Villanueva-Margalef,
D. E. Thurston and G. Zinzalla, Org. Biomol. Chem., 2010, 8, 5294;
(c) G. Zinalla and D. E. Thurston, Future Med. Chem., 2009, 1, 65;
(d) H. Kobayashi, K. Shin-ya, K. Furihata, Y. Hayakawa and H. Seto,
Tetrahedron Lett., 2001, 42, 4021; (e) D. Ma and J. Yang, J. Am. Chem.
Soc., 2001, 123, 9706; (f) H. Watanabe, M. Okue, H. Kobayashi and
T. Kitahara, Tetrahedron Lett., 2002, 43, 861; (g) M. Kawasaki, T.
Shinada, M. Hamada and Y. Ohfune, Org. Lett., 2005, 7, 4165.
2 (a) A. Blum, J. Bo¨ttcher, A. Heine, G. Klebe and W. E. Diederich,
J. Med. Chem., 2008, 51, 2078; (b) G. J. Morriello, H. R. Wendt, A.
Bansal, J. D. Salvo, S. Feighner, J. He, A. L. Hurley, D. L. Hreniuk,
G. M. Salituro, M. V. Reddy, S. M. Galloway, K. K. McGettigan,
G. Laws, C. McKnight, G. A. Doss, N. N. Tsou, R. M. Black, J.
Morris, R. G. Ball, A. T. Sanfiz, E. Streckfuss, M. Struthers and S.
D. Edmondson, Bioorg. Med. Chem. Lett., 2011, 21, 1865; (c) M. C.
Lucas, R. J. Weikert, D. S. Carter, H.-Y. Cai, R. Greenhouse, P. S. Iyer,
C. J. Lin, E. K. Lee, A. M. Madera, A. Moore, K. Ozboya, R. C.
Schoenfeld, S. Steiner, Y. Zhai and S. M. Lynch, Bioorg. Med. Chem.
Lett., 2010, 20, 5559; (d) C. A. Van Huis, A. Casimiro-Garcia, C. F.
Bigge, W. L. Cody, D. A. Dudley, K. J. Filipski, R. J. Heemstra, J. T.
Kohrt, R. J. Leadley, L. S. Narasimhan, T. McClanahan, I. Mochalkin,
M. Pamment, J. T. Peterson, V. Sahasrabudhe, R. P. Schaum and J. J.
Edmunds, Bioorg. Med. Chem., 2009, 17, 2501; (e) C. F. Klitzke and R.
A. Pilli, Tetrahedron Lett., 2001, 42, 5605; (f) K. B. Lindsay and S. G.
Pyne, J. Org. Chem., 2002, 67, 7774; (g) L. Rambaud, P. Compain and
O. R. Martin, Tetrahedron: Asymmetry, 2001, 12, 1807.
To demonstrate the utility of the tandem chemistry, the products
for the tandem reaction 4a and 4p can be conveniently hydro-
genated to the chiral pyrrolidine derivatives with four contiguous
stereocentres (Scheme 2). The three component product 4 was
transformed to the cyclic amine 5 under 1 atm of hydrogen
using Pd/C as catalyst at 40 ◦C with subsequent protection of
amine with toluenesulfonyl chloride in CH2Cl2 in excellent yields
in the presence of triethylamine. The enantiomeric excess of 5a
and 5p were determined to be 90% and 86% ee respectively by
HPLC. During the hydrogenation, no erosions of enantioselec-
Scheme 2 Synthesis of chiral pyrrolidine derivatives and the determina-
tion of absolute configuration.
This journal is
The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 6211–6214 | 6213
©

View Article Online
3 For reviews, see: (a) P. I. Dalko and L. Moisan, Angew. Chem., Int. Ed.,
2001, 40, 3726; (b) P. I. Dalko and L. Moisan, Angew. Chem., Int. Ed.,
2004, 43, 5138; (c) M. S. Taylor and E. N. Jacobsen, Angew. Chem.,
Int. Ed., 2006, 45, 1520; (d) P.-O. Delaye, M. Ahari, J.-L. Vasse and J.
Szymoniak, Tetrahedron: Asymmetry, 2010, 21, 2505.
346; (e) N. Krause and A. Hoffmann-Ro¨der, Synthesis, 2001, 171;
(f) K. Endo, M. Ogawa and T. Shibata, Angew. Chem., Int. Ed., 2010,
49, 2410; (g) J. Tauchman, I. C´ısarˇova´ and P. Steˇpnicˇka, Eur. J. Org.
ˇ
Chem., 2010, 4276; (h) Y. Xie, H. Huang, W. Mo, X. Fan, Z. Shen, Z.
Shen, N. Sun, B. Hu and X. Hu, Tetrahedron: Asymmetry, 2009, 20,
1425; (i) K. Kawamura, H. Fukuzawa and M. Hayashi, Org. Lett., 2008,
10, 3509; (j) Q.-L. Zhao, M. K. Tse, L.-L. Wang, A.-P. Xing and X.
Jiang, Tetrahedron: Asymmetry, 2010, 21, 2788; (k) M. Rachwalski, S.
Les´niak and P. Kiełbasin´ski, Tetrahedron: Asymmetry, 2010, 21, 1890;
(l) N. Mikla´sˇova´, O. Jul´ınek, M. Mesˇkova´, V. Setnicˇka and M. Putala,
Tetrahedron Lett., 2010, 51, 1966; (m) J. Escorihuela, M. I. Burguete
and S. V. Luis, Tetrahedron Lett., 2008, 49, 6885; (n) Z.-B. Dong, B.
Liu, C. Fang and J.-S. Li, J. Organomet. Chem., 2008, 693, 17; (o) A.
4 F. J. Sardina and H. Rapoport, Chem. Rev., 1996, 96, 1825.
5 (a) F.-X. Felpin and J. Lebreton, Eur. J. Org. Chem., 2003, 3693; (b) F.
Couty, F. Durrat, G. Evano and J. Marrot, Eur. J. Org. Chem., 2006,
4214.
¨
6 (a) H. U. Kaniskan and P. Garner, J. Am. Chem. Soc., 2007, 129, 15460;
(b) C. Alvarez-Ibarra, A. G. Csa´ky¨, I. L. de Silanes and M. L. Quiroga,
J. Org. Chem., 1997, 62, 479; (c) D. J. Denhart, D. A. Griffith and C.
H. Heathcock, J. Org. Chem., 1998, 63, 9616; (d) P. Garner, P. B. Cox,
J. T. Anderson, J. Protasiewicz and R. Zaniewski, J. Org. Chem., 1997,
¨
Isleyen and O. Dogan, Tetrahedron: Asymmetry, 2007, 18, 679; (p) A.
¨
62, 493; (e) P. Garner, H. U. Kaniskan, J. Hu, W. J. Youngs and M.
Alexakis and C. Benhaim, Eur. J. Org. Chem., 2002, 3221; (q) K. Li
and A. Alexakis, Tetrahedron Lett., 2005, 46, 8019; (r) K. Li and A.
Alexakis, Tetrahedron Lett., 2005, 46, 5823.
Panzner, Org. Lett., 2006, 8, 3647; (f) P. Garner, J. Hu, C. G. Parker, W.
J. Youngs and D. Medvetz, Tetrahedron Lett., 2007, 48, 3867.
7 (a) G. Pandey, P. Banerjee and S. R. Gadre, Chem. Rev., 2006, 106,
4484; (b) K. V. Gothelf and K. A. Jjrgensen, Chem. Rev., 1998, 98,
863; (c) V. Nair and T. D. Suja, Tetrahedron, 2007, 63, 12247; (d) I.
Coldham and R. Hufton, Chem. Rev., 2005, 105, 2765; (e) J. L. Vicario,
S. Reboredo, D. Bad´ıa and L. Carrillo, Angew. Chem., Int. Ed., 2007,
46, 5168; (f) I. Ibrahem, R. Rios, J. Vesely and A. Co´rdova, Tetrahedron
Lett., 2007, 48, 6252.
12 (a) H.-C. Guo and J.-A. Ma, Angew. Chem., Int. Ed., 2006, 45, 354;
(b) E. Keller, J. Maurer, R. Naasz, T. Schader, A. Meetsma and B. L.
Feringa, Tetrahedron: Asymmetry, 1998, 9, 2409; (c) S. Guo, Y. Xie, X.
Hu, C. Xia and H. Huang, Angew. Chem. Int. Ed., 2010, 49, 2728; (d) M.
Kitamura, T. Miki, K. Nakano and R. Noyori, Tetrahedron Lett., 1996,
37, 5141; (e) B. L. Feringa, M. Pineschi, L. A. Arnold, R. Imbos and
A. H. M. de Vries, Angew. Chem., Int. Ed. Engl., 1997, 36, 2620; (f) L.
A. Arnold, R. Naasz, A. J. Minnaard and B. L. Feringa, J. Org. Chem.,
2002, 67, 7244; (g) R. Nassz, L. A. Arnold, M. Pineschi, E. Keller and
B. L. Feringa, J. Am. Chem. Soc., 1999, 121, 1104; (h) H. Mizutani,
S. J. Degrado and A. H. Hoveyda, J. Am. Chem. Soc., 2002, 124, 779;
(i) X. Rathgeb, S. March and A. Alexakis, J. Org. Chem., 2006, 71,
5737; (j) O. Knopff and A. Alexakis, Org. Lett., 2002, 4, 3835; (k) A.
Alexakis and S. March, J. Org. Chem., 2002, 67, 8753; (l) K. Agapiou,
D. F. Cauble and M. J. Krische, J. Am. Chem. Soc., 2004, 126, 4528;
(m) K. Li and A. Alexakis, Chem.–Eur. J., 2007, 13, 3765; (n) Y. J. Xu,
Q.-Z. Liu and L. Dong, Synlett, 2007, 273.
13 (a) D. Amantini, F. Fringuelli, O. Piermatti, F. Pizzo and L. Vaccaro, J.
Org. Chem., 2003, 68, 9263; (b) E. C. Taylor and B. Liu, J. Org. Chem.,
2003, 68, 9938; (c) M.-A. Poupart, G. Fazal, S. Goulet and L. T. Mar,
J. Org. Chem., 1999, 64, 1356; (d) M. J. Kamlet, L. A. Kaplan and J. C.
Dacons, J. Org. Chem., 1961, 26, 4371.
14 D. Roca-Lopez, D. Sadaba, I. Delso, R. P. Herrera, T. Tejero and P.
Merino, Tetrahedron: Asymmetry, 2010, 21, 2561.
8 Reviews: (a) T.-L. Huo, Tandem Organic reactions, New York, Wiley,
1992; (b) L.-F. Tietze, Chem. Rev., 1996, 96, 115; (c) K. C. Nicolaou,T.
Montagnon and S. A. Snyder, Chem. Commun., 2003, 551.
9 (a) A. Do¨mling and I. Ugi, Angew. Chem., Int. Ed., 2000, 39, 3168;
(b) J. Zhu and H. Bienayme, Multicomponent reactions, Wiley-VCH,
Weinheim, 2005; (c) R. V. A. Orru and M. de Greef, Synthesis, 2003,
1471; (d) A. Do¨mling, Chem. Rev., 2006, 106, 17; (e) B. Ganem, Acc.
Chem. Res., 2009, 42, 463.
10 Selected recent reviews about asymmetric conjugate additions: (a) J.
Christoffers, G. Koripelly, A. Rosiak and M. Ro¨ssle, Synthesis, 2007,
1279; (b) A. Alexakis, J. E. Ba¨ckvall, N. Krause, O. Pa`mies and M.
Die´guez, Chem. Rev., 2008, 108, 2796; (c) S. R. Harutyunyan, T. den
Hartog, K. Geurts, A. J. Minnaard and B. L. Feringa, Chem. Rev.,
2008, 108, 2824; (d) S. Jautze and R. Peters, Synthesis, 2010, 365.
11 (a) A. Alexakis, in transition Metal Catalysed Reactions, S.-I. Mura-
hashi and S.-G. Davies, ed., IUPAC Blackwell Science, Oxford, 1999;
(b) T. Ibuka, Organocopper Reagents in Organic synthesis, Rose Press,
Osaka, 2000; (c) N. Krause, Modern Organocopper Chemistry, Wiley-
VCH Weinheim, 2002; (d) B. L. Feringa, Acc. Chem. Res., 2000, 33,
15 A. Martorell, R. Naasz, B. L. Feringa and P. G. Pringle, Tetrahedron:
Asymmetry, 2001, 12, 2497.
6214 | Org. Biomol. Chem., 2011, 9, 6211–6214
This journal is
The Royal Society of Chemistry 2011
©