Aziridine ring-containing chiral ligands as highly efficient catalysts in asymmetric synthesis

Article abstract of DOI:10.1016/j.tetasy.2013.03.001

Enantiomerically pure bidentate heteroorganic ligands built on an achiral skeleton containing hydroxyl and aziridine moieties as nucleophilic centers, capable of binding various organometallic reagents, have proven to be highly efficient catalysts in the enantioselective addition of diethylzinc and phenylethynylzinc to aryl and alkyl aldehydes to give the desired chiral products in high chemical yields (up to 90%) and with ees of up to 95%. The influence of the stereogenic center located in the carbon atom in the aziridine moiety on the stereochemical course of the reaction is reported.

Full text of DOI:10.1016/j.tetasy.2013.03.001

Tetrahedron: Asymmetry 24 (2013) 421–425
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Tetrahedron: Asymmetry
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Aziridine ring-containing chiral ligands as highly efficient catalysts
in asymmetric synthesis
⇑
´
´
Michał Rachwalski , Szymon Jarzynski, Stanisław Lesniak
´
´
Department of Organic and Applied Chemistry, University of Łódz, Tamka 12, 91-403 Łódz, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 February 2013
Accepted 4 March 2013
Enantiomerically pure bidentate heteroorganic ligands built on an achiral skeleton containing hydroxyl
and aziridine moieties as nucleophilic centers, capable of binding various organometallic reagents, have
proven to be highly efficient catalysts in the enantioselective addition of diethylzinc and phenylethynyl-
zinc to aryl and alkyl aldehydes to give the desired chiral products in high chemical yields (up to 90%) and
with ees of up to 95%. The influence of the stereogenic center located in the carbon atom in the aziridine
moiety on the stereochemical course of the reaction is reported.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
ity of the ligands in the asymmetric addition of diethylzinc and
phenylethynylzinc to aldehydes.
Enantiopure compounds are interesting for synthetic organic
chemists due to the importance of chirality in industrial sectors
(e.g., pharmaceuticals and food). So far, enantioselective
carbon–carbon bond formation using organozinc reagents is com-
monly used in the synthesis of chiral non-racemic compounds.1–4
As an example, the asymmetric addition of alkynylzinc to carbonyl
compounds5 is very useful in the synthesis of chiral propargyl alco-
hols, which are important building blocks in the preparation of var-
ious natural and biologically active products.6
Previously, we have reported on a seven-step synthesis of
chiral, diastereomerically pure aminoalcohols,7 which have proven
to be very efficient catalysts in various asymmetric processes, such
as asymmetric diethyl- and phenylethynylzinc additions to alde-
hydes,8,9 enantioselective conjugate Michael additions of diethyl-
zinc to enones10 (catalysts bearing chiral aziridinyl moieties),
nitroaldol (Henry) reactions,11 aza-Henry reactions,12 asymmetric
direct aldol condensations13 and, more recently, asymmetric Man-
nich reactions14 (catalysts bearing chiral secondary amines). More-
over, it was possible to access both enantiomeric products of all the
reactions using readily available isomers of the catalysts.
2. Results and discussion
2.1. Synthesis of the ligands
In the first step of the synthesis, phthalide 1 was treated with
sodium hydroxide and then with benzoyl chloride to form com-
pound 2. The chemical yield of this process was low (26%) but sim-
ilar findings were described previously.18 The obtained 2-
benzoyloxymethylbenzoic acid 2 was then treated with thionyl
chloride in benzene at reflux in the presence of pyridine to afford
the corresponding acyl chloride 3 in 90% yield (Scheme 1).19 First,
we attempted to synthesize 2-acetoxymethylbenzoic acid but this
appeared to be too unstable for isolation (this acetoxy derivative is
described in the literature as a co-product formed in only 0.6%
yield).20
In the next step, 2-benzoyloxymethylbenzoyl chloride 3 and O-
acetylsalicyloyl chloride 4 (prepared according to the literature21
)
were subjected to reactions with enantiomerically pure aziridines
5a–c (synthesized as reported previously22) in diethyl ether at
room temperature in the presence of triethylamine to form the cor-
responding amides 6a–b and 7a–c (Scheme 2). The chemical yields
and absolute configuration of the amides are collected in Table 1.
Finally, amides 6a–b and 7a–c were reduced to the correspond-
ing aziridine alcohols 8a–b and 9a–c using a protocol reported by
Das et al.,23 which employed triethoxysilane in the presence of zinc
acetate in boiling THF (Scheme 3). It should be noted that under
these reaction conditions, deprotection of the acetyl group occurs
spontaneously, whereas deprotection of the benzoyl group re-
quires harsher conditions (NaBH4, THF/MeOH). The chemical
In continuation of the aforementioned results8–10 and having in
mind that aziridines are known to efficiently coordinate organo-
zinc compounds,15–17 we decided to synthesize a series of new li-
gands built on simple achiral skeletons (salicylic acid and 2-
hydroxymethylbenzoic acid) and containing an aziridine moiety
as an amino function. We also decided to study the catalytic activ-
⇑
Corresponding author. Tel.: +48 42 6355756.
E-mail address: mrach14@wp.pl (M. Rachwalski).
0957-4166/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetasy.2013.03.001

422
M. Rachwalski et al. / Tetrahedron: Asymmetry 24 (2013) 421–425
Table 1
HO
O
O
Synthesis of amides 6a–b and 7a–c
O
O
Entry
Amide
Yield (%)
Absolute configuration
NaOH/H2O
C6H5COCl
O
1
2
3
4
5
6a
6b
7a
7b
7c
92
96
89
89
94
(S)
(S)
(S)
(S)
(R)
2
1
SOCl2
benzene reflux
pyridine
results were obtained using ligand 8b built on the skeleton of 2-
hydroxymethylbenzoic acid bearing an (S)-2-isopropylaziridine
moiety as the amino function. Moreover, the reactions promoted
by two enantiomeric catalysts 9b and 9c led to formation of the
opposite enantiomers of the products 10a and 11a. From these re-
sults it can be seen that the stereogenic center located in the aziri-
dine moiety has a decisive influence on the stereochemistry of both
additions and hence on the absolute configuration of the products.
Cl
O
O
O
3
2.3. Asymmetric addition of diethyl- and phenylethynylzinc to
various aldehydes in the presence of ligand 8b
Scheme 1. Synthesis of 2-benzoyloxymethylbenzoyl chloride 3.
Having obtained the best results with ligand 8b, we then
decided to determine the scope of its activity. To this end, it was
used to catalyze the title transformations performed with a series
of aldehydes (Scheme 5). The results are shown in Table 4.
The results shown in Tables 3 and 4 clearly indicate that the se-
lected ligand 8b is an effective catalyst for the title reactions and
give the appropriate chiral products in good chemical yields and
ees. As mentioned earlier, each enantiomeric ligand is easily acces-
sible and leads to the formation of the opposite enantiomer of the
addition product. This means that the desired enantiomer of the
product can be obtained by choosing the appropriate enantiomeric
aziridine to synthesize an enantiomeric ligand starting from the
same achiral precursor.
yields, specific rotation values, and absolute configurations are
shown in Table 2.
2.2. Screening of the ligands
In order to determine the ability of ligands 8a–b and 9a–c to
catalyze the enantioselective addition of diethyl- and alkynylzinc
to aldehydes, we chose the addition of diethyl- and phenylethynyl-
zinc to benzaldehyde as reference transformations. The reactions
were performed under standard conditions (Scheme 4) and the re-
sults are shown in Table 3.
From Table 3 it can be seen that chiral products 10a and 11a
were formed in good chemical yields and with high ees. The best
R1
R2
R2
R1
N
O
Cl
O
O
O
N
H
, Et3N
O
O
Et2O, rt
6a-b
3
R1
R2
R2
N
O
Cl
O
R1
N
H
O
Me
O
Me
, Et3N
O
Et2O, rt
O
7a-c
4
aziridines
Pri
Me
H
Pri
H
5a (-)-(S)-2-methylaziridine
H
N
H
N
H
N
H
5b
5c
(-)-(S)-2-isopropylaziridine
(+)-(R)-2-isopropylaziridine
5c
5a
5b
Scheme 2. Synthesis of amides 6a–b and 7a–c.

M. Rachwalski et al. / Tetrahedron: Asymmetry 24 (2013) 421–425
423
R1
R1
R2
R2
R1
R2
N
N
N
O
O
O
1.(EtO)3SiH
Zn(OAc)2, THF
NaBH4
OH
O
O
MeOH
THF
2. NaOH
8a-b
8a`-b`
6a-b
R1
R1
R2
R2
N
O
N
1.(EtO)3SiH
Zn(OAc)2, THF
O
Me
OH
2. NaOH
O
9a-c
7a-c
Scheme 3. Reduction of amides to form ligands 8a–b and 9a–c.
Table 2
OH
8b
ligand , Et2Zn
Reduction of amides 6a–b and 7a–c to form ligands 8a–b and 9a–c
RCHO
a
R
Entry
Ligand
Yield (%)
[
a
]
Absolute configuration
toluene
D
1
2
3
4
5
8a
8b
9a
9b
9c
96
94
94
92
90
+21.8
ꢀ38.4
+4.5
(S)
(S)
(S)
(S)
(R)
10a-e
ꢀ42.0
OH
ligand 8b, Et2Zn
+42.0
RCHO
Ph
Ph
+
a
In chloroform (c 1).
THF
R
11a-e
OH
ligand, Et2Zn
toluene
Scheme 5. Addition of diethyl- and phenylethynylzinc to aldehydes in the presence
of ligand 8b.
PhCHO
Ph
10a
and phenylethynylzinc to aldehydes. The stereogenic centers lo-
cated in the amine moieties exerted a decisive influence on the ste-
reochemistry of the reaction and the absolute configuration of the
products. Each enantiomer of the product can be obtained by using
easily available ligands. Moreover, it should be noted that all the
ligands were built on the achiral skeletons of salicylic acid and 2-
hydroxymethylbenzoic acid.
OH
ligand, Et2Zn
THF
Ph
PhCHO
Ph
+
Ph
11a
Scheme 4. Asymmetric addition of diethyl- and phenylethynylzinc to
benzaldehyde.
4. Experimental
4.1. General
3. Conclusion
Chiral bidentate ligands containing one stereogenic center lo-
cated in the carbon atom in the aziridine moiety were found to
be efficient catalysts for the enantioselective addition of diethyl-
Unless otherwise specified, all reagents were purchased from
commercial suppliers and used without further purification. Tetra-
hydrofuran and benzene were distilled from sodium benzophe-
Table 3
Screening of ligands 8a–b and 9a–c
Entry
Ligand
Product 10a
Product 11a
a
a
Yield (%)
[
a
]
D
ee (%)b
Absolute configuration
Yield (%)
[
a
]
D
ee (%)b
Absolute configurationc
1
2
3
4
5
8a
8b
9a
9b
9c
90
93
76
85
82
ꢀ42.7
ꢀ44.1
ꢀ36.0
ꢀ40.2
+38.8
95
96
80
92
86
(S)
(S)
(S)
(S)
(R)
86
95
82
88
80
ꢀ4.8
ꢀ4.9
ꢀ3.9
ꢀ4.8
+4.3
93
95
76
93
84
(S)
(S)
(S)
(S)
(R)
a
b
c
In chloroform (c 1).
Determined using chiral HPLC.
Taken from the literature.24

424
M. Rachwalski et al. / Tetrahedron: Asymmetry 24 (2013) 421–425
Table 4
Addition of diethyl- and phenylethynylzinc to aldehydes in the presence of ligand 8b
Entry
R
Products 10a–e
Products 11a–e
a
a
Yield (%)
[
a
]
D
ee (%)b
Absolute configurationc
Yield (%)
[
a
]
D
ee (%)b
Absolute configurationc
1
2
3
4
5
Ph
93
91
82
89
80
ꢀ44.1
ꢀ47.6
+6.0
92
91
85
90
89
(S)
(S)
(S)
(S)
(S)
95
92
89
82
91
ꢀ4.9
ꢀ7.5
ꢀ3.0
+3.7
95
90
86
86
88
(S)
(R)
(S)
(R)
(R)
2-MeOC6H4
n-Pr
4-BrC6H4
2-MeC6H4
ꢀ7.9
ꢀ39.8
ꢀ11.0
a
b
c
In chloroform (c 1).
Determined using chiral HPLC.
Taken from the literature.4,8,9,25
none ketyl radical. NMR spectra were recorded on a Bruker instru-
ment at 600 MHz with CDCl3 as solvent and relative to TMS as
internal standard. Data are reported as s = singlet, d = doublet,
t = triplet, q = quartet, m = multiplet, and b = broad. Optical rota-
tions were measured on a Perkin–Elmer 241 MC polarimeter with
a sodium lamp at room temperature (c 1). Melting points were
measured on a MELTEMP apparatus and are uncorrected. Column
chromatography was carried out using Merck 60 silica gel. TLC
was performed on Merck 60 F254 silica gel plates. Visualization
was accomplished with UV light. The enantiomeric excess (ee) val-
ues were determined by chiral HPLC (Knauer, Chiralcel OD). The
enantiomerically pure aziridines 5a–c were prepared according
to the literature.22
1H), 7.42–7.48 (m, 3H), 7.52–7.59 (m, 1H), 7.57–7.61 (m, 2H),
8.01–8.02 (m, 1H), 8.08–8.09 (m, 2H).
Amide 6b (colorless oil, 1.365 g, 96%); 1H NMR (CDCl3): d = 0.96
(d, J = 7.2 Hz, 3H), 1.08 (d, J = 7.2 Hz, 3H), 1.67–1.73 (m, 1H), 2.18
(d, J = 3.6 Hz, 1H), 2.40–2.43 (m, 2H), 5.70 (d, J = 13.8 Hz, 1H),
5.78 (d, J = 13.8 Hz, 1H), 7.40–7.43 (m, 1H), 7.45–7.48 (m, 2H),
7.50–7.53 (m, 1H), 7.57–7.60 (m, 2H), 7.97–7.99 (m, 1H), 8.07–
8.09 (m, 2H).
Amide 7a (colorless oil, 1.212 g, 89%); 1H NMR (CDCl3): d = 1.35
(d, J = 5.5 Hz, 3H), 2.09 (d, J = 3.6 Hz, 1H), 2.30 (s, 3H), 2.51 (d,
J = 5.8 Hz, 1H), 2.61–2.66 (m, 1H), 7.10–7.11 (m, 1H), 7.32–7.35
(m, 1H), 7.53–7.59 (m, 1H), 7.96–7.97 (m, 1H).
Amide 7b (1.212 g, 89%); 1H NMR (CDCl3): d = 0.96 (d, J = 6.8 Hz,
3H), 1.02 (d, J = 6.8 Hz, 3H), 1.65–1.71 (m, 1H), 2.12 (d, J = 3.6 Hz,
1H), 2.26 (s, 3H), 2.37 (d, J = 6.0 Hz, 1H), 2.44–2.46 (m, 1H), 7.07–
7.08 (m, 1H), 7.28–7.31 (m, 1H), 7.49–7.52 (m, 1H), 7.93–7.94
(m, 1H).
4.2. Synthesis of ligands 8a–b and 9a–c
4.2.1. Synthesis of 2-benzoyloxymethylbenzoyl chloride 319
Phthalide 1 (10 g, 0,074 mol) was dissolved in 20% NaOH
(54 mL, 0.26 mol) and the solution was heated at 60 °C for
30 min. Next, water (440 mL) was added and after 10 min of vigor-
ous stirring, benzoyl chloride (11.2 mL, 0.096 mol) was added. The
mixture was stirred and after 1 h was diluted with water (440 mL).
Next, 10% HCl was added to reach pH 2 (around 70 mL). The white
precipitate was filtered off under reduced pressure and crystallized
from the mixture of ethanol and water to afford 2-benzoyloxym-
ethylbenzoic acid 2 in 26% yield (5.6 g) as colorless crystals,
mp = 130–131 °C; 1H NMR (CDCl3)19: d = 5.71 (s, 2H), 7.48–7.56
(m, 3H), 7.60–7.66 (m, 1H), 7.66–7.70 (m, 2H), 8.12–8.14 (m,
2H), 8.33 (s, 1H).
To a suspension of 2-benzoyloxymethylbenzoic acid 2 (2.41 g,
9.4 mmol) in toluene (4 mL), pyridine (0.74 g, 9.4 mmol) and thio-
nyl chloride (10 mL) were added. The mixture was heated at 80 °C
on an oil bath for 20 min after which it was cooled to room temper-
ature and concentrated in vacuo. The solid residue was extracted
with dry hexane (3 ꢁ 25 mL) and, after concentration in vacuo,
the crude product was recrystallized from petroleum ether to yield
Amide 7c (colorless oil, 1.28 g, 94%); 1H NMR (CDCl3): d = 0.96
(d, J = 6.8 Hz, 3H), 1.02 (d, J = 6.8 Hz, 3H), 1.65–1.71 (m, 1H), 2.12
(d, J = 3.6 Hz, 1H), 2.26 (s, 3H), 2.37 (d, J = 6.0 Hz, 1H), 2.44–2.46
(m, 1H), 7.07–7.08 (m, 1H), 7.28–7.31 (m, 1H), 7.49–7.52 (m,
1H), 7.93–7.94 (m, 1H).
4.2.3. Reduction of amides 6a–b and 7a–c to form chiral ligands
8a–b and 9a–c—general procedure
In a round-bottomed flask, zinc acetate (0.64 g, 3.5 mmol), tri-
ethoxysilane (2.296 g, 14 mmol), and freshly distilled dry THF
(10 mL) were mixed. The mixture was stirred for 30 min under ar-
gon followed by the addition of the corresponding amide
(3.5 mmol) in THF (6 mL). The mixture was refluxed on an oil bath
and after 6 h was cooled to room temperature and treated with
1 M NaOH (10 mL). After 3 h of stirring, the mixture was extracted
with ethyl acetate (4ꢁ), and the combined organic phases were
dried over anhydrous Na2SO4 and concentrated in vacuo to afford
the crude products which after recrystallization from a mixture
of diethyl ether and hexane gave the final ligand structures 9a–c.
In order to reduce amides 6a–b to aziridine alcohols 8a–b, an addi-
tional protocol was required, which included deprotection of the
hydroxymethyl group. The crude products 8a0–b0 were dissolved
in THF (4 mL) and NaBH4 (0.11 g, 2.89 mmol) was added. The mix-
ture was heated at reflux and dry methanol was added carefully.
After heating for 2 h, the mixture was cooled to room temperature
and water was added, THF was evaporated and the residue was ex-
tracted with ethyl acetate. The combined organic layers were dried
over anhydrous Na2SO4 and the solvent was removed in vacuo. The
resulting oil was dissolved in methanol (3 mL), after which sodium
methoxide (3 mL) was added and the mixture was refluxed for 2 h.
Then, methanol was removed in vacuo, water was added and the
mixture was extracted with ethyl acetate, dried over anhydrous
Na2SO4 and after concentration on a rotary evaporator the final li-
gands 8a–b were obtained. Chemical yields, specific rotation val-
ues, and absolute configurations of all of the ligands 8a–b and
9a–c are shown in Table 2.
2-benzoyloxymethylbenzoyl chloride
3 as colorless crystals
(1.44 g, 56%), mp = 50–52 °C; 1H NMR (CDCl3): d = 5.71 (s, 2H),
7.48–7.56 (m, 3H), 7.60–7.66 (m, 1H), 7.66–7.70 (m, 2H), 8.12–
8.14 (m, 2H), 8.33 (s, 1H).
4.2.2. Synthesis of amides 6a–b and 7a–c—general procedure
In a round-bottomed flask aziridine (3 mmol), triethylamine
(3 mmol), and diethyl ether (30 mL) were placed. The mixture
was cooled to 0 °C using an ice bath and the corresponding acyl
chloride (3 mmol) in Et2O was added dropwise. After 30 min of
stirring at room temperature, the precipitate was filtered off and
the filtrate was concentrated on a rotary evaporator to yield the
corresponding amides 6a–b and 7a–c.
Amide 6a (colorless oil, 1.007 g, 92%); 1H NMR (CDCl3): d = 1.35
(d, J = 5.5 Hz, 3H), 2.13 (d, J = 3.6 Hz, 1H), 2.53 (d, J = 5.8 Hz, 1H),
2.53–2.61 (s, 1H), 5.70 (d, J = 13.8 Hz, 1H), 5.78 (d, J = 13.8 Hz,

M. Rachwalski et al. / Tetrahedron: Asymmetry 24 (2013) 421–425
425
Ligand 8a (colorless crystals, 0.58 g, 96%), mp = 54–55 °C; 1H
4.4. Asymmetric addition of phenylethynylzinc to aldehydes—
general procedure9
NMR (CDCl3): d = 1.14 (d, J = 5.4 Hz, 3H), 1.47 (d, J = 6.4 Hz, 1H),
1.58 (d, J = 3.8 Hz, 1H), 1.65–1.69 (m, 1H), 3.46 (d, J = 12.6 Hz,
1H), 3.57 (d, J = 12.6 Hz, 1H), 4.70 (d, J = 12.0 Hz, 1H), 4.73 (d,
J = 12.0 Hz, 1H), 7.13–7.15 (m, 1H), 7.26–7.29 (m, 1H), 7.32–7.34
(m, 1H), 7.39–7.41 (m, 1H); 13C NMR (CDCl3): d = 17.9 (CH3), 34.5
(CH), 35.0 (CH2), 63.7 (CH2), 64.5 (CH2), 127.9 (CHar), 128.3 (CHar),
129.8 (CHar), 130.2 (CHar), 137.7 (Cq ar), 141.4 (Cq ar); MS (CI): m/z
177 (M+H); HRMS (CI): calcd for C11H15NO: 177.0429; found
177.0428.
To a solution of ligand 8a–b or 9a–c (0.2 mmol) in THF (5 mL),
was added a solution of diethylzinc (1.4 mL, 1.4 mmol, 1.0 M in
hexane) at room temperature under argon. After the mixture was
stirred at ambient temperature for 30 min, phenylacetylene
(0.154 mL, 1.4 mmol) was added, and stirring was continued for
another 30 min. The solution was cooled to 0 °C (ice bath) and trea-
ted with the corresponding aldehyde (1 mmol). The resultant mix-
ture was stirred for 2 h at 0 °C and then overnight at room
temperature. After completion of the reaction (TLC), it was
quenched by 5% aqueous HCl. The resulting mixture was extracted
with diethyl ether and the combined organic phases were washed
with brine, dried over anhydrous MgSO4 and the solvent was re-
moved in vacuo. The residue was purified by column chromatogra-
phy (silica gel, ethyl acetate with hexane in gradient) to afford the
corresponding products 11a–e. Yields, specific rotations, enantio-
meric excess values, and absolute configurations of the products
11a–e are shown in Table 4. The spectroscopic data are in full
agreement with those reported in the literature.4,8,9,24
Ligand 8b (colorless crystals, 0.574 g, 94%), mp = 70–71 °C; 1H
NMR (CDCl3): d = 0.75 (d, J = 6.8 Hz, 3H), 0.86 (d, J = 6.8 Hz, 3H),
1.21–1.27 (m, 1H), 1.37–1.40 (m, 1H), 1.47 (d, J = 6.6 Hz, 1H),
1.69 (d, J = 3.8 Hz, 1H), 3.34 (d, J = 12.2 Hz, 1H), 3.67 (d,
J = 12.2 Hz, 1H), 4.68 (d, J = 12.0 Hz, 1H), 4.77 (d, J = 12.0 Hz, 1H),
7.13–7.14 (m, 1H), 7.26–7.29 (m, 1H), 7.31–7.34 (m, 1H), 7.40–
7.41 (m, 1H); 13C NMR (CDCl3): d = 19.4 (CH3), 19.8 (CH3), 30.9
(CH), 32.7 (CH2), 46.7 (CH), 63.9 (CH2), 64.6 (CH2), 127.8 (CHar),
128.3 (CHar), 129.9 (CHar), 130.2 (CHar), 137.8 (Cq ar), 141.3 (Cq
ar); MS (CI): m/z 206 (M+H); HRMS (CI): calcd for C13H19NO:
206.0358; found 206.0357.
Ligand 9a (colorless crystals, 0.54 g, 94%), mp = 42–43 °C; 1H
NMR (CDCl3): d = 1.23 (d, J = 5.4 Hz, 3H), 1.47 (d, J = 6.4 Hz, 1H),
1.63–1.67 (m, 1H), 1.70 (d, J = 4.2 Hz, 1H), 3.60 (d, J = 13.8 Hz,
1H), 3.63 (d, J = 13.8 Hz, 1H), 6.78–6.81 (m, 1H), 6.88–6.92 (m,
2H), 7.18–7.21 (m, 1H); 13C NMR (CDCl3): d = 17.7 (CH3), 34.8
(CH), 35.3 (CH2), 63.1 (CH2), 116.6 (CHar), 118.9 (CHar), 122.9 (CHar),
127.9 (CHar), 128.6 (CHar), 157.6 (Cq ar); MS (CI): m/z 164 (M+H);
HRMS (CI): calcd for C10H13NO: 164.1163; found 164.1161.
Ligand 9b (colorless crystals, 0.526 g, 92%), mp = 28–29 °C; 1H
NMR (CDCl3): d = 0.92 (d, J = 3.6 Hz, 3H), 0.93 (d, J = 3.6 Hz, 3H),
1.38–1.44 (m, 3H), 1.79 (d, J = 3.6 Hz, 1H), 3.74 (d, J = 13.8 Hz,
1H), 3.82 (d, J = 13.8 Hz, 1H), 6.78–6.81 (m, 1H), 6.88–6.92 (m,
2H), 7.18–7.21 (m, 1H); 13C NMR (CDCl3): d = 19.3 (CH3), 19.9
(CH3), 30.6 (CH), 32.5 (CH2), 46.9 (CH), 63.4 (CH2), 116.6 (CHar),
118.9 (CHar), 123.1 (CHar), 127.9 (CHar), 128.6 (CHar), 157.6 (Cq
ar); MS (CI): m/z 192 (M+H); HRMS (CI): calcd for C12H17NO:
192.0256; found 192.0257.
Acknowledgements
Financial support by the National Science Centre (NCN), Grant
No. 2012/05/D/ST5/00505 for M.R., is gratefully acknowledged.
The scientific award of the Foundation of University of Łódz for
´
M.R. is also acknowledged.
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