Enantioselective Addition of Diethylzinc to Aromatic Aldehydes Using Chiral Oxazoline-Based Ligands

Article abstract of DOI:10.1134/S1070428020070271

Abstract: Chiral oxazoline ligands containing an aromatic ring were prepared fromnorephedrine and pyrrole-2-carbonitrile or 2-hydroxybenzoyl chloride. Thesynthesized ligands were used in the copper-catalyzed asymmetric addition ofdiethylzinc to aromatic aldehydes to provide optically active 1-arylpropan-1-olswith high conversion (92%) and enantioselectivity (up to 99% ee).

Full text of DOI:10.1134/S1070428020070271

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2020, Vol. 56, No. 7, pp. 1304–1312. © Pleiades Publishing, Ltd., 2020.
Enantioselective Addition of Diethylzinc to Aromatic Aldehydes
Using Chiral Oxazoline-Based Ligands
A. E. Aydina,*
a Department of Chemistry, Arts and Science Faculty, Hatay Mustafa Kemal University, Hatay, 31040 Turkey
*e-mail: aebruaydin@gmail.com
Received April 4, 2020; revised July 21, 2020; accepted July 22, 2020
Abstract—Chiral oxazoline ligands containing an aromatic ring were prepared from norephedrine and pyrrole-
2-carbonitrile or 2-hydroxybenzoyl chloride. The synthesized ligands were used in the copper-catalyzed
asymmetric addition of diethylzinc to aromatic aldehydes to provide optically active 1-arylpropan-1-ols with
high conversion (92%) and enantioselectivity (up to 99% ee).
Keywords: asymmetric catalysis, enantioselective synthesis, chiral oxazoline-based ligands, 1,2-addition
DOI: 10.1134/S1070428020070271
INTRODUCTION
It is well known that oxazolines are synthetically
and biologically significant molecular structures
[29, 30]. These compounds are used as protecting
groups for carboxylic acids and hydroxylamines [31].
Chiral oxazolines have also been extensively used in
asymmetric syntheses as chiral catalysts [32, 33].
Chiral ligands containing one or more oxazoline rings
have been synthesized and used to prepare enantio-
merically pure compounds in many metal-catalyzed
asymmetric reactions. Examples of widely used ligands
of this type are pyridyloxazolines [34–37], bisoxazo-
line [38], bisoxazolinopyridine [39–43], BINOL-oxa-
zoline [44–46], and phosphine-oxazoline [47–50]
derivatives. These chiral ligands have been applied to
a wide range of catalytic reactions including hydro-
silylations [51–53], Diels–Alder reactions [54], cyclo-
propanations, [39, 55, 56], allylic alkylation [57],
enantioselective addition of diethylzinc to aldehydes
[58–61], and asymmetric Henry reactions [62–66].
Enantioselective addition of dialkyzinc to carbonyl
compounds is one of the most important reactions
forming a new carbon–carbon bond in asymmetric syn-
thesis [1–3]. The asymmetric addition of organometal-
lic reagents to carbonyl substrates usually occurs with
low enantiomeric excesses due to high chemical yields
[4, 5]. On the other hand, enantioselective catalytic
addition of dialkyzinc to aldehydes is by far one of
the most studied enantioselective addition reactions.
This reaction provides an important method for the
synthesis of optically active secondary alcohols [6–9]
that are widely found in nature and are also important
building blocks in organic synthesis [9]. Enantioselec-
tive addition of diethylzinc to aldehydes was applied to
obtain optically active lactones [10], cyclopropyl alco-
hols [11], as well as the natural product (+)-(R)-gos-
sonorol which shows antifungal, anticancer, and anti-
oxidant activities [12].
However, only a few examples of chiral pyrrole
oxazoline ligands have been reported so far. The first
chiral pyrrolyloxazoline ligands with unsubstituted
pyrrole nitrogen atom were synthesized and applied to
copper-catalyzed asymmetric cyclopropanations by
Brunner in 1998. However, the corresponding product
was obtained with a low enantiomeric excess (3–
14% ee) [67, 68]. The use of pyrrole-containing chiral
oxazoline ligands to catalyze Henry reaction was
reported by us in 2013 [69]. Chiral oxazoline-based
ligands were synthesized from 1H-pyrrole-2-carboni-
trile and 2-hydroxybenzoyl chloride and were applied
The enantioselectivity of a reaction depends mainly
on the chiral ligand structure; therefore, search for new
ligands for this important asymmetric transformation is
a field of continuous interest. Among the chiral ligand
families, primary amino alcohols [13–16] amino-
phenols [17, 18], diamines [19–21], disulfonamides
[22–25], diols [26–28], and their derivatives have been
widely employed in such reactions. Although a number
of chiral ligands have been prepared, research focused
on the development of new active, enantioselective,
easily obtainable, and economically viable catalysts
continues.
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ENANTIOSELECTIVE ADDITION OF DIETHYLZINC TO AROMATIC ALDEHYDES
1305
in copper-catalyzed asymmetric Henry reactions. There
are a few examples of the use of oxazoline-based
ligands in the addition of organozinc reagents to car-
bonyl compounds, and most of them utilized 4,5-dihy-
dro-1,3-oxazoles containing a side-chain hydroxy
group in the α- or β-position relative to C2 [70–73].
hyde (5a) as a model substrate and the addition reac-
tion was performed at 0°C in toluene for 12 h in the
presence of 2 mol % of chiral ligands 3a, 3b, 4a, and
4b. The results are summarized in Table 1. The use of
enantiomeric chiral ligands (4S,5R)-3a and (4R,5S)-3b
led to the opposite configurations of the resulting
secondary alcohol 6a with 80 and 78% ee, respec-
tively. It was found that the absolute configuration of
6a is determined mainly by the stereogenic centers
of norephedrine on chiral ligands. Chiral ligand
(4S,5R)-3a with the R configuration at the OH-bearing
carbon gave the S isomer, whereas chiral ligand
(4R,5S)-3b gave rise to (R)-6a (Table 1, entry
nos. 1, 2). Thus, the configuration of 6a depended on
the configuration of the alcohol part of the chiral
ligand. In the presence of ligands (4S,5R)-4a and
(4R,5S)-4b, addition product 6a was obtained in 82%
yield with 78 and 79% ee, respectively (Table 1, entry
nos. 3, 4).
Bolm et al. [74] described the application of the
ferrocene ligand containing a chiral oxazoline unit to
catalyze the reaction of diethylzinc with aromatic, ali-
phatic, and α,β-unsaturated aldehydes at 0°C in
toluene with 83–94% yield and 78–95% ee. Reiser and
co-workers [75] reported the activity of bis-oxazolines
in the addition of diethylzinc to aromatic and aliphatic
aldehydes. High enantioselectivities (83–95% ee) have
been achieved, especially with aromatic aldehydes. In
the case of aliphatic aldehydes, both yield and enantio-
selectivity could be considerably increased in the pres-
ence of a catalytic amount of n-BuLi.
To the best of our knowledge, chiral oxazoline
ligands containing a pyrrole ring have not been used
previously in the enantioselective addition of diethyl-
zinc to aldehydes. Herein, chiral oxazolines synthe-
sized from pyrrole-2-carbonitrile and 2-hydroxyben-
zoyl chloride were applied as ligands in the copper-
catalyzed asymmetric addition of diethylzinc to alde-
hydes with excellent enantioselectivities.
Since (4R,5S)-3b showed the highest enantioselec-
tivity in the addition of diethylzinc to benzaldehyde, it
was selected for further optimization of the reaction
conditions, including solvent, chiral ligand loading,
metal catalyst, reaction time, and temperature. The
results are listed in Tables 2 and 3. Moderate yields and
medium enantioselectivities were obtained in chlorinat-
ed solvents such as chloroform and methylene chloride
(Table 2, entry nos. 1 and 2), as well as in a polar protic
solvent such as methanol (entry no. 6). Lower enan-
tioselectivity was also achieved in diethyl ether, aceto-
nitrile, and THF (entry nos. 3–5). The highest enantio-
selectivity (84% ee) and 83% yield were observed in
toluene (entry no. 7). When the loading of chiral ligand
(4R,5S)-3b was increased to 20 mol %, both yield and
ee value increased to 79 and 87%, respectively (entry
no. 8). An increase in the loading of chiral ligand from
10 to 30 mol % led to a significant increase in the yield
(from 83 to 87%; entry nos. 8, 9) without any change
RESULTS AND DISCUSSION
As described previously [69], chiral 2-oxazolines
3a, 3b, 4a, and 4b were synthesized by reacting both
enantiomers of norephedrine with 1H-pyrrole-2-carbo-
nitrile (1) or 2-hydroxybenzoyl chloride as shown in
Scheme 1. Taking into account successful application
of these ligands in the enantioselective Henry reaction
[69], we envisioned that this catalytic system should
also be suitable for the addition of diethylzinc to alde-
hydes. We started our investigation by using benzalde-
Scheme 1.
Me
*
Ph
K2CO3, ethylene glycol–glycerol (2:1)
120°C, 24 h
O
N
*
*
Ph
+
CN
H2N
N
H
*
OH
N
H
Me
1
(1R,2S)-2a
(1S,2R)-2b
(4S,5R)-3a
(4R,5S)-3b
OH
COOH
OH
COCl
Ph
SOCl2, CH2Cl2
2a, 2b
O
N
*
*
OH
Me
(4S,5R)-4a
(4R,5S)-4b
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 7 2020

AYDIN
Table 1. Enantioselective addition of diethylzinc to benzaldehyde in the presence of chiral ligands 3a, 3b, 4a, and 4ba
1306
OH
Chiral ligand
PhCHO
+
Et2Zn
Me
Ph
5a
6a
Entry no.
Ligand no.
(4S,5R)-3a
(4R,5S)-3b
(4S,5R)-4a
(4R,5S)-4b
Yield,b %
ee,c %
78
Configurationd
1
2
3
4
75
74
82
82
S
R
S
80
78
79
R
a
The reactions were carried out in methylene chloride using 1 mmol of benzaldehyde (5a), 10 mol % of Cu(OAc)2·H2O, and 2.2 mmol of
diethylzinc (1 M solution in hexane) at 0°C to room temperature.
b Yield refers to the pure product after column chromatography.
c
The ee values were determined by HPLC with a Chiralcel OD-H column.
d The absolute configurations were assigned by comparison of HPLC retention time with literature data [76–78].
Table 2. Enantioselective addition of diethylzinc to benzaldehyde (5a) under different conditions
OH
(4R,5S)-3b
PhCHO
+
Et2Zn
Me
Ph
5a
6a
Entry no.
Ligand, mol %
Solvent
Temperature, °C
0 to room temp.
0 to room temp.
0 to room temp.
0 to room temp.
0 to room temp.
0 to room temp.
0 to room temp.
0 to room temp.
0 to room temp.
0
Yield,a %
74
ee,b %
80
72
48
52
50
65
84
87
85
78
55
0
1
2
10
10
10
10
10
10
10
20
30
20
20
20
Methylene chloride
Chloroform
Diethyl ether
Acetonitrile
Tetrahydrofuran
Methanol
68
3
75
4
73
5
65
6
80
7
Toluene
83
8
Toluene
79
9
Toluene
87
10
11
12
Toluene
82
Toluene
–20
62
Toluene
–50
36
a
Yield of 6a isolated by column choratography.
The ee values were determined by HPLC with a Chiralcel OD-H column.
b
in the ee value. When the reaction was performed at
0°C, the ee value of the addition product was 78% with
82% yield (Table 2, entry no. 10). When the reaction
temperature was reduced from room temperature to
–20°C, the product was obtained in 62% yield with
55% ee (entry no. 11). A racemic mixture of (R)- and
(S)-secondary alcohol was obtained when the reaction
was carried out at –50°C (entry no. 12).
On the basis of the above experimental data, the
optimized reaction conditions were toluene as solvent,
0°C to room temperature, 24 h, 20 mol % of
(4R,5S)-3b as chiral ligand.
The effect of various copper salts was examined
using ligands (4R,5S)-3b and (4R,5S)-4b. The results
are summarized in Table 3. The copper source signif-
icantly affected the reactivity and enantioselectivity
(Table 3, entry nos. 2–8). The reactions with CuI,
CuCl, CuBr, Cu(OAc)2·H2O, Cu(MeCN)ClO4, and
Cu(OTf)2 afforded moderate to good yields and high
ee values (Table 3, entry nos. 2–3). In the presence of
20 mol % Cu(OAc)2·H2O and (4R,5S)-3b and
(4R,5S)-4b, the corresponding products were obtained
in 77 and 78% yield with 94 and 93% ee, respectively
(entry no. 5). By keeping the ligand (4R,5S)-3b and
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ENANTIOSELECTIVE ADDITION OF DIETHYLZINC TO AROMATIC ALDEHYDES
1307
Table 3. Enantioselective addition of diethylzinc to benzaldehyde (5a) in the presence of different copper salts and ligands 3b
and 4ba
(4R,5S)-3b, (4R,5S)-4b
Copper salt, PhMe, 0°C to r.t.
OH
PhCHO
+
Et2Zn
Me
Ph
5a
6a
(4R,5S)-3b
yield,b %
(4R,5S)-4b
yield,b %
Entry no.
Copper salt
None
ee,c %
ee,c %
85
1
2
3
4
5
6
7
8d
79
78
75
72
77
70
75
77
87
93
91
92
94
65
88
96
76
77
75
74
78
72
76
77
CuI
92
CuCl
90
CuBr
92
Cu(OAc)2·H2O
Cu(OTf)2
93
68
Cu(MeCN)ClO4
Cu(OAc)2·H2O
90
95
a
The reactions were carried out in toluene using 1 mmol of benzaldehyde (5a), 20 mol % of copper salt, 20 mol % of ligand 3b or 4b, and
2.2 mmol of diethylzinc (1 M solution in hexane) at 0°C to room temperature.
b Yield refers to pure product after column chromatography.
c
The ee values were determined by HPLC with a Chiralcel OD-H column.
d 10 mol % Cu(OAc)2·H2O.
Table 4. Enantioselective addition of diethylzinc to aromatic aldehydes in the presence of chiral ligand (4R,5S)-3ba
(4R,5S)-3b, Cu(OAc)2·H2O
PhMe, 0°C to r.t.
OH
ArCHO
+
Et2Zn
Me
Ar
5a–5m
6a–6m
Entry no.
Aldehyde
Product
Yield,b %
ee,c %
1
2
Benzaldehyde (5a)
6a
6b
6c
6d
6e
6f
77
80
78
75
85
75
76
72
75
68
72
83
74
96
84
89
94
80
90
90
90
92
99
86
60
83
2-Methoxybenzaldehyde (5b)
3-Methoxybenzaldehyde (5c)
4-Methoxybenzaldehyde (5d)
2-Methylbenzaldehyde (5e)
3-Methylbenzaldehyde (5f)
4-Methylbenzaldehyde (5g)
3-Chlorobenzaldehyde (5h)
4-Chlorobenzaldehyde (5i)
4-(Trifluoromethyl)benzaldehyde (5j)
Naphtalene-1-carbaldehyde (5k)
Naphtalene-2-carbaldehyde (5l)
Thiophene-2-carbaldehyde (5m)
3
4
5
6
7
6g
6h
6i
8
9
10
11
12
13
6j
6k
6l
6m
a
The reactions were carried out in toluene using 1 mmol of benzaldehyde (5a), 20 mol % of copper salt, 20 mol % of ligand 3b or 4b, and
2.2 mmol of diethylzinc (1 M solution in hexane) at 0°C to room temperature.
b Yield refers to pure product after column chromatography.
c
The ee values were determined by HPLC with a Chiralcel OD-H column.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 7 2020

AYDIN
1308
(4R,5S)-4b at 20 mol % and reducing the Cu(OAc)2·
H2O loading from 20 to 10 mol %, the enantioselec-
tivity was increased to 96 and 95% ee, respectively,
without any change in the yield (entry nos. 5, 8). Thus,
the most suitable metal-to-ligand ratio proved to be
2:1 (entry no. 8).
spectrometer (400 MHz for 1H) using CDCl3 as solvent
and tetramethylsilane as internal standard. Enantio-
meric excesses (% ee) were determined by HPLC with
an Agilent 1100 Series liquid chromatograph using
different chiral columns (see below).
Chiral ligands 3a, 3b, 4a, and 4b were synthesized
Since ligand (4R,5S)-3b showed the highest enan-
tioselectivity, it was used in the enantioselective addi-
tions of diethylzinc to different aromatic aldehydes
with electron-withdrawing and electron-donating sub-
stituents. The results are summarized in Table 4. It
appeared that the position of substituent on the phenyl
ring had significant effect on the reaction. para-Sub-
stituted substrates (entry nos. 4, 7, 9) tended to give
higher enantioselectivities. Lower ee values were
observed for aromatic aldehydes bearing substituents at
the ortho position (entry nos. 2, 5), presumably due to
steric hindrance. Electron-withdrawing substituents
(e.g., CF3; entry no. 10) gave higher enantioselectivity
than did electron-donating groups. It is known that
electron-withdrawing groups in aromatic aldehydes
increase the electrophilicity of the carbonyl carbon
atom, while electron-donating groups reduce it. Sub-
strates with an electron-withdrawing substituent were
expected to react at a higher rate, leading to higher
enantioselectivity. For instance, heteroaromatic thio-
phene-2-carbaldehyde in the presence of chiral ligand
(4R,5S)-3b afforded diethylzinc addition product with
83% ee (Table 4, entry no. 13).
according to our previous report [69] (Scheme 1).
General procedure for enantioselective addition
of diethylzinc to aromatic aldehydes. A 1.0 M solu-
tion of diethylzinc in hexane (2.2 mmol) was added via
a syringe over a period of 5 min to a solution of chiral
ligand 3a, 3b, 4a, or 4b (20 mol %) and Cu(OAc)2·H2O
(20 mol %) in dry toluene (5 mL) at 0°C under argon.
The mixture was stirred for 1 h at that temperature,
aldehyde 5a–5m (1 mmol) was added, and the mixture
was stirred for 24 h at room temperature (TLC). The
reaction was quenched with 5 mL of 1 M aqueous HCl.
The organic layer was separated, the aqueous layer was
extracted with diethyl ether (3×15 mL), and the com-
bined organic phases were washed with 10 mL of brine,
dried over anhydrous MgSO4, and evaporated under
reduced pressure. The crude product was purified by
flash column chromatography (EtOAc–hexane, 1:5).
Known compounds were characterized by comparing
their 1H NMR spectra with those given in [79–85]. The
absolute configuration of the products was assigned by
comparison with published data [79–85]. For details,
see Supplementary Materials.
(R)-1-Phenylpropan-1-ol (6a). Yield 77%, ee 96%
(Chiralcel OD-H column; eluent 10% propan-2-ol in
hexane, flow rate 0.5 mL/min; detection at λ 254 nm;
retention times 9.04 min for the R enantiomer and
11.79 min for the S enantiomer). 1H NMR spectrum, δ,
ppm: 0.94 t (3H, J =7.4 Hz), 1.71–1.88 m (2H), 1.92–
1.99 br.s (1H), 4.61 t (1H, J = 6.6 Hz, 1H), 7.26–
7.42 m (5H).
In summary, the use of chiral oxazoline ligands
containing a pyrrole ring in copper-catalyzed enantio-
selective addition of diethylzinc to aromatic aldehydes
has been reported for the first time. The reactions
provide high yields and enantioselectivities. Studies
aimed at defining the utility of these ligands for other
substrates and reactions are now in progress.
EXPERIMENTAL
(R)-1-(2-Methoxyphenyl)propan-1-ol (6b). Yield
80%, ee 84% [Chiralcel OD-H; 10% propan-2-ol in
hexane, 0.5 mL/min; λ 254 nm; 12.21 min (R),
13.77 min (S)]. 1H NMR spectrum, δ, ppm: 0.98 t (3H),
1.78–1.89 m (2H), 2.81 d (1H), 3.87 s (3H), 4.80–
4.86 m (1H), 6.88–7.37 m (4H).
All reactions were carried out under argon atmo-
sphere. Commercially available reagents and solvents
were used as received. Tetrahydrofuran and diethyl
ether were purified by distillation over sodium in the
presence of benzophenone; methylene chloride and
toluene were dried by distillation over calcium hydride.
Column chromatography was performed on silica
gel 60 (230–400 mesh). Analytical thin-layer chroma-
tography was performed on silica gel 60 F254 plates
(Merck); spots were visualized under UV light and by
(R)-1-(3-Methoxyphenyl)propan-1-ol (6c). Yield
78%, ee 89% [Chiralpak OD-H; 2% propan-2-ol in
hexane, 0.8 mL/min; λ 210 nm; 9.09 min (R),
11.97 min (S)]. 1H NMR spectrum (300 MHz), δ, ppm:
0.96 t (3H, J = 7.5 Hz), 1.75–1.89 m (3H), 3.85 s (3H),
4.61 t (1H, J = 6.5 Hz), 6.79–6.89 m (1H), 6.90–6.99 m
(2H), 7.25–7.32 m (1H).
1
staining with phosphomolybdic acid. The H and 13C
NMR spectra were recorded on a Bruker DPX 400
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ENANTIOSELECTIVE ADDITION OF DIETHYLZINC TO AROMATIC ALDEHYDES
1309
(R)-1-(4-Methoxyphenyl)propan-1-ol (6d). Yield
75%, ee 94% [Chiralpak AD-H; 2% propan-2-ol in
hexane, 0.8 mL/min; λ 210 nm; 14.26 min (R),
18.49 min (S)]. 1H NMR spectrum, δ, ppm: 0.88 t (3H),
1.63–1.90 m (2H), 2.26–2.68 br.s (1H), 3.81 s (3H),
4.51 s (1H), 6.82–7.28 m (4H).
hexane, 0.8 mL/min; λ 210 nm; 18.33 min (S),
21.41 (R)]. 1H NMR spectrum, δ, ppm: 1.05 t (3H, J =
7.5 Hz), 1.91–2.08 m (2H), 2.16 s (1H), 5.44 d.d (1H,
J = 7.5, 5.0 Hz), 7.48–7.59 m (3H), 7.67 d (1H, J =
7.1 Hz), 7.82 d (1H, J = 8.1 Hz), 7.88–7.95 m (1H),
8.11–8.18 m (1H).
(R)-1-Naphthalen-2-yl)propan-1-ol (6l). Yield
83%, ee 60% [Chiralcel AS-H; 2% propan-2-ol in
hexane, 0.8 mL/min; λ 210 nm; 9.84 min (S),
17.73 min (R)]. 1H NMR spectrum, δ, ppm: 1.02 t (3H,
J = 7.3 Hz), 1.83–2.07 m (2H), 2.96 s (1H), 5.31 t (1H,
J = 6.4 Hz), 7.43–8.16 m (7H).
(R)-1-(2-Methylphenyl)propan-1-ol (6e). Yield
85%, ee 80% [Chiralpak AD-H, 1% propan-2-ol in
hexane, 0.8 mL/min; λ 215 nm; 25.41 min (R),
30.08 min (S)]. 1H NMR spectrum, δ, ppm: 1.02 t (3H,
J = 7.4 Hz), 1.74–1.83 m (2H), 2.18 br.s (1H), 2.38 s
(3H), 4.88 t (1H), 7.12–7.51 m (4H).
(R)-1-(Thiophen-2-yl)propan-1-ol (6m). Yield
74%, ee 92% [Chiralcel OD-H; 10% propan-2-ol in
hexane, 1.0 mL/min; λ 220 nm; 32.72 min (R),
34.61 min (S)]. 1H NMR spectrum, δ, ppm: 0.97 t (3H,
J = 7.4 Hz), 1.75–1.96 m (2H), 3.15 br.s (1H), 4.79 t
(1H, J = 6.5 Hz), 6.91–7.28 m (3H).
(R)-1-(3-Methylphenyl)propan-1-ol (6f). Yield
75%, ee 90% [Chiralcel OD-H; 5% propan-2-ol in
hexane, 0.8 mL/min; λ 215 nm; 8.79 min (R),
10.14 min (S)]. 1H NMR spectrum , δ, ppm: 0.95 t (3H,
J = 7.5 Hz), 1.73–1.90 m (2H), 1.91 s (1H), 2.38 s
(3H), 4.59 t (1H, J = 6.7 Hz), 7.09–7.23 m (3H), 7.23–
7.29 m (1H).
FUNDING
(R)-1-(4-Methylphenyl)propan-1-ol (6g). Yield
76%, ee 90% [Chiralpak AD-H; 1% propan-2-ol in
hexane, 0.8 mL/min; λ 215 nm; 28.86 min (R),
33.46 min (S)]. 1H NMR spectrum, δ, ppm: 0.95 t (3H,
J = 7.5 Hz), 1.73–1.91 m (2H), 1.92 br.s (1H), 2.39 s
(3H), 4.59 t (1H, J = 6.7 Hz), 7.20 d (2H, J = 8.1 Hz),
7.27 d (2H, J = 8.1 Hz).
This research (1005M0115) is financially supported by
the Scientific Research Commission of Mustafa Kemal
University.
CONFLICT OF INTEREST
The author declares the absence of conflict of interest.
SUPPLEMENTARY MATERIALS
(R)-1-(3-Chlorophenyl)propan-1-ol (6h). Yield
72%, ee 90% [Daicel Chiralcel OJ-H; 2% propan-2-ol
in hexane, 0.8 mL/min; λ 210 nm; 8.79 min (S),
1
10.14 min (R)]. H NMR spectrum, δ, ppm: 0.93 t
Supplementary materials are available for this article at
https://doi.org/10.1134/S1070428020070271 and are acces-
sible for authorized users.
(3H, J = 7.5 Hz), 1.73–1.88 m (3H), 4.62 t (1H, J =
6.4 Hz), 7.21–7.28 m (2H), 7.28–7.34 m (1H), 7.34–
7.38 m (1H).
(R)-1-(4-Chlorophenyl)propan-1-ol (6i). Yield
75%, ee 92% [Chiralcel OD-H; 5% propan-2-ol in
hexane, 0.8 mL/min; λ 215 nm; 8.98 min (S), 9.56 min
(R)]. HNMR spectrum, δ, ppm: 0.86 t (3H, J =
7.5 Hz), 1.63–1.82 m (2H), 2.31–2.39 br.s (1H), 4.54 t
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