Highly enantioselective addition of arylzinc reagents to aldehydes promoted by chiral aziridine alcohols

Article abstract of DOI:10.1016/j.tetasy.2016.10.005

Enantiomerically pure, chiral secondary and tertiary aziridine alcohols have proven to be highly efficient catalysts for enantioselective asymmetric additions of arylzinc species to aldehydes leading to products in high chemical yields (up to 90%) and with ee's up to 90%. The influence of the stereogenic centers located at the aziridine subunit on the stereochemical course of the reaction is discussed.

Full text of DOI:10.1016/j.tetasy.2016.10.005

Tetrahedron: Asymmetry xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Highly enantioselective addition of arylzinc reagents to aldehydes
promoted by chiral aziridine alcohols
⇑
´
´
Zuzanna Wujkowska, Szymon Jarzynski, Adam M. Pieczonka, Stanisław Lesniak, Michał Rachwalski
´
´
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:
Enantiomerically pure, chiral secondary and tertiary aziridine alcohols have proven to be highly efficient
catalysts for enantioselective asymmetric additions of arylzinc species to aldehydes leading to products
in high chemical yields (up to 90%) and with ee’s up to 90%. The influence of the stereogenic centers
located at the aziridine subunit on the stereochemical course of the reaction is discussed.
Ó 2016 Elsevier Ltd. All rights reserved.
Received 9 September 2016
Accepted 7 October 2016
Available online xxxx
1. Introduction
Superchi et al. applied catalysts with 1,10-binaphthylazepine skele-
ton for this reaction.19 On the other hand, simple amine alcohols
The enantioselective preparation of new carbon–carbon bonds
is one of the most important and fundamental strategies in modern
organic chemistry.1 Among them, the enantioselective aryl transfer
to aldehydes is a current topic in synthetic organic chemistry.2
Diarylmethanols are precursors of many compounds that exhi-
bit biological and pharmacological activity.3–5 For example, this
moiety can be found in the structure of (R)-orphenadrine, (R)-
neobenodine,6 and (S)-cetirizine7 (Fig. 1), which display antihis-
taminic and anticholinergic action. (S)-BMS 184394 (Fig. 1) is
active against breast cancer and leukemia.8,9 Moreover, com-
pounds possessing a chiral diarylmethane nucleus have been found
to behave as antimuscarinics10 and antidepressants.11 Therefore,
their synthesis remains an important issue. In contrast to the addi-
tion of alkylzinc compounds to aldehydes, the addition of arylzinc
derivatives is still a big challenge.
based on cyclohexylamine or pyrrolidine were introduced by Zhao
et al.,20 Bolm et al.21 and other researchers.22–24
On the basis of the aforementioned results and in order to con-
tinue our studies on stereocontrolled reactions for the formation of
carbon–carbon bonds,25–29 we decided to utilize a series of previ-
ously synthesized secondary and tertiary aziridine alcohols as cat-
alysts for the enantioselective synthesis of diarylmethanols. The
asymmetric aryl transfer reaction to aldehydes will be performed
via two independent methods. In the first method (Knochel’s
method), a diarylzinc species will be generated in situ from an aryl
iodide with ZnEt2 in the presence of Li(acac) and N-methyl-2-
pyrrolidone (NMP).30 The second one, described by Bolm et al.,31
involves the in situ formation of arylzinc systems from arylboronic
acids and diethylzinc.
In 1997, Fu et al. reported the first enantioselective catalytic
addition of diphenylzinc to an aldehyde but with only 57% ee.12
Over the last few years, both catalysts and methodologies for con-
ducting such reactions have been modified, allowing diaryl-
methanols to be obtained in good yields and with high
enantiomeric excess.3,13–15 However, the search for efficient cata-
lysts for these reactions is still an important issue. Until now, the
most extensively applied catalysts, which gave the best results,
were modified 1,1-bi-2-naphthols (BINOLs). In 2002 Ha et al.
reported on the preparation of binaphthyl-based amine alcohols
and their applications in asymmetric diphenylzinc addition to
aldehydes.16 A few years later, Pu et al. described the use of BINOL
derivatives in asymmetric arylzinc addition to aldehydes.17,18 Also,
2. Results and discussion
2.1. Chiral aziridine alcohols used as catalysts
Chiral aziridine alcohols used as catalysts for the title reaction
can be divided into two groups: secondary aziridine alcohols
1a–d derived from (S)-(+)-mandelic acid (Fig. 2),32 and second, var-
ious secondary and tertiary aziridine alcohols 2–9 synthesized as
described previously (except compound 9 synthesized herein for
the first time) through several steps starting from
L- or D-serine
(Fig. 3).33,34
2.2. Knochel’s method: screening of the catalysts
All of the aforementioned aziridine alcohols were tested as
chiral catalysts in the asymmetric addition of arylzinc species
⇑
Corresponding author.
E-mail address: mrach14@wp.pl (M. Rachwalski).
http://dx.doi.org/10.1016/j.tetasy.2016.10.005
0957-4166/Ó 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Wujkowska, Z.; et al. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.10.005

2
Z. Wujkowska et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
CO2H
O
NMe2
HO
N
N
O
HO2C
Me
(S)-BMS-184394
Cl
2-Me: (R)-orphenandrine
4-Me: (R)-neobenodine
Cetirizine; Virlix; Cetryn; Zirtek;
NMe2
O
O
N
CO2H.PhSO3H
N
N
Cl
Bepotastine besilate
Cl
Carbinoxamine
Figure 1. Diarylmethane-based drugs.
OH
OH
Ph
N
R2
R1
I
1. Et2Zn, Li(acac), NMP, 0 oC, 12 h
2. Cat. (20 mol%), THF, 0 oC, 1h
3. Benzaldehyde, rt
1
OMe
OMe
10
11
aziridines
I
Pri
H
Me
Me
Me
OH
Ph
Pri
a
H
) 2,2`-dimethylaziridine
H
N
H
N
H
N
H
N
H
MeO2C
b) (-)-(S)-2-methylaziridine
c
) (-)-(S)-2-isopropylaziridine
12
MeO2C
d) (+)-(R)-2-isopropylaziridine
a
d
b
c
13
Figure 2. Chiral aziridine alcohols 1 derived from (S)-(+)-mandelic acid.
Scheme 1. Asymmetric addition of arylzinc species to benzaldehyde.
generated in situ from m-iodoanisole 10 and methyl p-iodoben-
zoate 12 to benzaldehyde, following the procedure described by
Pu et al. (Scheme 1).17 The results are shown in Table 1.
opposite configuration (Table 1, entries 3, 4 and 8, 9). Based on this
phenomenon, we can assume that aziridine ring has a decisive
influence on the stereochemistry of the addition reaction. Hence,
by using both isomeric catalysts, we were able to have access to
both enantiomeric addition products.
From Table 1 it can be seen that catalysts 1 derived from (S)-(+)-
mandelic acid are prone to efficiently catalyze the title reaction
except for ligand 1a, which bears an achiral 2,2-dimethylaziridine
subunit (Table 1, entry 1). Lower chemical yield and ee for the reac-
tions promoted by the 1a system have been observed previ-
ously.29,32 The best results in terms of the yield and enantiomeric
excess were obtained using catalysts 1c bearing an (S)-2-isopropy-
laziridine moiety (Table 1, entry 3). However, compounds 2–9
2.3. Knochel’s method: reactions of various aldehydes in the
presence of catalyst 1c
With the most active aziridine alcohol 1c in hand, we decided to
use it in order to catalyze an asymmetric arylzinc additions to var-
ious aromatic and aliphatic aldehydes (Scheme 2). The results are
summarized in Table 2.
From the results in Table 2, it can be seen that aziridine alcohol
1c is an efficient catalyst for the enantioselective addition of
arylzinc generated from in situ from m-iodoanisole and methyl
p-iodobenzoate to aldehydes, leading to the desired products in
high chemical yields and with high enantiomeric excess values.
derived from L- and D-serine exhibited only moderate catalytic
activity leading to desired chiral adducts in yields ranging from
23% to 55% and with similar values of ee. It should be also men-
tioned that the use of ligands 1c, 1d and 5, 6, which have an oppo-
site absolute configuration at the carbon atom located in the
aziridine subunit, led to the formation of the products also with
2.4. Asymmetric addition of arylzinc systems generated from
phenylboronic acid and diethylzinc to p-tolualdehyde:
screening of the catalysts
OH
OH
Ph
Ph
Ph
Ph
Ph
Bn
OH
OH
N
N
N
N
Trt
Trt
H
Trt
Aziridine alcohols 1a-d derived from (S)-(+)-mandelic acid and
3–9 obtained from L- or D-serine were tested in terms of their
5
4
3
2
catalytic activity in the asymmetric addition of arylzinc system
generated in situ from phenylboronic acid and diethylzinc to p-
tolualdehyde following the general protocol described previously
(Scheme 3).31,40 We did not use aziridine alcohol 2 for this reaction
since Ryberg and Hartwig described its efficient action in the syn-
thesis of diarylmethanols,41 and Carlos et al. elaborated upon the
use of 2 in the asymmetric arylation of aliphatic aldehydes.42 Addi-
tionally, in the case of our catalysts, the reaction mixtures were
F
OH
CF3
OH
OH
OH
Bn
Bn
Bn
N
N
N
N
Trt
Trt
Trt
Trt
F
CF3
9
8
7
6
Figure 3. Aziridine alcohols 2–9 derived from L- or D-serine.
Please cite this article in press as: Wujkowska, Z.; et al. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.10.005

Z. Wujkowska et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
3
Table 1
Asymmetric addition of arylzinc systems generated from m-iodoanisole 10 and methyl p-iodobenzoate 12 to benzaldehyde
Entry
Ligand
Product 11
ee [%]b
Product 13
ee [%]b
a
a
Yield [%]
[
a
]
D
Abs. conf.c
Yield [%]
[
a
]
D
Abs. conf.c
1
2
3
4
5
6
7
8
1a
1b
1c
1d
2
3
4
5
6
52
85
92
90
35
23
30
38
37
41
43
46
ꢀ9.7
49
86
92
91
31
29
28
41
43
47
49
53
(R)
(R)
(R)
(S)
(R)
(R)
(R)
(R)
(S)
(R)
(R)
(R)
55
87
94
91
38
27
32
41
39
45
52
55
ꢀ14.0
ꢀ25.2
ꢀ28.5
+27.5
ꢀ12.1
ꢀ9.6
46
82
92
89
40
32
35
43
47
51
55
53
(R)
(R)
(R)
(S)
(R)
(R)
(R)
(R)
(S)
(R)
(R)
(R)
ꢀ17.0
ꢀ18.2
+17.9
ꢀ6.1
ꢀ5.7
ꢀ5.5
ꢀ8.1
+8.5
ꢀ10.9
ꢀ13.4
+14.5
ꢀ15.8
ꢀ17.0
ꢀ16.5
9
10
11
12
7
8
9
ꢀ9.3
ꢀ9.7
ꢀ10.5
a
b
c
In chloroform (c 1).
Determined by chiral HPLC using Chiralpak AD-H column.
Taken from the literature17 (on the basis of the sign of the specific rotation and retention times in HPLC chromatograms).
OH
2.5. Asymmetric addition of arylzinc systems generated from
phenylboronic acid and diethylzinc to aldehydes in the
presence of catalyst 7
I
R
1. Et2Zn, Li(acac), NMP, 0 oC, 12 h
2. 1c (20 mol%), THF, 0 oC, 1h
3. RCHO, rt
OMe
OMe
The aziridine alcohol 7 derived from L-serine, which exhibited
10
14-17
the highest catalytic activity in the testing reaction, was chosen
to catalyze the addition reactions of the arylzinc system to various
aldehydes under the same conditions (Scheme 4). The results are
shown in Table 4.
The results clearly indicate that aziridine alcohol 7 is an effi-
cient chiral catalyst for the enantioselective addition of arylzinc
system to aromatic aldehydes, leading to the corresponding prod-
ucts 23–26 in high chemical yields and with high enantiomeric
excess.
I
OH
R = 4-MeC6H4 14 and 18
15
19
and
R = 4-ClC6H4
R = i-Pr 16 and 20
17 21
R
MeO2C
R = Cy
and
12
MeO2C
18-21
Scheme 2. Asymmetric addition of the arylzinc species to various aldehydes in the
presence of catalyst 1c.
3. Conclusions
additionally stirred for 24 h at room temperature after the addition
of the aldehyde.
The chiral aziridine alcohols derived from commercially avail-
able (S)-(+)-mandelic acid and from L- or D-serine have proven to
The results of the asymmetric transformations are summarized
in Table 3.
be efficient catalysts for the asymmetric addition of arylzinc sys-
tems generated in situ both from aryl iodides and phenylboronic
acid with diethylzinc to aldehydes. The stereogenic centers located
at the aziridine moiety exerted a decisive influence on the stereo-
chemical outcome of the aforementioned arylzinc addition reac-
tion. Each enantiomer of the desired product can be obtained
using the respective ligands. On the basis of the comparison of
the results from Tables 1 and 3, we are able to conclude that chiral
aziridine alcohols derived from (S)-(+)-mandelic acid are more
effective in the addition of arylzinc systems generated from aryl
iodides, however, compounds synthesized from serine exhibited
higher catalytic activity in the addition of the arylzinc species
formed from phenylboronic acid. Overall we have shown that the
From Table 3 it can be seen that catalysts 1a–d derived from (S)-
(+)-mandelic acid are less effective (entries 1–4) leading to the
addition product 22 in low chemical yields and also with low
ee’s. Secondary aziridine alcohols 3–6 exhibited moderate catalytic
activity leading to the product 22 with yields and ee’s around 50–
60%. However, tertiary alcohols 7–9 were the most active chiral
catalysts promoting the formation of chiral adduct 22 with chem-
ical yields and enantiomeric excesses of approximately 90%. It
should be also stressed that similar to the results from Knochel’s
method, the use of catalysts 1c, 1d and 5, 6 with an opposite abso-
lute configuration at carbon atom located in aziridine subunit, led
to the formation of products also with an opposite configuration
(Table 3, entries 3, 4 and 8, 9).
Table 2
Asymmetric addition of arylzinc systems to aldehydes in the presence of catalyst 1c
Entry
R
Products 14–17
Products 18–21
ee [%]b
Abs. conf.c
Yield [%]
[
a
]
D
ee [%]b
Abs. conf.c
a
a
Yield [%]
[
a
]
D
1
2
3
4
4-MeC6H4
4-ClC6H4
i-Pr
92
93
85
86
+23.0
ꢀ1.4
90
92
87
89
(R)
(R)
(R)
(R)
93
91
86
88
+4.8
92
91
89
90
(R)
(R)
(R)
(R)
ꢀ9.0
+35.0
+16.3
+37.5
+19.5
Cy
a
b
c
In chloroform (c 1).
Determined by chiral HPLC using Chiralpak AD-H column.
Taken from the literature17,35–39 (on the basis of the sign of the specific rotation and retention times in HPLC chromatograms).
Please cite this article in press as: Wujkowska, Z.; et al. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.10.005

4
Z. Wujkowska et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
1. ZnEt2, toluene, 60 oC, 15 min.
2. Cat. (10 mol%), toluene, rt, 15 min.
3. p-Tolualdehyde, rt, 24 h
26.5 (CH3), 36.0 (Cq), 41.2 (CH2), 61.3 (CH2), 72.5 (CH), 125.9 (Car),
OH
B(OH)2
126.0 (Car), 127.4 (Car), 128.3 (Car), 142.4 (Cq ar) (as a superposition
for invertomers); minor invertomer d = 17.3 (CH3), 26.7 (CH3), 35.4
(CH), 41.8 (CH2), 60.7 (CH2), 73.9 (CH), 125.6 (Car), 126.3 (Car), 127.8
(Car), 128.9 (Car), 142.4 (Cq ar) (as a superposition for invertomers);
MS (CI): m/z 192 (M+H); HRMS (CI): calcd for C12H18NO: 192.1384;
found 192.1388.
22
Scheme 3. Asymmetric addition of arylzinc generated from phenylboronic acid and
Et2Zn to p-tolualdehyde.
Catalyst 1b (colorless oil); 1H NMR (CDCl3): d = 1.13 (d,
J = 5.4 Hz, 3H), 1.27 (d, J = 6.6 Hz, 2H), 1.43–1.47 (m, 1H), 1.50 (d,
J = 3.6 Hz, 1H), 2.28 (dd, J = 3.6 Hz, 12.0 Hz, 1H), 2.69 (dd,
J = 9.0 Hz, 12.0 Hz, 1H), 4.82 (dd, J = 3.6 Hz, 9.0 Hz, 1H), 7.25–7.38
(m, 5H); 13C NMR (CDCl3): d = 18.2 (CH3), 34.2 (CH2), 35.0 (CH),
68.4 (CH2), 72.9 (CH), 125.90 (2Car), 127.5 (Car), 128.3 (Car), 142.2
(Cq ar); MS (CI): m/z 178 (M+H); HRMS (CI): calcd for C11H16NO:
178.1236; found 178.1232.
enantioselective arylation of aromatic aldehydes may be effec-
tively catalyzed by aziridine alcohols.
4. Experimental
4.1. General
Catalyst 1c (colorless oil); 1H NMR (CDCl3): d = 0.91 (d,
J = 6.6 Hz, 3H), 1.01 (d, J = 6.6 Hz, 3H), 1.28–1.32 (m, 2H), 1.60 (d,
J = 3.2 Hz, 2H), 2.10 (dd, J = 3.0 Hz, 12.0 Hz, 1H), 2.81 (dd,
J = 10.0 Hz, 12.0 Hz, 1H), 3.39 (br s, 1H), 4.80 (dd, J = 3.6 Hz,
10.0 Hz, 1H), 7.25–7.28 (m, 2H), 7.32–7.37 (m, 3H); 13C NMR
(CDCl3): d = 19.3 (CH3), 20.2 (CH3), 31.4 (CH), 32.6 (CH2), 46.1
(CH), 69.1 (CH2), 73.0 (CH), 125.9 (2Car), 127.5 (Car), 128.3 (Car),
142.0 (Cq ar); MS (CI): m/z 206 (M+H); HRMS (CI): calcd for
Toluene and tetrahydrofuran were distilled from a sodium ben-
zophenone ketyl radical. 1H, 13C and 19F NMR spectra were
recorded on a Bruker instrument at 600 MHz and 200 MHz, respec-
tively, with CDCl3 as solvent and TMS as internal standard. Data are
reported as s = singlet, d = doublet, t = triplet, q = quartet, m = mul-
tiplet, br s = broad singlet. Optical rotations were measured on a
Perkin-Elmer 241 MC polarimeter with a sodium lamp at room
temperature (c 1). 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
(254 nm) or using iodine vapors. The enantiomeric excess (ee) val-
ues were determined by chiral HPLC (Chiralcel AD-H column).
Aziridines a–d were prepared according to the literature
procedure.44
C
13H20NO: 206.1552; found 206.1545.
Catalyst 1d (colorless oil); 1H NMR (CDCl3): d = 0.95 (d,
J = 6.6 Hz, 3H), 1.06 (d, J = 6.6 Hz, 3H), 1.25–1.30 (m, 2H), 1.60 (d,
J = 3.0 Hz, 2H), 2.10 (dd, J = 3.0 Hz, 12.0 Hz, 1H), 2.81 (dd,
J = 10.0 Hz, 12.0 Hz, 1H), 3.63 (br s, 1H), 4.79 (dd, J = 3.0 Hz,
10.0 Hz, 1H), 7.24–7.27 (m, 2H), 7.31–7.37 (m, 3H); 13C NMR
(CDCl3): d = 19.6 (CH3), 20.4 (CH3), 31.3 (CH), 32.9 (CH2), 46.7
(CH), 68.8 (CH2), 73.1 (CH), 125.9 (Car), 127.4 (Car), 128.3 (2Car),
141.9 (Cq ar); MS (CI): m/z 206 (M+H); HRMS (CI): calcd for
4.2. Synthesis of the catalysts
C13H20NO: 206.1544; found 206.1544.
Aziridine alcohols 2 and 3 were synthesized as described previ-
Aziridine alcohols 1a–d derived from (S)-(+)-mandelic acid
were synthesized according to the protocol previously described.32
For the sake of convenience, the spectroscopic data of 1a–d are
listed below while copies of the NMR spectra are included in the
Supporting information.
Catalyst 1a (as almost equimolar mixture of invertomers) (col-
orless oil); 1H NMR (CDCl3): first invertomer d = 1.10 (s, 3H), 1.15
(s, 3H), 1.75 (s, 3H), 2.52 (dd, J = 9.0 Hz, 12.0 Hz, 1H), 2.77 (dd,
J = 3.6 Hz, 12.0 Hz, 1H), 3.64 (br s, 1H), 4.73 (dd, J = 3.6 Hz, 9.0 Hz,
1H), 7.25–7.28 (m, 2H), 7.32–7.39 (m, 3H); second invertomer
d = 1.16 (s, 3H), 1.19 (s, 3H), 1.21 (s, 3H), 1.77 (s, 1H), 2.31 (dd,
J = 3.6 Hz, 12.0 Hz, 1H), 2.78 (dd, J = 8.4 Hz, 12.0 Hz, 1H), 3.94 (br
s, 1H), 4.78 (dd, J = 3.6 Hz, 8.4 Hz, 1H), 7.25–7.28 (m, 2H), 7.32–
7.39 (m, 3H); 13C NMR (CDCl3): major invertomer d = 17.6 (CH3),
ously.33 For the sake of convenience, the spectroscopic data of 2
and 3 are listed below while copies of the NMR spectra are
included in the Supporting information.
Alcohol 2: 1H NMR (CDCl3): d = 1.36 (d, J = 6.2 Hz, 1H), 2.10 (d,
J = 3.1 Hz, 1H), 2.39 (dd, J = 6.2, 3.1 Hz, 1H), 4.45 (s, 1H), 7.13–
7.22 (m, 15H), 7.32–7.35 (m, 8H), 7.45 (d, J = 7.4 Hz, 2H); 13C
NMR (CDCl3): d = 23.9 (CH2), 41.6 (CH), 74.1, 74.0 (Cq), 125.9
(Car), 126.3 (Car), 126.7 (Car), 126.8 (Car), 126.8 (Car), 127.4 (Car),
127.8 (Car), 128.0 (Car) 129.3 (Car), 143.7 (Cq ar), 145.6 (Cq ar),
145.6 (Cq ar), 147.1 (Cq ar). Other spectroscopic data of 2 in agree-
ment with literature.33
Alcohol 3: 1H NMR (CDCl3): d = 1.76 (d, J = 3.6 Hz, 1H), 1.88 (d,
J = 6.0 Hz, 1H), 2.94 (dd, J = 6.0, 3.6 Hz, 1H), 7.24–7.27 (m, 2H),
Table 3
Asymmetric addition of arylzinc systems generated from phenylboronic acid and Et2Zn to p-tolualdehyde
Entry
Ligand
Product 22
ee [%]b
Abs. conf.c
a
Yield [%]
[a]
D
1
2
3
4
6
7
8
9
1a
1b
1c
1d
3
4
5
6
7
14
21
24
23
36
64
64
62
89
87
85
ꢀ1.40
ꢀ2.20
ꢀ2.40
+2.03
ꢀ4.55
ꢀ3.75
ꢀ4.62
+4.40
ꢀ7.64
ꢀ7.64
ꢀ7.00
17
27
29
25
56
46
56
53
93
93
86
(S)
(S)
(S)
(R)
(S)
(S)
(S)
(R)
(S)
(S)
(S)
10
11
12
8
9
a
b
c
In chloroform (c 1).
Determined by chiral HPLC using Chiralcel AD-H column.
Taken from the literature41 (on the basis of the sign of the specific rotation and retention times in HPLC chromatograms).
Please cite this article in press as: Wujkowska, Z.; et al. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.10.005

Z. Wujkowska et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
5
Alcohol 7 (colorless solid), mp. 69–70 °C; 1H NMR (CDCl3):
d = 0.92 (d, J = 6.2 Hz, 1H), 1.43–1.44 (1H, m), 1.53–1.55 (1H, m),
2.65 (d, J = 13.8 Hz, 1H), 2.66 (d, J = 13.8 Hz, 1H), 2.82 (d,
J = 13.8 Hz, 1H), 2.99 (d, J = 13.8 Hz, 1H), 2.92 (1H, d, Jgem = 13.7 -
Hz), 3.33 (s, 1H), 7.04–7.06 (m, 2H), 7.09–7.11 (m, 2H), 7.16–7.27
(m, 9H), 7.29–7.47 (m, 12H); 13C NMR (CDCl3): d = 24.4 (CH2),
39.4 (CH), 43.0 (CH2), 47.7 (CH2), 71.43, 73.94 (Cq), 125.95 (Car),
126.21(Car), 126.91(Car), 127.57 (Car), 127.94 (Car), 129.59 (Car),
130.71 (Car), 130.86 (Car), 137.50, 137.57 (Cq ar), 144.01 (Cq ar).
Other spectroscopic data in agreement with literature.45
1. ZnEt2, toluene, 60 oC, 15 min.
2. (10 mol%), toluene, rt, 15 min.
3. Aldehyde, rt, 24 h
B(OH)2
OH
7
Ar
Ar = 4-ClC6H4 23
24
Ar = 4-MeOC6H4
23-26
Ar = 2-MeOC6H4 25
26
Ar = 4-BrC6H4
Scheme 4. Addition of arylzinc system to aldehydes in the presence of catalyst 7.
7.31–7.34 (m, 4H), 7.43–7.47 (m, 4H); 13C NMR (CDCl3): d = 22.1
(CH2), 37.2 (CH), 74.4 (Cq), 126.4 (Car), 126.6 (Car), 127.2 (Car),
126.2 (Car), 128.1 (Car), 128.2 (Car), 145.2 (Cq ar), 147.2 (Cq ar). Other
spectroscopic data of 2 in agreement with literature.33
Alcohol 8 (white powder), mp. 159 °C; 1H NMR (CDCl3): d = 1.35
(d, J = 6,2 Hz, 1H), 2.08 (d, J = 3,1 Hz, 1H), 2.48 (dd, J = 6.2, 3.1 Hz,
1H), 4.60 (s, 1H), 7.19–7.21 (m, 9H), 7.32–7.33 (m, 6H), 7.46 (d,
J = 8.1 Hz, 4H), 7.51 (d, J = 8.1 Hz, 2H), 7.59 (d, J = 8.1 Hz, 2H); 13C
NMR (CDCl3): 23.9 (CH2), 40.4 (CH), 73.8, 74.0 (Cq), 124.9 (Cq,
CF3), 125.1 (Cq, CF3),126.1 (Car), 126.5 (Car), 127.05 (Car), 127.5
(Car), 129.1 (Car), 143.2 (Cq ar), 148.4, 150.4 (Cq ar); 19F NMR (CDCl3):
d = ꢀ63.38 (s, CF3). Other spectroscopic data in agreement with
literature.46
Catalysts 4–9 were obtained according to the known protocol.34
For the sake of convenience, the spectroscopic data of 4–9 are
listed below while copies of the NMR spectra are included in the
Supporting information.
Alcohol 4 (colorless solid), mp 47–49 °C (as a 59:41 mixture of
diastereoisomers); 1H NMR (CDCl3): major diastereoisomer
d = 1.25 (d, J = 6.2 Hz, 1H), 1.73–1.76 (m, 1H), 2.00 (d, J = 3.2 Hz,
1H), 2.78 (d, J = 4.0 Hz, OH), 4.66–4.68 (m, 1H), 7.23–7.34 (m,
14H), 7.49–7.53 (m, 6H); minor diastereoisomer d = 1.12 (d,
J = 6.2 Hz, 1H), 1.77–1.79 (m, 1H), 2.12 (d, J = 3.2 Hz, 1H), 3.71 (s,
OH), 5.09–5.10 (m, 1H), 7.23–7.34 (m, 14H), 7.49–7.53 (m, 6H);
13C NMR (CDCl3): major diastereoisomer d = 25.4 (CH), 39.8
(CH2), 69.3 (CH), 74.0 (Cq), 125.9 (Car), 127.0 (Car), 127.6 (Car),
127.7 (Car), 128.3 (Car), 129.4 (Car), 142.1 (Cq ar), 144.2 (Cq ar) (as
superposition for both diastereoisomers); minor diastereoisomer
d = 22.4 (CH), 37.5 (CH2), 73.8 (CH), 75.0 (Cq), 126.3 (Car), 126.8
(Car), 127.4 (Car), 127.7 (Car), 128.2 (Car), 129.3 (Car), 141.6 (Cq ar),
144.1 (Cq ar); MS (CI): m/z 392 (M+H); HRMS (EI): calcd for
Alcohol 9 (white solid), mp. 89–91 °C; [
a
]
D = ꢀ65.5 (c 1, CHCl3);
1H NMR (CDCl3): d = 1.36 (d, J = 6,2 Hz, 1H), 2.10 (d, J = 3,1 Hz, 1H),
2.29 (dd, J = 6.2, 3.1 Hz, 1H), 4.44 (s, 1H), 6.84–6.90 (m, 9H), 7.18–
7.19 (m, 9H), 7.23–7.25 (m, 2H), 7.31–7.32 (m, 6H), 7.34–7.37 (m,
2H); 13C NMR (CDCl3): d = 24.0 (CH2), 41.4 (CH), 73.6, 74.1 (Cq),
1
1
114.6 (d, JCF = 21.0 Hz, Cq ar), 114.8 (d, JCF = 21.0 Hz, Cq ar), 126.9
(Car), 127.50 (Car), 127.7 (d, 2JCF = 8.8 Hz, Car), 127.9 (d, 2JCF = 8.8 Hz,
3
3
Car), 129.3 (Car), 141.2 (d, JCF = 3.6 Hz, Car), 142.8 (d, JCF = 3.6 Hz,
Car), 143.6 (Cq ar), 161.0 (Cq ar), 162.6 (Cq ar); 19F NMR (CDCl3):
d = ꢀ116.26 to ꢀ116.41 (m, 1F), ꢀ116.92 to ꢀ117.07 (m, 1F); Anal.
Calcd for C34H27F2NO: C, 81.09; H, 5.04; N, 2.78. Found: C, 81.19; H,
5.28; N, 2.78.
C
28H25NO: 391.1920, found: 391.1936.
Alcohol 5 (colorless solid), mp 51–52 °C (as a 59:41 mixture of
4.3. Asymmetric addition of arylzinc systems generated from
aryl iodides and diethylzinc to aldehydes: general procedure17
diastereoisomers); 1H NMR (CDCl3): major diastereoisomer
d = 1.12 (d, J = 6.4 Hz, 1H), 1.51–1.54 (m, 1H), 1.85 (d, J = 3.2 Hz,
1H), 2.64 (d, J = 5.8 Hz, 1H), 2.69–2.74 (m, AB part of ABX system,
2H), 2.89–2.93 (m, X part of ABX system, 1H), 3.86–3.90 (m, 1H),
7.01–7.02 (m, 2H), 7.20–7.33 (m, 14H), 7.51–7.52 (m, 6H); minor
diastereoisomer d = 1.11 (d, J = 6.4 Hz, 1H), 1.60–1.62 (m, 1H),
1.94 (d, J = 3.2 Hz, 1H), 2.69–2.74 (m, AB part of ABX system, 2H),
2.89–2.93 (m, X part of ABX system, 1H), 3.20 (s, 1H), 4.21–4.24
(m, 1H), 7.01–7.02 (m, 2H), 7.20–7.33 (m, 14H), 7.45–7.46 (m,
6H); 13C NMR (CDCl3): major diastereoisomer d = 24.6 (CH), 36.3
(CH2), 41.2 (CH2), 68.4 (CH), 73.7 (Cq), 126.2 (Car), 126.8 (Car),
127.5 (Car), 128.3 (Car), 129.3 (Car), 129.5 (Car), 138.2 (Cq ar),
144.1 (Cq ar) (as superposition for both diastereoisomers); minor
diastereoisomer d = 22.3 (CH), 35.9 (CH2), 42.4 (CH2), 72.3 (CH),
73.8 (Cq), 126.2 (Car), 126.9 (Car), 127.6 (Car), 128.2 (Car), 129.2
(Car), 129.4 (Car), 138.3 (Cq ar), 144.2 (Cq ar); MS (CI): m/z 406 (M
+H); HRMS (EI): calcd for C29H27NO: 405.2077, found: 405.2092.
Alcohol 6 (white powder), mp 52–54 °C, the spectroscopic data
are analogous with those for the compound 5.
Li(acac) (24 mg, 0.23 mmol), the corresponding aryl iodide
(2.0 mmol) and NMP (1.5 mL) were placed sequentially in the
round bottom flask under nitrogen. The mixture was cooled to
0 °C and diethylzinc solution (115 lL, 1.1 mmol) was added drop-
wise. The mixture was stirred for 12 h at this temperature, after
which a solution of the catalyst (10 mol %) in THF (5 mL) was
added. After stirring at 0 °C for 1 h, the solution was warmed to
room temperature and an aldehyde (0.91 mmol) was added. The
reaction was monitored by TLC and upon completion, saturated
aqueous solution of ammonium chloride was added in order to
quench the reaction. The mixture was extracted three times using
dichloromethane, and the combined organic phases were dried
over anhydrous Na2SO4, concentrated and the residue was purified
on the column (silica gel, hexane and ethyl acetate in gradient) to
afford the desired products 11, 13–21. Their chemical yield, speci-
fic rotation and enantiomeric excess values are listed in Tables 1
and 2.
Table 4
Addition of arylzincs to aldehydes promoted by catalyst 7
Entry
Ar
Products 23–26
ee [%]b
Abs. conf.c
a
Yield [%]
[
a
]
D
1
2
3
4
4-ClC6H4
88
92
89
90
+21.4
ꢀ6.2
92
91
88
93
(S)
(S)
(S)
(S)
4-MeOC6H4
2-MeOC6H4
4-BrC6H4
ꢀ33.7
+24.0
a
b
c
In chloroform (c 1).
Determined by chiral HPLC using Chiralcel AD-H column.
Taken from the literature43 (on the basis of the sign of the specific rotation and retention times in HPLC chromatograms).
Please cite this article in press as: Wujkowska, Z.; et al. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.10.005

6
Z. Wujkowska et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
4.3.1. (R)-(ꢀ)-(3-Methoxyphenyl)phenylmethanol 11
1H and 13C spectra in agreement with the literature.17 The
enantiomeric excess was determined by chiral HPLC (Chiral
AD-H, iPrOH/n-hexane 10/90, flow: 1 ml/min, k = 254 nm):
tR = 28.2 min (minor), tR = 37.1 min (major).
4.4. Asymmetric addition of arylzinc systems generated from
phenylboronic acid and diethylzinc to aldehydes: general
procedure31,40
Diethylzinc solution (7.2 mmol) was added dropwise to a solu-
tion of phenylboronic acid (2.4 mmol) in toluene (4 mL) under
nitrogen. After stirring for 15 min at 60 °C, the mixture was cooled
to ambient temperature and a solution of the catalyst (10 mol %) in
toluene (2 mL) was added. The mixture was stirred for 15 min,
cooled to 0 °C and the corresponding aldehyde (1 mmol) was
added. After stirring for 24 h, the reaction was quenched by the
addition of water and the aqueous phase was extracted three times
with dichloromethane. The combined organic layers were dried
over anhydrous Na2SO4, filtered and the solvents were evaporated
in vacuo. The desired pure diarylmethanols 22–26 were obtained
after column chromatography (silica gel, hexane with ethyl acetate
in gradient). The chemical yield, specific rotation and enantiomeric
excess values of compounds 22–26 are listed in Tables 3 and 4.
4.3.2. (R)-(ꢀ)-(4-Methoxycarbonylphenyl)(phenyl)methanol 13
1H and 13C spectra in agreement with the literature.17 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 5/95, flow: 1 ml/min, k = 254 nm): tR = 55.3 min
(major), tR = 68.6 min (minor).
4.3.3. (R)-(+)-(3-Methoxyphenyl)(p-tolyl)methanol 14
1H and 13C spectra in agreement with the literature.17 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 10/90, flow: 1 ml/min, k = 254 nm): tR = 12.5 min
(minor), tR = 14.2 min (major).
4.3.4. (R)-(ꢀ)-(4-Chlorophenyl)(3-methoxyphenyl)methanol 15
1H and 13C spectra in agreement with the literature.17 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 10/90, flow: 1 ml/min, k = 254 nm): tR = 14.2 min
(major), tR = 18.2 min (minor).
4.4.1. (S)-(ꢀ)-(4-Methylphenyl)phenylmethanol 22
1H and 13C spectra in agreement with literature.40 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 10/90, flow: 1 ml/min, k = 254 nm): tR = 18.8 min
(major), tR = 20.8 min (minor).
4.3.5. (R)-(+)-1-(3-Methoxyphenyl)-3-methylbutan-1-ol 16
1H and 13C spectra in agreement with the literature.17 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 5/95, flow: 1 ml/min, k = 254 nm): tR = 10.4 min
(minor), tR = 12.7 min (major).
4.4.2. (S)-(+)-(4-Chlorophenyl)(p-tolyl)methanol 23
1H and 13C spectra in agreement with literature.43 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 5/95, flow: 1 ml/min, k = 254 nm): tR = 21.4 min
(minor), tR = 24.8 min (major).
4.3.6. (R)-(+)-Cyclohexyl(3-methoxyphenyl)methanol 17
1H and 13C spectra in agreement with the literature.17 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 5/95, flow: 1 ml/min, k = 254 nm): tR = 11.3 min
(minor), tR = 16.1 min (major).
4.4.3. (S)-(ꢀ)-(4-Methoxyphenyl)(p-tolyl)methanol 24
1H and 13C spectra in agreement with literature.43 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 5/95, flow: 1 ml/min, k = 254 nm): tR = 30.8 min
(minor), tR = 32.7 min (major).
4.4.4. (S)-(ꢀ)-(2-Methoxyphenyl)(p-tolyl)methanol 25
1H and 13C spectra in agreement with literature.43 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 5/95, flow: 1 ml/min, k = 254 nm): tR = 24.8 min
(major), tR = 31.7 min (minor).
4.3.7. (R)-(+)-(4-Methoxycarbonylphenyl)(4-methylphenyl)
methanol 18
1H and 13C spectra in agreement with the literature.39 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 15/85, flow: 1 ml/min, k = 254 nm): tR = 12.4 min
(minor), tR = 14.3 min (major).
4.4.5. (S)-(+)-(4-Bromophenyl)(p-tolyl)methanol 26
1H and 13C spectra in agreement with literature.43 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 5/95, flow: 1 ml/min, k = 254 nm): tR = 24.9 min
(minor), tR = 27.1 min (major).
4.3.8. (R)-(ꢀ)-(4-Methoxycarbonylphenyl)(4-chlorophenyl)
methanol 19
1H and 13C spectra in agreement with the literature.17 The enan-
tiomeric excess was determined by chiral HPLC (as described pre-
viously17) (Chiral AD-H, iPrOH/n-hexane 5/95, flow: 1 ml/min,
k = 254 nm): tR = 67.5 min (minor), tR = 80.1 min (major).
Acknowledgement
Financial support by the National Science Centre (NCN), Poland,
Grant No. 2012/05/D/ST5/00505 for M. R. is gratefully
acknowledged.
4.3.9. (R)-(+)-1-(4-Methoxycarbonylphenyl)-3-methyl-1-
butanol 20
1H and 13C spectra in agreement with the literature.17 The enan-
tiomeric excess was determined by chiral HPLC (Chiral AD-H,
iPrOH/n-hexane 5/95, flow: 1 ml/min, k = 254 nm): tR = 19.2 min
(major), tR = 23.4 min (minor).
A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetasy.2016.10.
005.
4.3.10. (R)-(+)-Methyl 4-(cyclohexyl(hydroxy)methyl)benzoate
21
1H and 13C spectra in agreement with the literature.17 The enan-
tiomeric excess was determined by chiral HPLC (as described pre-
viously17) (Chiral AD-H, iPrOH/n-hexane 5/95, flow: 1 ml/min,
k = 254 nm): tR = 8.6 min (major), tR = 10.8 min (minor).
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