The use of bifunctional catalyst systems in the asymmetric addition of alkynylzinc to aldehydes

Article abstract of DOI:10.1016/j.tetasy.2004.08.024

The bifunctional ligand 2a showed a more enhanced reactivity than that of the corresponding amino alcohol ligand in the asymmetric addition of alkynylzinc to benzaldehyde. The bifunctional ligand 2a can catalyze the addition of phenylacetylene to various

Full text of DOI:10.1016/j.tetasy.2004.08.024

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 3155–3159
The use of bifunctional catalyst systems in the asymmetric
addition of alkynylzinc to aldehydes
a
a
Yong-Feng Kang,a Lei Liu,a Rui Wang,a,b, Wen-Jin Yan and Yi-Feng Zhou
*
aDepartment of Biochemistry, Molecular Biology, School of Life Sciences, Lanzhou University, Lanzhou, Gansu 730000, China
bState Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics,
Chinese Academy of Sciences, Lanzhou, Gansu 730000, China
Received 19 July 2004; accepted 23 August 2004
Abstract—The bifunctional ligand 2a showed a more enhanced reactivity than that of the corresponding amino alcohol ligand in the
asymmetric addition of alkynylzinc to benzaldehyde. The bifunctional ligand 2a can catalyze the addition of phenylacetylene to var-
ious types of aldehydes including aromatic aldehydes, aliphatic aldehydes, and a,b-unsaturated aldehydes with high enantioselec-
tivity (81–98% ee). The conditions of this catalytic process are both mild and simple.
Ó 2004 Elsevier Ltd. All rights reserved.
R
1. Introduction
Et
X
Et
H
Zn
t-Bu
R2
O
O
The use of catalyst systems containing bifunctional lig-
ands in the asymmetric construction of C–C bonds is
an attractive method of emulating the reactivity of nat-
ural enzymes.1 The most representative examples of this
concept are a series of bifunctional Lewis acid–Lewis
base (LALB) catalysts 1 (Fig. 1) derived from BINOL
as the chiral scaffold, developed by Shibasaki and
Kanai.1f Indeed, these catalyst systems containing chiral
ligands with two or more reactive sites have proven suc-
cessful in this class of reactions,2 and separation of the
Lewis acid and Lewis base sites in these ligands is
proposed to account for this difference in reactivity.
Recently, DiMauro and Kozlowski3 have found that
bifunctional Lewis acid–Lewis base catalyses 2 (Fig. 1)
were much more reactive when compared to the Noyori
DAIB or the Nugent MIB catalysts in the alkylation of
aldehydes and a-ketoesters. Based on our recent report
on the catalytic asymmetric addition of alkynylzinc to
aldehydes,4 we supposed that these catalyst systems
containing bifunctional ligand would also enhance the
reactivity in the asymmetric addition of alkynylzinc to
aldehydes.
Cl Al
O
N
X
N
N
activates
nucleophile
O
R'= H ;
X= P(O)Ar2, PPh2, SEt,
CHP2(O)Ph2,CHR2,
P(O)(C6H4-p-NMe2)2
R'= (CH2)3CH=CH(CH2)3OCH2-
Zn
O
activates
electrophile
N
t-Bu
X=P(O)Ph2
1
2
Figure 1.
propargyl alcohols, which are important versatile build-
ing blocks of many biologically active compounds and
natural products,7 and has gained considerable signifi-
cance in recent years. Among the catalytic methods
developed for the asymmetric alkyne addition to alde-
hydes, the following two are currently considered the
most practical. Carreira et al. discovered a catalyst
based on the chiral amino alcohol N-methyl ephedrine
for the alkynylzinc addition to aldehydes.8 High enan-
tioselectivity and high product yields were achieved for
the reaction of alkynylzincs with a variety of aliphatic
aldehydes. Pu et al.9 and Chan et al.10 have found that
1,10-bi-2-naphthol (BINOL) in combination with
Ti(Oi-Pr)4 can catalyze the alkynylzinc addition to
aromatic aldehydes or aliphatic aldehydes with high
The enantioselective alkynylzinc addition to carbonyl
compounds5,6 is very useful for the synthesis of chiral
*
Corresponding author. Tel.: +86 931 891 2567; fax: +86 931 891
2561; e-mail: wangrui@lzu.edu.cn
0957-4166/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.08.024

3156
Y.-F. Kang et al. / Tetrahedron: Asymmetry 15 (2004) 3155–3159
Table 1. Asymmetric addition phenylacetylene to benzaldehyde using
2 as ligands
enantioselectivity. However the ligands and current
methods for these reaction need to be further modified,
CarreiraÕs method is not catalytic for the addition to
benzaldehyde and the BINOL method requires the use
of both alkylzinc and Ti(Oi-Pr)4. In addition, the rela-
tionship between ligand structure enantioselectivity
and the catalytic activity need to be studied, and there
is a growing need to find a new catalyst, which can cat-
alyze the asymmetric addition of terminal acetylenes to
aldehydes with high ee values under mild and convenient
conditions. Herein, we report a highly enantioselective
alkyne addition to aldehydes catalyzed by catalyst sys-
tems containing a bifunctional ligand.
Entry
Ligand
Time (h)
Yield (%)
Ee (%)
Configna
1
2
3
4
2a
2b
2c
2d
20
24
20
24
95
80
87
88
94
46
76
57
S
S
S
R
a The absolute configuration is based on measurements of the specific
rotation and comparison with the literature values.6a,8b,13
tal findings and related mechanism suggested by
literature,11 a possible transition state is proposed in
Figure 2. When b-aminoalkoxyl zinc catalyst 3 was em-
ployed, this reaction proceeded by dual activation of the
aldehyde electrophile and dialkylzinc nucleophile (Fig.
2).6j,12 When bifunctional catalyst 4 was used in this
reaction, the b-aminoalkoxyl zinc atom could act as
the Lewis acid center (LA) to activate the aldehyde,
while the nitrogen atom of pyridyl group could act as
the base center (LB) independently to activate the alkyn-
ylzinc nucleophile (Fig. 2).
2. Results and discussion
Unlike ShibasakiÕs and KozlowskiÕs C2-symmetric chiral
bifunctional ligands (Fig. 1), we designed and synthe-
sized a class of dissymmetric chiral bifunctional ligands.
We used a natural amino acid as a starting material.
After four simple steps, we got the bifunctional ligands
2a–c and amino alcohol ligand 2d in high yields (Scheme
1).11
activates
activates
electrophile
Ph
nucleophile
Ph
H
Ph
Ph
Ph
Ph
O
i) SOCl2, MeOH, -30oC,
to rt, then reflux for 2h;
Ph
Et
Zn
S
Ph
R1
R1
COOH
O
H
R
Ph
NH
Zn
O
Et Zn
N
O
OH
NH2
NH
Ph
H2N
Zn
Et
ii) PhMgBr, THF
Et
1a-1c
activates
nucleophile
activates
electrophile
Ph
Ph
Ph
Ph
R1
3
4
R1
R2CHO
NaBH (OAc)3,
DCE, rt
OH
Figure 2.
NH
2a-2d
C6H6,
Reflux
OH
N
R2
R2
Among the bifunctional ligands 2a, 2b and 2c, 2a
showed the best asymmetric induction, with 94% ee ob-
tained (Table 1, entries 1–3). Obviously, the presence of
an i-Pr group at the stereogenic carbon atom was crucial
for the best asymmetric induction.
2a: R1=iPr, R2=2-pyridyl
2b: R1=iBu, R2=2-pyridyl
2c: R1=Bn, R2=2-pyridyl
2d: R1=iPr, R2=phenyl
Scheme 1. Preparation of ligands 2a–d.
We then explored the conditions for the use of ligand 2a
in the reaction of phenylacetylene with benzaldehyde,
with these experiments summarized in Table 2. We
found that this reaction was strongly influenced by the
solvent. In entries 1–5, various solvents including
CH2Cl2, ether, THF, hexane, and toluene were tested,
among which, THF–hexane was found to be the best.
Decreasing the reaction temperature from 0°C to
ꢀ15°C or increasing the reaction temperature from
0°C to room temperature all led to a lower ee (entries
6 and 7). When we decreased the amount of ZnEt2 from
4 to 3, 2, and 1.4equiv on this reaction, we found the
enantioselectivity was improved, and the appropriate
amount of ZnEt2 was 1.4equiv (entries 8–10). Increasing
the amount of 2a from 10 to 20mmol% in entry 11 gave
enhanced ee. Reducing the amount of THF from 2 to
1mL in entry 12 led to an increased ee.
Bifunctional ligands 2a–c and amino alcohol ligand 2d
were used to catalyze the reaction of phenylacetylene
with benzaldehyde in the presence of Et2Zn. The reac-
tions were conducted at 0°C in hexane–THF by the
sequential treatment of chiral ligand, Et2Zn, phenyl-
acetylene, and then benzaldehyde (Scheme 2). The
results are summarized in Table 1.
OH
Ligand, Et2Zn
solvent
Ph
Ph
+ PhCHO
Ph
Scheme 2. Addition of phenylacetylene to benzaldehyde.
We found that bifunctional ligand 2a showed an en-
hanced reactivity over that of amino alcohol ligand 2d
in the asymmetric addition of alkynylzinc to benzalde-
hyde (Table 1, entries 1 and 4). Based on our experimen-
Under the optimized reaction conditions of entry 12 in
Table 2, ligand 2a was employed to catalyze the enantio-

Y.-F. Kang et al. / Tetrahedron: Asymmetry 15 (2004) 3155–3159
3157
Table 2. Asymmetric addition phenylacetylene to benzaldehyde using
2a as liganda
ligand 2a can catalyze the addition of phenylacetylene
to both aromatic and aliphatic aldehydes with ee values
up to 98%. The conditions of this catalytic process are
both mild and simple.
Entry
2a
(mmol%)
Solvent
(mL)
Et2Zn
(equiv)
Temp.
(°C)
Eeb
(%)
1
10
10
10
10
10
10
10
10
10
10
20
20
CH2Cl2 (2)
Ether (2)
2
0
0
11
56
85
19
43
79
66
90
82
73
92
94
2
2
4. Experimental
3
THF–Hex (2)
Hexc (2)
2
0
4
2
0
5
Toluene (2)
THF–Hex (2)
THF–Hex (2)
THF–Hex (2)
THF–Hex (2)
THF–Hex (2)
THF–Hex (2)
THF–Hex (1)
2
0
4.1. General methods
6
2
Rtd
ꢀ15
0
7
2
All reactions were carried out under an argon atmos-
phere and solvents dried according to established proce-
dures. Reactions were monitored by thin layer
chromatography (TLC). Column chromatography
purifications were carried out using silica gel. All alde-
hydes and amino acid were purchased from Acros or
Fluka. Diethylzinc was prepared from EtI with Zn and
then diluted with toluene or hexane to 1.0M. Melting
points are uncorrected and were recorded on an X-4
8
1.4
3
9
0
10
11
12
4
0
1.4
1.4
0
0
a Phenylacetylene/Et2Zn = 1:1, benzaldehyde: 0.25mmol.
b The enantiomeric excess was determined by HPLC analysis of the
corresponding products on a Chiralcel OD column.
c Hex = hexane.
1
d Rt = room temperature.
melting point apparatus. H NMR spectra were meas-
ured on DRX-200MHz spectrometers (NMR in CDCl3
with TMS as an internal standard). IR spectra were
obtained on Nicolet NEXUS 670 FT-IR. Optical
rotations were recorded on a Perkin–Elmer 341 polari-
meter. HR-MS were measured with an APEX II 47e
mass spectrometer and the ESI-MS was recorded on a
MarinerÒ biospectrometer. The ee value determination
was carried out using chiral HPLC with a Daicel
ChiracelÒ OD column on WatersÒ with a 996 UV-
detector.
selective addition of phenylacetylene to a variety of alde-
hydes (Table 3). High enantioselectivity was achieved
for the addition of phenylacetylene to aromatic alde-
hydes, aliphatic aldehydes, and a,b-unsaturated alde-
hydes with an ee value up to 98%.
Table 3. Asymmetric addition phenylacetylene to aldehydes promoted
by ligand 2aa,b
4.2. Preparation of 1a–c and 2a–d
Entry Aldehydes
Time Isolated
(h)
Eec
yield (%) (%)
Amino alcohols 1a–c were synthesized according to lit-
eratures: Refs. 11 and 14. The bifunctional ligand 2a–c
and amino alcohol ligand 2d were synthesized according
to literature procedures: Ref. 11.
1
Benzaldehyde
3-Tolualdehyde
20
24
24
24
24
24
32
24
32
24
24
32
32
32
95
85
82
90
86
94
84
95
88
80
92
80
87
91
88
82
94
93
90
92
93
85
87
85
86
98
91
90
91
91
90
81
2
3
4-Tolualdehyde
3-Anisaldehyde
4-Anisaldehyde
4
5
4.2.1. (S)-2-Amino-3-methyl-1,1-diphenylbutan-1-ol 1a.
Colorless needle crystals, yield 65%; mp: 95–
6
3-Bromobenzaldehyde
4-Bromobenzaldehyde
2-Chlorobenzaldehyde
4-Chlorobenzaldehyde
3-Nitrobenzaldehyde
4-Fluorobenzaldehyde
a-Naphthaldehyde
b-Naphthaldehyde
Isobutylaldehyde
7
18
D
97°C; ½aꢁ ¼ ꢀ124:0 (c 1.27, CHCl3); 1H NMR
8
9
(200MHz, CDCl3, TMS): d = 7.60 (d, J = 8Hz, 2H,
Ph–H), 7.48 (dd, J = 8.6Hz, J = 1.4Hz, 2H, Ph–H),
7.33–7.10 (m, 6H, Ph–H), 4.436 (s, 1H, OH), 3.83 (d,
J = 2.2Hz, 1H, CHN), 1.73 (m, 1H, CH(CH3)2), 1.157
(br, 2H, NH2), 0.91 (d, J = 8.2Hz, 3H, CH3), 0.87 (d,
J = 7Hz, 3H, CH3); 13C NMR (50MHz, CDCl3):
d = 16.39, 23.27, 28.13, 60.46, 79.97, 125.78, 126.20,
126.55, 126.87, 128.30, 128.68, 145.20, 148.34; IR(KBr):
3341, 3059, 3082, 3023, 2959, 2926, 2873, 1591, 1490,
1446, 1382, 1367, 1174, 1049, 965, 940, 896, 748, 700,
668cmꢀ1; MS (ESI): m/z: 256 [M + H]+.
10
11
12
13
14
15
16
Cyclohexanecarboxaldehyde 32
Cinnamicaldehyde 32
a In all of the entries: Et2Zn/phenylacetylene/aldehyde/2a =
1.4:1.4:1.0:0.2.
b All the reactions were processed under argon and at 0°C.
c The enantiomeric excess was determined by HPLC analysis of the
corresponding products on a Chiralcel OD column.
4.2.2. (S)-2-Amino-4-methyl-1,1-diphenylpentan-1-ol 1b.
Colorless needle crystals, yield 55%; mp: 132–
18
D
3. Conclusion
134°C; ½aꢁ ¼ ꢀ105:0 (c 1.36, CHCl3); 1H NMR
(300MHz, CDCl3, TMS): d = 7.61 (d, J = 7.5Hz, 2H,
Ph–H), 7.47 (d, J = 8.1Hz, 2H, Ph–H), 7.33–7.13 (m,
6H, Ph–H), 3.98 (d, J = 10.2Hz, 1H, CHN), 1.58 (m,
1H, CH(CH3)2), 1.25 (m, 1H, CHACH(CH3)2), 1.11
(m, 1H, CHBCH(CH3)2), 0.89 (d, J = 7.8Hz, 3H,
CH3), 0.86 (d, J = 7.2Hz, 3H, CH3); 13C NMR
(50MHz, CDCl3): d = 21.25, 24.00, 25.28, 39.41, 54.45,
We have conveniently synthesized a series of bifunc-
tional ligands 2a–c and amino alcohol ligand 2d with
high yields. We have discovered that the bifunctional lig-
and 2a showed an enhanced reactivity over that of ami-
no alcohol ligand 2d in the asymmetric addition of
alkynylzinc to benzaldehyde, and that the bifunctional

3158
Y.-F. Kang et al. / Tetrahedron: Asymmetry 15 (2004) 3155–3159
79.03, 125.53, 125.82, 126.29, 126.57, 127.97, 128.37,
144.50, 147.16; IR(KBr): 3332, 3262, 2950, 2864, 1589,
1490, 1468, 1445, 1387, 1179, 1054, 1006, 972, 948,
899, 837, 744, 699cmꢀ1; MS (ESI): m/z: 270 [M + H]+.
(200MHz, CDCl3): d = 8.30 (d, J = 4.2Hz,1H, Py-a-
H), 7.74–6.98 (m, 17H, Ph–H, Py–H), 6.64 (d,
J = 7.6Hz, 1H, Ph–H), 4.00 (dd, J = 2.2Hz,
J = 10.2Hz, 1H, CHN), 3.26 (s, 2H, PyC–H2), 2.95
(d, J = 14.6, 1H, PhCH), 2.45 (dd, J = 10.4, J = 14.6,
1H, PhCH); 13C NMR (50MHz, CDCl3): d = 37.90,
54.23, 66.02, 78.64, 121.66, 121.87, 125.86, 126.20,
126.48, 126.71, 128.20, 129.00, 136.06, 139.61, 145.19,
147.52, 149.05, 159.10; IR(KBr): 3370, 3159, 3083,
3057, 3024, 2918, 2848, 1597, 1566, 1491, 1446, 1388,
1350, 1181, 1150, 1120, 1105, 1056, 1030, 1002, 969,
891, 763, 745, 699, 660, 627, 565cmꢀ1; MS (ESI): m/z:
395 [M + H]+. Anal. Calcd for C27H26N2O: C,
82.20; H, 6.64; N, 7.10. Found: C, 82.24; H, 6.724; N,
7.156.
4.2.3. (S)-2-Amino-1,1,3-triphenylpropan-1-ol 1c. Col-
orless crystals, yield 70%; mp: 134–136°C;
18
D
½aꢁ ¼ ꢀ85:0 (c 1.10, CHCl3); 1H NMR (200MHz,
CDCl3, TMS): d = 7.65–7.57 (m, 4H, Ph–H), 7.35–7.15
(m, 11H, Ph–H), 4.514 (s, 1H, OH), 4.16 (dd, 1H,
J = 2.6Hz, J = 10.6Hz, CHN), 2.63 (d, 1H,
J = 11.6Hz, PhCHA), 2.43 (dd, 1H, J = 10.8Hz,
J = 13.8Hz, PhCHB), 1.161 (s, 2H, NH2); 13C NMR
(50MHz, CDCl3): d = 37.10, 58.55, 78.86, 125.73,
126.12, 126.78, 127.10, 128.56, 128.82, 128.99, 129.42,
139.98, 144.67, 147.14; IR(KBr): 3511, 3335, 3243,
3083, 3058, 3025, 2920, 2850, 1596, 1490, 1445, 1362,
1324, 1272, 1169, 1103, 1056, 1030, 960, 900, 857, 749,
699cmꢀ1; MS (ESI): m/z: 304 [M + H]+.
4.2.7. (S)-3-Methyl-2-benzylamino-1,1-diphenylbutan-1-
ol 2d. Colorless crystals, yield 76%; mp: 132–134°C;
25
D
½aꢁ ¼ ꢀ34 (c 1.24, CH2Cl2); 1H NMR (300MHz,
CDCl3): d = 7.76 (d, J = 7.5Hz, 2H, Ph–H), 7.61 (d,
J = 8.7Hz, 2H, Ph–H), 7.36–7.12 (m, 11H, Ph–H),
3.67 (s, 1H, CNH), 3.47 (d, J = 12Hz, 1H, PhC–HA),
3.28 (d, J = 12Hz, 1H, PhC–HB), 2.08 (m, 1H,
CH(CH3)2), 1.00 (d, J = 6.6Hz, 3H, CH3), 0.73 (d,
J = 6.6Hz, 3H, CH3); 13C NMR (60MHz, CDCl3):
d = 15.90, 22.63, 28.72, 55.00, 68.48, 78.57, 125.81,
126.07, 126.45, 127.19, 127.87, 128.04, 128.28, 128.38,
140.11, 145.29, 148.86; IR(KBr): 3340, 3085, 3060,
3026, 2955, 2870, 2834, 1656, 1598, 1491, 1472, 1449,
1373, 1177, 1077, 1058, 1028, 986, 943, 903, 750, 725,
701, 669, 636cmꢀ1; MS (ESI): m/z: 346 [M + H]+. Anal.
Calcd for C24H27NO: C, 83.44; H, 7.88; N, 4.06. Found:
C, 83.27; H, 7.767; N, 4.256.
4.2.4. (S)-3-Methyl-2-[(2-pyridylmethyl)amino]-1,1-
diphenylbutan-1-ol 2a. Colorless crystals, yield 82.4%;
21
D
mp: 119–121°C; ½aꢁ ¼ ꢀ63:0 (c 1.01, CH2Cl2); 1H
NMR (200MHz, CDCl3): d = 8.49 (d, J = 4.8Hz, 1H,
Py-a-H), 7.72–7.12 (m, 12H, Ph–H, Py–H), 6.85 (d,
J = 7.6Hz, 1H, Ph–H), 5.193 (s, 1H, OH), 3.58 (d,
J = 2Hz, 1H, CHN), 3.49 (d, J = 14Hz, 1H, PyC–HA),
3.34 (d, J = 14Hz, 1H, PyC–HB), 2.186 (s, 1H, NH),
1.98 (m, 1H, CH(CH3)2), 0.92 (d, J = 6.6Hz, 3H,
CH3), 0.76 (d, J = 6.6Hz, 3H, CH3); 13C NMR
(50MHz, CDCl3): d = 15.95, 22.48, 28.92, 55.50, 68.74,
78.59, 121.95, 122.33, 125.74, 126.06, 126.34, 127.83,
127.98, 136.20, 145.44, 149.15, 159.23; IR(KBr): 3332,
3058, 3026, 2956, 2871, 1593, 1570, 1490, 1473, 1449,
1430, 1390, 1371, 1177, 1151, 1088, 1056, 1029, 994,
750, 703, 668, 630cmꢀ1; MS (ESI): m/z: 347 [M + H]+.
Anal. Calcd for C23H26N2O: C, 79.73; H, 7.56; N,
8.09. Found: C, 79.96; H, 7.260; N, 8.185.
4.3. General procedures for the addition of phenylacetyl-
ene to aldehydes
To a solution of ligand 2a (0.05mmol, 17.4mg) in THF
(1mL), was added a solution of Et2Zn (0.35mmol, 1.0M
in hexane, 0.35mL) at room temperature. After the mix-
ture was stirred at the room temperature for 1h, phenyl-
acetylene (0.35mmol, 38lL) was added, and stirring
continued for another 1h. The solution was cooled to
0°C and treated with aldehyde (0.25mmol, 25lL) and
then the resultant mixture stirred for 20–32h at 0°C.
After the reaction was complete (checked by TLC), it
was quenched by 5% aqueous HCl at 0°C. The mixture
was extracted with ether. The organic layer was washed
with brine, dried over Na2SO4, and concentrated under
vacuum. The residue was purified by flash column chro-
matography (silica gel, 12.5% EtOAc in hexane) to give
the product.
4.2.5. (S)-4-Methyl-2-[(2-pyridylmethyl)amino]-1,1-
diphenylpentan-1-ol 2b. Colorless crystals, yield 87%;
25
D
mp: 100–101°C; ½aꢁ ¼ ꢀ45 (c 0.97, CH2Cl2); 1H
NMR (200MHz, CDCl3): d = 8.48 (d, J = 4.8Hz,1H,
Py-a-H), 7.67–7.06 (m, 12H, Ph–H, Py–H), 6.85 (d,
J = 7.6Hz, 1H, Ph–H), 4.899 (s, 1H, OH), 3.66 (dd,
J = 4.2Hz, J = 8.6Hz, 1H, CHN), 3.44 (d, J = 14Hz,
1H, PyC–HA), 3.25 (d, J = 14Hz, 1H, PyC–HB), 1.889
(s, 1H, NH), 1.59 (m, 1H, CH(CH3)2), 1.27 (m, 2H,
CH2), 0.79 (d, J = 6.6Hz, 3H, CH3), 0.75 (d,
J = 6.4Hz, 3H, CH3); 13C NMR (50MHz, CDCl3):
d = 21.57, 23.93, 25.20, 40.58, 54.52, 62.95, 78.57,
121.91, 122.32, 125.88, 126.12, 126.20, 126.42, 127.91,
128.02, 136.22, 145.20, 148.07, 149.15, 159.41; IR(KBr):
3340, 3085, 3059, 3027, 2955, 2868, 1592, 1571, 1490,
1468, 1449, 1383, 1365, 1314, 1176, 1153, 1096, 1052,
1032, 998, 907, 751, 703, 662, 638cmꢀ1; MS (ESI):
m/z: 361 [M + H]+. Anal. Calcd for C24H28N2O: C,
79.96; H, 7.83; N, 7.77. Found: C, 80.10; H, 7.284; N,
7.950.
Acknowledgements
We are grateful to the National Natural Science Foun-
dation of China (No. 20372028), the Ministry of Science
and Technology of China, the Teaching and Research
Award Program for Outstanding Young Teachers, the
Specialized Research Fund for the Doctoral Program
in Higher Education Institutions of the Ministry of Edu-
cation of China.
4.2.6. (S)-2-[(2-Pyridylmethyl)amino]-1,1,3-triphenylpro-
pan-1-ol (2c). Colorless needle crystals, yield 83%; mp:
25
D
80–82°C; ½aꢁ ¼ ꢀ40 (c 1.1, CH2Cl2); 1H NMR

Y.-F. Kang et al. / Tetrahedron: Asymmetry 15 (2004) 3155–3159
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