Highly efficient and convenient asymmetric hydrosilylation of ketones catalyzed with zinc Schiff base complexes

Article abstract of DOI:10.1016/j.tet.2011.12.054

Several chiral Schiff base ligands derived from α-amino acids were prepared, and zinc complexes with these chiral Schiff base ligands prepared were tested for the catalytic asymmetric hydrosilylation of ketones, and the results showed that excellent ee va

Full text of DOI:10.1016/j.tet.2011.12.054

Tetrahedron 68 (2012) 1371e1375
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Highly efficient and convenient asymmetric hydrosilylation of ketones catalyzed
with zinc Schiff base complexes
*
*
Shuai Liu, Jiajian Peng , Hu Yang, Ying Bai, Jiayun Li, Guoqiao Lai
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, 222 Wenyi Rd, Hangzhou 310012, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Several chiral Schiff base ligands derived from a-amino acids were prepared, and zinc complexes with
Received 20 September 2011
Received in revised form 13 December 2011
Accepted 20 December 2011
Available online 28 December 2011
these chiral Schiff base ligands prepared were tested for the catalytic asymmetric hydrosilylation of
ketones, and the results showed that excellent ee values were obtained, which are the prominent ex-
amples of catalytic asymmetric hydrosilylation of ketones catalyzed with zinc complexes in the presence
of readily available and inexpensive
a
-amino acids based Schiff base ligands.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Asymmetric catalysis
Ketones
Hydrosilylation
a
-Amino acids based Schiff base
1. Introduction
Recent work in the enantioselective hydrosilylation of ketones
reported by Gajewy and co-workers has demonstrated that an
efficient enantioselective catalyst can be prepared from
ZinceMacrocyclic Oligoamine Complexes, with enantioselectiv-
ities up to 89% ee.13 These procedures usually make the use of
inexpensive, easily handled, non-toxic, and air and moisture stable
polymethylhydrosiloxane (PMHS) or monomeric silanes as the
reducing agents.14 One of the main goal of current studies on AHS
is the development of catalytic systems that would comply with
the criteria of high efficiency (yield, enantioselectivity), low cost
and feasibility of recovery of the catalyst as well as with possible
environmental friend.15 Herein we reported that enantioselective
reduction of ketones by HSi(OEt)3 was catalyzed with diethylzinc
coordinated with Schiff bases ligands derived from substituted
Chiral secondary alcohols are important chiral building blocks
in synthetic organic chemistry, especially in the preparations of
pharmaceuticals, flavor and fragrance, and agrochemicals.1e3 As
regards the preparation of chiral secondary alcohols, in compari-
son with other major catalytic methods for the reduction of car-
bonyl groups, i.e., hydrogenation and hydrogen transfer,
asymmetric hydrosilylation (AHS) presents the advantages of
simplicity of the procedure combined with the use of inexpensive
and stable silanes as reducing agents.4 Asymmetric hydrosilylation
of prochiral ketones has been known since the early 1970s, and
chiral rhodium phosphines, or nitrogen complexes,5,6 titanium
complexes coordinated by chiral diamines7 or binaphthol,8 and
chiral ammonium fluoride9 etc. had been proved to be effective
catalysts. Recently, the use of copper hydride in the hydrosilylation
of aryl ketones with excellent results has been reported by Lip-
schutz.10 Zinc complexes of chiral secondary amines were in-
troduced by Mimoun as chiral catalysts for the enantioselective
hydrosilylation of ketones.3 Most frequently used chiral secondary
amines include derivatives of 1-phenylethylamine, trans-1,2-
diaminocyclohexane, trans-1,2-diaminocyclopentane, and 1,2-
diphenyl-1,2-diaminoethane. Introduction of two chiral centers
into the ligand gave rise to synergistic effects, leading to an in-
crease of the enantioselectivity of hydrosilylation reaction.11,12
salicylaldehydes and inexpensive chiral
Fig. 1).
a-amino acids 1e9 (see
2. Results and discussion
2.1. Asymmetric hydrosilylation
The effect of the volume ratio of THF/tert-butanol and the re-
action temperature on the catalytic activity and enantioselectivity
are summarized in Table 1. The optical purity of product alcohol
was largely influenced by addition of tert-butanol as co-solvent.
Thus, the ee values of product were varied from 78% to 96% along
with the increasing volume of tert-butanol added from 0 mL to
0.4 mL (entries 1e5, Table 1). It was found that the best result was
obtained when the ratio of THF/tert-butyl alcohol (v/v) was 3:0.4
* Corresponding authors. Fax: þ86 571 28865135; e-mail addresses: jjpeng@
hznu.edu.cn (J. Peng), gqlai@hznu.edu.cn (G. Lai).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.12.054

1372
S. Liu et al. / Tetrahedron 68 (2012) 1371e1375
Table 2
a
Asymmetric hydrosilylation of acetophenone with HSi(OEt)3
COOK
COOK
COOK
t-Bu
N
t-Bu
N
t-Bu
N
Entry
Ligands (see Fig. 1)
Yieldc (%)
eeb (%)
1
2
3
4
5
6
7
8
1
2
3
4
5a
5b
5c
6
7
8
71
72
75
75
80
82
75
85
67
96(S)
92(R)
88(S)
68(S)
87(S)
30(S)
15(S)
86(R)
87(S)
70(S)
d
OH
OH
OH
t-Bu
1
t-Bu
2
t-Bu
3
COOK
COOK
COOK
t-Bu
N
t-Bu
N
t-Bu
N
9
10
11
OH
OH
OH
70
Trace
t-Bu
4
t-Bu
t-Bu
9
5a M=K
5b M=Na
5c M=Li
6
a
Reaction conditions: (EtO)3SiH 2.5 equiv, ZnEt2 3 mol %, chiral ligand 3 mol %,
THF/tert-butanol(v/v, 3:0.4), ꢀ40 ꢁC, 30 h.
b
Enantiomeric excess determined by GC analysis with a CP-ChiralSil-Dex CB
column.
c
Isolated yields.
COOK
t-Bu
N
t-Bu
N
COOK
N
respectively. Meanwhile, by comparison ligands 1e8 with 9, it
showed that eCOOK group plays crucial operation on the catalytic
properties.
OH
OH
OH
8
t-Bu
7
t-Bu
9
In order to investigate the scope and limitation of such catalyst
system for catalytic asymmetric hydrosilylation of prochiral ke-
Fig. 1. Structures of Schiff base ligands prepared.
tones, the hydrosilylation of substituted aryl ketones with (EtO)3
-
SiH in the presence of 1/ZnEt2 was conducted, and the results were
summarized in Table 3. However, lower yields as well as enan-
tioselectivity were obtained when aryl ethyl ketone or benzyli-
deneacetone was used as substrate (entries 1 and 2, Table 3). It can
be seen that excellent ee values were obtained when aryl ketones
with either electron-donating or electron withdrawing sub-
stituents were used as substrates (entries 3e6, Table 3). The ex-
perimental results showed that substituents on the aromatic ring
have little effect on the enantioselective. Nevertheless, the yields
achieved from the aryl ketones with electron withdrawing sub-
stituents were higher than that of aryl ketones with electron-
donating substituents. o-Substituents on the aromatic ring have
a certain extent effect on the enantioselective (entry 11, Table 3).
This may be due to o-substituents steric hindrance resulting
enantioselective decrease.
Table 1
Effect of the volume ratio of THF/tert-butanol and the reaction temperature on the
catalytic activity and enantioselectivitya
Entry
Solvent
(THF/tert-butanol, v/v)
T (ꢁC)
Yieldc (%)
eeb (%)
1
2
3
4
5
6
7
8
3.4:0
3:0.1
3:0.2
3:0.3
3:0.4
3:0.5
3:0.4
3:0.4
3:0.4
3:0.4
3:0.4
3:0.4
3:0.4
ꢀ40
ꢀ40
ꢀ40
ꢀ40
ꢀ40
ꢀ40
25
77
76
73
72
71
62
91
88
82
79
74
71
52
78
80
85
89
96
96
65
71
77
80
89
96
97
0
9
ꢀ10
ꢀ20
ꢀ30
ꢀ40
ꢀ50
10
11
12
13
a
Reaction conditions: (EtO)3SiH 2.5 equiv, ZnEt2 3 mol %, chiral ligand 1, 3 mol %,
2.2. Mechanistic insights
30 h.
b
Enantiomeric excess (ee) determined by GC analysis with a CP-ChiralSil-Dex CB
column.
Herein, the reaction mechanism was proposed as follows
(Scheme 1).
c
Isolated yields.
Complexation of ZnEt2 by the Schiff base ligand to form A,
complex A reacted with (EtO)3SiH to give ZnH active species B,
which contacted carbonyl group to form the four-membered
metallacycle intermediate C and then to the five-membered
metallacycle intermediate D, in which zinc achieved the tetra-
coordination including ZneN and ZneO bond. Since alkoxo li-
gands easily transfer from zinc to silicium,3 thus formation of
hydrosilylation product (EtO)3SiOCHR1R2 and recycle of catalytic
species B were undertaken when D was contacted with (EtO)3SiH.
Though this proposed mechanism is not relevant to the enantio-
selective hydrosilylation, the key operation of eCOOM group
containing in Schiff base ligands on the catalytic properties may
be interpreted.
In conclusion, chiral Schiff base ligands 1e9 were used in the
enantioselective hydrosilylation of prochiral ketones. It was found
that the ligand plays an important role on the catalytic activity and
the enantioselectivity. The substituents attached on aromatic ring
of substituted salicylaldehyde have a great impact on ees. And the
eCOOK group derived from chiral a-amino acids plays crucial op-
eration on the catalytic properties, and the reaction mechanism
was proposed.
(entry 5, Table 1). Additionally, lower reaction temperature, for
example, ꢀ40 ꢁC, was need to achieve higher ee hydrosilylation
product (entry 6, Table 1). Elevating the reaction temperature from
ꢀ40 ꢁC to 25 ꢁC (entries 6e10, Table 1) caused a significant loss of
enantioselectivity.
The ligands 1e7 were readily obtained from simple condensa-
tion of 3,5-di-tert-butylsalicyldehyde with the corresponding
a-
amino acid via established methods. According to the general
procedures described for the enantioselective hydrosilylation of
prochiral ketones,3,12 acetophenone was treated with 3 mol % of
diethylzinc, and 3 mol % of the chiral ligand in THF solvent in the
presence of 2.5 equiv of (EtO)3SiH ꢀ40 ꢁC for 30 h, and the results
are summarized in Table 2.
The results listed in Table 2 indicated that the ligand plays an
important role on the catalytic activity and the enantioselectivity.
Meanwhile, substituents attached on aromatic ring of substituted
salicylaldehyde have a great impact on ee values. Interestingly, we
investigated other carboxylate such as eCOONa and eCOOLi derived
from L-leucine it was found that ee values decreased to 30% and 15%,

S. Liu et al. / Tetrahedron 68 (2012) 1371e1375
1373
Table 3
R'
a
Asymmetric hydrosilylation of various ketones with HSi(OEt)3
R'
∗
COOM
∗
N
Entry
1
Ketones
Yieldd (%)
ee (%)
87b
N
O
C
ZnEt2
O
Zn
Et
O
OH
M
R
55
O
R
A
O
O
3
2
3
63
82
85c
94b
R'
R'
COOM
∗
R2
∗
N
Zn
R1
N
O
O
C
Cl
R1
Zn
M
O
R2
O
H
O
O
O
R
H
R
4
81
92b
C
B
Br
(EtO)3SiH
O
O
-(EtO)3SiOCHR1R2
F3C
5
6
90
80
92b
90c
R'
∗
N
O
M
R1
C
Zn
O
O
R
O
R2
O2N
H
D
O
Scheme 1. Proposal mechanism of hydrosilylation of ketones catalyzed with ZnEt2/
Schiff base.
7
8
59
68
93b
performed over silica (100e200 mesh). NMR spectra were recorded
on a 400 MHz spectrometer (Avance 400). 13C NMR spectra were
obtained with broadband proton decoupling. For spectra recorded
in DMSO-d6, unless otherwise noted, chemical shifts were recorded
relative to the internal TMS (tetramethylsilane) reference signal. IR
spectra were recorded on FT-IR apparatus (Nicolot 5700).
O
93b
MeO
O
3.2. General procedure for the preparation of Schiff base
ligands
9
70
71
93c
90b
O
3.2.1. Ligands 1e7. Synthesis was adapted from a previously re-
ported procedure.16 To an argon purged methanolic solution
(15 mL) of KOH (5.5 mmol), L-valine (5.5 mmol) was dissolved by
agitation, and the solution was kept in ice-water bath. 3,5-Di-tert-
butylsalicyldehyde (5 mmol) dissolved in methanol (10 mL) was
then rapidly added to the ice-cooled alkaline solution of the amino
acid, and the color of the solution immediately turned yellow. The
reaction mixture was stirred for 3 h and then subjected to evapo-
ration at rota-evaporator. A mixture of hexane (10 mL) and diethyl
ether (10 mL) was added to the residue and then filtered to remove
the remaining amino acid salt. Evaporation of the filtrate yielded
the desired ligand, which was kept in a desiccator over CaCl2.
10
O
11
85
81b
Cl
a
Reaction conditions: (EtO)3SiH 2.5 equiv, ZnEt2 3 mol %, chiral ligand 3 mol %,
THF/tert-butanol(v/v, 3:0.4), ꢀ40 ꢁC, 30 h.
b
Enantiomeric excess determined by GC analysis with a CP-ChiralSil-Dex CB
column.
c
The ee was determined by HPLC with a Chiralcel OD column.
d
3.2.1.1. Ligand 1. Yellow powder, mp 102e103 ꢁC; yield, 1.5 g
Isolated yields.
(81%); 1H NMR (DMSO-d6, 400 MHz)
d 8.253 (s, 1H), 7.103e7.219 (d,
2H), 3.368e3.381 (d, J¼5.2 Hz, 1H), 2.191e2.289 (m, 1H), 1.361 (s,
3. Experimental section
3.1. General
9H), 1.233 (s, 9H), 0.859 (br m, 3H), 0.841 (br m, 3H); 13C NMR
(DMSO-d6, 100 MHz),
d 173.14, 164.77, 162.48, 137.58, 137.01, 126.28,
117.54, 79.08, 35.04, 34.14, 31.77, 31.40, 29.78, 20.8, 18.92; IR (cmꢀ1
,
KBr): 3421, 3052, 2959, 1630, 1527, 1478, 1402, 1360, 1307, 1251,
1173, 1024, 911, 873, 803, 537. Anal. Calcd for C20H30NO3K: C, 64.63;
H, 8.06; N, 3.80; O, 12.95. Found: C, 64.65; H, 8.07; N, 3.77; O, 12.92.
All reaction flask and solvent were dried according to standard
methods prior to use. Flash column chromatography was

1374
S. Liu et al. / Tetrahedron 68 (2012) 1371e1375
3.2.1.2. Ligand 2. Yellow powder, mp 105e106 ꢁC; yield, 1.5 g
(81%); 1H NMR (DMSO-d6, 400 MHz)
8.251 (s, 1H), 7.102e7.218 (d,
Heinert and Martell. The L-valine was added to a solution of po-
d
tassium hydroxide (1 mmol) in i-propanol. The amino acid was
stirred with gentle warming until it had completely dissolved. The
salicylaldehyde (1 mmol) was added and the reaction mixture was
refluxed for 3 h. The mixture was then cooled and the product was
filtered, and washed with ethanol and petroleum ether. The com-
pounds were recrystallized from methanol and ether and dried in
vacuo.17,18 The product was obtained as a light yellow powder, mp
2H), 3.367e3.380 (d, J¼5.2 Hz, 1H), 2.191e2.289 (m, 1H) 1.360 (s,
9H), 1.232 (s, 9H), 0.859 (s, 3H), 0.841 (s, 3H); 13C NMR (DMSO-d6,
100 MHz),
d 173.12, 164.75, 162.49, 137.55, 137.01, 126.26, 117.53,
79.07, 35.04, 34.13, 31.76, 31.40, 29.76, 20.8, 18.92; IR (cmꢀ1, KBr):
3421, 3050, 2959, 1630, 1527, 1478, 1402, 1360, 1307, 1251, 1173,
1024, 911, 873, 803, 537. Anal. Calcd for C20H30NO3K: C, 64.61; H,
8.01; N, 3.87; O, 12.98. Found: C, 64.65; H, 8.07; N, 3.77; O, 12.92.
92e95 ꢁC. Yield, 0.83 g (67%); 1H NMR (DMSO-d6, 400 MHz)
d 8.291
(s, 1H), 6.611e7.302 (m, 4H), 3.432e3.444 (d, J¼4.8 Hz, 1H),
3.2.1.3. Ligand 3. Yellow powder, mp 112e115 ꢁC; yield, 1.6 g
2.226e2.307 (m, 1H), 0.859e0.864 (d, J¼2 Hz, 3H), 0.843e0.847 (d,
(83%); 1H NMR (DMSO-d6, 400 MHz)
d
8.267 (s, 1H), 7.106e7.219 (d,
J¼1.6 Hz, 3H); 13C NMR (DMSO-d6, 100 MHz),
d 177.02, 171.92,
2H), 3.450e3.464 (d, J¼5.6 Hz, 1H), 1.978e2.040 (m, 1H), 1.358 (s,
168.64, 137.95, 137.16, 123.92, 122.82, 120.72, 82.63, 36.19, 25.41,
23.37; IR (cmꢀ1, KBr): 3373, 3050, 2862, 1638, 1605, 1523, 1406,
1376, 1217, 1154, 1013, 890, 760, 739, 574, 537, 480. Anal. Calcd for
C12H15NO3K: C, 55.42; H, 5.55; N, 5.36; O, 18.60. Found: C, 55.56; H,
5.78; N, 5.40; O, 18.51.
9H),1.232 (s, 9H),1.025e1.069 (m, 2H), 0855 (m, 3H), 0.838 (m, 3H);
13C NMR (DMSO-d6, 100 MHz),
d 173.45, 164.75, 162.33, 137.63,
136.97, 126.24, 117.60, 78.56, 38.05, 35.01, 34.09, 31.74, 29.78, 25.27,
16.94, 12.01; IR (cmꢀ1, KBr): 3410, 3052, 2961, 2874, 1630, 1478,
1402, 1361, 1250, 1202, 1174, 1025, 877, 802, 537. Anal. Calcd for
C21H32NO3K: C, 65.44; H, 8.31; N, 3.65; O, 12.48. Found: C, 65.42; H,
8.30; N, 3.63; O, 12.46.
3.2.1.9. Ligand 9. (S)-(ꢀ)-
a-Methylbenzylamine (0.61 g 5 mmol)
and 3,5-di-tert-butylsalicyldehyde (1.175 g, 5 mmol) were dissolved
in dry EtOH (25 mL) over molecular sieves for 2 h. The reaction
mixture was refluxed and stirred for 6 h. The reaction was followed
by TLC. The solution was filtered and the solvent was removed
under reduced pressure to afford 9 ligand as a yellow oil.19,20 Yield,
3.2.1.4. Ligand 4. Yellow powder, mp 113e115 ꢁC; yield, 1.3 g
(76%); 1H NMR (DMSO-d6, 400 MHz)
d
8.335 (s, 1H), 7.106e7.222 (d,
2H), 3.748e3.765 (t, J¼6.8 Hz, 1H), 1.358 (s, 9H), 1.358 (br m, 3H),
1.236 (s, 9H); 13C NMR (DMSO-d6, 100 MHz),
173.89, 164.19,
d
1.34 g, 75%; 1H NMR (DMSO-d6, 400 MHz):
d 14.055 (s, 1H), 8.674 (s,
162.83, 137.44, 137.20, 126.61, 126.40, 117.42, 66.67, 35.04, 34.15,
31.77, 29.79, 20.92; IR (cmꢀ1, KBr): 3422, 3052, 2960, 2871, 1629,
1528, 1477, 1400, 1361, 1250, 1203, 1173, 1026, 877, 540. Anal. Calcd
for C18H26NO3K: C, 63.02; H, 8.56; N, 4.17; O, 13.92. Found: C, 62.95;
H, 8.57; N, 4.07; O, 13.97.
1H), 7.388e7.391 (m, 3H), 7.280e7.388 (m, 5H), 4.628e4.644 (q,
J¼6.4 Hz, 1H), 1.548e1.565 (d, J¼6.8 Hz, 3H), 1.365 (s, 9H), 1.251 (s,
9H); 13C NMR (DMSO-d6, 100 MHz):
d 166.15, 157.86, 144.46, 140.18,
136.06, 129.09, 127.61, 127.00, 126.86, 126.69, 118.28, 67.39, 35.03,
34.32, 31.77, 29.76, 24.67; IR (cmꢀ1, KBr): 3421, 3052, 2960, 2867,
1630, 1443, 1250, 1172, 829, 765, 703. Anal. Calcd for C23H31NO: C,
81.85; H, 9.25; N, 4.15; O, 4.75. Found: C, 81.50; H, 9.26; N, 4.14; O,
5.10.
3.2.1.5. Ligand 5. Yellow powder, mp 121e123 ꢁC; yield, 1.5 g
(78%); 1H NMR (DMSO-d6, 400 MHz)
d 8.342 (s, 1H), 7.136e7.222 (d,
2H), 3.684e3.718 (t, J1¼4.8 Hz, J2¼4 Hz, 1H), 1.572e1.731 (m, 2H),
1.468e1.571 (m, 1H), 1.354 (s, 9H), 1.233 (s, 9H), 0.870e0.887 (d,
J¼6.8 Hz, 3H), 0.834e0.850 (d, J¼6.4 Hz, 3H); 13C NMR (DMSO-d6,
3.3. General procedure for the hydrosilylation of ketones
100 MHz),
d 174.14, 164.76, 161.54, 137.97, 136.74, 126.30, 117.78,
In a Schlenk flask ZnEt2 (0.03 mL, 1 M in hexanes, 0.03 mmol)
and chiral ligand (0.03 mmol) were dissolved in 3 mL of THF and
stirred under nitrogen atmosphere for 30 min. Then the tert-bu-
tanol (0.4 mL) and the corresponding ketone (1 mmol) was added,
and then HSi(OEt)3 (5 mL, 2.5 mmol) was added slowly to the
mixture. The reaction was kept at (ꢀ40 ꢁC) for 30 h. The reaction
mixture was poured on KOH 15% aqueous solution (5 mL) and
extracted with CH2Cl2 (3 mLꢂ3). The organic layer was washed
with water (3 mLꢂ2), dried over MgSO4, and concentrated in vacuo.
The product was purified by column chromatography on silica gel
with hexane-EtOAc (10:1) as eluent.
71.30, 43.47, 34.99, 34.12, 31.76, 29.77, 25.07, 23.93, 22.12; IR (cmꢀ1
,
KBr): 3421, 3052, 2958, 2869, 1630, 1474, 1361, 1298, 1249, 1172,
1071, 926, 879, 826, 802, 540. Anal. Calcd for C21H32NO3K: C, 65.43;
H, 8.31; N, 3.65; O, 12.48. Found: C, 65.42; H, 8.30; N, 3.63; O, 12.45.
3.2.1.6. Ligand 6. Yellow powder, mp 123e126 ꢁC; yield, 1.6 g
(83%); 1H NMR (DMSO-d6, 400 MHz)
d 8.342 (s, 1H), 7.135e7.222 (d,
2H), 3.684e3.718 (d, J¼4.8 Hz, 1H), 1.572e1.730 (m, 1H),
1.468e1570 (m, 1H), 1.354 (s, 9H), 1.233 (s, 9H), 0.870e0.887 (d,
J¼6.8 Hz, 3H), 0.833e0.849 (d, J¼6.4 Hz, 3H); 13C NMR (DMSO-d6,
100 MHz),
d 173.34, 164.77, 161.48, 137.58, 136.71, 126.30, 117.77,
71.30, 43.47, 34.98, 34.12, 31.75, 29.78, 25.06, 23.92, 22.12; IR (cmꢀ1
,
3.4. Conditions for the analysis and assignment of
configuration of the chiral secondary alcohol products from
the enantioselective reductions
KBr): 3421, 3052, 2958, 2869, 1630, 1474, 1361, 1298, 1249, 1172,
1071, 926, 879, 826, 802, 540. Anal. Calcd for C21H32NO3K: C, 65.44;
H, 8.32; N, 3.62; O, 12.49. Found: C, 65.42; H, 8.30; N, 3.63; O, 12.45.
Chiral
capillary
GC:
CP-ChiralSil-Dex
CB
column
3.2.1.7. Ligand 7. Yellow powder, mp 140e142 ꢁC; yield, 1.5 g
25 mꢂ0.25 mmꢂ0.39 mm. Carrier gas H2. Detector FID, 275 ꢁC.
(73%); 1H NMR (DMSO-d6, 400 MHz)
d 8.140 (s, 1H), 7.198e7.203 (d,
Injector 250 ꢁC.
2H), 7.039e7.187 (m, 5H), 3.812e3.844 (d, J1¼4.4 Hz, J2¼4.8 Hz, 1H),
Chiral HPLC: Chiralcel OD column, 254 nm UV detector.
3.408e3.422 (m, 2H), 1.358 (s, 9H), 1.211 (s, 9H); 13C NMR (DMSO-
d6, 100 MHz), d 173.21, 165.22, 160.65, 140.68, 138.37, 136.49, 129.71,
Acknowledgements
128.42, 126.30, 126.21, 126.06, 117.94, 74.94, 35.03, 34.15, 31.78,
29.79; IR (cmꢀ1, KBr): 3421, 3052, 2957,1628,1527, 1478,1399,1361,
1251, 1202, 1173, 1088, 701, 495. Anal. Calcd for C24H30NO3K: C,
68.74; H, 7.16; N, 3.37; O, 11.47. Found: C, 68.70; H, 7.15; N, 3.34; O,
11.44.
We are grateful to the Fund of Zhejiang province (2008C14041)
and the Fund of Zhejiang province (Y4100248) for financial support.
References and notes
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