Catalytic anti-selective asymmetric Henry (nitroaldol) reaction catalyzed by Cu(I)-amine-imine complexes

Article abstract of DOI:10.1016/j.tetasy.2011.12.010

Chiral complex derived from N-methyl-C₁-tetrahydro-1,1′- bisisoquinolines (R)-1b and Cu(I)Cl promoted the diastereoselective Henry reaction of nitroethane with a series of aromatic and aliphatic aldehydes. The nitroalcohol adducts were obtained in excellent yields (up to 95%), moderate anti-selectivity (up to 2.6:1), and good enantioselectivity (up to 92% ee) without any special precautions to exclude moisture or air.

Full text of DOI:10.1016/j.tetasy.2011.12.010

Tetrahedron: Asymmetry 22 (2011) 2065–2070
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Catalytic anti-selective asymmetric Henry (nitroaldol) reaction catalyzed
by Cu(I)–amine–imine complexes
⇑
Yao Qiong Ji, Gao Qi, Zaher M.A. Judeh
School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, N1.2 B1-14, Singapore 637459, Singapore
a r t i c l e i n f o
a b s t r a c t
Chiral complex derived from N-methyl-C1-tetrahydro-1,10-bisisoquinolines (R)-1b and Cu(I)Cl promoted
the diastereoselective Henry reaction of nitroethane with a series of aromatic and aliphatic aldehydes.
The nitroalcohol adducts were obtained in excellent yields (up to 95%), moderate anti-selectivity (up
to 2.6:1), and good enantioselectivity (up to 92% ee) without any special precautions to exclude moisture
or air.
Article history:
Received 7 September 2011
Revised 19 December 2011
Accepted 20 December 2011
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
common characteristic features between them. We previously re-
ported a highly enantioselective Henry reaction between various
The asymmetric nitroaldol (Henry) reaction1–6 provides an
atom-economical route to synthetically important enantioenriched
aldehydes and nitromethane using a chiral C1-1,10-bisisoquino-
line/Cu(I)Cl catalyst and briefly mentioned its potential for diaste-
reoselective applications.58–61 To expand the application of this
amine–imine type catalyst, it was logical to further examine its
application in the diastereoselective Henry reaction considering
that these ligands have been utilized in many other asymmetric
transformations.62–70 We report herein the application of amine–
imine chiral ligands based on 1,10-bisisoquinoline framework
(Fig. 1) in the diastereoselective Henry reaction between nitroe-
thane and various aromatic and aliphatic aldehydes.
a-hydroxy nitroalkanes. Manipulation of the nitro group can
generate chiral compounds such as -hydroxy ketones, b-amino
a
alcohols, azides, aldehydes, carboxylic acids, and sulfides.7–19
While highly enantioselective Henry reactions using nitromethane
has been achieved successfully using various chiral metal cata-
lysts,20–28 organocatalysts29–34 and enzymes,35,36 highly diastereo-
and enantioselective Henry reactions using other nitroalkanes still
remain a challenge and are quite limited.2 The first example of a
direct syn-selective Henry reaction was reported by Shibasaki
et al. in 1995 using modified BINOL heterobimetallic com-
plexes.37,38 Subsequently other syn-diastereoselective ligands
such as guanidinium–thiourea,39,40 bisimadozoline,41 bisoxazoli-
dine,42,43 brucine,44 and diamines45–48 were reported with variable
successes. On the other hand, the more notorious anti-diastereose-
lective version has been reported using enzymes,36 tetraamino-
phosphonium salts,49 quaternary ammonium biflourides,50 amino
alcohols,51 amides52, and amine-type ligands.53–56 Two distinctive
mechanistic models have been proposed to account for the syn and
anti-selectivities: the chelation model gives syn-selectivity while a
non-chelation model gives anti-selectivity.57 Some of the limita-
tions encountered in diastereoselective Henry reactions include
the use of a narrow range of aldehydes and nitroalkanes as well
as the requirement for activated substrates, low reaction tempera-
tures, and long reaction times.2 Therefore, more robust and effi-
cient catalysts for diastereoselective (especially anti-selective)
Henry reactions are highly desirable.
N
N
N
N
N
N
H
H
H
H
1a
(R)-
1b
(R)-
1c
(R)-
N
N
N
N
H
H
A closer look at the above reported ligands for diastereoselec-
tive Henry reactions reveals their wide diversity and the lack of
1d
(R)-
1e
(R)-
⇑
Corresponding author. Tel.: +65 67906738; fax: +65 67947553.
E-mail address: zaher@ntu.edu.sg (Z.M.A. Judeh).
Figure 1. C1-Tetrahydro-1,10-bisisoquinoline and its chiral N-alkyl derivatives.
0957-4166/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2011.12.010

2066
Y. Qiong Ji et al. / Tetrahedron: Asymmetry 22 (2011) 2065–2070
Table 2
2. Results and discussion
Screening of solvents for the diastereoselective Henry reaction using ligand (R)-1b
OH
OH
O
10 mol% (R)-1b
Chiral ligands (R)-1a–1e (Fig. 1) have been easily synthe-
sized.58–60 Having alkyl substituents with differing bulkiness at
the sp3 nitrogen allows us to examine the crowding effect on the
reactivity, diastereo- and enantioselectivities in the Henry reaction.
We have started our screening of ligands (R)-1a–1e (Fig. 1) using
the optimal conditions developed for the reaction of benzaldehyde
with nitromethane (10 mol % ligand, 10% CuCl in (i-Pr)2O, rt,
48 h).60 The results are summarized in Table 1. The reaction of
benzaldehyde 2a with nitroethane proceeded smoothly to give ad-
ducts anti- and syn-3a. Among ligands (R)-1a–1e, the parent ligand
(R)-1a bearing no substituent afforded 3a with the lowest diastere-
oselectivity (anti/syn = 1.7:1) while ligand (R)-1b bearing the small-
est N-alkyl (i.e. N–CH3) substituent proved to be the most efficient
giving a 64% yield of 3a with an anti/syn diastereoselectivity of 2.0:1
and with ee values of 72:78, respectively (Table 1, entry 2). Ligands
(R)-1c–1e having relatively larger N-alkyl substituents afforded 3a
in comparable diastereoselectivities to (R)-1b but in lower yields
and ee’s (Table 1, entries 3–5). The reaction conditions were then
optimized.
10 mol% CuCl
+
Ph
Ph
H
+ EtNO2
solvent, r.t., 48 h
NO2
NO2
anti
syn
3a
2a
Entry
Solvent
Yielda (%)
anti/synb
eec (%)
1
2
3
4
5
6
7
(i-Pr)2O
Dioxane
THF
CH2Cl2
EtOH
64
55
65
38
89
22
19
2.0:1
2.1:1
2.6:1
2.3:1
1.3:1
2.3:1
1.3:1
72:78
74:80
83:90
72:80
73:64
82:80
47:53
CH3CN
Toluene
a
b
c
Yields of isolated products.
Determined by 1H NMR analysis and HPLC using a Chiralpak AD-H column.
Enantiomeric excesses values were determined by HPLC using Chiralpak AD-H
column.55
reaction (Table 3, entry 4). Attempts to increase the catalyst load-
ing from 10 to 20 mol % provided 3a in a higher yield (79%) but
with lower diastereo- and enantioselectivities (Table 3, entries 2
vs 5). At a lower catalyst loading of 5 mol %, the nitroaldol adduct
3a was obtained in comparable diastereoselectivity (anti/
syn = 2.4:1; ee values 84% and 87%, respectively) but at a disap-
pointingly lower yield (17%) (Table 2, entry 2 vs 6). Overall, the
most effective condition used 10 mol % loading of (R)-1b and CuCl
in a ratio of 1:1 (Table 3, entry 2).
Table 1
Screening of ligands (R)-1a–1e and copper sources for the diastereoselective Henry
reaction
O
10 mol% Ligand
OH
OH
10 mol% Copper salts
+ EtNO2
+
Ph
H
Ph
(i-Pr)2O, r.t., 48 h
NO2
NO2
anti
syn
2a
3a
Entry
Ligand
Copper source
Yielda (%)
anti/synb
eec (%)
Table 3
Screening of catalyst loading and ratios of (R)-1b to CuCl for the diastereoselective
Henry reaction
1
2
3
4
5
6
7
8
9
(R)-1a
(R)-1b
(R)-1c
(R)-1d
(R)-1e
(R)-1b
(R)-1b
(R)-1b
(R)-1b
(R)-1b
CuCl
CuCl
CuCl
CuCl
CuCl
CuBr
CuI
CuCl2
Cu(OAc)2
Cu(OAc)
49
64
50
43
36
55
34
17
79
70
1.7:1
2.0:1
2.1:1
1.9:1
2.0:1
2.0:1
1.9:1
1.7:1
2.0:1
1.7:1
64:70
72:78
68:64
66:67
65:68
63:73
56:61
54:40
30:24
44:47
O
OH
OH
(R)-1b/CuCl
H
+
+
EtNO2
Ph
Ph
THF, r.t., 48 h
NO2
NO2
syn
anti
2a
3a
10
a
b
c
Yields of isolated products.
Entry
Ratio (R)-1b/CuCl
Yielda (%)
anti/synb
eec (%)
Determined by 1H NMR analysis and HPLC using a Chiralpak AD-H column.
Enantiomeric excesses values were determined by HPLC using Chiralpak AD-H
1
2
3
4
1:0.5
1:1.0
1:1.5
1:2.0
2:2.0
0.5:0.5
70
65
36
—
79
17
2.3:1
2.6:1
2.3:1
—
2.0:1
2.4:1
81:80
83:90
76:83
—
61:75
84:87
column.55
The effects of different copper sources (Table 1) were examined
5
using the most efficient ligand (R)-1b. The results obtained
revealed that Cu(I) sources are superior to Cu(II) sources in terms
of enantioselectivities (Table 1, entries 2, 6, and 7 vs entries
8–10). The use of different Cu(I) sources did not alter the
diastereoselectivity of 3a indicating that the counterions have little
effect. However, CuCl gave better yields and enantioselectivities
compared to CuBr and CuI (Table 1, entry 2 vs entry 6 vs entry 7)
and thus was used for further reactions.
Subsequently, the effects of various solvents were examined
(Table 2). THF gave the best anti/syn selectivity of 2.6:1, and the
ee values were 83% (anti) and 90% (syn) (Table 2, entry 3). Further
reactions were conducted using THF as the solvent.
Next, the effects of ratio of (R)-1b to CuCl and catalyst loading
were examined. While keeping the amount of ligand (R)-1b con-
stant at 10 mol %, a gradual increase in the amount of CuCl from
5, 10, 15 to 20 mol % gave comparable diastereoselectivities but re-
sulted in a remarkable decrease in the yield of 3a (Table 3, entries
1–4). The optimal ratio of ligand (R)-1b to CuCl is 1:1 (Table 3,
entry 2) and the use of 20 mol % CuCl caused inhibition of the
6d
a
b
c
Yields of isolated products.
Determined by 1H NMR analysis and HPLC using Chiralpak AD-H column.
Enantiomeric excesses values were determined by HPLC using Chiralpak AD-H
column.55
d
Reaction time is 120 h.
The scope for the reaction was studied under the optimized
conditions as described in Table 3, entry 2. For a variety of
aldehydes, the reaction proceeded cleanly to afford the desired
nitroaldol adducts as single product with predominately anti
diastereoselectivity in good ee values and yields. In case of
aromatic aldehydes, the electronic nature of the substituent on
the aromatic ring has little effect on the diastereoselectivity,
irrespective of its electron withdrawing or donating effect (Table 4,
entries 2–9). However, electron donating substituents exhibited
higher ee (Table 4, entries 2–5 vs entries 6–9). 2-Naphthylaldehyde
(Table 4, entry 10) gave a lower anti adduct and ee in comparison
to the syn isomer possibly due to fast retro-Henry reaction and

Y. Qiong Ji et al. / Tetrahedron: Asymmetry 22 (2011) 2065–2070
2067
Table 4
Table 5
Diastereoselective Henry reaction of aldehydes with nitroethane catalyzed by (R)-1b/
CuCl
Time-course studies of diastereoselective Henry reaction of benzaldehyde with EtNO2
catalyzed by (R)-1b/CuCla
OH
O
OH
OH
OH
10 mol% (R)-1b
10 mol% (R)-1b
O
10 mol% CuCl
10 mol% CuCl
R'
NO2
R'
NO2
+
R'NO2
+
+
R
H
R
Ph
+
EtNO2
Ph
THF, r.t.
R
H
THF, r.t., 48 h
NO2
NO2
anti
syn
syn
3
anti
2
2a
3a
Entry
R
R0
Product Yielda (%) anti/
eec
(%)
Entry
Time (h)
anti-3a/syn-3ab
synb
1
2
3
4
5
6
7
8
9
8
3.7:1
3.0:1
2.7:1
2.6:1
2.6:1
2.6:1
2.6:1
2.5:1
2.4:1
1
2
3
4
Ph
2-FC6H4
CH3CH2
CH3CH2
CH3CH2
CH3CH2
CH3CH2
CH3CH2
CH3CH2
CH3CH2
CH3CH2
3a
3b
3c
3d
3e
3f
65 2.6:1
80 2.1:1
83 1.5:1
85 1.6:1
95 1.5:1
70 1.6:1
65 1.6:1
75 1.7:1
70 2.1:1
83:90
72:86
63:86
61:87
50:66
75:92
77:87
85:91
84:90
14.5
23.5
31.5
48.5
55.5
62.5
80.5
96
4-ClC6H4
4-BrC6H4
4-NO2C6H4
2-MeC6H4
3-MeC6H4
4-MeC6H4
2-
5
6d
7d
8d
9d
3g
3h
3i
a
MeOC6H4
All reactions were performed on a 0.2 mmol scale of benzaldehyde in the
10
11
12
13
14
15
2-Naphthyl CH3CH2
3j
3k
3l
70 0.8:1
80 1.3:1
81 1.3:1
73 1.3:1
79 1.1:1
77 1.1:1
40:75
90:91
90:89
86:90
85:87
86:89
presence of ligand (R)-1b (10 mol %) and CuCl (10 mol %) using EtNO2 (20 equiv) in
i-Bu
n-Pr
i-Bu
n-Pr
Et
CH3CH2
CH3CH2
CH3CH2CH2 3m
CH3CH2CH2 3n
CH3CH2CH2 3o
THF (1.5 ml).
b
Determined by 1H NMR analysis.
a
Yields of isolated products.
Determined by 1H NMR analysis and HPLC using Chiralcel OD-H, OJ-H and OB-
b
H, Chiralpak AD-H, AS-H columns.
c
Enantiomeric excesses values were determined by HPLC using Chiralcel OD-H,
OJ-H and OB-H, Chiralpak AD-H, AS-H columns.39,43,51,53–55
d
Reaction time is 96 h.
epimerization (see below for an explanation). Addition of nitroe-
thane to aliphatic aldehydes gave lower diastereoselectivities,
however, the products were obtained in very good yields and
excellent ee’s (up to 80% yield and 91% ee) (Table 4, entries 11–15).
Under the reaction conditions utilized (Table 4), we observed
that reaction time greatly affects the anti/syn ratio of the nitroaldol
adducts. This is not surprising considering that yjr Henry reaction
is known to be reversible (retro-nitroaldol or retro-Henry) and the
Figure 2. Time-course studies of diastereoselective Henry reaction of benzaldehyde
with EtNO2 catalyzed by (R)-1b/CuCl.
nitroaldol adducts are easily epimerized at the carbon
a to the NO2
group. Therefore, we decided to further elucidate the stereochem-
istry of the reaction by conducting both cross-over and time-
course studies.71
3. Conclusion
We have shown that chiral C1-1,10-bisisoquinoline (R)-1b is an
effective ligand in the Cu(I)-catalyzed diastereoselective Henry
reaction. The desired products were obtained in very good yields
(up to 95%), moderate diastereoselectivities and good enantioselec-
tivities (up to 92%) using a range of aliphatic and aromatic alde-
hydes. The major diastereomer obtained is the anti isomer which
has proven difficult to obtain using various ligands. Cross-over
and time-course studies suggest a competition between the kinet-
ically and thermodynamically controlled products. The enantioin-
duction is governed by the substituents at the nitrogen of (R)-1a.
The operational procedure using the present catalyst system is
simple and no exclusion of air or moisture is required. Further
investigation of the detailed reaction mechanism is still in progress.
In the cross-over reaction, treatment of a THF solution of nitro-
aldol adducts anti-3a and syn-3a with (R)-1b/CuCl (10 mol %, 1:1)
and MeNO2 (20 mol %) resulted in the formation of benzaldehyde
2a and 1-phenyl-2-nitroethanol along with anti-3a and syn-3a.
This result clearly indicates that a retro-Henry reaction is taking
place. Further evidence for a retro-Henry reaction comes from
the time-course studies (Table 5). As clearly seen from Table 5, en-
tries 1–4, the amount of the more dominant anti-3a gradually de-
creases as the reaction proceeds and then equilibrates with syn-3a
(Table 5, entries 4–9).38,72 We believe that there is a competing ki-
netic versus thermodynamic control. Initially, we have a reaction
that allows for the formation of the more dominant and thermody-
namically stable anti-3a along with the kinetically formed syn-3a,
indicating thermodynamic control. As the reaction proceeds over
time and as a result of retro-Henry reaction, the kinetically syn-
3a equilibrates with the thermodynamically anti-3a and an equi-
librium is established after ca. 30 h (Fig. 2).38,52,73 In addition, after
63 h, more of the anti-3a slowly converts to the syn-3a. Moreover,
as shown in Table 4, the ee values of the anti- and syn-nitroaldol
adducts are similar but with a slight bias toward the syn-product,
indicating the probability of in situ epimerization of the anti-3a ad-
duct to the syn-3a adduct.38,52,73
4. Experimental
4.1. General
All commercial chemicals were reagent grade unless otherwise
specified. Analytical thin layer chromatography (TLC) was per-
formed using F254 pre-coated silica gel plates (0.2 mm thickness).
Separation of products was achieved using column chromatography

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Y. Qiong Ji et al. / Tetrahedron: Asymmetry 22 (2011) 2065–2070
on Silica Gel 60 (230–400 mesh). FTIR were recorded as thin films
(KBr). NMR spectra were recorded at 300 MHz for 1H and at
75.6 MHz for 13C. Chemical shifts are given in ppm relative to TMS
(d = 0 ppm) or solvent residual peaks (CDCl3: 1H, d = 7.26 ppm;
13C, d = 75 ppm) as internal standards. 1H NMR multiplicities were
designated as singlet (s), doublet (d), doublet of doublet (dd), dou-
blet of doublet of doublet (ddd), triplet (t), triplet of doublet (td),
quartet (q), pentet (p), multiplet (m) and broad (br). HPLC separa-
tions were performed on using Diacel Chiralcel OD-H, OJ-H, AS-H
and AD-H chiral columns.
(4H, m); 13C NMR (75.6 MHz, CDCl3, d ppm): anti isomer—12.0,
73.2, 87.2, 127.4, 129.0, 134.4, 136.9; syn isomer—16.4, 75.5,
88.2, 128.3, 129.2, 135.1, 136.8.
4.2.4. 1-(4-Bromophenyl)-2-nitropropan-1-ol 3d
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a yellow oil (85% yield); diastereomeric ratios (anti/
syn, 1.6:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak AD-H column (90:10 n-hex–IPA, 1.0 ml/min, 210 nm);
antiminor (1S,2R) tr = 9.84 min, antimajor (1R,2S) tr = 10.45 min, synma-
4.2. General procedure for the asymmetric Henry reaction
(1R,2R) tr = 13.26 min, synminor (1S,2S) tr = 15.27 min. anti/
jor
syn = 61%/87% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—1.40 (3H, d, J = 6.9 Hz), 2.89 (1H, d, J = 3.9 Hz), 4.53–4.69
(1H, m), 5.25–5.31 (1H, m), 7.16–7.20 (2H, m), 7.42–7.47 (2H,
m); syn isomer—1.24 (3H, d, J = 6.9 Hz), 2.83 (1H, d,, J = 3.9 Hz),
4.53–4.69 (1H, m), 4.90–4.94 (1H, m), 7.16–7.20 (2H, m), 7.42–
7.47 (2H, m); 13C NMR (75.6 MHz, CDCl3, d ppm): anti isomer—
12.0, 73.3, 87.2, 122.5, 127.7, 131.9, 137.6; syn isomer—16.3,
75.5, 88.2, 123.2, 128.6, 132.1, 137.4.
T first, (R)-1b (0.02 mmol, 10 mol %) and CuCl (0.02 mmol,
10 mol %) were mixed in THF (1.5 mL) and allowed to stir at rt
for 1 h. Aldehydes (0.2 mmol) and nitroethane/nitropropane
(4 mmol, 20 equiv) were then added sequentially. The reaction
mixture was then stirred at the given temperature for a specific
time (TLC). The b-nitroalcohol product was purified on silica gel
by flash column chromatography.
4.2.1. 1-Phenyl-2-nitropropan-1-ol 3a
4.2.5. 1-(4-Nitrophenyl)-2-nitropropan-1-ol 3e
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a yellow oil (65% yield); diastereomeric ratios (anti/
syn, 2.6:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak AD-H column (90:10 n-hex–IPA, 1.0 ml/min, 210 nm);
antiminor (1S,2R) tr = 8.38 min, antimajor (1R,2S) tr = 9.16 min, synmi-
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
4:1) to give a yellow oil (95% yield); diastereomeric ratios (anti/
syn, 1.5:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralcel OD-H + Chiralpak AD-H (80:20 n-hex–IPA, 1.0 ml/min,
210 nm); antimajor (1R,2S) tr = 16.95 min, antiminor (1S,2R)
tr = 18.65 min, synmajor (1R,2R) tr = 21.60 min, synminor (1S,2S)
tr = 24.81 min. anti/syn = 50%/66% ee. 1H NMR (300 MHz, CDCl3, d
ppm): anti isomer—1.49 (3H, d, J = 6.9 Hz), 3.10 (1H, s), 4.68–4.82
(1H, m), 5.54–5.61 (1H, m), 7.58–7.62 (2H, m), 8.24–8.28 (2H,
m); syn isomer—1.39 (3H, d, J = 6.9 Hz), 3.10 (1H, s), 4.68–4.82
(1H, m), 5.20 (1H, d, J = 9.0 Hz), 7.58–7.62 (2H, m), 8.24–8.28
(2H, m); 13C NMR (75.6 MHz, CDCl3, d ppm): anti isomer—11.9,
72.9, 86.8, 124.0, 127.0, 145.6, 148.5; syn isomer—16.1, 75.0,
87.8, 124.1, 127.9, 145.6, 148.0.
(1S,2S) tr = 10.69 min, synmajor (1R,2R) tr = 11.83 min. anti/
nor
syn = 83%/90% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—1.48 (3H, d, J = 6.9 Hz), 3.05 (1H, s), 4.65–4.82 (1H, m),
5.33–5.39 (1H, m), 7.31–7.42 (5H, m); syn isomer—1.30 (3H, d,
J = 6.9 Hz), 3.05 (1H, s), 4.65–4.82 (1H, m), 5.01 (1H, d, J = 9.0 Hz),
7.31–7.42 (5H, m); 13C NMR (75.6 MHz, CDCl3, d ppm): anti
isomer—12.1, 73.9, 87.4, 125.9, 128.6, 128.8, 138.4; syn
isomer—16.5, 76.3, 88.4, 126.9, 129.0, 129.2, 138.3.
4.2.2. 1-(2-Fluorophenyl)-2-nitropropan-1-ol 3b
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a yellow oil (80% yield); diastereomeric ratios (anti/
syn, 2.1:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak AD-H column (95:5 n-hex–IPA, 1.0 ml/min, 210 nm);
antiminor (1S,2R) tr = 11.54 min, antimajor (1R,2S) tr = 14.12 min, syn-
4.2.6. 2-Nitro-1-o-tolylpropan-1-ol 3f
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a yellow oil (70% yield); diastereomeric ratios (anti/
syn, 1.6:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak AD-H column (95:5 n-hex–IPA, 1.0 ml/min, 210 nm);
antiminor (1S,2R) tr = 11.44 min, antimajor (1R,2S) tr = 12.80 min, syn-
(1S,2S) tr = 18.89 min, synmajor (1R,2R) tr = 22.64 min. anti/
minor
syn = 72%/86% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—1.49 (3H, d, J = 6.9 Hz), 2.91 (1H, d, J = 6.9 Hz), 4.79–4.88
(1H, m), 5.70–5.76 (1H, m), 7.03–7.13 (1H, m), 7.19–7.59 (3H,
m); syn isomer—1.41 (3H, d, J = 6.9 Hz), 2.77 (1H, s), 4.79–4.88
(1H, m), 5.38–5.39 (1H, m), 7.03–7.13 (1H, m), 7.19–7.59 (3H,
m); 13C NMR (75.6 MHz, CDCl3, d ppm): anti isomer—11.9, 68.3,
85.2, 115.4, 124.6, 125.4, 127.8, 130.1, 157.5; syn isomer—16.2,
70.0, 87.9, 115.8, 125.0, 125.6, 128.3, 130.6, 160.8.
(1S,2S) tr = 15.60 min, synmajor (1R,2R) tr = 19.43 min. anti/
minor
syn = 75%/92% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—1.43 (3H, d, J = 6.9 Hz), 2.29 (3H, s), 2.58 (1H, s), 4.54–4.57
(1H, m), 5.54 (1H, s), 7.08–7.19 (3H, m), 7.46 (1H, d, J = 7.2 Hz);
syn isomer—1.22 (3H, d, J = 6.9 Hz), 2.36 (3H, s), 2.48 (1H, s),
4.77–4.80 (1H, m), 5.27–5.30 (1H, m), 7.08–7.19 (3H, m), 7.29–
7.32 (1H, m); 13C NMR (75.6 MHz, CDCl3, d ppm): anti isomer—
11.5, 18.9, 70.9, 85.4, 126.0, 126.4, 128.4, 130.8, 134.3, 136.7; syn
isomer—16.1, 19.6, 72.2, 88.8, 126.5, 126.8, 128.8, 131.0, 135.9,
136.6.
4.2.3. 1-(4-Chlorophenyl)-2-nitropropan-1-ol 3c
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a yellow oil (83% yield); diastereomeric ratios (anti/
syn, 1.5:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak AD-H column (95:5 n-hex–IPA, 1.0 ml/min, 210 nm);
antiminor (1S,2R) tr = 16.13 min, antimajor (1R,2S) tr = 17.29 min, syn-
4.2.7. 2-Nitro-1-m-tolylpropan-1-ol 3g
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a yellow oil (65% yield); diastereomeric ratios (anti/
syn, 1.6:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak AS-H column (90:10 n-hex–IPA, 1.0 ml/min, 210 nm);
antiminor (1S,2R) tr = 8.74 min, antimajor (1R,2S) tr = 9.73 min, synmi-
(1R,2R) tr = 22.84 min, synminor (1S,2S) tr = 25.37 min. anti/
major
syn = 63%/86% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—1.49 (3H, d, J = 6.0 Hz), 2.82 (1H, s), 4.62–4.75 (1H, m), 5.66
(1H, br s), 7.30–7.40 (4H, m); syn isomer—1.33 (3H, d, J = 6.0 Hz),
2.71 (1H, s), 4.62–4.75 (1H, m), 5.39 (1H, d, J = 8.1 Hz), 7.30–7.40
(1S,2S) tr = 10.44 min, synmajor (1R,2R) tr = 12.91 min. anti/
nor
syn = 77%/87% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—1.44 (3H, d, J = 6.9 Hz), 2.29 (3H, s), 2.63 (1H, d, J = 3.6 Hz),

Y. Qiong Ji et al. / Tetrahedron: Asymmetry 22 (2011) 2065–2070
2069
4.57–4.74 (1H, m), 5.28 (1H, dd, J = 3.6, 3.4 Hz), 7.05–7.11 (3H, m),
7.17–7.24 (1H, m); syn isomer—1.23 (3H, d, J = 6.9 Hz), 2.30 (3H, s),
2.51 (1H, d, J = 3.6 Hz), 4.57–4.74 (1H, m), 4.90 (1H, dd, J = 3.6,
3.6 Hz), 7.05–7.11 (3H, m), 7.17–7.24 (1H, m); 13C NMR
(75.6 MHz, CDCl3, d ppm): anti isomer—12.1, 21.4, 74.0, 87.5,
123.0, 126.6, 128.6, 129.3, 138.5, 138.6; syn isomer—16.5, 21.5,
76.3, 88.5, 124.1, 127.5, 128.9, 130.0, 138.3, 138.9.
Chiralpak AD-H column (98:2 n-hex–IPA, 0.8 ml/min, 220 nm);
antiminor (1S,2R) tr = 20.18 min, antimajor (1R,2S) tr = 21.70 min, syn-
(1R,2R) tr = 26.09 min, synminor (1S,2S) tr = 28.00 min. anti/
major
syn = 90%/91% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—0.86–0.91 (6H, m), 1.15–1.23 (1H, m), 1.48 (3H, d,
J = 6.6 Hz), 1.76–1.80 (2H, m), 2.28 (1H, br s), 4.20 (1H, d,
J = 6.6 Hz), 4.40–4.46 (1H, m); syn isomer—0.86–0.91 (6H, m),
1.06–1.14 (1H, m), 1.30–1.39 (2H, m), 1.49 (3H, d, J = 6.9 Hz),
2.28 (1H, br s), 3.86–3.90 (1H, m), 4.40–4.46 (1H, m); 13C NMR
(75.6 MHz, CDCl3, d ppm): anti isomer—16.3, 21.7, 23.6, 24.3,
42.0, 71.2, 86.7; syn isomer—12.4, 21.4, 23.3, 24.5, 41.8, 70.2, 88.2.
4.2.8. 2-Nitro-1-p-tolylpropan-1-ol 3h
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a yellow oil (75% yield); diastereomeric ratios (anti/
syn, 1.7:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak AD-H column (95:5 n-hex–IPA, 1.0 ml/min, 210 nm);
antiminor (1S,2R) tr = 14.56 min, antimajor (1R,2S) tr = 16.40 min, syn-
4.2.12. 2-Nitrohexan-3-ol 3l
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a clear oil (81% yield); diastereomeric ratios (anti/
syn, 1.3:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak AD-H column (98:2 n-hex–IPA, 0.8 ml/min, 220 nm);
antiminor (1S,2R) tr = 25.40 min, antimajor (1R,2S) tr = 27.92 min, syn-
(1S,2S) tr = 22.50 min, synmajor (1R,2R) tr = 26.66 min. anti/
minor
syn = 85%/91% ee. 1H NMR (300 MHz, CDCl3,
d ppm): anti
isomer—1.51 (3H, d, J = 6.9 Hz), 2.36 (3H, s), 2.62 (1H, br s),
4.67–4.79 (1H, m), 5.32–5.39 (1H, m), 7.21–7.28 (4H, m); syn
isomer—1.31 (3H, d, J = 6.9 Hz), 2.36 (3H, s), 2.49 (1H, br s),
4.67–4.79 (1H, m), 5.06 (1H, d, J = 8.1 Hz), 7.21–7.28 (4H, m); 13C
NMR (75.6 MHz, CDCl3, d ppm): anti isomer—12.3, 21.1, 73.9,
87.5, 125.9, 129.4, 135.4, 138.4; syn isomer—16.5, 29.7, 76.2,
88.5, 126.8, 129.7, 133.4, 139.2.
(1R,2R) tr = 31.55 min, synminor (1S,2S) tr = 35.12 min. anti/
major
syn = 90%/89% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—0.87–0.92 (5H, m), 1.34–1.40 (2H, m), 1.46 (3H, d,
J = 6.9 Hz), 2.13 (1H, br s), 4.12–4.15 (1H, m), 4.45–4.50 (1H, m);
syn isomer—0.87–0.92 (5H, m), 1.34–1.40 (2H, m), 1.49 (3H, d,
J = 6.9 Hz), 2.22 (1H, br s), 3.75–3.85 (1H, m), 4.45–4.50 (1H, m);
13C NMR (75.6 MHz, CDCl3, d ppm): anti isomer—13.8, 16.3, 18.4,
35.1, 72.7, 86.4; syn isomer—12.4, 13.9, 19.0, 29.7, 71.8, 87.7.
4.2.9. 1-(2-Methoxyphenyl)-2-nitropropan-1-ol 3i
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
8:1) to give a yellow oil (70% yield); diastereomeric ratios (anti/
syn, 2.1:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak OJ-H column (95:5 n-hex–IPA, 0.6 ml/min, 210 nm);
antiminor (1S,2R) tr = 47.22 min, antimajor (1R,2S) tr = 53.95 min, syn-
4.2.13. 2-Methyl-5-nitroheptan-4-ol 3m
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a clear oil (73% yield); diastereomeric ratios (anti/
syn, 1.3:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak AD-H column (99:1 n-hex–IPA, 0.6 ml/min, 210 nm);
antiminor (1S,2R) tr = 22.13 min, antimajor (1R,2S) tr = 25.02 min, syn-
(1S,2S) tr = 60.84 min, synmajor (1R,2R) tr = 64.25 min. anti/
minor
syn = 84%/90% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—1.47 (3H, d, J = 6.9 Hz), 3.11 (1H, br s), 3.88 (3H, s), 4.86–
4.97 (1H, m), 5.53 (1H, s), 6.88–7.02 (2H, m), 7.26–7.37 (2H, m);
syn isomer—1.33 (3H, d, J = 6.9 Hz), 3.32 (1H, d, J = 3 Hz), 3.88
(3H, s), 5.00–5.03 (1H, m), 5.11–5.17 (1H, m), 6.88–7.02 (2H, m),
7.41–7.44 (2H, m); 13C NMR (75.6 MHz, CDCl3, d ppm): anti iso-
mer—12.6, 55.4, 70.8, 85.1, 110.4, 121.0, 126.3, 127.6, 129.5,
155.8; syn isomer—16.6, 55.5, 74.1, 87.7, 111.0, 121.2, 125.9,
129.0, 130.1, 156.8.
(1S,2S) tr = 30.79 min, synmajor (1R,2R) tr = 32.07 min. anti/
minor
syn = 86%/90% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—0.84–0.96 (9H, m), 1.11–1.23 (2H, m), 1.34–1.41 (1H, m),
1.76–1.84 (2H, m), 2.02–2.19 (1H, m), 4.08–4.13 (1H, m), 4.25–
4.30 (1H, m); syn isomer—0.84–0.96 (9H, m), 1.11–1.23 (2H, m),
1.34–1.41 (1H, m), 1.76–1.84 (2H, m), 2.02–2.19 (1H, m), 3.89–
3.92 (1H, m), 4.25–4.30 (1H, m); 13C NMR (75.6 MHz, CDCl3, d
ppm): anti isomer—10.5, 21.3, 21.5, 23.5, 24.5, 42.0, 70.4, 94.2;
syn isomer—10.2, 21.5, 23.4, 23.9, 24.3, 42.5, 70.0, 94.8.
4.2.10. 1-(Naphthyalen-2-yl)-2-nitropropan-1-ol 3j
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a clear oil (70% yield); diastereomeric ratios (anti/
syn, 0.8:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak AD-H column (90:10 n-hex–IPA, 1.0 ml/min, 210 nm);
antiminor (1S,2R) tr = 11.55 min, antimajor (1R,2S) tr = 13.91 min, syn-
4.2.14. 3-Nitroheptan-4-ol 3n
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a clear oil (79% yield); diastereomeric ratios (anti/
syn, 1.1:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak AD-H column (99.5:0.5 n-hex–IPA, 1.0 ml/min, 215 nm);
antiminor (1S,2R) tr = 27.38 min, antimajor (1R,2S) tr = 29.19 min, syn-
(1S,2S) tr = 17.96 min, synmajor (1R,2R) tr = 20.55 min. anti/
minor
syn = 40%/75% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—1.52 (3H, d, J = 6.9 Hz), 2.84 (1H, br s), 4.79–4.93 (1H, m),
5.58 (1H, s), 7.43–7.55 (3H, m), 7.84–7.94 (4H, m); syn isomer—
1.33 (3H, d, J = 6.9 Hz), 2.69 (1H, br s), 4.79–4.93 (1H, m), 5.20
(1H, d, J = 9.3 Hz), 7.43–7.55 (3H, m), 7.84–7.94 (4H, m); 13C
NMR (75.6 MHz, CDCl3, d ppm): anti isomer—12.0, 74.0, 87.3,
123.3, 125.3, 126.5, 126.6, 127.7, 128.09, 128.7, 133.11, 133.2,
135.7; syn isomer—16.6, 76.5, 88.4, 123.8, 126.7, 126.74, 126.8,
127.8, 128.07, 129.1, 133.09, 133.6, 135.6.
(1S, 2S) tr = 38.67 min, synmajor (1R,2R) tr = 40.70 min. anti/
minor
syn = 85%/87% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—0.85–0.95 (6H, m), 1.32–1.49 (4H, m), 1.80–1.85 (1H, m),
2.00–2.06 (2H, m), 3.90–4.00 (1H, m), 4.30–4.39 (1H, m); syn iso-
mer—0.85–0.95 (6H, m), 1.32–1.49 (4H, m), 1.80–1.85 (1H, m),
2.00–2.06 (2H, m), 3.81–3.88 (1H, m), 4.30–4.39 (1H, m); 13C
NMR (75.6 MHz, CDCl3, d ppm): anti isomer—10.5, 13.7, 18.8,
21.5, 35.2, 72.0, 93.9; syn isomer—10.2, 13.8, 18.5, 23.9, 35.5,
71.6, 94.4.
4.2.11. 5-Methyl-2-nitrohexan-3-ol 3k
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a clear oil (80% yield); diastereomeric ratios (anti/
syn, 1.3:1) were determined by 1H NMR and HPLC. HPLC analysis:
4.2.15. 3-Nitrohexan-4-ol 3o
This compound was prepared according to the General Proce-
dure and purified by column chromatography (Hexane–EtOAc
5:1) to give a clear oil (77% yield); diastereomeric ratios (anti/

2070
Y. Qiong Ji et al. / Tetrahedron: Asymmetry 22 (2011) 2065–2070
syn, 1.1:1) were determined by 1H NMR and HPLC. HPLC analysis:
Chiralpak OB-H column (98:2 n-hex–IPA, 0.6 ml/min, 210 nm);
antiminor (1S,2R) tr = 18.71 min, antimajor (1R,2S) tr = 22.05 min, syn-
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(1R,2R) tr = 28.02 min, synminor (1S,2S) tr = 32.17 min. anti/
major
syn = 86%/89% ee. 1H NMR (300 MHz, CDCl3, d ppm): anti iso-
mer—0.96–0.99 (6H, m), 1.26–1.41 (2H, m), 1.65–1.91 (2H, m),
2.33–2.60 (1H, m), 3.77–3.83 (1H, m), 4.16–4.21 (1H, m); syn iso-
mer—0.96–0.99 (6H, m), 1.26–1.41 (2H, m), 1.65–1.91 (2H, m),
2.33–2.60 (1H, m), 3.60–3.75 (1H, m), 4.16–4.21 (1H, m); 13C
NMR (75.6 MHz, CDCl3, d ppm): anti isomer—10.0, 10.5, 21.5,
26.3, 73.6, 93.7; syn isomer—9.6, 10.2, 24.0, 26.5, 73.1, 94.1.
Acknowledgements
We are grateful to the Nanyang Technological University for
financial support (RG5/04), and also appreciate scholarship sup-
port for Yao Qiong Ji from the China Scholarship Council.
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