Sugar thiourea catalyzed highly enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinone to β-nitroalkenes

Article abstract of DOI:10.1039/c2ra22270a

A highly enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinone to β-nitrostyrenes has been achieved using a novel class of sugar-Cinchona thiourea conjugates. The method offers significant advantages such as low catalyst loading (1 mol%), high

Full text of DOI:10.1039/c2ra22270a

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Sugar thiourea catalyzed highly enantioselective
Michael addition of 2-hydroxy-1,4-naphthoquinone to
Cite this: RSC Advances, 2013, 3, 930
b-nitroalkenes3
B. V. Subba Reddy,* S. Madhusudana Reddy and Manisha Swain
Received 24th September 2012,
Accepted 5th November 2012
A highly enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinone to b-nitrostyrenes has been
achieved using a novel class of sugar-Cinchona thiourea conjugates. The method offers significant
advantages such as low catalyst loading (1 mol%), high enantioselectivity (up to 99% ee), short reaction
times and ambient reaction conditions.
DOI: 10.1039/c2ra22270a
www.rsc.org/advances
In this article, we wish to report for the first synthesis and
application of glucose-Cinchona thiourea conjugates for the
Introduction
Nitroolefins are important intermediates in organic synthesis
since the nitro group can easily be transformed into the
corresponding amine and carbonyl compounds.1 Asymmetric
Michael reaction of nitroalkenes is one of the most important
methods for C–C bond formation, which provides direct access
to enantiopure nitroalkanes.2 The conjugate addition of 1,4-
naphthoquinone to nitroalkenes3 is particularly attractive as it
provides easy access to nitroalkyl substituted naphthoqui-
nones which are very useful precursors for the synthesis of
various biologically active compounds.
Naphthoquinones are important structural units in many
natural products. They are mainly used as dyes in industry.
Many quinone containing compounds are found to exhibit
potent biological activity.4 Quinone containing antitumor
drugs such as mitoxantrone, ametantrone and doxorubicin
have been used as effective anticancer agents for the treatment
of leukemia.5,6
Recently, bifunctional thiourea derivatives have been
recognized as effective organocatalysts for asymmetric
Michael addition reactions.7 Therefore, the development of
simple and efficient bifunctional thiourea catalysts is of great
interest. In this context, carbohydrates are easily accessible
chiral precursors for asymmetric synthesis.8 In particular,
glucose is very attractive because of its ready availability and
well defined stereochemistry. Inspired by thiourea based
organocatalysis, we attempted the synthesis of novel sugar-
Cinchona hybrids for asymmetric Michael reaction (Fig. 1).
enantioselective Michael addition of 2-hydroxy-1,4-naphtho-
quinone to b-nitrostyrenes. Accordingly, a novel class of sugar
based bifunctional thiourea catalysts II, IV, VI and IX were
prepared from 1-isothiocyanatoglucose and Cinchona amines.
The starting glycosyl isothiocyanate was prepared from b-D-
glucopyranose by means of sequential acetylation, bromina-
tion and isothiocyanation.9 Addition of Cinchona amines to
glycosyl isothiocyanate gave the bifunctional thiourea catalysts
II, IV, VI and IX in good yields. These sugar-Cinchona based
thiourea catalysts show a remarkable catalytic effect in the
Michael addition of 2-hydroxy-1,4-naphthoquinone to nitroalk-
enes. These new catalysts furnish the Michael adducts in good
yields with a high degree of enantioselectivity. Remarkably, the
reaction proceeds even at very low catalyst loading (1 mol%)
under ambient conditions (Table 1).
Initially, we investigated the reactivity of various catalysts in
the Michael addition of 2-hydroxy-1,4-naphthoquinone (1) to
b-nitrostyrene (2a) using 2 mol% of the thiourea derivatives I,
III,
V and VIII in toluene at room temperature. The
corresponding Michael adduct 3a was obtained with 88, 90,
80 and 87% ee respectively (Table 1, entries, 1,3,5 and 15). The
same reaction was also carried out with catalysts VII and X to
evaluate their efficiency. Surprisingly, these catalysts gave the
product 3a with low enantioselectivity (77 and 86% ee
respectively, Table 1, entries 14 and 17).
After screening the known catalysts, we performed the
above reaction with sugar-Cinchona based thiourea catalysts II,
IV, VI and IX. Of these, thiourea catalysts II, IV and IX afforded
the desired product 3a with moderate enantioselectivity (86, 85
and 89% ee, Table 1, entries 2, 4 and 16). Interestingly, catalyst
VI gave the product 3a with a higher enantioselectivity (97%
ee, Table 1, entry 6) than the others. Therefore, catalyst VI was
shown to be superior to the others in terms of enantioselec-
tivity. For further optimization of the reaction, we screened the
Natural Product Chemistry, Centre for Nuclear Magnetic Resonance, Laboratory of
X-ray Crystallography, Indian Institute of Chemical Technology, Uppal Road,
Tarnaka, Hyderabad, 500607, India. E-mail: basireddy@iict.res.in;
Fax: (+)91 40 27160512
Electronic supplementary information (ESI) available: Detailed procedures and
3
spectroscopic data for novel compounds (copies of 1H and 13C NMR spectra of
products). See DOI: 10.1039/c2ra22270a
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Table 1 Screening of various thiourea catalysts for enantioselective Michael
addition of 2-hydroxy-1,4-naphthoquinone to b-nitrostyrenea
Entry Catalyst Solvent T (uC) Time (h) Yield (%)b ee (%)c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
I
II
III
IV
V
VI
VI
VI
VI
VI
VI
VI
VI
VII
VIII
IX
X
PhCH3
PhCH3
PhCH3
PhCH3
PhCH3
PhCH3
PhCH3
PhCH3
PhCH3
CH2CI2
CH3CN
THF
CH3OH
PhCH3
PhCH3
PhCH3
PhCH3
30
30
30
30
30
30
0
225
30
30
30
30
30
30
30
30
30
4
4
4
4
4
94
95
94
95
94
96
90
80
96
94
96
96
87
92
95
96
92
88
86
290
285
80
97
95
4
10
18
6
4
4
4
4
5
4
82
97d
95
88
90
75
77
287
289
286
4
5
a
Reaction was carried out with 1 (0.3 mmol), 2 (0.33 mmol) in the
b
c
presence of 2 mol% of organocatalyst. Isolated yield. Determined
by chiral HPLC. 1 mol% catalyst used.
d
3-alkylnitro-2-hydroxynaphthoquinones (3a–3t) were prepared
in good yields with excellent enantioselectivities (up to 99%
ee). ortho-Substituted and para-substituted halogen containing
aromatic nitroalkenes gave high ee values compared with the
meta-substituted counterpart(Table 2, entries 2–10).
2-Naphthyl substituted and di-substituted nitroalkenes also
gave high enantioselectivities (Table 2, entries 11–14).
However, aliphatic and heteroaromatic nitroalkenes afforded
comparatively lower enantioselectivities (Table 2, entries 15–17
and 19). ortho-Substituted aromatic nitroalkenes like 2-benzy-
loxy- and 2-methoxy derivatives gave slightly low enantioselec-
tivities (Table 2, entry 18 and 20) due to the unfavorable
interaction between the ortho-substituent and the nucleophile.
Next we studied the diastereoselectivity of the reaction with an
a-branched nitroolefin. Accordingly, treatment of (E)-(2-nitro-
prop-1-enyl)benzene with 2-hydroxy-1,4-naphthoquinone in
the presence of ligand VI under similar reaction conditions
gave the anti-2-hydroxy-3-((1S,2R)-2-nitro-1-phenylpropyl)-
naphthalene-1,4-dione 3u as a major isomer in 82% yield
with 85% ee (entry 21, Table 2).
Based on the above results, a possible transition state
model was proposed in Fig. 2. The model has no difference
with the one drawn in previous reports.3
The nitro group likely participates in hydrogen bonding
with the thiourea of the organocatalyst VI. The 2-hydroxy-1,4-
naphthoquinone was assumed to be deprotonated by the basic
nitrogen of the tertiary amine. The resulting deprotonated
2-hydroxy-1,4-naphthoquinone is then attacked by the
nitroalkene from the Re face to afford the (S)-isomer. The
Fig. 1 Representative bifunctional thiourea catalysts.
effect of solvents, temperature and catalyst loading. Of the
several solvents tested, high conversions and excellent
enantioselectivities (96 and 95% ee) were achieved in CH2Cl2
and toluene respectively, whereas moderate enantioselectivity
was observed in CH3CN and THF. Furthermore, lower
enantioselectivities and poorer yields were obtained in protic
solvents like methanol. This is due to the competitive
hydrogen bond interaction between methanol and either the
organocatalyst or the substrate. Thus toluene was chosen as
the optimal solvent for this reaction (97% ee). The yield and
enantioselectivities were decreased when the reaction tem-
perature was reduced to 0 uC. The quantity of catalyst had no
significant effect on enantioselectivity and yield when the
catalyst loading was reduced to 1 mol% (97% ee and 96%
yield, Table 1, entry 9).
The scope of this Michael reaction was explored under the
optimized reaction conditions and the results are summarized
in Table 2. By using this procedure, a wide range of
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tion works well with low catalyst loading under ambient
conditions and also provides the products in high yields with
excellent enantioselectivity which makes it more attractive.
Further investigation into the enantioselective C–C bond
forming reactions using this novel catalyst is under progress
in our laboratory.
Table 2 Chiral thiourea VI catalyzed asymmetric addition of 2-hydroxy-1,4-
naphthoquinone with b-nitrostyrenesa
Entry
R
R9
Product
Yield (%)b
ee (%)c
Experimental
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
C6H5
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
CH3
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
96
97
96
96
98
95
95
97
95
94
93
94
95
92
93
92
94
92
94
95
82
97
98
97
97
99
96
93
96
97
95
95
96
98
94
95
93
93
93
91
90
85
Preparation of ligands
4–MeC6H4
4–MeOC6H4
4–FC6H4
4–CIC6H4
4–BrC6H4
3–CIC6H4
2–FC6H4
2–CIC6H4
2–BrC6H4
2–Naphthyl
2,4–Cl2C6H3
3,4–Cl2C6H3
3,5–(Me)2C6H3
Cyclohexyl
2–Furanyl
Butyl
2–BnOC6H4
2–Thienyl
2–MeOC6H4
C6H5
Catalysts I, III, V and were prepared according to the literature
procedures.10
GENERAL PROCEDURE FOR PREPARING THIOUREA CATALYSTS II, IV, VI
AND IX. To a stirred solution of the chiral amine10 (4 mmol) in
methylene chloride (10 mL) was added dropwise a solution of
glycosyl isothiocyanate (4.4 mmol) in methylene chloride (15
mL) under nitrogen atmosphere. The resulting mixture was
stirred at room temperature until total consumption of the
isothiocyanate (monitored by TLC). After removal of the
solvent, the residue was purified through column chromato-
graphy on silica gel (EtOAc/MeOH = 85/15) to give the thiourea
catalyst as a white solid.
3s
3t
3u
SPECTRAL DATA FOR LIGAND II. White solid, yield 76%, m.p. =
101–103 uC, [a]2D8 = +116.8 (c = 0.5, CHCl3). 1H NMR (300 MHz,
CDCl3): d 1.17–1.32 (m, 1H), 1.40–1.52 (m, 1H), 1.75 (s, 2H),
1.79–1.94 (m, 2H), 1.96–2.14 (m, 14H), 2.65 (brs, 1H), 3.11–3.50
(m, 2H), 3.72–3.86 (m, 1H), 4.03 (s, 3H), 4.08–4.17 (m, 1H),
4.22–4.51 (m, 5H), 4.93–5.13 (m, 2H), 5.21–5.50 (m, 2H), 5.70
(brs, 1H), 5.86–6.02 (m, 1H), 7.32–7.42 (m, 1H), 7.48 (d, J = 14.5
Hz, 1H), 7.88 (brs, 1H), 7.93–8.02 (m, 1H), 8.65–8.73 (d, J = 4.5
Hz, 1H). 13C NMR (75 MHz, CDCl3): d 20.4, 20.6, 23.2, 23.9,
24.2, 26.4, 36.9, 46.2, 48.6, 55.7, 60.2, 61.5, 68.0, 70.2, 73.2,
73.3, 82.6, 101.8, 116.7, 120.3, 122.5, 127.7, 129.3, 131.3, 137.3,
142.3, 144.5, 147.3, 158.2, 169.4, 169.8, 169.9, 170.6, 178.9,
184.1. IR (KBr): u 2935, 1752, 1622, 1545, 1373, 1227, 1035, 912,
759 cm21; MS (ESI) m/z 714 [M+H]+; HRMS (ESI): Exact mass
calcd for C35H45O10N4S 713.28509. Found: 713.28602.
SPECTRAL DATA FOR LIGAND IV. White solid, yield 74%, m.p. =
a
Reaction was carried out with 1 (0.3 mmol), 2 (0.33 mmol), and in
b
c
0.7 mL of toluene. Isolated yield. Determined by chiral HPLC.
sugar moiety may help to block one of the faces of the
substrate to facilitate high stereocontrol.
Conclusion
In summary, the sugar-Cinchona conjugates have been
demonstrated as highly efficient bifunctional organocatalysts
for asymmetric Michael addition. They are highly active
catalysts in promoting the enantioselective Michael addition
of nitroalkenes with 2-hydroxy-1,4-naphthoquinone. The reac-
1
110–112 uC, [a]2D8 250.2 (c = 0.5, CHCl3). H NMR (500 MHz,
CDCl3): d 1.22–1.30 (m, 5H), 1.33–1.42 (m, 1H), 1.56–1.74 (m,
2H), 1.95–2.09 (m, 13H), 2.30–2.40 (brs, 1H), 2.75–2.91 (brs,
1H), 3.12–3.33 (m, 2H), 3.78–3.88 (m, 1H), 3.99 (s, 3H), 4.09–
4.17 (m, 4H), 4.27–4.35 (m, 1H), 4.89–5.14 (m, 4H), 5.32 (t, J =
9.8 Hz, 1H), 5.65–5.76 (m, 1H), 7.29–7.37 (m, 1H), 7.41 (d, J =
8.9 Hz, 1H), 8.04 (d, J = 8.9 Hz, 1H), 8.75 (d, J = 3.9 Hz, 1H). 13
C
NMR (75 MHz, CDCl3): d 20.5, 20.6, 23.5, 26.8, 37.2, 40.9, 53.7,
55.8, 60.8, 61.4, 68.1, 70.4, 73.2, 82.4, 102.2, 116.8, 122.2,
127.8, 131.7, 144.8, 147.7, 158.2, 169.2, 169.4, 170.3, 170.6,
180.0, 183.9. IR (KBr): u 2944, 1753, 1622, 1544, 1371, 1231,
1037, 915, 761, 604 cm21; MS (ESI) m/z 714 [M+H]+; HRMS
(ESI): Exact mass calcd for C35H45O10N4S 713.28509. Found:
713.28547.
SPECTRAL DATA FOR LIGAND VI. White solid, yield 71%, m.p. =
116–118 uC, [a]2D8 = +128.2 (c = 0.5, CHCl3). 1H NMR (500 MHz,
CDCl3): d 0.85–1.01 (m, 4H), 1.26 (t, J = 7.4 Hz, 2H), 1.35–1.62
(m, 6H), 1.86–2.15 (m, 13H), 2.60 (brs, 1H), 2.86–3.21 (m, 4H),
3.78 (d, J = 9.6 Hz, 3H), 3.99 (s, 3H), 4.06–4.17 (m, 1H), 4.20–
Fig. 2 A proposed transition state.
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4.32 (m, 1H), 4.84–4.95 (m, 1H), 5.02 (t, J = 9.6 Hz, 1H), 5.26–
5.34 (m, 2H), 5.64–5.78 (m, 1H), 7.32–7.72 (m, 3H), 8.03 (d, J =
9.6 Hz, 1H), 8.73 (d, J = 4.2 Hz, 1H). 13C NMR (75 MHz, CDCl3):
d 11.9, 20.5, 20.6, 20.7, 24.8, 25.5, 25.8, 26.8, 36.9, 48.8, 48.9,
55.5, 61.6, 68.1, 70.9, 72.8, 73.3, 82.9, 101.5, 122.1, 128.4,
128.6, 131.8, 132.0, 132.1, 142.0, 144.7, 147.5, 157.8, 169.6,
169.8, 170.5, 171.0, 177.9, 183.7; IR (KBr): u 2935, 1752, 1622,
1511, 1372, 1225, 1036, 910, 762, 602 cm21; MS (ESI) m/z 716
[M+H]+; HRMS (ESI): Exact mass calcd for C35H47O10N4S
715.30074. Found: 715.30103.
25.7, 29.8, 33.3, 34.5, 35.8, 37.3, 37.6, 37.9, 41.5, 45.5, 55.3,
55.9, 59.9, 102.4, 120.1, 120.5, 122.6, 123.5, 124.0, 126.6, 127.9,
129.3, 131.2, 134.8, 143.1, 144.6, 145.3, 147.2, 147.4, 158.4,
177.1, 183.0. IR (KBr): u 3251, 2926, 2867, 1731, 1621, 1549,
1376, 1230, 1030, 828, 726 cm21; MS (ESI) m/z 654 [M+H]+;
HRMS (ESI): Exact mass calcd for C41H57ON4S 653.42476.
Found: 653.42559.
General procedure for the organocatalytic asymmetric
addition of 2-hydroxy-1,4-naphthoquinones to nitroolefins
SPECTRAL DATA FOR LIGAND IX. White solid, yield 70%, m.p. =
To a stirred solution of organocatalyst VI (1 mol%) and
nitroolefin (2) (0.33 mmol) in toluene (0.7 mL) was added
2-hydroxy-1,4-naphthoqnuinone (1) (0.3 mmol). The resulting
mixture was stirred for 6 h at room temperature. After
completion of the reaction, the mixture was concentrated in
vacuo and the resulting residue was purified by column
chromatography on silica gel (hexane/EtOAc) to afford the
corresponding Michael adduct (3).
(S)-2-HYDROXY-3-(2-NITRO-1-PHENYLETHYL)NAPHTHALENE-1,4-DIONE
(3A). (Entry 1, Table 2). Orange solid, yield 96% with 97% ee.
m.p. 150–152 uC. [a]2D8 = +34.3 (c = 0.5, acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate 1.0
mL min21, 254 nm; tR = 15.4 min (major) and 31.8 min
(minor); 1H NMR (500 MHz, CDCl3): d 5.15 (dd, J = 6.5, 13.1 Hz,
1H), 5.28–5.34 (m, 1H), 5.44–5.51 (m, 1H), 7.23–7.28 (m, 1H),
7.32 (t, J = 7.5 Hz, 2H), 7.46 (d, J = 7.5 Hz, 2H), 7.69 (t, J = 7.5
Hz, 1H), 7.73–7.80 (m, 2H), 8.07 (d, J = 7.5 Hz, 1H), 8.12 (d, J =
7.5 Hz, 1H); 13C NMR (75 MHz, CDCl3+DMSO-D6): d 38.8, 76.2,
120.5, 126.0, 126.8, 127.6, 128.0, 129.2, 132.0, 132.4, 134.0,
138.0, 155.4, 181.0, 183.5.
1
114–116 uC, [a]2D8 259.0 (c = 0.5, CHCl3). H NMR (300 MHz,
CDCl3): d 0.78–0.94 (m, 3H), 1.14–1.44 (m, 4H), 1.53–1.70 (m,
1H), 1.75–2.22 (m, 17H), 2.66 (brs, 1H), 3.10 (brs, 1H), 3.57–
4.06 (m, 6H), 4.07–4.25 (m, 1H), 4.90–5.11 (m, 2H), 5.22–5.34
(m, 1H), 5.78 (brs, 1H), 6.74 (brs, 1H), 7.23–7.74 (m, 3H), 7.94–
8.12 (m, 1H), 8.77 (d, J = 4.5 Hz, 1H). 13C NMR (75 MHz,
CDCl3): d 11.3, 20.5, 22.8, 23.2, 24.6, 24.8, 25.7, 34.7, 55.4, 55.9,
59.6, 61.4, 68.0, 70.3, 73.1, 73.3, 82.3, 102.4, 120.4, 121.0,
122.4, 128.4, 129.4, 131.5, 131.9, 132.1, 144.8, 147.7, 158.4,
169.4, 170.0, 170.2, 170.7, 178.4, 183.8. IR (KBr): u 2955, 1751,
1622, 1547, 1372, 1229, 1035, 910, 759, 608 cm21; MS (ESI) m/z
716 [M+H]+; HRMS (ESI): Exact mass calcd for C35H47O10N4S
715.30074. Found: 715.30117.
General procedure for preparing thiourea catalysts VII and X
To a stirred solution of the chiral amine (2 mmol) in
methylene chloride (8 mL) was added dropwise a solution of
dehydroabietic isothiocyanate11 (2.4 mmol) in methylene
chloride (12 mL) under nitrogen atmosphere. After completion
of the reaction, the resulting mixture was concentrated under
reduced pressure and the residue was purified through
column chromatography on silica gel (hexane/EtOAc = 5/95)
to give the thiourea catalyst as a white solid.
SPECTRAL DATA FOR LIGAND VII. White solid, yield 67%, m.p. =
132–134 uC, [a]2D8 = +119.9 (c = 0.5, CHCl3). 1H NMR (500 MHz,
CDCl3): d 0.62–0.76 (m, 3H), 0.90–0.96 (m, 3H), 1.10 (s, 3H),
1.18–1.25 (m, 9H), 1.31–1.88 (m, 13H) 2.10–2.21 (m, 2H), 2.58–
2.89 (m, 5H), 2.94–3.15 (m, 3H), 3.20–3.37 (m, 2H), 3.42–3.59
(m, 1H), 3.90 (s, 3H), 4.16 (s, 1H), 6.81 (s, 1H), 6.97 (d, J = 7.7
Hz, 1H), 7.10 (d, J = 7.7 Hz, 1H), 7.34–7.51 (m, 2H), 7.68 (t, J =
6.6 Hz, 1H), 8.01 (d, J = 8.8 Hz, 1H), 8.67 (s, 1H). 13C NMR (75
MHz, CDCl3): d 11.8, 18.1, 18.4, 18.9, 23.9, 24.4, 25.2, 25.8,
29.6, 30.1, 33.4, 36.1, 36.3, 37.2, 37.3, 38.0, 46.0, 48.8, 49.0,
55.7, 56.4, 60.8, 102.4, 120.1, 120.5, 122.6, 123.7, 124.1, 126.7,
129.3, 129.6, 131.9, 133.6, 134.6, 145.0, 145.4, 146.9, 147.6,
158.3, 178.7, 182.5. IR (KBr): u 3258, 2928, 2865, 1735, 1620,
1547, 1374, 1231, 1031, 826, 724 cm21; MS (ESI) m/z 654
[M+H]+; HRMS (ESI): Exact mass calcd for C41H57ON4S
653.42476. Found: 653.42689.
(S)-2-HYDROXY-3-(2-NITRO-1-p-TOLYLETHYL)NAPHTHALENE-1,4-
DIONE (3B). (Entry 2, Table 2). Orange solid, yield 97% with 98%
ee. m.p. 166–168 uC. [a]2D8 = +28.8 (c = 0.5, acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate 1.0
mL min21, 254 nm; tR = 24.4 min (major) and 77.6 min
1
(minor); H NMR (300 MHz, CDCl3): d 2.30 (s, 3H), 5.07–5.18
(m, 1H), 5.23–5.32 (m, 1H), 5.40–5.52 (m, 1H), 7.12 (d, J = 7.9
Hz, 2H), 7.35 (d, J = 8.1 Hz, 2H), 7.68–7.85 (m, 2H), 8.02–8.15
(m, 2H); 13C NMR (75 MHz, CDCl3): d 21.0, 39.3, 76.3, 121.0,
126.3, 127.2, 128.1, 129.0, 129.6, 132.6, 133.2, 134.5, 135.4,
137.6, 153.1, 181.2, 183.7.
(S)-2-HYDROXY-3-(1-(4-METHOXYPHENYL)-2-NITROETHYL)NAPHTHALENE-
1,4-DIONE (3C). (Entry 3, Table 2). Orange solid, yield 96% with 97%
ee. m.p. 172–174 uC. [a]2D8 = +32.8 (c = 0.5, acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate 1.0 mL
1
min21, 254 nm; tR = 32.5 min (major) and 72.1 min (minor); H
NMR (300 MHz, CDCl3): d 3.76 (s, 3H), 5.11 (dd, J = 7.0, 13.0 Hz,
1H), 5.21–5.30 (m, 1H), 5.44 (dd, J = 8.9, 13.0 Hz, 1H), 6.84 (d, J =
8.7 Hz, 2H), 7.40 (d, J = 8.7 Hz, 2H), 7.63–7.82 (m, 3H), 8.04–8.15
(m, 2H); 13C NMR (75 MHz, CDCl3+DMSO-D6): d 38.3, 54.8, 76.8,
113.7, 121.1, 125.6, 126.1, 129.0, 129.5, 131.9, 132.7, 134.3, 155.3,
158.4, 181.0, 183.8.
(S)-2-(1-(4-FLUOROPHENYL)-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-
1,4-DIONE (3D). (Entry 4, Table 2). Orange solid, yield 96% with
97% ee. m.p. 160–162 uC. [a]D28 = +32.6 (c = 0.5, acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate 1.0
mL min21, 254 nm; tR = 16.2 min (major) and 30.6 min (minor);
1H NMR (300 MHz, CDCl3): d 5.15 (dd, J = 6.8, 12.6 Hz, 1H), 5.30
SPECTRAL DATA FOR LIGAND X. White solid, yield 68%, m.p. =
1
128–130 uC, [a]2D8 292.04 (c = 0.5, CHCl3). H NMR (500 MHz,
CDCl3): d 0.68–0.85 (m, 6H), 1.08 (s, 3H), 1.10–1.42 (m, 15H),
1.46–1.67 (m, 4H), 1.68–1.91 (m, 3H), 1.97 (s, 3H), 2.01–2.17
(m, 2H), 2.56–2.90 (m, 5H), 3.34–3.55 (m, 3H), 3.76–3.87 (m,
1H), 3.96 (s, 3H), 6.88 (d, J = 7.2 Hz, 1H), 6.99–7.12 (m, 1H),
7.19 (s, 1H), 7.22 (d, J = 4.3 Hz, 1H), 7.30–7.35 (m, 1H), 7.38–
7.46 (m, 1H), 7.95 (d, J = 9.3 Hz, 1H), 8.70 (s, 1H); 13C NMR (75
MHz, CDCl3): d 11.2, 18.4, 19.1, 22.3, 23.2, 23.9, 24.5, 25.2,
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(t, J = 6.8 Hz, 1H), 5.41 (dd, J = 8.5, 12.6 Hz, 1H), 7.00 (t, J = 8.7 Hz,
2H), 7.40–7.49 (m, 2H), 7.66–7.83 (m, 2H), 8.04–8.15 (m, 2H); 13C
NMR (75 MHz, CDCl3): d 39.0, 76.4, 115.9 (d, J = 21.4 Hz), 120.6,
126.4, 127.2, 128.9, 129.9, 130.0, 132.6, 133.3, 133.4, 135.5, 153.1,
162.2, 181.0, 183.6.
(S)-2-(1-(4-CHLOROPHENYL)-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-
1,4-DIONE (3E). (Entry 5, Table 2). Orange solid, yield 98% with
99% ee. m.p. 204–206 uC. [a]D28 = +20.13 (c = 0.5, acetone). HPLC
on Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate 1.0
mL min21, 254 nm; tR = 15.5 min (major) and 36.9 min (minor););
1H NMR (300 MHz, CDCl3): d 5.16 (dd, J = 6.8, 12.5 Hz, 1H), 5.29
(t, J = 6.8, 8.1 Hz, 1H), 5.34–5.44 (m, 1H), 7.29 (d, J = 8.5 Hz, 3H),
7.41 (d, J = 8.5 Hz, 2H), 7.67–7.83 (m, 2H), 8.05–8.15 (m, 2H); 13C
NMR (75 MHz, CDCl3+DMSO-D6): d 38.3, 54.8, 76.8, 113.7, 121.1,
125.6, 126.1, 129.0, 129.5, 131.9, 132.7, 134.3, 155.3, 158.4, 181.0,
183.8.
1H NMR (300 MHz, CDCl3+DMSO-D6): d 4.96 (dd, J = 6.0, 13.8 Hz,
1H), 5.34–5.50 (m, 1H), 5.73 (dd, J = 6.0, 10.0 Hz, 1H), 7.15–7.28
(m, 2H), 7.36–7.50 (m, 2H), 7.65–7.84 (m, 2H), 8.10 (t, J = 6.0 Hz,
2H); 13C NMR (75 MHz, CDCl3): d 34.8, 73.6, 116.7, 123.9, 124.2,
125.2, 126.8, 127.6, 128.1, 130.4, 131.0, 131.4, 132.4,133.9, 156.8,
179.7, 181.3.
(S)-2-(1-(2-BROMOPHENYL)-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-1,
4-DIONE (3J). (Entry 10, Table 2). Orange solid, yield 94% with 95%
ee. m.p. 60–62 uC. [a]2D8 = +151.4 (c = 0.25, acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 80 : 20, flow rate 1.0 mL
min21, 254 nm; tR = 22.1 min (major) and 27.2 min (minor); 1H
NMR (300 MHz, CDCl3): d 4.85–4.96 (m, 1H), 5.37–5.49 (m, 1H),
5.70 (dd, J = 5.8, 10.4 Hz, 1H), 7.09–7.19 (m, 1H), 7.21–7.31 (m,
2H), 7.42 (dd, J = 1.1, 7.7 Hz, 1H), 7.61 (d, J = 7.9 Hz, 1H), 7.67–7.84
(m, 2H), 8.07–8.17 (m, 2H); 13C NMR (125 MHz, CDCl3+DMSO-
D6): d 39.1, 74.5, 118.9, 123.7, 125.4, 125.9, 127.2, 128.4, 129.2,
131.2, 132.3, 134.1,136.3, 156.9, 180.8, 183.4.
(S)-2-(1-(4-BROMOPHENYL)-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-
1,4-DIONE (3F). (Entry 6, Table 2). Orange solid, yield 95% with
96% ee. m.p. 208–210 uC. [a]2D8 = +11.2 (c = 0.5, acetone). HPLC
on Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate
1.0 mL min21, 254 nm; tR = 20.4 min (major) and 39.8 min
(minor); 1H NMR (300 MHz, CDCl3): d 5.10–5.21 (m, 1H), 5.27–
5.36 (m, 1H), 5.43–5.56 (m, 1H), 7.22–7.39 (m, 3H), 7.47 (d, J =
7.0 Hz, 2H), 7.66–7.85 (m, 2H), 8.04–8.18 (m, 2H); 13C NMR (75
MHz, CDCl3+DMSO-D6): d 38.0, 75.8,119.9, 125.3, 125.8, 129.1,
129.3, 130.9, 131.5, 132.3, 133.9, 136.9, 155.6, 180.5, 183.2.
(S)-2-(1-(3-CHLOROPHENYL)-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-
1,4-DIONE (3G). (Entry 7, Table 2). Orange solid, yield 95% with
93% ee. m.p. 64–66 uC. [a]2D8 = +18.9 (c = 0.5, acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 80 : 20, flow rate 1.0
mL min21, 254 nm; tR = 23.8 min (major) and 28.3 min (minor);
1H NMR (300 MHz, CDCl3): d 5.11–5.21 (m, 1H), 5.25–5.34 (m,
1H), 5.36–5.46 (m, 1H), 7.20–7.30 (m, 2H), 7.32–7.41 (m, 1H),
7.45 (s, 1H), 7.67–7.87 (m, 2H), 8.05–8.17 (m, 2H); 13C NMR (125
MHz, CDCl3): d 39.2, 75.9, 120.1, 126.3, 126.4, 127.2, 128.4, 128.9,
130.1, 132.4, 133.4, 134.6, 135.5, 139.4, 153.3, 180.9, 183.5; IR
(KBr): u 3376, 1645, 1590, 1551, 1471, 1373, 1276, 1055, 725
cm21; MS (ESI) m/z 380 [M+Na]+; HRMS (ESI): Exact mass calcd
for C18H12O5NClNa 380.02962. Found: 380. 03127.
(S)-2-(1-(2-FLUOROPHENYL)-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-
1,4-DIONE (3H). (Entry 8, Table 2). Orange solid, yield 97% with
96% ee. m.p. 82–84 uC. [a]2D8 = +49.9 (c = 0.5, acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate 1.0
mL min21, 254 nm; tR = 16.8 min (major) and 40.7 min (minor);
1H NMR (300 MHz, CDCl3+DMSO-D6): d 5.14 (dd, J = 7.0, 13.1
Hz, 1H), 5.48–5.57 (m, 1H), 5.64–5.71 (m, 1H), 6.92–7.02 (m, 2H),
7.09–7.19 (m, 1H), 7.52–7.74 (m, 3H), 7.98 (d, J = 7.0 Hz, 1H),
8.09 (d, J = 8.1 Hz, 1H); 13C NMR (75 MHz, CDCl3): d 33.3, 75.3,
115.7, 116.0, 119.3, 124.4, 126.4, 127.2, 128.9, 129.6, 132.6,
133.3, 135.5, 153.8, 158.8, 180.9, 183.5; IR (KBr): u 3415, 1662,
1589, 1516, 1379, 1287, 1228, 1160, 1101, 746, 695 cm21; MS
(ESI) m/z 342 [M+H]+; HRMS (ESI): Exact mass calcd for
C18H12O5NFNa 364.05917. Found: 364.06039.
(S)-2-HYDROXY-3-(1-(NAPHTHALEN-2-YL)-2-NITROETHYL)NAPHTHALENE-
1,4-DIONE (3K). (Entry 11, Table 2). Orange solid, yield 93% with
95% ee. m.p. 152–154 uC. [a]D28 = +11.8 (c = 0.5, acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate 1.0 mL
min21, 254 nm; tR = 27.1 min (major) and 61.3 min (minor); 1H
NMR (300 MHz, CDCl3): d 5.27 (dd, J = 6.0, 12.1 Hz, 1H), 5.44–5.60
(m, 2H), 7.55–7.61 (m, 1H), 7.65–7.87 (m, 5H), 7.91 (s, 1H), 8.10
(dd, J = 7.5, 15.9 Hz, 2H). 13C NMR (125 MHz, CDCl3+DMSO-D6):
d 37.9, 75.5, 124.5, 124.6, 124.8, 124.9, 125.0, 125.3, 126.1, 126.4,
126.9, 128.6, 130.8, 130.9, 131.6, 131.7, 133.3, 134.7, 155.3, 179.9,
182.5; IR (KBr): u 3343, 1667, 1647, 1593, 1551, 1460, 1373, 1279,
1217, 1060, 1004, 861, 819, 755, 726, 664 cm21; MS (ESI) m/z 396
[M+Na]+; HRMS (ESI): Exact mass calcd for C22H15O5NNa
396.08424. Found: 396.08545.
(S)-2-(1-(2,4-DICHLOROPHENYL)-2-NITROETHYL)-3-HYDROXY
NAPHTHALENE-1,4-DIONE (3L). (Entry 12, Table 2). Orange solid,
yield 94% with 96% ee. m.p. 118–120 uC. [a]2D8 = +31.6 (c = 0.5,
acetone). HPLC on Chiralcel OJ–H column, hexane/i-PrOH =
70 : 30, flow rate 1.0 mL min21, 254 nm; tR = 13.2 min (major)
and 21.0 min (minor); 1H NMR (300 MHz, CDCl3): d 4.97 (dd, J
= 6.4, 13.6 Hz, 1H), 5.35 (dd, J = 9.6, 13.8 Hz, 1H), 5.63–5.71 (m,
1H), 7.22 (dd, J = 1.9, 8.5 Hz, 1H), 7.38–7.41 (m, 2H), 7.69–7.88
(m, 2H), 8.11 (d, J = 7.7 Hz, 2H). 13C NMR (75 MHz, CDCl3): d
36.6, 74.8, 118.8, 126.5, 127.2, 127.5, 128.9, 129.8, 130.4, 132.5,
133.2, 133.4, 134.3, 134.7, 135.6, 154.2, 180.8, 183.6; IR (KBr): u
3263, 1675, 1638, 1588, 1550, 1469, 1431, 1370, 1275, 1222,
1058, 1026, 877, 819, 728, 688 cm21; MS (ESI) m/z 392 [M+H]+;
HRMS (ESI): Exact mass calcd for C18H11Cl2NO5Na 413.99120.
Found: 413.99213.
(S)-2-(1-(3,4-DICHLOROPHENYL)-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-
1,4-DIONE (3M). (Entry 13, Table 2). Orange solid, yield 95% with 98%
ee. m.p. 104–106 uC. [a]2D8 = +13.4 (c = 0.5, acetone). HPLC on Chiralcel
OJ–H column, hexane/i-PrOH = 70 : 30, flow rate 1.0 mL min21, 254
nm; tR = 16.1 min (major) and 22.8 min (minor); 1H NMR (500 MHz,
CDCl3+DMSO-D6): d 5.22–5.38 (m, 3H), 7.34–7.41 (m, 2H), 7.56–7.64
(m, 1H), 7.68–7.73 (m, 1H), 7.77 (t, J = 7.3 Hz, 1H), 8.02–8.10 (m, 2H).
13C NMR (125 MHz, CDCl3+DMSO-D6): d 36.6, 74.8, 117.9, 124.3,
124.6, 126.5, 128.4, 128.8, 130.0, 130.7, 131.3, 133.0, 136.5, 138.0,
156.7, 180.2, 181.7; IR (KBr): u 3260, 1675, 1639, 1588, 1550, 1469,
1431, 1370, 1275, 1219, 1132, 1058, 1027, 881, 728, 687 cm21; MS
(S)-2-(1-(2-CHLOROPHENYL)-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-
?1,4-DIONE (3I). (Entry 9, Table 2). Orange solid, yield 95% with
97% ee. m.p. 52–54 uC. [a]2D8 = +96.3 (c = 0.5, acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate 1.0
mL min21, 254 nm; tR = 15.2 min (major) and 21.9 min (minor);
934 | RSC Adv., 2013, 3, 930–936
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(ESI) m/z 414 [M+Na]+; HRMS (ESI): Exact mass calcd for
C18H11Cl2NO5Na 413.99120. Found: 413.99281.
128.5, 128.9, 132.7, 133.0, 135.2, 136.5, 153.8, 155.9, 181.0, 183.7; IR
(KBr): u 3370, 2924, 1661, 1591, 1548, 1491, 1451, 1379, 1329, 1240,
1156, 1105, 1052, 1030, 977, 756, 724, 693 cm21 ; MS (ESI) m/z 452
[M+Na]+; HRMS (ESI): Exact mass calcd for C25H19O6NNa 452.11046.
Found: 452.11298.
(S)-2-HYDROXY-3-(2-NITRO-1-(THIOPHEN-2-YL)ETHYL)NAPHTHALENE-
1,4-DIONE (3S). (Entry 19, Table 2). Orange solid, yield 94% with
91% ee. m.p. 119–121 uC. [a]2D8 = +65.2 (c = 0.5, acetone). HPLC
on Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate
1.0 mL min21, 254 nm; tR = 25.4 min (major) and 56.0 min
(minor); 1H NMR (500 MHz, CDCl3): d 5.14 (dd, J = 7.2, 13.5 Hz,
1H), 5.39–5.46 (m, 1H), 5.62 (t, J = 8.0 Hz, 1H), 6.94 (t, J = 4.0
Hz, 1H), 7.11 (d, J = 3.2 Hz, 1H), 7.20 (d, J = 5.6 Hz, 1H), 7.68–
7.74 (m, 1H), 7.75–7.83 (m, 2H), 8.09 (d, J = 8.0 Hz, 1H), 8.15 (d,
J = 8.0 Hz, 1H); 13C NMR (75 MHz, CDCl3): d 34.8, 76.7, 119.9,
125.4, 126.4, 126.5, 126.9, 127.2, 129.0, 132.5, 133.4, 135.5,
138.9, 153.1, 181.0, 183.3.
(S)-2-(1-(3,5-DIMETHYLPHENYL)-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-
1,4-DIONE (3N). (Entry 14, Table 2). Orange solid, yield 92% with 94%
ee. m.p. 108–110 uC. [a]2D8 = +16.1 (c = 0.5, acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate 1.0 mL
1
min21, 254 nm; tR = 22.0 min (major) and 26.0 min (minor); H
NMR (300 MHz, CDCl3): d 2.28 (s, 1H), 5.09 (dd, J = 6.6, 13.2 Hz, 1H),
5.19–5.28 (m, 1H), 5.42–5.54 (m, 1H), 6.89 (s, 1H), 7.06 (s, 2H), 7.64–
7.84 (m, 2H), 8.10 (dd, J = 7.5, 15.5 Hz, 2H); 13C NMR (125 MHz,
CDCl3+DMSO-D6): d 20.6, 45.1, 77.4, 117.3, 124.8, 125.3, 125.4, 127.4,
130.1, 130.2, 133.6, 134.3, 136.6, 140.6, 153.7, 180.7, 181.4; IR (KBr): u
3419, 2921, 1661, 1592, 1577, 1516, 1374, 1282, 1038, 855, 705, 554
cm21; MS (ESI) m/z 352 [M+H]+; HRMS (ESI): Exact mass calcd for
C20H17O5NNa 374.09989. Found: 374.10160.
(S)-2-(1-CYCLOHEXYL-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-1,4-
DIONE (3O). (Entry 15, Table 2). Orange solid, yield 93% with
95% ee. m.p. 114–116 uC. [a]2D8 247.9 (c = 0.5, in acetone).
HPLC on Chiralcel AS–H column, hexane/i-PrOH = 95 : 5, flow
rate 1.0 mL min21, 254 nm; tR = 26.9 min (minor) and 34.2
(S)-2-HYDROXY-3-(1-(2-METHOXYPHENYL)-2-NITROETHYL)NAPHTHALENE-
1,4-DIONE (3T). (Entry 20, Table 2). Orange solid, yield 95% with
90% ee. m.p. 94–96 uC. [a]2D8 = +147.8 (c = 0.25, acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate 1.0 mL
1
min (major); H NMR (300 MHz, CDCl3): d 0.92–1.22 (m, 5H),
1
min21, 254 nm; tR = 16.8 min (major) and 28.1 min (minor); H
1.51–1.71 (m, 3H), 1.73–1.96 (m, 3H), 3.74–3.88 (m, 1H), 4.73–
4.86 (m, 1H), 5.01–5.16 (m, 1H), 7.67–7.87 (m, 2H), 8.07–8.20
(m, 2H). 13C NMR (75 MHz, CDCl3): d 26.0, 31.0, 31.1, 38.2,
40.3, 75.8, 120.8, 125.9, 126.8, 129.2, 132.4, 132.9, 134.9, 154.3,
180.5, 183.9.
(S)-2-(1-(FURAN-2-YL)-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-1,4-
DIONE (3P). (Entry 16, Table 2). Orange solid, yield 92% with
93% ee. m.p. 112–114 uC. [a]2D8 = +9.04 (c = 0.5, acetone). HPLC
on Chiralcel OJ–H column, hexane/i-PrOH = 70 : 30, flow rate
1.0 mL min21, 254 nm; tR = 25.6 min (major) and 48.3 min
(minor); 1H NMR (300 MHz, CDCl3): d 5.17 (dd, J = 6.8, 13.6 Hz,
1H), 5.23–5.34 (m, 1H), 5.48 (t, J = 7.5 Hz, 1H), 6.24 (d, J = 3.0
Hz, 1H), 6.30–6.34 (m, 1H), 7.33 (s, 1H), 7.68–7.88 (m, 3H),
8.08–8.22 (m, 2H). 13C NMR (75 MHz, CDCl3+DMSO-D6): d
33.2, 75.1, 106.9, 110.6, 118.3, 126.1, 126.6, 128.9, 132.2, 133.1,
134.8, 141.7, 150.7, 156.7, 181.2, 183.6.
NMR (300 MHz, CDCl3): d 3.88 (s, 3H), 4.96 (dd, J = 5.5, 13.6 Hz,
1H), 5.36–5.49 (m, 1H), 5.62–5.72 (m, 1H), 6.85–6.97 (m, 2H), 7.21–
7.35 (m, 2H), 7.65–7.87 (m, 3H), 8.07–8.19 (m, 2H); 13C NMR (75
MHz, CDCl3+DMSO-D6): d 33.2, 54.8, 74.8, 109.9, 119.7, 119.8,
124.5, 125.2, 125.7, 127.9, 129.1, 131.7, 132.2, 133.9, 155.7, 156.0,
180.5, 183.2.
2-HYDROXY-3-((1S,2R)-2-NITRO-1-PHENYLPROPYL)NAPHTHALENE-1,
4-DIONE (3U). (Entry 21, Table 2). Orange solid, yield 82% with
85% ee. m.p. 119–121 uC. [a]D28 = +61.8 (c = 0.25, acetone). HPLC
on Chiralcel AD–H column, hexane/i-PrOH = 70 : 30, flow rate
1.0 mL min21, 220 nm; tR = 14.1 min (major) and 15.8 min
1
(minor); H NMR (300 MHz, CDCl3): d 1.53 (d, J = 6.8 Hz, 3H),
4.94 (d, J = 11.3 Hz, 1H), 6.03–6.16 (m, 1H), 7.27–7.37 (m, 3H),
7.50–7.57 (m, 2H), 7.66 (dt, J = 1.5, 7.5 Hz, 1H), 7.75 (dt, J = 1.5,
7.5 Hz, 1H), 8.03 (dd, J = 1.5, 7.5 Hz, 1H), 8.11(dd, J = 1.5, 7.5
Hz, 1H); 13C NMR (75 MHz, CDCl3): d 19.6, 46.6, 83.4, 116.3,
121.2, 126.1, 127.8, 128.0, 129.2, 130.4, 131.0, 133.1,135.2,
137.4, 158.9, 171.1, 181.1, 183.5.
(S)-2-HYDROXY-3-(1-NITROPENTAN-2-YL)NAPHTHALENE-1,4-DIONE
(3Q). (Entry 17, Table 2). Orange solid, yield 94% with 93% ee.
m.p. 92–94 uC. [a]2D8 237.4 (c = 0.5, acetone). HPLC on Chiralcel
AS–H column, hexane/i-PrOH = 95 : 5, flow rate 1.0 mL min21
,
1
254 nm; tR = 22.9 min (minor) and 26.2 min (major); H NMR
(300 MHz, CDCl3): d 0.92 (m, 3H), 1.21–1.42 (m, 2H), 1.56–1.72
(m, 1H), 1.81–1.97 (m, 1H), 3.98–4.13 (m, 1H), 4.65–4.74 (dd, J
= 6.0, 12.1 Hz, 1H), 4.95–5.05 (m, 1H), 7.61 (s, 1H), 7.68–7.84
(m, 2H), 8.08–8.16 (m, 2H). 13C NMR (75 MHz, CDCl3): d 13.8,
20.5, 32.4, 34.4, 77.1, 120.9, 126.3, 127.0, 129.0, 132.6, 133.2,
135.3, 153.9, 180.8, 183.9.
Acknowledgements
S.M.S.R thanks CSIR, New Delhi for the award of fellowship.
References
(S)-2-(1-(2-(BENZYLOXY)PHENYL)-2-NITROETHYL)-3-HYDROXYNAPHTHALENE-
1,4-DIONE (3R). (Entry 18, Table 2). Orange solid, yield 92% with 93%
ee. m.p. 58–60 uC. [a]2D8 = +91.2 (c = 0.25, in acetone). HPLC on
Chiralcel OJ–H column, hexane/i-PrOH = 90 : 10, flow rate 1.0 mL
min21, 254 nm; tR = 72.2 min (major) and 83.1 min (minor); 1H NMR
(500 MHz, CDCl3): d 4.98 (dd, J = 5.3, 13.2 Hz, 1H), 5.12 (s, 2H), 5.35–
5.43 (m, 1H), 5.68–5.74 (m, 1H), 6.88–6.98 (m, 2H), 7.19–7.24 (m, 1H),
7.28–7.38 (m, 3H), 7.42 (d, J = 7.9 Hz, 2H), 7.51 (s, 1H), 7.66–7.71 (m,
1H), 7.72–7.78 (m, 1H), 8.04–8.12 (m, 2H). 13C NMR (75 MHz, CDCl3):
d 34.4, 70.3, 75.3, 112.2, 120.2, 120.9, 125.2, 126.2, 127.1, 127.4, 127.9,
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