Chiral binuclear copper(II) catalyzed nitroaldol reaction: scope and mechanism

Article abstract of DOI:10.1016/j.tet.2008.10.009

Chiral binuclear copper(II) Schiff base complexes 4a-g have been prepared from aldehydes 1a,b, (S)-amino alcohols 2a-f, and Cu(OAc)₂·1H₂O in high yield. Their catalysis is studied for the addition of nitroalkanes to aldehydes at ambi

Full text of DOI:10.1016/j.tet.2008.10.009

Tetrahedron 64 (2008) 11724–11731
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Chiral binuclear copper(II) catalyzed nitroaldol reaction: scope
and mechanism
Suribabu Jammi, Prasenjit Saha, Sridhar Sanyashi, Sekarpandi Sakthivel,
*
Tharmalingam Punniyamurthy
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Chiral binuclear copper(II) Schiff base complexes 4a–g have been prepared from aldehydes 1a,b, (S)-
amino alcohols 2a–f, and Cu(OAc)2$1H2O in high yield. Their catalysis is studied for the addition of
nitroalkanes to aldehydes at ambient conditions with 76:24 er.
Received 25 June 2008
Received in revised form
30 September 2008
Accepted 1 October 2008
Available online 14 October 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Binuclear copper(II) complex
Bifunctional catalyst
Homogeneous process
Nitroaldol reaction
Aldehydes
Nitroalkanes
1. Introduction
were then treated with Cu(OAc)2$1H2O in EtOH to give the
complexes 4a–g as green colored powder (Scheme 1). During
Copper is an abundant element in the earth crust. It is also
present in proteins such as tyrosinase, hemocyanins, and copper
oxidases.1 Many of these proteins are believed to contain the copper
ions in dissymmetric ligand arrangements and therefore modeling
the structural aspects of this dissymmetric ligand environment
around copper is currently of great interest.2 Chiral binuclear com-
plexes of copper(II) have received special attention because of their
importance in molecular recognition.3,4 Herein we describe the
synthesis and application of a series of chiral binuclear copper(II)
complexes 4a–g, from aldehydes 1a,b, (S)-amino alcohols 2a–f, and
Cu(OAc)2$1H2O, for addition of nitroalkanes to aldehydes with upto
76:24 er. The reactions are free from the addition of an additive or
base and the complexes 4a–g act as bifunctional catalysts. Both the
aryl and alkyl aldehydes are compatible with this protocol providing
the nitroaldol products in highyields. Nitromethane is more reactive
compared to nitroethane and nitropropane.
recrystallization in a mixture of MeOH and CH2Cl2, the complex
4e was yielded as single crystals whose X-ray analysis showed as
a binuclear complex having Cu–O–Cu bridge with the alkyl OH
group (Fig. 1).5 The copper(II) atoms are tetracoordinated with
R'
CHO
R'
OH
N
i
R
OH
+
H2N
2a-f
R'
R
OH
OH
1a-b
R
3a-g
R
R
R= t-Bu, H
N
O
O
O
N
R
ii
Cu
Cu
R
O
R
R'
4a-g
R
R'
4
Yield [%]
76
2. Results and discussion
a
b
c
d
e
f
Me
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
H
i-Pr
88
s-Bu
i-Bu
t-Bu
Bn
79
90
95
82
70
Aldehydes 1a,b were reacted with (S)-amino alcohols 2a–f in
EtOH to provide Schiff bases 3a–g in high yield. The latter
g
t-Bu
Scheme 1. Synthesis of the binuclear copper(II) complex 4a–g: (i) EtOH, 25 ꢀC, 24 h;
(ii) Cu(OAc)2$1H2O, EtOH, 25 ꢀC, 12 h.
* Corresponding author. Fax: þ91 361 2690762.
E-mail address: tpunni@iitg.ernet.in (T. Punniyamurthy).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.10.009

S. Jammi et al. / Tetrahedron 64 (2008) 11724–11731
11725
Figure 1. ORTEP diagram of 4e with thermal ellipsoid set to 50% probability. H-atoms are omitted for clarity.
a distorted square planar geometry. The Cu–Cu distances (2.853–
2.907 Å), bond lengths of the bridged (1.856–1.939 Å) and
terminal (1.8351–1.876 Å) Cu–O, Cu–N (1.886–1.927 Å), and the
bond angles of Cu–O–Cu (96.04ꢀ–101.50ꢀ) agree with the reported
data.6 The five-membered rings, arising from the coordination of
the bridged O and imine N of 4e with Cu(II), exist in envelope
conformation.
The catalytic activity of the complexes 4a–g was then studied for
the addition of nitroalkanes to aldehydes.7–10 The optimization of
the reaction conditions was carried out with the addition of ni-
tromethane to p-nitrobenzaldehyde as a model substrate (Table 1).
The best results observed when substrates were stirred for 24 h in
the presence of 2.5 mol % of 4e at ambient temperature. Of the
solvents studied, CH2Cl2, toluene, THF, EtOH, CH3CN, and CHCl3,
the former found to be the choice for these reactions (Table 2). The
reaction with complex 4e was superior to that used 4a–d and 4f,-g
as the catalysts.
The reactions of other aldehydes were next studied with nitro-
methane (Table 3). Benzaldehyde underwent reaction with
92% yield and 60:40 er. Similar results observed with 2-bromo-, 2-
methoxy-, 3-bromo-, 3-nitro-, 4-bromo-, 4-chloro-, 4-fluoro-,
4-methoxy-, and 4-methylbenzaldehydes. Likewise, 2-naph-
thaldehyde, 2-thiophenecarboxaldehyde, 2-furaldehyde, cyclo-
hexanecarboxaldehyde, ethyl glyoxalate, and isobutyraldehyde
underwent reaction to give nitroaldol products with upto 89% yield
and 68:32 er. In aryl aldehydes, the substrates bearing electron-
withdrawing groups exhibited greater reactivity compared to that
having electron-donating groups.
The observed experimental results suggest that the complexes 4
act as bifunctional catalysts in these reactions: first, as Brønsted
base, and then, as Lewis acid. To reveal, the complex 4e was titrated
with HCl whose electronic spectra showed that the intensity of the
bands at 384 nm and 283 nm decreased with respect to the in-
creasing concentration of HCl, and shifted to lower wavelength at
327 nm and 263 nm, respectively (Fig. 2).11 These studies clearly
reveal that the phenolate oxygen is selectively protonated (Fig. 3).
Thus, the phenolate oxygen acts as a stronger base compared to
Table 1
Reaction of 4-nitrobenzaldehyde: screening of complexes 4a–g and nitroalkanes
OH
CHO
2.5 mol% 4a-g
NO2
10 equiv RCH2NO2
CH2Cl2, RT
R
O2N
R = H, Et, Me
O2N
Table 2
Reaction of 4-nitrobenzaldehyde with nitromethane using 4e: solvent effect
Entry
Catalyst
RCH2NO2
Product
OH
Yielda (%)
erd
Configuratione
CHO
NO2
2.5 mol% 4e
1
2
3
4
5
6
7
8
9
10
4a
4b
4c
4d
4e
4f
4g
4e
4e
4e
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
EtNO2
55
86
77
53:47
58:42
57:43
S
S
S
10 equiv MeNO2
Solvent, RT
O2N
O2N
75
90
82
75
56:44
66:34
53:47
45:55
56:44, 64:36
55:45, 59:41
d
S
S
S
S
nd
nd
d
Entry
Solvent
Product
Yielda (%)
erb
Configurationc
78 (11:9)b,c
45 (11:9)b,c
nrf
1
2
3
4
5
6
EtOH
THF
CH3CN
Toluene
CHCl3
CH2Cl2
40
53
20
49
84
90
61:39
57:43
56:44
60:40
60:40
66:34
S
S
S
S
S
S
PrNO2
i-PrNO2
a
4-Nitrobenzaldehyde (0.5 mmol), 4a–g (2.5 mol %), and nitroalkane (5 mmol)
stirred for 24 h in CH2Cl2 (1 mL).
b
syn/anti ratio.
c
a
Reaction time¼48 h.
4-Nitrobenzaldehyde (0.5 mmol), 4e (2.5 mol %), and nitromethane (5 mmol)
d
Determined by HPLC with Chiralcel OD-H column using hexane/isopropanol
stirred for 24 h in appropriate solvent (1 mL).
b
(85:15).
Determined by HPLC analysis with Chiralcel OD-H column using hexane/iso-
e
Determined from sign of optical rotation.
nr¼no reaction.
propanol (85:15).
f
c
Determined from sign of optical rotation.

11726
S. Jammi et al. / Tetrahedron 64 (2008) 11724–11731
Table 3
Reaction of alkyl, aryl, and 2-naphthyl aldehydes with nitromethane
Entry
1
Substrate
Time (h)
Product
Yielda,b (%)
92
erc
Configurationd
OH
CHO
NO2
NO2
28
60:40
S
OH
CHO
Br
2
3
20
34
93
89
55:45
65:35
S
S
Br
OH
CHO
OMe
NO2
NO2
OMe
OH
CHO
4
5
30
26
85
90
60:40
76:24
nd
Br
Br
OH
CHO
NO2
S
NO2
NO2
OH
CHO
NO2
6
7
8
24
23
22
95
90
94
58:42
54:46
55:45
nd
S
Br
Cl
F
Br
Cl
F
OH
OH
CHO
CHO
NO2
NO2
S
OH
CHO
CHO
CHO
NO2
9
38
84
66:34
S
MeO
Me
MeO
Me
OH
NO2
NO2
10
11
30
36
90
81
64:36
61:39
S
S
OH
12
13
30
16
65
74
54:46
55:45
S
S
NO2
CHO
S
S
OH
NO2
NO2
O
CHO
CHO
O
OH
OH
14
15
24
20
89
86
68:32
64:36
S
S
OH
CHO
NO2
OH
O
CHO
O
NO2
16
30
55
57:43
nd
O
O
a
Substrate (0.5 mmol), 4e (2.5 mol %), and nitromethane (5 mmol) stirred in CH2Cl2 (1 mL) at ambient temperature.
Isolated yield.
Determined by HPLC analysis using Chiralcel OD-H (for entries 1–12 and 16) and Chiralpak AD-H (for entries 13–15) columns with n-hexane/isopropanol.
Determined from sign of optical rotation.
b
c
d

S. Jammi et al. / Tetrahedron 64 (2008) 11724–11731
11727
0.6
0.5
0.4
0.3
0.2
0.1
0.0
R
N
t-Bu
O
Catalyst 4e
O
Catalyst 4e+HCl (1:0.4)
Catalyst 4e+HCl (1:0.8)
Catalyst 4e+HCl (1:1.2)
Catalyst 4e+HCl (1:1.6)
Catalyst 4e+HCl (1:2.0)
t-Bu
Cu
Cu
t-Bu
O
O
N
4a-f
t-Bu
R
2CH3NO2, 2R'CHO
R
II
N
O
O
HO
R'
Cu
NO2
H
t-Bu
O
H
H
t-Bu
R'
O
+
-O
N
R'CHO
R
R
CH2
a
II
II
N
O
N
O
O
250
300
350
400
Wavelength (nm)
450
500
Cu
Cu
t-Bu
O
t-Bu
O
O
H
NO2
H
H
O
N
R'
H
R'
CH2
O-
t-Bu
+
t-Bu
Figure 2. UV–vis spectra of 4e (3.3ꢂ10ꢁ2 mM) with an increasing concentration of HCl
(0.0–6.6ꢂ10ꢁ2 mM) in CH2Cl2.
+
HO
-O
N
c
b
CH2
CH3NO2
Scheme 2. Proposed catalytic cycle.
0.6
Catalyst 4e
Catalyst 4e+HCl (1:2.0)
2,4-Di-tert-butylphenol
spectrometer. FTIR spectra obtained from Nicolet-410 spectrometer.
HPLC analysis was carried out on Waters-2478 with chiral stationary
phase columns (chiralcel OD-H and chiralpak AD-H). UV–vis spectra
obtained from Perkin–Elmer Lambda-25 spectrophotometer. Ther-
mogravimetric analysis recorded using TGA/SDTA-851 Mettler To-
ledo analyzer. EPR spectra recorded using JES-FA-200 spectrometer.
X-ray data collected on Bruker SMARTAPEXequipped with CCD area
0.5
0.4
0.3
0.2
0.1
0.0
detector using Mo Ka radiation. The structure solved using SHELXL-
97 Go¨ttingen, Germany. Column chromatography performed on 60–
120 mesh silica gel. Elemental analysis carried out in this de-
partment using Perkin–Elmer-2400 CHNS analyzer.
4.2. General procedure for the preparation of 3a–g
250
300
350
400
Wavelength (nm)
450
500
Aldehydes 1a,b (5 mmol) and (S)-amino alcohols 2a–f (5 mmol)
was stirred in EtOH (10 mL) for 24 h at ambient temperature. Re-
moval of the solvent provided a residue, which was purified on
silica gel column chromatography using ethyl acetate and hexane
(1:19) to give 3a–g as yellow compounds.
The ligands 2,4-bis(1,1-dimethylethyl)-6-[[[(1S)-1-hydroxy-
methyl-2-methylpropyl]imino]methyl]-phenol 3b,13a 2,4-bis(1,
-1-dimethylethyl)-6-[[[(1S,2S)-1-(hydroxymethyl)-2-methylbutyl]-
imino]methyl]-phenol 3c,13b 2,4-bis(1,1-dimethylethyl)-6-[[[(1S)-1-
(hydroxymethyl)-2,2-dimethylpropyl]imino]methyl]-phenol 3e13a
are known and spectral data are consistent with those reported in
the literature. The ligands 3a, 3d, 3f, and 3g are known in the liter-
ature but their data are not reported.
Figure 3. UV–vis spectra of 4e, 4eþHCl and 2,4-di-tert-butylphenol in CH2Cl2.
carboxylate oxygen under these conditions. Hence, the reaction of
complex 4 with nitroalkane and aldehyde can generate monomeric
complex a that could transform to intermediate c via intra-
molecular addition of nitronate to aldehyde b followed by reaction
with fresh nitroalkane. The intermediate c can complete the cata-
lytic cycle by reaction with fresh aldehyde (Scheme 2).
3. Conclusions
In summary, the synthesis of chiral copper(II) Schiff base com-
plexes 4a–g has been accomplished in high yield. They have been
studied for the addition of nitroalkanes to aldehydes as bifunctional
catalysts with 76:24 er.
4.2.1. 2,4-Bis(1,1-dimethylethyl)-6-[[[(1S)-2-hydroxy-1-
methylethyl]imino]methyl]-phenol 3a13c
A mixture of 3,5-di-tert-butylsalicylaldehyde (1.17 g, 5 mmol)
and (S)-alaninol (0.375 g, 5 mmol) in EtOH (10 mL) was stirred for
24 h. Evaporation of the solvent gave a residue that was purified
on column chromatography (5% hexane/ethyl acetate) to give the
title compound 3a (1.19 g, 82%) as yellow liquid; [found: C, 74.28;
4. Experimental section
4.1. General
H, 10.10; N, 4.88. C18H29NO2 requires: C, 74.18; H, 10.03; N, 4.81%];
25
Rf (5% hexane/ethyl acetate) 0.40; [
a
]
ꢁ37.6 (c 0.516, CH2Cl2); 1
H
D
L-Amino acids, 2,4-di-tert-butylphenol (98%), aldehydes,
NMR (400 MHz, CDCl3)
d
8.32 (1H, s, CHN), 7.30 (1H, d, J¼2.0 Hz,
nitroalkanes, and Cu(OAc)2$1H2O (>99%) purchased from Aldrich.
(S)-Amino alcohols obtained by reduction of amino acids according
to the literature.12a 3,5-Di-tert-butylsalicylaldehyde prepared from
2,4-di-tert-butylphenol.12b NMR spectra recorded using Varian-400
CH), 7.02 (1H, d, J¼2.4 Hz, CH), 3.55 (2H, d, J¼6.8 Hz, CH2OH), 3.33
(1H, m, CHCH3), 1.35 (9H, s, (CH3)3C), 1.26 (9H, s, (CH3)3C), 1.13 (3H,
d, J¼6.4 Hz, CH3CH); 13C NMR (100 MHz, CDCl3)
d 166.4, 158.3,
140.4, 136.9, 127.3, 126.3, 117.9, 67.4, 66.8, 35.2, 34.3, 31.8, 29.6,

11728
S. Jammi et al. / Tetrahedron 64 (2008) 11724–11731
18.5; IR (neat) 3391, 2966, 2879, 1634, 1470, 1373, 1271, 1102,
1035 cmꢁ1
solvent yielded a residue that was purified by column chromato-
graphy (10% hexane/ethyl acetate) to give the title compound 4a
(1.61 g, 76%) as green powder; [found: C, 61.36; H, 7.72; N, 4.01.
.
4.2.2. 2,4-Bis(1,1-dimethylethyl)-6-[[[(1S)-1-(hydroxymethyl)-3-
methylbutyl]imino]methyl]-phenol 3d13c
C36H54N2O4Cu2 requires: C, 61.25; H, 7.71; N, 3.97%]; Rf (10% hexane/
25
ethyl acetate) 0.41; [
a
]
þ520 (c 0.02, CH2Cl2); IR (KBr):
n 2957,1627,
D
A mixture of 3,5-di-tert-butylsalicylaldehyde (1.17 g, 5 mmol)
and (S)-isoleucinol (0.585 g, 5 mmol) in EtOH (10 mL) was stirred
for 24 h. Evaporation of the solvent afforded a residue that was
purified on column chromatography (5% hexane/ethyl acetate) to
give the title compound 3d (1.53 g, 92%) as yellow liquid; [found: C,
1530, 1433, 1325, 1255, 1167, 1054, 874, 690, 626, 520 cmꢁ1; UV–vis
(CH2Cl2): lmax
) 610 (7931), 388 nm (14,981 molꢁ1 dm3 cmꢁ1); EPR
(MeOH): liquid N2 temp; g ¼2.12, gt¼2.03, A ¼320 mT.
(
3
k
k
4.3.2. Complex 4b
75.73; H, 10.60; N, 4.31. C21H35NO2 requires: C, 75.63; H, 10.58; N,
A mixture of 3b (0.958 g, 3 mmol) and Cu(OAc)2$1H2O (0.598 g,
3 mmol) in EtOH (10 mL) was stirred for 12 h. Evaporation of the
solvent gave a residue, which was purified on column chromatog-
raphy (15% hexane/ethyl acetate) to give the title compound 4b
(2.01 g, 88%) as green powder; [found: C, 63.12; H, 8.22; N, 3.75.
25
4.20%]; Rf (5% hexane/ethyl acetate) 0.33; [
a
]
ꢁ23.3 (c 0.316,
D
CH2Cl2); 1H NMR (400 MHz, CDCl3)
d
8.40 (1H, s, CHN), 7.40 (1H, d,
J¼2.4 Hz, CH), 7.13 (1H, d, J¼2.4 Hz, CH), 3.72–3.64 (2H, m, CH2OH),
3.40–3.36 (1H, m, CHCH2OH), 1.63–1.53 (3H, m, CH2CHCH3), 1.44
(9H, s), 1.28 (9H, s), 0.91–0.99 (6H, m, (CH3)2C); 13C NMR (100 MHz,
C40H62N2O4Cu2 requires: C, 63.05; H, 8.20; N, 3.68%]; Rf (15% hex-
25
CDCl3)
35.2, 34.4, 31.7, 29.6, 24.6, 23.8, 21.7; IR (neat) 3412, 2960, 2868,
1633, 1457, 1396, 1360, 1251, 1171, 1097, 1045, 1017 cmꢁ1
d
166.9, 158.3, 140.4, 136.9, 127.3, 126.3, 117.8, 70.2, 66.8, 41.1,
ane/ethyl acetate) 0.60; [
a
]
þ492 (c 0.02, CH2Cl2); IR (KBr):
n
D
2958, 1626, 1528, 1433, 1323, 1255, 1164, 1054, 837, 525 cmꢁ1; UV–
vis (CH2Cl2): lmax
) 597 (3352), 382 nm (25,832 molꢁ1 dm3 cmꢁ1);
EPR (MeOH): liquid N2 temp; g ¼2.05, gt¼2.01, A ¼317 mT.
.
(3
k
k
4.2.3.
methylene]amino]-(
b
-[[[3,5-Bis(1,1-dimethylethyl)-2-hydroxyphenyl]-
S)-benzenepropanol 3f13d
b
4.3.3. Complex 4c
A mixture of 3,5-di-tert-butylsalicylaldehyde (1.17 g, 5 mmol)
and (S)-phenylalaninol (0.756 g, 5 mmol) in EtOH (10 mL) was
stirred for 24 h. Evaporation of the solvent provided a residue that
was purified by column chromatography (5% hexane/ethyl acetate)
to give the title compound 3f (1.47 g, 80%) as yellow liquid; [found:
A mixture of 3c (1.0 g, 3 mmol) and Cu(OAc)2$1H2O (0.598 g,
3 mmol) in EtOH (10 mL) was stirred for 12 h. Evaporation of the
solvent provided a residue, which was purified by column chro-
matography (5% hexane/ethyl acetate) to yield the title compound
4c (1.87 g, 79%) as green powder; [found: C, 63.80; H, 8.50; N, 3.59.
C, 78.58; H, 9.10; N, 3.79. C18H29NO2 requires: C, 78.43; H, 9.05; N,
C42H66N2O4Cu2 requires: C, 63.85; H, 8.42; N, 3.55%]; Rf (5% hexane/
25
25
3.81%]; Rf (5% hexane/ethyl acetate) 0.38; [
a
]
ꢁ17.2 (c 0.28,
ethyl acetate) 0.83; [
a
]
þ476 (c 0.02, CH2Cl2); IR (KBr):
n 2959,
D
D
CH2Cl2); 1H NMR (400 MHz, CDCl3)
d
8.19 (1H, s, CHN), 7.40 (1H, s,
1625, 1528, 1459, 1432, 1324, 1255, 1166, 1057, 837, 526 cmꢁ1; UV–
vis (CH2Cl2): lmax
) 605 (9282), 382 nm (29,270 molꢁ1 dm3 cmꢁ1);
EPR (MeOH): liquid N2 temp; g ¼2.13, gt¼2.04, A ¼320 mT.
CH), 7.29–7.25 (2H, m, CH), 7.21–7.16 (3H, m, CH), 7.01 (1H, s, CH),
3.81–3.75 (2H, m, CH2OH), 3.53–3.50 (1H, m, CHCH2OH), 2.97–2.89
(2H, m, CH2Ph), 1.46 (9H, s, (CH3)3C), 1.28 (9H, s, (CH3)3C); 13C NMR
(3
k
k
(100 MHz, CDCl3)
d
167.4, 158.2, 140.4, 138.2, 136.8, 129.7, 128.7,
4.3.4. Complex 4d
127.4, 126.6, 126.4, 117.8, 73.4, 66.1, 39.4, 35.3, 34.3, 31.7, 29.6; IR
(neat) 3395, 3055, 2960, 2875, 1644, 1503, 1475, 1386, 1275, 1245,
A mixture of 3d (1.0 g, 3 mmol) and Cu(OAc)2$1H2O (0.598 g,
3 mmol) in EtOH (10 mL) was stirred for 12 h. Evaporation of the
solvent provided a residue, which was purified by column chro-
matography (10% hexane/ethyl acetate) to give the title compound
4d (2.13 g, 90%) as green powder; [found: C, 63.79; H, 8.45; N, 3.59.
1165, 1053, 1028 cmꢁ1
.
4.2.4. 2-[[[(1S)-1-(Hydroxymethyl)-2,2-dimethylpropyl]-
imino]methyl]-phenol 3g13e
C42H66N2O4Cu2 requires: C, 63.85; H, 8.42; N, 3.55%]; Rf (10% hex-
25
A mixture of salicylaldehyde (0.610 g, 5 mmol) and (S)-tert-
leucinol (0.585 g, 5 mmol) in EtOH (10 mL) was stirred for 24 h.
Evaporation of the solvent gave a residue that was purified by
column chromatography (5% hexane/ethyl acetate) to give the title
compound 3g (1.02 g, 92%) as yellow liquid; [found: C, 70.63; H,
ane/ethyl acetate) 0.50; [
a
]
þ395 (c 0.02, CH2Cl2); IR (KBr)
n 2959,
D
1625, 1528, 1459, 1432, 1324, 1255, 1164, 1057, 837, 526 cmꢁ1; UV–
vis (CH2Cl2): lmax
) 613 (8492), 384 nm (18,723 molꢁ1 dm3 cmꢁ1);
EPR (MeOH): liquid N2 temp; g ¼2.10, gt¼2.02, A ¼313 mT.
(
3
k
k
8.69; N, 6.35. C13H19NO2 requires: C, 70.56; H, 8.65; N, 6.33%]; Rf (5%
4.3.5. Complex 4e
25
hexane/ethyl acetate) 0.32; [
(400 MHz, CDCl3)
a
]
ꢁ22 (c 0.5, CHCl3); 1H NMR
A mixture of 3e (1.0 g, 3 mmol) and Cu(OAc)2$1H2O (0.598 g,
3 mmol) in EtOH (10 mL) was stirred for 12 h. Evaporation of the
solvent afforded a residue, which was purified by column chroma-
tography (5% hexane/ethyl acetate) to give the title compound 4e
(2.25 g, 95%) as green powder; [found: C, 63.75; H, 8.53; N, 3.68.
D
d
8.34 (1H, s, CHN), 7.33–7.26 (2H, m, CH), 6.96–
6.87 (2H, CH), 3.94 (1H, d, J¼10.8 Hz, CHOH), 3.72 (1H, t, J¼9.6 Hz,
CHCH2OH), 2.95 (1H, d, J¼9.2 Hz, CHOH), 0.97 (9H, s); 13C NMR
(100 MHz, CDCl3) d 196.9, 166.1, 161.6, 132.6, 131.7, 118.8, 117.2, 81.2,
62.5, 33.3, 27.2; IR (neat) 3365, 2958, 2871, 1633, 1469, 1390, 1361,
C42H66N2O4Cu2 requires: C, 63.85; H, 8.42; N, 3.55%]; Rf (5% hexane/
25
1274, 1252, 1173, 1062, 1047 cmꢁ1
.
ethyl acetate) 0.53; [
a
]
þ400 (c 0.02, CH2Cl2); IR (KBr):
n 2960,1619,
D
1537, 1260, 1163, 1076, 840, 554, 426 cmꢁ1; UV–vis (CH2Cl2): lmax
(3)
4.3. General procedure for the preparation of 4a–g
385(4272), 281 nm(10,303 molꢁ1 dm3 cmꢁ1); EPR (MeOH): liquid N2
temp; g ¼2.28, gt¼2.02, A ¼317 mT; meff (powder, 298 K):1.58 mB/Cu.
k
k
The ligands 3a–g (3 mmol) reacted with Cu(OAc)2$1H2O
(0.597 g, 3 mmol) in EtOH (10 mL) for 12 h at ambient tempera-
ture. The solvent was evaporated under reduced pressure, and the
residue purified on silica gel column chromatography using ethyl
acetate and hexane as eluent to give 4a–g as a green colored
powder.
4.3.6. Complex 4f
A mixture of 3f (1.10 g, 3 mmol) and Cu(OAc)2$1H2O (0.598 g,
3 mmol) in EtOH (10 mL) was stirred for 12 h. Evaporation of the
solvent gave a residue, which was purified by column chroma-
tography (5% hexane/ethyl acetate) to afford the title compound 4f
(2.11 g, 82%) as green powder; [found: C, 67.30; H, 7.35; N, 3.29.
4.3.1. Complex 4a
A mixture of 3a (0.874 g, 3 mmol) and Cu(OAc)2$1H2O (0.598 g,
3 mmol) in EtOH (10 mL) was stirred for 12 h. Evaporation of the
C48H62N2O4Cu2 requires: C, 67.18; H, 7.28; N, 3.26%]; Rf (5% hex-
25
ane/ethyl acetate) 0.63; [
a]
þ320 (c 0.02, CH2Cl2); IR (KBr):
n
D
2966, 1635, 1540, 1441, 1322, 1266, 1178, 1076, 890, 855, 564,

S. Jammi et al. / Tetrahedron 64 (2008) 11724–11731
11729
20
446 cmꢁ1
;
UV–vis (CH2Cl2): lmax
(3)
615 (9137), 390 nm
55:45, 59:41 er; syn/anti ratio 55:45; [
a
]
D
ꢁ0.2 (c 0.28, CH2Cl2).
(12,526 molꢁ1 dm3 cmꢁ1); EPR (MeOH): liquid N2 temp; g ¼2.13,
Anal. Calcd for C10H12N2O5: C, 50.00; H, 5.04; N 11.66. Found: C,
50.03; H, 5.05; N, 11.70.
k
gt¼2.06, A ¼314 mT.
k
4.3.7. Complex 4g
4.4.4. (S)-(þ)-2-Nitro-1-phenylethanol (Table 3, entry 1)14a
A mixture of 3g (0.664 g, 3 mmol) and Cu(OAc)2$1H2O (0.598 g,
3 mmol) in EtOH (10 mL) was stirred for 12 h. Evaporation of the
solvent gave a residue, which was purified by column chromatog-
raphy (5% hexane/ethyl acetate) to provide the title compound 4g
(1.18 g, 70%) as green powder; [found: C, 55.32; H, 6.09; N, 5.07.
A mixture of benzaldehyde (53.0 mg, 0.5 mmol), nitromethane
(305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %) in CH2Cl2
(1 mL) was stirred for 28 h. Evaporation of the solvent afforded
a residue, which was purified by column chromatography (20%
hexane/ethyl acetate) to yield the title compound (76.8 mg, 92%) as
yellow oil; Rf (20% hexane/ethyl acetate) 0.60; HPLC: Chiralcel OD-H
C26H34N2O4Cu2 requires: C, 55.21; H, 6.06; N, 4.95%]; Rf (5% hexane/
ethyl acetate) 0.44; [
25
a]
þ430 (c 0.02, CH2Cl2); IR (KBr):
n
2961,
column, n-hexane/isopropanol (85:15), wavelength: 215 nm, flow
rate: 0.6 mL/min, retention time: 34.1 min, 39.5 min; 60:40 er; [a]
D
þ10 (c 0.1, CH2Cl2).
D
20
1631,1536,1447,1348,1194,1072,1016, 902, 852, 760, 671, 582, 544,
461 cmꢁ1
;
UV–vis (CH2Cl2): lmax
(3
)
614 (4943), 385 nm
(9859 molꢁ1 dm3 cmꢁ1); EPR (MeOH): liquid N2 temp; g ¼2.14,
k
gt¼2.05, A ¼315 mT.
4.4.5. (S)-(þ)-2-Nitro-1-(2-bromophenyl)ethanol (Table 3,
k
entry 2)14b,c
4.4. General procedure for nitroaldol reaction
A mixture of 2-bromobenzaldehyde (92.5 mg, 0.5 mmol), ni-
tromethane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %)
in CH2Cl2 (1 mL) was stirred for 20 h. Evaporation of the solvent
gave a residue, which was purified by column chromatography
(20% hexane/ethyl acetate) to provide the title compound
(144.4 mg, 93%) as colorless oil; Rf (20% hexane/ethyl acetate) 0.58;
HPLC: Chiralcel OD-H column, n-hexane/isopropanol (85:15),
Aldehyde (0.5 mmol), nitroalkane (5 mmol), and complex 4a–g
(2.5 mol %) were stirred in appropriate solvent (1 mL) at ambient
temperature. The progress of the reaction was monitored by TLC.
After completion, the solvent was evaporated and the residue was
purified on silica gel column chromatography using ethyl acetate
and hexane as eluent.
wavelength: 215 nm, flow rate: 0.8 mL/min, retention time:
20
11.43 min, 12.14 min; 55:45 er; [
a
]
þ3.5 (c 1, CHCl3).
D
4.4.1. (S)-(þ)-2-Nitro-1-(4-nitrophenyl)ethanol (Table 1,
entry 5)14a
4.4.6. (S)-(þ)-2-Nitro-1-(2-methoxyphenyl)ethanol (Table 3,
entry 3)14c
A mixture of 4-nitrobenzaldehyde (75.5 mg, 0.5 mmol), nitro-
methane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %) in
CH2Cl2 (1 mL) was stirred for 24 h. Evaporation of the solvent gave
a residue, which was purified by column chromatography (20%
hexane/ethyl acetate) to give the title compound (95.6 mg, 90%) as
colorless solid; Rf (20% hexane/ethyl acetate) 0.43; mp 84–85 ꢀC;
HPLC: Chiralcel OD-H column, n-hexane/isopropanol (85:15),
A mixture of 2-methoxybenzaldehyde (68.07 mg, 0.5 mmol),
nitromethane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg,
2.5 mol %) in CH2Cl2 (1 mL) was stirred for 34 h. Evaporation of the
solvent gave a residue, which was purified by column chromatog-
raphy (20% hexane/ethyl acetate) to afford the title compound
(87.7 mg, 89%) as yellow oil; Rf (20% hexane/ethyl acetate) 0.56;
HPLC: Chiralcel OD-H column, n-hexane/isopropanol (85:15),
wavelength: 215 nm, flow rate: 1 mL/min, retention time: 14.7 min,
20
18.1 min; 66:34 er; [
a]
þ8.4 (c 1, CH2Cl2).
wavelength: 215 nm, flow rate: 0.8 mL/min, retention time:
D
20
12.5 min, 14.3 min; 65:35 er; [
a
]
þ12 (c 1.06, CH2Cl2).
D
4.4.2. 2-Nitro-1-(4-nitrophenyl)propanol (Table 1, entry 8)14a
A mixture of 4-nitrobenzaldehyde (75.5 mg, 0.5 mmol), nitro-
ethane (375.3 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %) in
CH2Cl2 (1 mL) was stirred for 48 h. Evaporation of the solvent gave
a residue, which was purified by column chromatography (20%
hexane/ethyl acetate) to provide the title compound (88.2 mg, 78%)
as colorless solid; Rf (20% hexane/ethyl acetate) 0.52; syn/anti ratio
55:45; mp 92–94 ꢀC; HPLC: Chiralcel OD-H column, n-hexane/iso-
propanol (85:15), wavelength: 215 nm, flow rate: 0.3 mL/min, re-
4.4.7. (þ)-2-Nitro-1-(3-bromophenyl)ethanol (Table 3, entry 4)14d
A mixture of 3-bromobenzaldehyde (92.5 mg, 0.5 mmol), ni-
tromethane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %)
in CH2Cl2 (1 mL) was stirred for 30 h. Evaporation of the solvent
provided a residue, which was purified by column chromatography
(20% hexane/ethyl acetate) to give the title compound (104.5 mg,
85%) as yellow oil; Rf (20% hexane/ethyl acetate) 0.66; HPLC: Chir-
alcel OD-H column, n-hexane/isopropanol (85:15), wavelength:
tention time: 32.6 min, 38.2 min, 41.0 min, 42.5 min; 56:44, 64:36
215 nm, flow rate: 1 mL/min, retention time: 17.45 min, 23.1 min;
20
20
er; [
a]
ꢁ0.3 (c 0.4, CH2Cl2).
60:40 er; [
a
]
D
þ2 (c 1, CH2Cl2).
D
4.4.3. 2-Nitro-1-(4-nitrophenyl)butanol (Table 1, entry 9)
4.4.8. (S)-(þ)-2-Nitro-1-(3-nitrophenyl)ethanol (Table 3,
entry 5)14a
A mixture of 4-nitrobenzaldehyde (75.5 mg, 0.5 mmol), 1-nitro-
propane (445.4 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %) in
CH2Cl2 (1 mL) was stirred for 48 h. Evaporation of the solvent
provided a residue, which was purified by column chromatography
(20% hexane/ethyl acetate) to give the title compound (54.0 mg,
45%) as colorless solid; Rf (20% hexane/ethyl acetate) 0.51; syn/anti
A mixture of 3-nitrobenzaldehyde (75.5 mg, 0.5 mmol), nitro-
methane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %) in
CH2Cl2 (1 mL) was stirred for 26 h at ambient temperature. Evap-
oration of the solvent gave a residue, which was purified by column
chromatography (20% hexane/ethyl acetate) to give the title com-
pound (94.5 mg, 90%) as yellow oil; Rf (20% hexane/ethyl acetate)
0.45; HPLC: Chiralcel OD-H column, n-hexane/isopropanol (85:15),
ratio 55:45; mp 97–98 ꢀC; 1H NMR (400 MHz, CDCl3)
d 8.25 (2H, d,
J¼8.8 Hz, CH), 7.57 (2H, d, J¼8.8 Hz, CH), 5.17–5.13 (1H, m, CHNO2),
4.61–4.56 (1H, m, CHOH), 2.96 (1H, d, J¼0.8 Hz, OH), 1.94–1.84 (1H,
m, CH2CH3), 1.50–1.41 (1H, m, CH2CH3), 0.90 (3H, t, J¼0.8 Hz,
wavelength: 215 nm, flow rate: 1 mL/min, retention time: 21.8 min,
20
24.4 min; 76:24 er; [
a
]
þ14 (c 0.4, CH2Cl2).
D
CH3CH2); 13C NMR (100 MHz, CDCl3)
d 148.4, 145.9, 145.8, 128.0,
127.5, 124.3, 128.1, 94.8, 94.3, 74.5, 73.4, 24.0, 21.4, 10.5, 10.2; IR
4.4.9. (þ)-2-Nitro-1-(4-bromophenyl)ethanol (Table 3, entry 6)14e
A mixture of 4-bromobenzaldehyde (92.5 mg, 0.5 mmol), ni-
tromethane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %)
in CH2Cl2 (1 mL) was stirred for 24 h at ambient temperature.
(KBr)
n
3460, 1557, 1520, 1345 cmꢁ1; HPLC: Chiralcel OD-H column,
n-hexane/isopropanol (85:15), wavelength: 215 nm, flow rate:
0.3 mL/min, retention time: 29.6 min, 32.2 min, 33.5 min, 35.2 min;

11730
S. Jammi et al. / Tetrahedron 64 (2008) 11724–11731
Evaporation of the solvent afforded a residue, which was purified
by column chromatography (20% hexane/ethyl acetate) to give the
title compound (116.8 mg, 95%) as yellow oil; Rf (20% hexane/ethyl
acetate) 0.51; HPLC: Chiralcel OD-H column, n-hexane/isopropanol
4.4.15. (S)-(ꢁ)-2-Nitro-1-(2-thiophenyl)ethanol (Table 3,
entry 12)14h
A mixture of 2-thiophenecarboxaldehyde (56.0 mg, 0.5 mmol),
nitromethane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg,
2.5 mol %) in CH2Cl2 (1 mL) was stirred for 30 h at ambient tem-
perature. Evaporation of the solvent afforded a residue, which was
purified by column chromatography (20% hexane/ethyl acetate) to
give the title compound (56.28 mg, 65%) as yellow oil; Rf (20%
hexane/ethyl acetate) 0.58; HPLC: Chiralcel OD-H column, n-hex-
(85:15), wavelength: 215 nm, flow rate: 0.8 mL/min, retention
20
time: 15.7 min, 18.9 min; 58:42 er; [
a
]
þ1.5 (c 0.5, CH2Cl2).
D
4.4.10. (S)-(þ)-2-Nitro-1-(4-chlorophenyl)ethanol (Table 3,
entry 7)14a
A mixture of 4-chlorobenzaldehyde (70.2 mg, 0.5 mmol), ni-
tromethane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %)
in CH2Cl2 (1 mL) was stirred for 23 h at ambient temperature.
Evaporation of the solvent provided a residue, which was purified
by column chromatography (20% hexane/ethyl acetate) to give the
title compound (90.7 mg, 90%) as yellow oil; Rf (20% hexane/ethyl
acetate) 0.64; HPLC Chiralcel OD-H column, n-hexane/isopropanol
ane/isopropanol (85:15), wavelength: 215 nm, flow rate: 1 mL/min,
20
retention time: 9.6 min, 10.4 min; 54:46 er; [
CH2Cl2).
a
]
ꢁ2.5 (c 0.2,
D
4.4.16. (S)-(ꢁ)-2-Nitro-1-(2-furanyl)ethanol (Table 3, entry 13)14h
A mixture of 2-furaldehyde (48.01 mg, 0.5 mmol), nitrometh-
ane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %) in
CH2Cl2 (1 mL) was stirred for 16 h at ambient temperature.
Evaporation of the solvent gave a residue, which was purified by
column chromatography (20% hexane/ethyl acetate) to provide
the title compound (58.1 mg, 74%) as yellow oil; Rf (20% hexane/
ethyl acetate) 0.53; HPLC: Chiralpak AD-H column, n-hexane/
(85:15), wavelength: 215 nm, flow rate: 0.8 mL/min, retention
20
time: 12.8 min, 16.09 min; 54:46 er; [
a
]
þ2 (c 0.5, CH2Cl2).
D
4.4.11. (S)-(þ)-2-Nitro-1-(4-fluorophenyl)ethanol (Table 3,
entry 8)14f
A mixture of 4-fluorobenzaldehyde (62.0 mg, 0.5 mmol), nitro-
methane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %) in
CH2Cl2 (1 mL) was stirred for 22 h. Evaporation of the solvent
afforded a residue, which was purified by column chromatography
(20% hexane/ethyl acetate) to give the title compound (87.0 mg,
94%) as yellow oil; Rf (20% hexane/ethyl acetate) 0.56; HPLC: Chir-
alcel OD-H column, n-hexane/isopropanol (85:15), wavelength:
isopropanol (95:5), wavelength: 215 nm, flow rate: 1 mL/min,
20
retention time: 26.6 min, 28.1 min; 55:45 er; [
CH2Cl2).
a
]
ꢁ7 (c 0.5,
D
4.4.17. (S)-(þ)-2-Nitro-1-cyclohexylethanol (Table 3, entry 14)14f
A
mixture
of
cyclohexanecarboxaldehyde
(56.08 mg,
0.5 mmol), nitromethane (305.2 mg, 5 mmol), and catalyst 4e
(9.8 mg, 2.5 mol %) in CH2Cl2 (1 mL) was stirred for 24 h. Evapo-
ration of the solvent provided a residue, which was purified by
column chromatography (20% hexane/ethyl acetate) to give the
title compound (77.0 mg, 89%) as yellow oil; Rf (20% hexane/ethyl
acetate) 0.72; HPLC: Chiralpak AD-H column, n-hexane/iso-
215 nm, flow rate: 0.8 mL/min, retention time: 12.1 min, 14.0 min;
20
55:45 er; [
a
]
þ1.7 (c 0.8, CH2Cl2).
D
4.4.12. (S)-(þ)-2-Nitro-1-(4-methoxyphenyl)ethanol (Table 3,
entry 9)14c
A mixture of 4-methoxybenzaldehyde (68.0 mg, 0.5 mmol), ni-
tromethane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %)
in CH2Cl2 (1 mL) was stirred for 38 h. Evaporation of the solvent
afforded a residue, which was purified by column chromatography
(20% hexane/ethyl acetate) to give the title compound (82.8 mg,
84%) as yellow oil; Rf (20% hexane/ethyl acetate) 0.53; HPLC: Chir-
alcel OD-H column, n-hexane/isopropanol (85:15), wavelength:
propanol (97:3), wavelength: 215 nm, flow rate: 0.8 mL/min, re-
20
tention time: 33.2 min, 35.8 min; 68:32 er; [
CH2Cl2).
a]
þ3.5 (c 2,
D
4.4.18. (S)-(þ)-3-Methyl-1-nitro-2-butanol (Table 3, entry 15)14a
A mixture of isobutyraldehyde (36.0 mg, 0.5 mmol), nitro-
methane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %) in
CH2Cl2 (1 mL) was stirred for 20 h. Evaporation of the solvent
yielded a residue, which was purified by column chromatography
(20% hexane/ethyl acetate) to give the title compound (57.2 mg,
86%) as colorless oil; Rf (20% hexane/ethyl acetate) 0.66; HPLC:
Chiralpak AD-H column, n-hexane/isopropanol (95:5), wavelength:
215 nm, flow rate: 0.8 mL/min, retention time: 16.9 min, 21.7 min;
20
66:34 er; [
a]
þ10 (c 1.4, CH2Cl2).
D
4.4.13. (S)-(þ)-2-Nitro-1-(4-methylphenyl)ethanol (Table 3,
entry 10)14g
A mixture of 4-methylbenzaldehyde (60.0 mg, 0.5 mmol), ni-
tromethane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %)
in CH2Cl2 (1 mL) was stirred for 30 h at ambient temperature.
Evaporation of the solvent provided a residue, which was purified
by column chromatography (20% hexane/ethyl acetate) to give the
title compound (81.5 mg, 90%) as colorless oil; Rf (20% hexane/ethyl
acetate) 0.66; HPLC: Chiralcel OD-H column, n-hexane/isopropanol
215 nm, flow rate: 1 mL/min, retention time: 11.5 min, 15.6 min;
20
64:36 er; [
a
]
þ1.2 (c 0.45, CH2Cl2).
D
4.4.19. (ꢁ)-2-Hydroxy-3-nitropropanoic acid ethyl ester (Table 3,
entry 16)14i
A mixture of ethyl glyoxalate (51.0 mg, 0.5 mmol), nitromethane
(305.2 mg, 5 mmol), and catalyst 4e (9.8 mg, 2.5 mol %) in CH2Cl2
(1 mL) was stirred for 30 h at ambient temperature. Evaporation of
the solvent gave a residue, which was purified by column chro-
matography (20% hexane/ethyl acetate) to afford the title com-
pound (4.8 mg, 55%) as colorless solid; Rf (20% hexane/ethyl
acetate) 0.41; HPLC: Chiralcel OD-H column, n-hexane/isopropanol
(90:10), wavelength: 215 nm, flow rate: 0.8 mL/min, retention
20
time: 16.5 min, 21.2 min; 64:36 er; [
a]
þ8 (c 1, CH2Cl2).
D
4.4.14. (S)-(þ)-2-Nitro-1-naphthylethanol (Table 3, entry 11)14g
A
mixture of naphthaldehyde (78.0 mg, 0.5 mmol),
nitromethane (305.2 mg, 5 mmol), and catalyst 4e (9.8 mg,
2.5 mol %) in CH2Cl2 (1 mL) was stirred for 36 h at ambient tem-
perature. Evaporation of the solvent gave a residue, which was
purified by column chromatography (20% hexane/ethyl acetate) to
yield the title compound (87.9 mg, 81%) as yellow oil; Rf (20%
hexane/ethyl acetate) 0.58; HPLC: Chiralcel OD-H column, n-hex-
(85:15), wavelength: 215 nm, flow rate: 1 mL/min, retention time:
20
8.1 min, 8.6 min; 57:43 er; [
a
]
D
ꢁ0.5 (c 0.38, CH2Cl2).
Acknowledgements
ane/isopropanol (85:15), wavelength: 215 nm, retention time:
This work was supported by Department of Science and Tech-
nology, New Delhi and Council of Scientific and Industrial Research,
New Delhi. We thank Mr. Babulal Das for crystal structure.
20
34.4 min, 49.7 min; flow rate: 0.8 mL/min, 61:39 er; [
CH2Cl2).
a]
þ10 (c 1,
D

S. Jammi et al. / Tetrahedron 64 (2008) 11724–11731
11731
Olmos, V.; Pedro, J. R. Tetrahedron: Asymmetry 2006, 17, 2046; (i) Lu, S.-F.; Du,
D.-M.; Zhang, S.-W.; Xu, J. Tetrahedron: Asymmetry 2004, 15, 3433; (j) Nguyen,
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2007, 13,1863; (m) Arai, T.; Watanabe, M.; Yanagisawa, A. Org. Lett. 2007, 9, 3595;
(n) Colak, M.; Demirel, N. Tetrahedron: Asymmetry 2008,19, 635; (o) Gan, C. Can. J.
Chem. 2008, 86, 261; (p) Tanaka, K.; Hachiken, S. Tetrahedron Lett. 2008, 49, 2533;
(q) Trost, B. M.; Yeh, V. S. C. Angew. Chem., Int. Ed. 2002, 41, 861; (r) Palomo, C.;
Oiarbide, M.; Laso, A. Angew. Chem., Int. Ed. 2005, 44, 3881; (s) Gao, J.; Zingaro, R.
A.; Reibenspies, J. H.; Martell, A. E. Org. Lett. 2004, 6, 2453; (t) Zhong, Y.-W.; Tian,
P.; Lin, G.-Q. Tetrahedron: Asymmetry 2004, 15, 771; (u) Tian, J.; Yamagiwa, N.;
Matsunaga, S.; Shibasaki, M. Angew. Chem., Int. Ed. 2002, 41, 3636; (v) Saa, J. M.;
Tur, F.; Gonzalez, J.; Vega, M. Tetrahedron: Asymmetry 2006, 17, 99; (w) Pandya, S.
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Supplementary data
Crystal data, EPR, TGA and UV–vis of 4e, and NMR (1H and 13C)
spectra of the ligands 3a–g are provided. Supplementary data as-
sociated with this article can be found in the online version, at
doi:10.1016/j.tet.2008.10.009.
References and notes
1. Ochiai, E. I. Bioinorganic Chemistry: An Introduction; Allyn and Bacon: Boston,
MA, 1977; Chapter 9.
2. Sorrell, T. N. Tetrahedron 1989, 45, 3.
9. For chiral organoligands catalyzed reactions see: (a) Du, D.-M.; Lu, S.-F.; Fang,
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green crystal 0.51ꢂ0.20ꢂ0.11 mm3, monoclinic, space group¼C2, a¼31.67(5),
b¼10.5061(16), c¼28.397(4) Å;
a
¼90,
b
¼112.432(9),
g
¼90ꢀ, V¼8734(2) Å3, Z¼8,
rcalcd¼1.202 mg/m3, Mo K
a
radiation,
l¼0.71073 Å; measured reflection¼24,401,
unique reflections¼14,178, temperature¼296(2) K, data were collected on
a Bruker smart CCD area detector system with graphite monochromator. The
structure was solved by direct methods and refined on F2 by full-matrix-block
least squares (G. M. Sheldrick. SHELXL-97 Program of the Solution of Crystal
Structure. University of Go¨ttingen: Go¨ttingen, Germany, 1997). In refinement,
data/restraints/parameters are 14,718/1/938. The final R1¼0.0646, wR2¼0.1608
(I>2
s
(I)); R1¼0.1107, wR2¼0.1858 (all data), GOF on F2¼0.864. CCDC-291783
contains the supplementary crystallographic data for this paper. These data can
be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB21EZ, UK; fax: þ44 1223 336 033; or deposit@ccdc.cam.ac.uk).
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