Per-6-amino-β-cyclodextrin catalyzed asymmetric Michael addition of nitromethane and thiols to chalcones in water

Article abstract of DOI:10.1016/j.tetasy.2008.08.014

An environmentally benign and enantioselective Michael addition of nitromethane/thiols to trans-chalcone catalyzed by per-6-amino-β-cyclodextrin (per-6-ABCD) is carried out in water at room temperature with good yield and enantiomeric excess. The catalyst

Full text of DOI:10.1016/j.tetasy.2008.08.014

Tetrahedron: Asymmetry 19 (2008) 2037–2044
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Per-6-amino-b-cyclodextrin catalyzed asymmetric Michael addition
of nitromethane and thiols to chalcones in water
*
Palaniswamy Suresh, Kasi Pitchumani
School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 June 2008
Accepted 18 August 2008
An environmentally benign and enantioselective Michael addition of nitromethane/thiols to trans-chal-
cone catalyzed by per-6-amino-b-cyclodextrin (per-6-ABCD) is carried out in water at room temperature
with good yield and enantiomeric excess. The catalyst is recovered and reused without loss in its activity.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
cally usable and environmentally friendly. In the search to remove
harmful organic solvents, water has emerged as a versatile solvent
Catalytic asymmetric addition of stabilized carbanions to
a,b-
for organic reactions.47,48
unsaturated enones (Michael reaction) is one of the fundamental
C–C bond-forming reactions and useful method for remote func-
tionalization in organic synthesis.1–8 In the case of nitroalkanes,
Cyclodextrins (CDs) are cyclic oligosaccharides possessing
hydrophobic cavities to bind substrates selectively and to catalyze
chemical reactions through the formation of reversible host–guest
complexes via non-covalent interactions.49–51 In asymmetric catal-
ysis, the chemical modification of cyclodextrins may improve the
enantioselectivity of most of the reactions.52 Aminocyclodextrins
and carboxymethylated cyclodextrins are employed as chiral dis-
criminating agents in enantioseparation in capillary electrophore-
sis,53 high performance liquid chromatography54 and chiral NMR
analysis.55 Peramino-CDs are homogeneous CD derivatives modi-
fied by persubstitution at the primary face with amino pendant
groups, which display combined hydrophobic and electrostatic
bindings of guest molecules relative to their native CDs. They are
employed as biomimetic catalysts for Kemp elimination,56 depro-
tonation57 and chiral recognition processes.58,59 They are also
widely employed as chiral selectors for the enantioseparation of
different anionic analytes such as amino acids.53 Aminocatalysts
are also receiving greater attention in asymmetric Michael addi-
tion.60–62 Native b-CD has been employed as a catalyst for thiol63,64
and aza-Michael addition65 in water medium with poor chiral
induction. In the present work, we have successfully employed as
aminomodified cyclodextrin namely, heptakis(6-amino-6-deoxy)-
b-cyclodextrin (per-6-ABCD) 1 as a chiral base catalyst and a host
for conjugate addition of nitromethane 3 and thiols to trans-chal-
cones in an aqueous medium at room temperature.
conjugate addition to a
,b-unsaturated carbonyl substrates9–13 is a
meaningful tool for further transformation of masked functional-
ities. The nitro group, described as a ‘synthetic chameleon’,14 can
undergo Nef reaction,15 nucleophilic displacements,16 reduction
to an amino group17 and conversion into a nitrile oxide.18 Several
attempts have been made towards achieving asymmetric conju-
gate addition of nitromethane to chalcones in the presence of lan-
thanum tris-binaphthoxide,19–21
L
-proline,22 natural cinchona
alkaloids,23 cinchona alkaloids-derived thiourea,24 polymer-an-
chored chiral catalyst LiAl-poly2A,25 chiral quaternary ammonium
salts,26 Ni(II) complexes27 and chiral imidazoline catalysts.28 On
the other hand, the conjugate addition of thiols to a,b-unsaturated
carbonyls29–34 provides useful route for the synthesis of chiral sul-
fur compounds, which have versatile applications in chemistry and
biology.35–37 However, the asymmetric Michael addition of thiols
to a,b-unsaturated carbonyl compounds is still a challenging pro-
cess.29–34 Catalysts such as heterobimetallic asymmetric com-
plexes,38–40 LaN3-tris(binaphthoxide), SmNa3tris(binaphthoxide),
chiral hafnium catalyst,41 cinchona alkaloids,42,43 proline and its
derivatives44–46 are employed to achieve good asymmetric induc-
tion. Although different catalysts have been used for the asymmet-
ric synthesis of sulfides from arenethiols, chiral catalysts have not
been utilized so far for the conjugate addition of aliphatic thiols to
chalcones. Considerable efforts have been expended in recent years
to develop methods towards the recovery and reuse of the chiral
catalysts, which will make asymmetric synthesis more economi-
2. Results and discussion
Table 1 shows the results of our preliminary studies with
per-6-ABCD 1 to mediate asymmetric 1,4-addition with different
Michael acceptors and donors in water. Compound 1 fails in the
conjugate addition of diethyl malonate and malononitrile with
* Corresponding author. Tel.: +91 452 2456614; fax: +91 452 2459181.
E-mail address: pit12399@yahoo.com (K. Pitchumani).
0957-4166/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2008.08.014

2038
P. Suresh, K. Pitchumani / Tetrahedron: Asymmetry 19 (2008) 2037–2044
Table 1
alyst for the conjugate addition of 3 to 2, resulting in good conver-
Per-6-ABCD
1 catalyzed asymmetric Michael addition with different Michael
sion as well as enantiomeric excess up to 68.5%. The absolute
configuration is determined as (S) by comparison with the reported
specific rotation values.27 When the reaction is carried out with the
native b-cyclodextrin in water, it completely fails to catalyze the
addition. When triethylamine is employed as an external base
along with native b-CD, good conversion is noticed, but with very
poor enantiomeric excess (ꢀ2.4%). These preliminary results
clearly show that 1 acts as a useful catalyst for the addition of 3
to 2 in aqueous medium.
acceptors and donorsa
Entry
Michael acceptor
Michael donor
Yieldb (%)
% eec
1
2
3
4
5
6
Chalcone
Chalcone
Diethyl malonate
Malononitrile
Nitromethane
Nitromethane
Nitromethane
Nitromethane
8
—
—
Nil
100
100
Nil
98
Benzylideneacetone
Chalcone
2.80
68.5 (S)d
—
ꢀ2.4
Chalconee
Chalconef
a
All reactions are carried out in water for 24 h at room temperature.
Analyzed by GC.
Analyzed by HPLC using Chiralcel AD-H column.
Influences of other experimental parameters such as solvent,
catalyst amount and temperature were also optimized using 1.
Conjugate addition of 3 to 2 is studied separately in water and in
four different organic solvents (Table 2). In ACN, toluene and
DMF, catalyst 1 is inactive. In methanol, a better yield but with
low ee is observed. In water in addition to complete conversion,
better enantiomeric excess is achieved under this reaction condi-
tion. Equimolar amounts of catalyst and substrate are employed
in all the reactions as these form a 1:1 complex, which gives good
chemical yield and ee. When the reaction is carried out at low tem-
perature (4 °C), no significant improvement in ee is noticed.
This procedure thus avoids environmentally hazardous organic
solvents. Use of aqueous medium also has several other advanta-
ges: the reaction proceeds under simpler experimental conditions
at ambient temperature with no metals and other harmful external
acids or bases. The reaction is also studied with various substituted
chalcones as substrates. As shown in Table 3, addition of 3 to
substituted chalcones 2a–k containing electron-withdrawing and
electron-donating groups on the phenyl ring was studied. In most
cases, the corresponding Michael adducts are obtained in good
yields and also with better enantiomeric excess, suggesting that
electronic factors have only a limited role to play. The highest ee
is observed with 2k, which contains a 3-nitro group (which may
ensure a stronger binding into the CD cavity). Chiral HPLC traces
showing the ee in the case of a representative reaction are given
in Figure 1.
b
c
d
Absolute configuration is determined by comparing the specific rotation with
that of the literature data.27
e
With native b-cyclodextrin.
With native b-cyclodextrin and triethylamine as an external base.
f
trans-chalcone 2; although the conjugate addition of 3 to benzyli-
deneacetone is effectively catalyzed, very poor enantioselectivity
was obtained. On the other hand, 1 turns out to be a very good cat-
Table 2
Per-6-ABCD 1 catalyzed asymmetric Michael addition in various solvents and with
different amounts of catalysta
Entry
Solvent
Per-6-ABCD:chalconeb
Yieldc (%)
% eed
1
2
3
4
5
6
7
8
9
ACN
1:1
1:1
1:1
Nil
Nil
100
Nil
—
—
34.6
—
Toluene
Methanol
DMF
1:1
Water
Water
Water
Water
Watere
1:1
100
100
100
100
100
68.5
66.0
66.8
67.2
63.6
1:0.25
1:0.50
1:2
1:1
a
All reactions are carried out at room temperature for 24 h. 10 mL of solvent is
used for each reaction. After completion of the reaction, solvents are evaporated in
vacuum and products are extracted with ethyl acetate.
The reusability of per-6-ABCD 1 as a catalyst is also examined.
Even after three consecutive reactions, it retained its catalytic
activity, resulting in 100% yield; however, the enantiomeric excess
decreased considerably in the third run (Table 4).
b
Mole ratio.
Analyzed by GC.
Analyzed by HPLC using Chiralcel AD-H column.
Carried out at 4 °C.
c
d
e
Table 3
Per-6-ABCD 1 catalyzed asymmetric Michael addition of nitromethane 3 to chalcones 2a–ka
NO2
O
O
(3)
CH3NO2
(1)
Per-6-ABCD
H2O, RT
R1
R1
R2
R2
2a-k
4a-k
Entry
Chalcones
R1
Yieldb (%)
% eec
R2
1
2
3
4
5
6
7
8
9
2a
2b
2c
2d
2e
2f
2g
2h
2i
H
H
H
H
4a
4b
4c
4d
4e
4f
4g
4h
4i
100
100
94
45
85
68.5
55.4
57.4
70.0
72.8
22.4
62.6
54.0
71.4
25.0
87.0
4-Cl
2,3-Cl
4-Cl
4-F
40-CH3
H
40-Br
H
H
92
4-OCH3
3-OCH3
H
H
3-NO2
100
90.0
100
57
H
40-OH
20-OH
H
10
11
2j
2k
4j
4k
100
a
All reactions are carried out in water at room temperature for 24 h. All the products are characterized by 1H and 13C NMR.
Isolated yield.
Analyzed by HPLC using Chiralcel AD-H column.
b
c

P. Suresh, K. Pitchumani / Tetrahedron: Asymmetry 19 (2008) 2037–2044
2039
Figure 1. HPLC traces of Michael adducts of (a) 4a with native b-CD + triethylamine, (b) 4a with per-6-ABCD and (c) 4k with per-6-ABCD.
Table 4
The observed reactivity and enantioselectivity in the presence of
1 are rationalized by proposing a suitable mechanism. Michael
addition of 3 to 2 takes place inside the cavity of 1, and the mode
of inclusion is visualized as shown in Scheme 1. The phenyl ring
along with olefinic double bond is deeply penetrated inside the cav-
ity and the benzoyl part of 2 stays out of the wider rim of 1. This
type of inclusion is preferred more and is evident from energy
minimization studies. This mode of inclusion (mode a, Fig. 2), has a
Reusability of per-6-ABCD 1 in asymmetric Michael addition of 3 with 2a
Entry
Substrate
Runb
Yieldc (%)
% eed
1
2
3
2a
2a
2a
First
Second
Third
100
100
100
68.5
66.8
58.0
a
Reaction is carried out in water for 24 h at room temperature.
After completion of the reaction 1 was filtered, washed with ethylacetate for
b
lower complexation energy (
D
E = ꢀ38.00 kcal Mꢀ1) than the other
three times, dried in vacuum and reused.
c
Analyzed by GC.
Analyzed by HPLC using Chiralcel AD-H.
mode (mode b, Fig. 2), in which the benzoyl moiety penetrates
inside the cavity and the phenyl group with olefinic double bond
d
stays outside (
D
E = ꢀ36.60 kcal Mꢀ1). This complexation is stabi-
lized by hydrogen bonding between the carbonyl group of chalcone
2 and per-6-ABCD’s 1 secondary hydroxyl groups (Fig. 2). During
the addition of 3, a ternary complex of 2 and 3 with 1 is formed,
which has a higher binding constant (3674 Mꢀ1). This ternary com-
plex is more stable than a binary complex (1391 Mꢀ1) of 1 and 2,
which is also supported by molecular modelling studies. Primary
amino groups present in the narrow rim of 1 act as an internal base
(pKa 6.5–8.9),66 activating the nitromethane by abstracting a proton
followed by nucleophilic attack, which is favoured from the amino
functionalized narrow rim side of 1. This leads to the formation of
the major (S)-isomer and was confirmed from the specific rota-
tion27 of the adduct. If the attack takes place from the wider rim
of CD, it may lead to formation of the (R)-enantiomer, which is ob-
tained as the major isomer in the b-CD triethylamine system (Table
1, entry 6) and not observed with 1. Active participation and catal-
ysis by the amino groups of 1 are also supported by the fact that
per-6-amino-b-cyclodextrin hydrochloride fails to catalyze the
addition of 3 to 2. The complexation energies of two enantiomers
Although various chiral catalysts are employed for the asym-
metric conjugate addition between
a,b-unsaturated ketone and
arenethiols, studies are not extended to the addition of aliphatic
thiols. To extend the scope of the present protocol further, per-6-
ABCD 1 is also employed in enantioselective Michael addition of
aliphatic thiols to trans-chalcones 2a,b,g under the present condi-
tions, and the observed results are given in Table 5. Butanethiol
undergoes addition to 2a with good yield and poor ee. With an
increase in chain length as in octanethiol, although the yield has
decreased, a marked improvement in ee is noticed. These results
provide additional support that co-inclusion of the Michael donor
and acceptor inside the CD cavity is necessary to achieve signifi-
cant ee in the present study. On the other hand when compared
with addition of nitromethane, the conversion is moderate and
only marginal ee is observed. With thiophenol, although the yield
is good, the ee is very low compared with aliphatic thiols. In all
cases, no disulfide formation is observed in water medium.
Table 5
Per-6-ABCD 1 catalyzed asymmetric Michael addition of thiols to chalcones 2a,b,ga
R
S
O
O
RSH
Per-6-ABCD (1)
H2O, RT
R1
R1
R2
R2
5a-f
2a, b, g
Entry
Chalcones
Thiols (RSH)
Yieldb (%)
% eec
R1
R2
1
2
3
4
5
6
2a
2a
2a
2b
2b
2g
H
H
H
H
H
H
H
H
H
n-Butanethiol
n-Octanethiol
Thiophenol
n-Butanethiol
n-Octanethiol
n-Octanethiol
5a
5b
5c
5d
5e
5f
100
23.0
42.2
4.00
29.0
60.6
18.2
50
75
82
50
54
4-Cl
4-Cl
4-OCH3
a
All reactions are carried out in water at room temperature for 24 h, and the products are characterized by 1H and 13C NMR.
Isolated yield.
Analyzed by HPLC using Chiralcel OD-H column.
b
c

2040
P. Suresh, K. Pitchumani / Tetrahedron: Asymmetry 19 (2008) 2037–2044
R
NO2
O
O
S
O
CH3NO2
RSH
Per-6-ABCD
Per-6-ABCD
H2O, RT
H2O, RT
R1
R1
R1
R2
R2
45-100 %
49 - 100 %
R2
22-87 % ee
18 - 61 % ee
Scheme 1. Per-6-ABCD catalyzed asymmetric Michael addition of nitromethane and thiols to chalcones.
Figure 2. CVFF-optimized inclusion complex of per-6-ABCD 1 with trans-chalcone 2a; In mode (a) the chalcone’s olefinic double bond is inside the CD-cavity and benzoyl part
is outside the cavity. In mode (b) olefinic double bond is outside the CD-cavity and benzoyl part is inside the cavity.
(R)- and (S)- of Michael adduct 4a with CD are also calculated, and
confirm that the (S)-enantiomer forms a more stable complex with
without any loss in its activity. The reaction takes place readily
at room temperature and does not require lower temperature to
achieve good ee. Other advantages include much more simpler
experimental conditions, ease of recovery and reuse of catalyst,
and the absence of hazardous external acids and bases (Scheme 2).
(D
E = ꢀ46.03 kcal Mꢀ1, mode c, Fig. 3) than the corresponding (R)-
enantiomer (
D
E = ꢀ35.47 kcal Mꢀ1, mode d, Fig. 3).
3. Conclusions
4. Experimental
4.1. Materials
In conclusion, per-6-ABCD is successfully employed for the first
time as a chiral catalyst and as a base for the asymmetric Michael
addition of nitromethane and aliphatic thiols to chalcones in aque-
ous medium. Per-6-ABCD 1 performs a dual role, acting both as a
base to catalyze the reaction and as a chiral inductor by enhancing
the enantiomeric excess. In the additions of both nitromethane and
thiols, better enantioselectivities are observed and water is
employed (without any cosolvent) as an eco-friendly solvent in
this asymmetric Michael addition, and the catalyst is reused
Per-6-amino-b-cyclodextrin was synthesized and purified
according to the procedure described in the literature.67 The prod-
uct was dried for 24 h in dryer under vacuum over phosphorus
pentoxide at 60 °C and then stored in a vacuum desiccator.
b-Cyclodextrin, trans-chalcone, nitromethane, diethyl malonate
and malononitrile were purchased from Aldrich. n-Butanethiol,
Figure 3. CVFF-optimized inclusion complex of per-6-ABCD 1 with (S)-enantiomer of Michael adduct 4a (mode c) and (R)-enantiomer of Michael adduct 4a (mode d).

P. Suresh, K. Pitchumani / Tetrahedron: Asymmetry 19 (2008) 2037–2044
2041
H
H
H
O
O
O
O
O
O
NO2
H2N
H
H
H3N
H2N
H
O
O
Cage
Escape
NO2
H2N
O
NO2
4a
Scheme 2. Proposed mechanism for asymmetric Michael addition catalyzed by per-6-ABCD 1.
n-octanethiol and thiophenol were purchased from Merck. Substi-
tuted chalcones and benzylideneacetone were prepared as
described in the literature.68 Double distilled water was used for
all reactions.
ued for an hour to complete complexation. Then, nitromethane 3
(0.024 mL, 0.4 mmol) was added and allowed to stir at room tem-
perature for 24 h. After completion of the reaction, the product was
extracted with ethyl acetate, dried with sodium sulfate and con-
centrated under reduced pressure. The resulting crude product
was purified by passing over a column of Silica Gel 60–120 mesh
using pet-ether/ethyl acetate (8/2 ratio as an eluant) affording
Michael adduct 4 as a pale yellow solid, which was analyzed by
NMR spectroscopy (300 MHz, CDCl3, T = 300 K, TMS = 0 ppm) and
CSP (Chiral Stationary Phase)-HPLC. Percentage ee was determined
by HPLC at 254 nm using chiralcel AD-H column, with n-hexane/
i-propanol (90/10) mixture at a flow rate of 1.0 mL/min. After
extraction of the product, per-6-ABCD was washed three times
with ethyl acetate, filtered, dried in vacuum and reused.
Nuclear magnetic resonance (NMR) spectra were acquired on a
Bruker DRX-300 (300 MHz) instrument using TMS as an internal
standard. Gas Chromatographic analysis was performed in Shima-
dzu 17A, using ZB-5, 30 m capillary column, FID detector and high
purity nitrogen as carrier gas. For column chromatography, Merck
Silica Gel 60–120 mesh is employed. Specific rotations were mea-
sured using a RUDOLPH AutopolÒ IV Polarimeter. Enantiomer
ratios were determined by chiral HPLC analysis using a Shimadzu
LC-10AT VP series and a Shimadzu LC-10A VP UV–vis detector with
Chiralcel AD-H and OD-H columns using n-hexane and i-propanol
as mobile phases. Binding constants were calculated by non-linear
regression using prism software (trial version) in an IBM compati-
ble personal computer with Microsoft Windows XP service pack 2
operating system.
4.4. Procedure for asymmetric Michael addition of thiols to
chalcones 2
Per-b-ABCD 1 (0.112 g, 0.1 mmol) was dissolved in water
(10 mL). trans-Chalcone 2 (0.02 g, 0.1 mmol) was dissolved in ace-
tone (1 mL) and was added dropwise to 1 with constant stirring
and continued for an hour to complete complexation. Then,
n-butanethiol (0.01 mL, 0.1 mmol) was added and allowed to stir
at room temperature for 24 h. After completion of the reaction,
the product was extracted with ethyl acetate, dried with sodium
sulfate and concentrated under reduced pressure, and resulting
crude product was purified by passing over a column of Silica
Gel 60–120 mesh using pet-ether/ethyl acetate (9/1 ratio as an elu-
ant) affording Michael adduct 5 as a yellow oily liquid, which was
analyzed by NMR spectroscopy (300 MHz, CDCl3, T = 300 K,
TMS = 0 ppm) and CSP-HPLC. Percentage ee was determined by
HPLC at 254 nm using chiralcel OD-H column, with n-hexane/i-
propanol (90/10) mixture at a flow rate of 1.0 mL/min.
4.2. Energy minimization studies
Energy minimized geometries of the complexes were obtained
using Molecular Mechanics Calculations by INSIGHT II
program.69–71 The initial structures of host and guest molecules
were constructed by INSIGHT II DISCOVER on Silicon Graphics IRIS work-
/DISCOVER
/
station. We have adapted CVFF force field to express the MM ener-
gies of per-6-ABCD host, trans-chalcone, Michael adducts and their
complexes. Structures were minimized using CVFF force field and
RMS derivative 0.001 was achieved in each case. Complexation
energies were calculated using the following equation:
EComplex EHost EGuest
DE =
D
ꢀ
D
ꢀ
D
.
4.3. Procedure for asymmetric Michael addition of
nitromethane 3 to chalcones 2
4.4.1. 4-Nitro-1,3-diphenylbutan-1-one 4a11
Per-b-ABCD 1 (0.112 g, 0.1 mmol) was dissolved in water
(10 mL). trans-Chalcone 2 (0.02 g, 0.1 mmol) dissolved in acetone
(1 mL) was added dropwise to 1 with constant stirring and contin-
The crude product was purified by column chromatography on
silica gel (pet-ether/ethyl acetate = 9/1 as eluant). ½a D25
¼ ꢀ11:1, (c
ꢁ
1.00, CH2Cl2), 1H NMR (300 MHz,CDCl3): d 7.91 (d, J = 8.4 Hz, 2H),

2042
P. Suresh, K. Pitchumani / Tetrahedron: Asymmetry 19 (2008) 2037–2044
7.25–7.60 (m, 8H), 4.83 (ABX, JAB = 12.3 Hz, JAX = 6.6 Hz,
JBX = 7.8 Hz, 1H), 4.71 (ABX, JAB = 12.3 Hz, JAX = 6.6 Hz, JBX = 7.8 Hz,
1H), 4.23 (br pseudo quintet, J = 7.2 Hz, 1H), 3.38–3.53 (m, 2H).
13C NMR (75 MHz, CDCl3): d 196.8, 139.0, 136.3, 133.5, 129.0,
128.7, 128.0, 127.8, 127.4, 79.5, 41.4, 39.2. HPLC: 68.5% ee, tmajor
15.5 min, tminor 20.2 min.
4.4.7. 3-(4-Methoxyphenyl)-4-nitro-1-phenylbutan-1-one 4g
The crude product was purified by column chromatography on
silica gel (pet-ether/ethyl acetate = 8/2 as eluant). 1H NMR
(300 MHz, CDCl3): d 7.92 (d, J = 7.9 Hz, 2H), 7.58 (t, J = 7.8 Hz,
1H), 7.46 (t, J = 7.8 Hz, 2H), 7.20 (d, J = 8.7 Hz, 2H), 6.86 (d,
J = 8.7Hz, 2H), 4.80 (ABX, JAB = 12.3 Hz, JAX = 6.6 Hz, JBX = 7.8 Hz,
1H), 4.64 (ABX, JAB = 12.3 Hz, JAX = 6.6 Hz, JBX = 7.8 Hz, 1H), 4.18
(br pseudo quintet, J = 7.2 Hz, 1H), 3.77 (s, 3H), 3.42 (dd, J = 6.6,
2.7 Hz, 2H). 13C NMR (75 MHz, CDCl3): d 197.3, 159.4, 136.7,
133.9, 131.3, 129.1, 128.9, 128.4, 114.8, 80.2, 55.6, 42.0, 39.0. HPLC:
62.6% ee, tmajor 23.1 min, tminor 29.0 min.
4.4.2. 3-(4-Chlorophenyl)-4-nitro-1-phenylbutan-1-one 4b
The crude product was purified by column chromatography on
silica gel (pet-ether/ethyl acetate = 8/2 as eluant). 1H NMR
(300 MHz, CDCl3): d 7.91 (d, J = 8.1 Hz, 2H), 7.59 (t, J = 7.2 Hz,
1H), 7.46 (t, J = 7.2 Hz, 2H), 7.31 (d, J = 8.7 Hz, 2H), 7.23 (d,
J = 3.4 Hz, 2H), 4.82 (ABX, JAB = 12.6 Hz, JAX = 6.6 Hz, JBX = 8.1Hz,
1H), 4.66 (ABX, JAB = 12.6 Hz, JAX = 6.6 Hz, JBX = 8.1 Hz, 1H), 4.22
(br pseudo quintet, J = 7.2 Hz, 1H), 3.46 (ABX, JAB = 18 Hz,
JAX = 6.6 Hz, JBX = 7.2 Hz, 1H), 3.40 (ABX, JAB = 18 Hz, JAX = 6.6 Hz,
JBX = 7.2 Hz, 1H). 13C NMR (75 MHz, CDCl3): d 196.4, 137.5, 136.1,
133.7, 132.2, 129.2, 128.8, 128.7, 127.9, 79.3, 41.3, 38.6. HPLC:
55.4% ee, tmajor 17.7 min, tminor 25.1 min.
4.4.8. 3-(3-Methoxyphenyl)-4-nitro-1-phenylbutan-1-one 4h
The crude product was purified by column chromatography on
silica gel (pet-ether/ethyl acetate = 8/2 as eluant). 1H NMR
(300 MHz, CDCl3): d 7.29 (d, J = 7.8 Hz, 2H), 7.58 (t, J = 8.1 Hz,
1H), 7.46 (t, J = 7.5 Hz, 2H), 7.26 (s, 1H). 6.18 (m, 3H), 4.82 (ABX,
JAB = 12.3 Hz, JAX = 6.6 Hz, JBX = 7.9 Hz, 1H), 4.67 (ABX, JAB = 12.3 Hz,
JAX = 6.6 Hz, JBX = 7.9 Hz, 1H), 4.20 (br pseudo quintet, J = 7.2 Hz,
1H), 3.45 (m, 2H), 3.78 (s, 3H). 13C NMR (75 MHz, CDCl3): d
196.7, 159.8, 140.6, 136.2, 133.5, 130.0, 128.7, 127.9, 119.4,
113.6, 112.8, 79.4, 55.1, 41.4, 39.2. HPLC: 54.0% ee, tmajor
18.9 min, tminor 22.6 min.
4.4.3. 3-(2,3-Dichlorophenyl)-4-nitro-1-phenylbutan-1-one 4c
The crude product was purified by column chromatography
on silica gel (pet-ether/ethyl acetate = 8/2 as eluant). 1H NMR
(300 MHz, CDCl3): d 7.92 (d, J = 8.1 Hz, 2H), 7.60 (t, J = 7.8 Hz,
1H), 7.40–7.50 (m. 4H), 7.15 (d, J = 8.1 Hz, 1H), 4.82 (ABX,
JAB = 12.7 Hz, JAX = 6.3 Hz, JBX = 8.1 Hz, 1H), 4.66 (ABX, JAB = 12.7 Hz,
JAX = 6.3, JBX = 8.1 Hz, 1H), 4.21 (br pseudo quintet, J = 6.9 Hz,
1H), 3.43 (d, J = 6.6 Hz, 2H). 13C NMR (75 MHz, CDCl3): d 196.0,
139.3, 135.9, 133.8, 133.1, 132.0, 130.9, 129.5, 128.8, 127.9,
126.9, 78.9, 41.1, 38.3. HPLC: 57.4% ee, tmajor 15.7 min, tminor
19.7 min.
4.4.9. 1-(4-Hydroxyphenyl)-4-nitro-3-phenylbutan-1-one 4i
The crude product was purified by column chromatography on
silica gel (pet-ether/ethyl acetate = 7/3 as eluant). 1H NMR
(300 MHz, CDCl3): d 7.85 (d, J = 8.7 Hz, 2H), 7.26–7.33 (m, 5H),
6.86 (d, J = 9 Hz, 2H), 6.23 (s, 1H), 4.83 (ABX, JAB = 12.3 Hz,
JAX = 6.6 Hz, JBX = 8.1 Hz, 1H) 4.68 (ABX, JAB = 12.3 Hz, JAX = 6.6 Hz,
JBX = 8.1 Hz, 1H), 4.21 (br pseudo quintet, J = 7.2 Hz, 1H), 3.40 (m,
2H). 13C NMR (75 MHz, CDCl3): d 195.6, 160.6, 139.1, 130.6,
129.0, 127.8, 127.4, 115.4, 79.6, 41.1, 39.4. HPLC: 71.4% ee, tmajor
15.6 min, tminor 20.2 min.
4.4.4. 3-(4-Chlorophenyl)-4-nitro-1-p-tolylbutan-1-one 4d
The crude product was purified by column chromatography on
silica gel (pet-ether/ethyl acetate = 8/2 as eluant). 1H NMR (300
MHz, CDCl3): d 7.81 (d, J = 8.1 Hz, 2H), 7.21–7.37 (m, 6H), 4.82
(ABX, JAB = 12.6 Hz, JBX = 8.4 Hz, 1H), 4.65 (ABX, JAB = 12.6 Hz,
JBX = 8.4 Hz, 1H) 4.21 (br pseudo quintet J = 6.9 Hz, 1H), 3.41
(ABX, JAB = 17.7 Hz, JAX = 6.9 Hz, JBX = 8.1 Hz, 1H), 3.39 (ABX,
JAB = 17.7 Hz, JAX = 6.9 Hz, JBX = 8.1 Hz, 1H), 2.14 (s, 3H). 13C NMR
(75 MHz, CDCl3): d 196.0, 144.6, 137.6, 133.6, 130.5, 129.4, 129.2,
128.8, 128.1, 79.3, 41.1, 38.6, 21.6. HPLC: 70.0% ee, tmajor
19.7 min, tminor 25.2 min.
4.4.10. 1-(2-Hydroxyphenyl)-4-nitro-3-phenylbutan-1-one 4j
The crude product was purified by column chromatography on
silica gel (pet-ether ethyl acetate = 7/3 as eluant). 1H NMR
(300 MHz, CDCl3): d 12.01 (s, 1H), 8.22 (t, J = 2.1 Hz, 1H), 8.18 (d,
J = 8.5 Hz, 2H), 7.95 (d, J = 8.1 Hz, 2H), 7.72 (d, J = 7.8 Hz, 2H),
7.52–7.66 (m, 1H), 7.50 (t, J = 7.8 Hz, 1H), 4.92 (ABX, JAB = 12.9 Hz,
JAX = 6.3 Hz, JBX = 8.4 Hz, 1H), 4.72 (ABX, JAB = 12.9 Hz, JAX = 6.3 Hz,
JBX = 8.4 Hz, 1H), 4.41 (br pseudo quintet J = 8.1 Hz, 1H), 3.55 (d,
J = 6.9Hz, 2H). 13C NMR (75 MHz, CDCl3): d 202.6, 162.4, 138.6,
136.8, 129.1, 128.6, 128.2, 127.3, 127.0, 118.8, 79.4, 55.8, 41.0,
39.0. HPLC: 25.0% ee, tmajor 13.0 min, tminor 15.3 min.
4.4.5. 3-(4-Fluorophenyl)-4-nitro-1-phenylbutan-1-one 4e
The crude product was purified by column chromatography on
silica gel (pet-ether/ethyl acetate = 8/2 as eluant). 1H NMR
(300 MHz, CDCl3): d 7.91 (d, J = 7.2 Hz, 2H), 7.58 (t, J = 7.5 Hz,
1H), 7.46 (t, J = 7.8 Hz, 2H), 7.26 (t, J = 8.1 Hz, 2H), 7.02 (t,
J = 8.1Hz, 2H), 4.82 (ABX, JAB = 12.3 Hz, JAX = 6.6 Hz, JBX = 8.1 Hz,
1H), 4.65 (ABX, JAB = 12.3 Hz, JAX = 6.6 Hz, JBX = 8.1 Hz,1H) 4.22 (br
pseudo quintet J = 7.5 Hz, 1H), 3.43 (dd, J = 6.9 Hz, 1.2 Hz, 2H).
13C NMR (75 MHz, CDCl3): d 196.5, 163.7, 136.2, 134.7, 133.6,
129.0 (d), 128.7, 127.6, 115.9 (d), 79.5, 41.4, 38.5. HPLC: 72.8%
ee, tmajor 16.9 min, tminor 23.3 min.
4.4.11. 4-Nitro-3-(3-nitrophenyl)-1-phenylbutan-1-one 4k
The crude product was purified by column chromatography on
silica gel (pet-ether/ethyl acetate = 8/2 as eluant). 1H NMR
(300 MHz, CDCl3): d 8.22 (t, J = 2.1 Hz, 1H), 8.18 (d, J = 8.5 Hz,
1H), 7.95 (d, J = 8.1 Hz, 2H), 7.72 (d, J = 7.8 Hz, 1H), 7.52–7.66 (m,
2H), 7.50 (t, J = 7.8 Hz, 2H), 4.92 (ABX, JAB = 12.9 Hz, JAX = 6.3 Hz,
JBX = 8.4 Hz, 1H), 4.72 (ABX, JAB = 12.9 Hz, JAX = 6.3 Hz, JBX = 8.4 Hz,
1H), 4.41 (br pseudo quintet, J = 8.1 Hz, 1H), 3.55 (d, J = 6.9 Hz,
2H). 13C NMR (75 MHz, CDCl3): d 196.3, 148.9, 141.7, 136.3,
134.8, 134.3, 130.5, 129.2, 128.4, 123.4.122.6, 79.3, 41.5, 39.2.
HPLC: 87.0% ee, tmajor 33.2 min, tminor 40.6 min.
4.4.6. 1-(4-Bromophenyl)-4-nitro-3-phenylbutan-1-one 4f
The crude product was purified by column chromatography on
silica gel (pet-ether/ethyl acetate = 8/2 as eluant). 1H NMR
(300 MHz, CDCl3): d 7.77 (d, J = 8.7 Hz, 2H), 7.59 (d, J = 8.4 Hz,
2H), 7.26–7.36 (m, 5H), 4. 81 (ABX, JAB = 12.3 Hz, JAX = 6.6 Hz,
JBX = 7.5 Hz, 1H), 4.68 (ABX, JAB = 12.3 Hz, JAX = 6.6 Hz, JBX = 7.5 Hz,
1H), 4.20 (br pseudo quintet, J = 7.2 Hz, 1H), 3.42 (dd, J = 6.6,
2.7 Hz, 2H). 13C NMR (75 MHz, CDCl3): d 195.8, 138.8, 134.9,
132.0, 129.5, 129.1, 128.8, 127.9, 127.4, 79.4, 41.4, 39.1. HPLC:
22.4% ee, tmajor 23.1 min, tminor 29.0 min.
4.4.12. 3-(Butylthio)-1,3-diphenylpropan-1-one 5a
The crude product was purified by column chromatography on
silica gel (pet-ether/ethyl acetate = 9/1 as eluant). 1H NMR
(300 MHz,CDCl3): d 7.91 (d, J = 7.5 Hz, 2H), 7.54 (t, J = 7.5 Hz, 1H),
7.43 (t, J = 7.8 Hz, 4H), 7.30 (t, J = 7.2 Hz, 2H), 7.20 (t, J = 7.5 Hz,
1H), 4.55 (s, J = 6.9 Hz, 1H), 3.53 (d, J = 6.9 Hz, 2H), 2.33 (m, 2H),
1.46 (m, 2H), 1.31 (m, 2H), 0.83 (t, J = 7.2 Hz, 3H). 13C NMR (75

P. Suresh, K. Pitchumani / Tetrahedron: Asymmetry 19 (2008) 2037–2044
2043
MHz, CDCl3): d 197.0, 142.2, 136.7, 133.2, 128.6, 128.0, 127.8,
Acknowledgements
127.1, 45.4, 44.2, 31.2, 31.1, 29.7, 21.9, 13.6. HPLC: 23.0% ee, tmajor
5.0 min, tminor 5.2 min.
Financial assistance from the Department of Science and Tech-
nology (DST), New Delhi, India, is gratefully acknowledged.
4.4.13. 3-(Octylthio)-1,3-diphenylpropan-1-one 5b
References
The crude product was purified by column chromatography
on silica gel (pet-ether/ethyl acetate = 9/1 as eluant). 1H NMR
(300 MHz, CDCl3): d 7. 90 (d, J = 7.9 Hz, 2H), 7.52 (t, J = 7.2 Hz,
1H), 7.42 (dd, J = 6.9 Hz, 1.8 Hz, 4H), 7.29 (t, J = 7.2 Hz, 2H),
7.20 (t, J = 7.2 Hz, 1H), 4.55 (t, J = 6.9 Hz, 1H), 3.54 (d, J = 6.6 Hz,
2H), 1.48 (m, 2H), 1.32 (m, 2H), 1.25 (m, 10H), 0.865 (t, J = 6.6,
3H). 13C NMR (75 MHz, CDCl3): d 196.9, 142.2, 136.7, 133.1,
128.5, 128.4, 128.0, 127.8, 127.1, 45.3, 44.2, 31.7, 31.4, 29.2,
29.1, 29.0, 28.8, 22.6, 14.1. HPLC: 42.2% ee, tmajor 4.6 min, tminor
4.8 min.
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The crude product was purified by column chromatography on
silica gel (pet-ether/ethyl acetate = 9/1 as eluant). 1H NMR
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d 7.91 (d, J = 7.8 Hz, 2H), 7.54 (t, 2H,
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The crude product was purified by column chromatography
on silica gel (pet-ether/ethyl acetate = 9/1 as eluant). 1H NMR
(300 MHz, CDCl3): d 7.93 (d, J = 7.2 Hz, 2H), 7.57 (t, J = 7.2 Hz,
1H), 7.46 (t, J = 7.8 Hz, 2H), 7.40 (d, J = 8.4 Hz, 2H), 7.29 (d,
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133.1, 130.0, 129.6, 129.06, 129.05, 128.4, 45.7, 44.0, 32.2, 31.8,
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The crude product was purified by column chromatography on
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158.5, 136.7, 134.1, 133.1, 128.8, 128.5, 128.0, 113.7, 55.1, 45.5,
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