Axially dissymmetric binaphthyldiimine chiral salen-type ligands for copper-catalyzed asymmetric aziridination

Article abstract of DOI:10.1016/S0957-4166(01)00534-1

Axially dissymmetric chiral salen-type ligands 1-4 and 7 were prepared from the reaction of (R)-(+)-1,1′-binaphthyl-2,2′-diamine with 2,6-dichlorobenzaldehyde, 2,3-dichlorobenzaldehyde, 3,4-dichlorobenzaldehyde or salicylaldehyde in high yields, respectively. The catalytic asymmetric aziridination of alkenes has been examined using these novel chiral ligands. Excellent enantioselectivity in the aziridination of cinnamates has been achieved using the C₂-symmetric chiral ligand 1.

Full text of DOI:10.1016/S0957-4166(01)00534-1

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 3105–3111
Axially dissymmetric binaphthyldiimine chiral salen-type ligands
for copper-catalyzed asymmetric aziridination
†
Min Shi,* Chuan-Jiang Wang and Albert S. C. Chan
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Lu, Shanghai 200032, China
Received 9 October 2001; accepted 16 November 2001
Abstract—Axially dissymmetric chiral salen-type ligands 1–4 and 7 were prepared from the reaction of (R)-(+)-1,1%-binaphthyl-
2
,2%-diamine with 2,6-dichlorobenzaldehyde, 2,3-dichlorobenzaldehyde, 3,4-dichlorobenzaldehyde or salicylaldehyde in high yields,
respectively. The catalytic asymmetric aziridination of alkenes has been examined using these novel chiral ligands. Excellent
enantioselectivity in the aziridination of cinnamates has been achieved using the C -symmetric chiral ligand 1. © 2002 Elsevier
2
Science Ltd. All rights reserved.
1
. Introduction
the copper complex bearing a bisoxazoline ligand was
an effective catalyst for the aziridination of styrene.
Jacobsen et al. utilized their own chiral diimine to serve
as an effective chiral auxiliary for the copper-catalyzed
Aziridines are versatile intermediates for the synthesis
of compounds bearing nitrogen functionalities. In
1
4
1
991, Evans et al. reported that cationic Cu(I) com-
plexes catalyzed the nitrene-transfer reaction [N-
p-tolylsulfonyl)imino]phenyliodane (PhI=NTs)
smoothly. Since then, many studies on asymmetric
aziridination have been carried out with chiral cop-
per(I) complexes as catalysts. Evans et al. were the first
to report that 4,4%-disubstuituted bisoxazolines are
excellent chiral ligands for enantioselective aziridina-
aziridination of aryl-substituted (Z)-olefins. In addi-
tion, Aggarwal disclosed catalytic asymmetric aziridina-
tion catalyzed by Rh (OAc) and mediated by chiral
(
2
4
1
5a
sulfur ylides, and Burrows and Katsuki employed
chiral Mn–salen complexes as catalyst for enantioselec-
5b,c
tive epoxidation and aziridination.
On the other
hand, axially dissymmetric 1,1%-binaphthyl and 1,1%-
biphenyl ligands bearing two identical groups in the 2-
and 2%-positions have proved remarkably useful in
2
a,b
3
tion.
Lowenthal and Masamune also reported that
Scheme 1.
*
Corresponding author. Fax: 86-21-64166128; e-mail: mshi@pub.sioc.ac.cn
The Hong Kong Polytechnic University.
†
0
957-4166/01/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(01)00534-1

3
106
M. Shi et al. / Tetrahedron: Asymmetry 12 (2001) 3105–3111
enantioselective catalysis, with enantioselectivities close
2,2%-diamine with 2,6-dichlorobenzaldehyde, gave the
highest e.e. (Table 1, entries 1–4) and the best result
(e.e. of 25%) was obtained with ligand 1 in the presence
to 100% enantiomeric excess (e.e.) being obtained in
6
several preparatively important reactions.
Very
recently, Scott disclosed that the highly enantioselective
aziridination of alkenes could be achieved using the
of Cu(MeCN) ClO in dichloromethane with 4 A MS
,
4 4
at −20°C (Table 1, entry 12). The solvent also played a
very important role in this reaction. Using benzene or
neat styrene as the solvents, the products were obtained
with lower e.e. (Table 1, entries 9–11). Especially when
the reaction was carried out in acetonitrile, no chiral
induction was observed (Table 1, entry 8). A copper(II)
I
7
[
(biaryldiimine)Cu ] catalyst system. Herein, we wish to
report the synthesis of axially dissymmetric binaph-
thyldiimine chiral salen-type ligands 1–4 and 7 from
C -symmetric (R)-(+)-1,1%-binaphthyl-2,2%-diamine and
2
the results from the catalytic asymmetric aziridination
8
of alkenes using these novel chiral ligands.
catalyst such as Cu(OTf) showed no chiral induction
2
ability for this reaction (Table 1, entry 6) and CuOTf
gave only 11% e.e. (Table 1, entry 7).
2
. Results and discussion
In order to reach higher enantioselectivity in the asym-
metric aziridination using chiral ligand 1, we next
examined the aziridination of other alkenes under the
optimized conditions. We were delighted to find that in
the asymmetric aziridination of indene, e.e. of 74%
could be achieved although the yield was only 22%
The axially chiral salen-type ligands 1–4 were prepared
by the reaction of C -symmetric (R)-(+)-1,1%-binaph-
2
thyl-2,2%-diamine as a chiral scaffold with the corre-
sponding arylaldehydes in anhydrous benzene in the
presence of 4 A molecular sieve (MS) (Scheme 1). After
,
(
Table 2, entry 3). In the presence of 4 A
the yield improved from 22 to 47% with 62% e.e. (Table
, entry 5). Reducing the temperature led to a slight
improvement of e.e. in the aziridination of indene
Table 2, entries 1–5). Excellent results were obtained in
the asymmetric aziridination of trans-cinnamates
Table 2, entries 6–16). In the aziridination of methyl
,
MS at −20°C,
the usual work-up and purification by silica gel column
chromatography or recrystallization, ligands 1–4 were
obtained as yellow solids in ca. 90% yields.
2
(
The C -symmetric chiral salen-type ligand 7 was pre-
1
pared in high yield by acylation of (R)-(+)-1,1%-binaph-
thyl-2,2%-diamine with acetic anhydride/acetic acid in
dichloromethane, reduction with LiAlH4 and subse-
quent reaction with 1,6-dichlorobenzaldehyde under the
same conditions as for 1–4 (Scheme 2).
(
cinnamate, e.e. of 69% was obtained at 20°C (reaction
time=4 h) and 75% e.e. was obtained at −20°C (reac-
tion time=24 h) with yields of over 90% in both cases
(
1
Table 2, entries 6 and 8). In acetonitrile, e.e. of only
1% was achieved under the same conditions (Table 2,
Catalytic asymmetric aziridination of the alkenes was
carried out in dichloromethane, THF or acetonitrile
with a molar ratio of copper:ligand:PhI=NTs:alkene of
entry 7). Moreover, using phenyl or tert-butyl cinna-
mate as the substrates under the same conditions, we
found that e.e.s of 88 and 97%, respectively, could be
achieved at −20°C with excellent yields (Table 2, entries
9 and 10).
0
.05:0.055:1:5. The e.e. of the product was determined
by HPLC analysis using a chiral stationary phase
column (CHIRALCEL OD, OJ or AB). The absolute
configuration of the major enantiomer was assigned
according to the sign of the specific rotation.
The substituents on the phenyl ring can also affect the
enantioselectivity of the aziridination of cinnamates.
For example, it was found that, using methyl, phenyl or
tert-butyl p-chlorocinnamate as substrates (Cl can be
seen as an electron-withdrawing group) 85%, 84% and
90% e.e., respectively, were achieved under the same
conditions (Table 2, entries 11, 12, and 13). The results
Using styrene as the substrate, we examined the chiral
induction abilities of chiral ligands 1–4 in catalytic
asymmetric aziridination. The results are summarized
in Table 1. We found that C -symmetric ligand 1,
derived from the reaction of (R)-(+)-1,1%-binaphthyl-
2
Scheme 2.

M. Shi et al. / Tetrahedron: Asymmetry 12 (2001) 3105–3111
3107
Table 1. Catalytic asymmetric aziridination of styrene
9
are very similar to those of cinnamates. However, using
methyl, phenyl or tert-butyl p-methoxycinnamate
asymmetric aziridination of alkenes (Scheme 3). But
only very poor enantioselectivities have been achieved.
We believe that this is because the catalytic site in
ligand 8 is relatively remote from the stereogenic center
in comparison with the best chiral ligand 1.
(
MeO is a typical electron-donating group) as substrate,
the aziridinations were relatively slow and these reac-
tions required 36 h to give the corresponding products
in yields of ca. 60%. The achieved e.e.s and chemical
yields are also lower than those observed for cinna-
mates (Table 2, entries 14, 15, and 16).
3
. Conclusions
On the other hand, using C -symmetric chiral ligand 7
in the aziridination of cinnamates under the same con-
ditions we found that the achieved e.e.s were in general
1
In conclusion, the chiral C -symmetric axially dissym-
2
metric chiral salen-type ligands 1–4 and C -symmetric
1
lower than those for C -symmetric chiral ligand 1,
salen-type ligand 7 were successfully synthesized. We
2
although the chemical yields were very similar (Table 3,
found that C -symmetric ligand 1, derived from the
2
entries 1–3). This result suggests that a C -symmetric
reaction of (R)-(+)-1,1%-binaphthyl-2,2%-diamine with
2,6-dichlorobenzaldehyde, gave excellent results in the
enantioselective aziridination of trans-cinnamate
derivatives. Although the achieved results are very sim-
2
ligand must be used in order to attain high e.e. in the
asymmetric aziridination reaction.
7
Previously, we reported a very similar axially dissym-
ilar to those reported by Scott, this is the first applica-
metric chiral(diimine) ligand 8 and Cu(OTf) -catalyzed
tion of ligand 1 in the asymmetric aziridination. Efforts
2

3
108
M. Shi et al. / Tetrahedron: Asymmetry 12 (2001) 3105–3111
Table 2. Catalytic asymmetric aziridination of alkenes
are underway to elucidate the mechanistic details of this
reaction and to disclose the exact structure of the active
species. Moreover, we are planning to synthesize more
bidentate C -symmetric chiral binaphthyldiimine lig-
ands in order to seek out more effective and stereoselec-
tive ligands, which can be utilized in other catalytic
2

M. Shi et al. / Tetrahedron: Asymmetry 12 (2001) 3105–3111
3109
Table 3. Catalytic asymmetric aziridination of alkenes in the presence of ligand 7
Cl
CH2
CH2
N
Cl
Cl
/
Cu(OTf)2
N
Ts
N
Cl
Ligand 8
+
PhI=NTs
Solvent
Scheme 3.
asymmetric reactions. Work along this line is currently
in progress.
Organic solvents used were dried by standard methods
when necessary. All solid compounds reported in this
paper gave satisfactory CHN microanalyses with an
Italian Carlo-Erba 1106 analyzer. Commercially
obtained reagents were used without further purifica-
tion. All reactions were monitored by TLC with
Huanghai GF254 silica gel coated plates. Flash column
chromatography was carried out using 300–400 mesh
silica gel at increased pressure. All aziridination experi-
ments were performed under argon using standard
Schlenk techniques. Dichloromethane and acetonitrile
were distilled from calcium hydride under nitrogen.
4. Experimental
4.1. General
MP was obtained with a Yanagimoto micro melting
point apparatus and is uncorrected. Optical rotations
were determined in a solution of CHCl at 20°C by
3
using a Perkin–Elmer-241 MC polarimeter; [h] values
D
−
1
2
−1
are given in units of 10 deg cm g . Infrared spectra
were measured on a Perkin–Elmer 983 spectrometer. H
CuClO and CuOTf were handled in the drybox under
4
1
an argon atmosphere. All olefins were distilled prior to
use. The enantiomeric purities of aziridines were deter-
mined by HPLC analyses using a chiral stationary
phase column (column, Daicel Co. Chiralcel OD, AB,
and OJ; eluent, 100:0.5–2 hexane–2-propanol mixture;
NMR spectra were recorded on a Bruker AM-300
spectrometer for solution in CDCl or C D with tetra-
3
6
6
methylsilane (TMS) as internal standard; coupling con-
stant (J) values are reported in Hz. Mass spectra were
recorded with a HP-5989 instrument and HRMS was
measured using a Finnigan MA+mass spectrometer.
−
1
flow rate, 1.0 mL min ; detection, 254 nm light) and
the absolute configuration of the major enantiomer was

3
110
M. Shi et al. / Tetrahedron: Asymmetry 12 (2001) 3105–3111
assigned according to the sign of the specific rotation.
R)-(+)-1,1%-Binaphthyl-2,2%-diamine was purchased
from Aldrich Co.
mg, 0.5 mmol), acetic acid (0.3 mL, 5.0 mmol) and
dichloromethane (5.0 mL) with ice-cooling. The mix-
ture was stirred at room temperature overnight, and
(
saturated NaHCO (5.0 mL) was added. After extrac-
3
4
.2. Representative experimental details for the synthe-
tion with dichloromethane, the combined organic layers
sis of ligands 1–4
were dried over MgSO . The residue obtained upon
4
evaporation was purified by column chromatography
on Al O (eluent: hexane:ethyl acetate=3:1) to afford 5
(
R)-(+)-1,1%-Binaphthyl-2,2%-diamine (0.2 mmol), aryl-
2
3
1
aldehyde (0.56 mmol) and MS (4 A, ca. 0.2 g) were
,
as a colorless solid (90 mg, 55%). H NMR (CHCl ,
3
stirred in anhydrous benzene (5.0 mL) at room temper-
ature for 10 h. After filtration, the solvent was removed
under reduced pressure and the corresponding Schiff
base was separated by flash chromatography on silica
TMS, 300 MHz) l 1.83 (s, 3H, Me), 3.60 (br, 3H,
amino-H), 6.85–7.44 (m, 7H, Ar H), 7.79–8.03 (m, 4H,
Ar), 8.40 (d, J=8.9 Hz, 2H, Ar). This compound was
used for the next reaction.
gel (eluent: hexane:EtOAc:Et N=250:10:1). The yields
of 1–4 were about 90%.
3
4.4. (R)-(+)-N-Ethyl-1,1%-binaphthyl-2,2%-diamine 6
4
.2.1. Ligand 1: (R)-(+)-N,N%-Bis(2,6-dichlorobenzyli-
To a stirred suspension of LiAlH (93 mg, 2.65 mmol)
4
20
dene)-1,1%-binaphthyl-2,2%-diamine. [h] −88 (c 0.089,
in anhydrous THF (20 mL) was added dropwise a
solution of 5 (170 mg, 0.53 mmol) in THF (2 mL). The
mixture was heated under reflux for 4 h. The reaction
mixture was cooled in an ice-bath and the remaining
hydride was carefully quenched by dropwise addition of
water (1.0 mL) and then 10% NaOH (1.0 mL). A white
precipitate was filtered off and thoroughly washed with
ether. The combined filtrate and ether washings were
D
−
1
acetone); mp: 180–181°C; IR (CH Cl ) w 1615 cm
2
2
1
(
CꢀN); H NMR (C D , TMS, 300 MHz) l 6.22 (m,
6
6
2
2
2
8
H), 6.64 (d, J=8.0 Hz, 4H), 7.12 (m, 2H), 7.23 (m,
H), 7.47 (d, J=8.67 Hz, 2H), 7.60 (d, J=8.58 Hz,
H), 7.78 (d, J=8.1 Hz, 2H), 7.86 (d, J=8.7 Hz, 2H),
+
.73 (s, 2H, imino-H); MS (EI) m/e 598 (M , 6.09), 441
+
+
(
M −158, 100), 424 (M −174, 29.8); anal. calcd for
C H Cl N requires C, 68.23; H, 3.34; N, 4.68; found:
washed with brine and dried over MgSO . After the
3
4
20
4
2
4
C, 68.53; H, 3.47; N, 4.32%.
solvents were evaporated under reduced pressure, the
product was purified by flash chromatography (Al O ,
2
3
4
.2.2. Ligand 2: (R)-(+)-N,N%-Bis-(2,3-dichlorobenzyli-
EtOAc:petroleum ether=1:6) affording 6 (130 mg,
20
1
dene)-1,1%-binaphthyl-2,2%-diamine. [h] +282 (c 0.13,
91%) as a colorless solid. H NMR (CDCl , TMS, 300
D
3
−
1
acetone); mp: 130–131°C; IR (CH Cl ) w 1607 cm
MHz) l 1.92 (t, J=6.7 Hz, 3H, Me), 3.14 (q, J=6.7
2
2
1
(
2
CꢀN); H NMR (C D , TMS, 300 MHz) l 6.29 (m,
Hz, 2H, CH ), 3.48 (br, 3H, amino-H), 6.84–7.20 (m,
6
6
2
H), 6.80–6.83 (m, 2H), 7.05–7.10 (m, 2H), 7.18–7.27
8H, Ar), 7.65–7.82 (m, 4H, Ar). This compound was
(
2
3
m, 4H), 7.55–7.64 (m, 4H), 7.71–7.78 (m, 4H), 8.77 (s,
used in the next reaction.
+
+
H, imino-H); MS (EI) m/e 598 (M , 27.42), 561 (M −
+
7, 1.01), 424 (M −174, 100); anal. calcd for
4.5. Chiral ligand 7: (R)-(+)-N-ethyl-N%-(2,6-
dichlorobenzylidene)-1,1%-binaphthyl-2,2%-diamine
C H Cl N requires C, 68.23; H, 3.34; N, 4.68; found:
C, 68.11; H, 3.37; N, 4.58%.
3
4
20
4
2
Compound 6 (63 mg, 0.2 mmol), 2,6-dichlorobenzalde-
4
.2.3. Ligand 3: (R)-(+)-N,N%-Bis-(3,4-dichlorobenzyli-
hyde (49 mg, 0.28 mmol), and MS (4 A, ca. 0.2 g) were
,
2
0
dene)-1,1%-binaphthyl-2,2%-diamine. [h] +15 (c 0.1, ace-
stirred in anhydrous benzene (5.0 mL) at room temper-
ature for 10 h. After filtration, the solvent was removed
under reduced pressure and the corresponding Schiff
base was separated by flash chromatography on silica
D
−
1
tone); mp: 162–163°C; IR (CH Cl ) w 1614 cm (CꢀN);
2
2
1
H NMR (C D , TMS, 300 MHz) l 6.71 (d, J=8.3 Hz,
6
6
2
6
7
H), 6.90 (m, 2H), 7.04–7.12 (m, 2H), 7.18–7.26 (m,
H), 7.55–7.64 (m, 4H), 7.58 (d, J=8.7 Hz, 2H), 7.75–
.82 (m, 4H), 7.84 (s, 2H, imino-H); MS (EI) m/e 598
gel (eluent: hexane:EtOAc:Et N=300:10:1) to afford a
3
2
0
yellowish viscous compound 7: 78 mg, 83%; [h] −60.5
D
+
+
+
−1
1
(M , 6.11), 561 (M −37, 1.60), 424 (M −174, 100); anal.
calcd for C H Cl N requires C, 68.23; H, 3.34; N,
(c 0.13, acetone); IR (CH Cl ) w 1615 cm (C=N); H
2 2
NMR (CDCl , TMS, 300 MHz) l 1.64 (t, J=6.7 Hz,
3
4
20
4
2
3
4
.68; found: C, 68.14; H, 3.31; N, 4.52%.
3H, Me), 2.78 (q, J=6.7 Hz, 2H, CH ), 3.59 (br, 1H,
2
amino-H), 6.18 (t, J=8.5 Hz, 1H), 6.61 (d, J=8.5 Hz,
2H), 6.98–7.23 (m, 4H), 7.44–7.60 (m, 2H), 7.70–7.83
4
.2.4. Ligand 4: (R)-(+)-N,N%-Bis-(2-hydroxylbenzyli-
2
0
+
dene)-1,1%-binaphthyl-2,2%-diamine. [h] −655 (c 0.12,
(m, 6H), 8.44 (s, 1H, imino-H); MS (EI) m/e 468 (M ,
D
1
+
+
acetone); H NMR (C D , TMS, 300 MHz) l 6.61 (d,
63.64), 424 (M −44, 14.61), 309 (M −159, 57.73), 280
6
6
+
J=7.9 Hz, 2H), 6.82 (t, J=7.2, 6.5 Hz, 2H), 7.20–7.34
m, 6H), 7.42–7.49 (m, 4H), 7.90 (d, J=8.9 Hz, 2H),
.07 (d, J=8.1 Hz, 2H), 8.22 (d, J=8.9 Hz, 2H), 8.98
s, 2H, imino-H). This is a known compound. The
(M −188, 100); anal. calcd for C H Cl N requires C,
29
22
2
2
(
8
74.36; H, 4.70; N, 5.98; found: C, 74.01; H, 4.41; N,
5.73%.
(
10
physical data are inconsistent with those reported.
4.6. Typical reaction procedure for the aziridination
reaction catalyzed by [Cu(CH CN) ]ClO
3
4
4
4.3. (R)-(+)-N-Acetyl-1,1%-binaphthyl-2,2%-diamine 5
To a schlenk tube placed with chiral ligand 1 (9.0 mg,
0.014 mmol), molecular sieve (MS) (4 A, ca. 40 mg) and
anhydrous dichloromethane (2 mL) were added
Acetic anhydride (52 mL, 0.55 mmol) was added to a
mixture of (R)-(+)-1,1%-binaphthyl-2,2%-diamine (142
,

M. Shi et al. / Tetrahedron: Asymmetry 12 (2001) 3105–3111
3111
[
Cu(CH CN) ]ClO (4.0 mg, 0.013 mmol) under an
5328; (b) Evans, D. A.; Woerpel, K. A.; Hinman, M. M.;
Faul, M. M. J. Am. Chem. Soc. 1991, 113, 726.
3. Lowenthal, R. E.; Masamune, S. Tetrahedron Lett. 1991,
32, 7373.
3
4
4
argon atmosphere. The reaction mixture was stirred for
2
1
h at room temperature. Methyl cinnamate (202 mg,
.23 mmol) was added and the solution was stirred for
a further 30 min. The solution was then cooled to
20°C and solid PhI=NTs (94 mg, 0.25 mmol) was
4. Li, Z.; Conser, K. R.; Jacobsen, E. N. J. Am. Chem. Soc.
−
1993, 115, 5326.
added against a positive argon counterflow. The hetero-
geneous mixture was stirred at −20°C for 1 h. After the
specified time interval the solution was filtered through
a plug of silica gel, and the product was separated by
flash chromatography on silica gel (eluent:
EtOAc:hexane=1:6). Enantiomeric excess (e.e.) was
readily determined using Chiral HPLC.
5
. (a) Aggarwal, V. K.; Thompson, A.; Jones, R. V. H.;
Standen, M. C. H. J. Org. Chem. 1996, 61, 8368; (b)
O’Connor, K. J.; Wey, S.-J.; Burrows, C. J. Tetrahedron
Lett. 1992, 33, 1001; (c) Noda, K.; Hosoya, N.; Irie, R.;
Ito, Y.; Katsuki, T. Synlett 1993, 469.
6. (a) Noyori, R.; Takaya, H. Acc. Chem. Res. 1990, 23,
345; (b) Noyori, R.; Suga, S.; Kawai, K.; Okada, S.;
Kitamura, M. Pure Appl. Chem. 1988, 60, 1597; (c)
Tomioka, K. Synthesis 1990, 541; (d) Brunner, H. Syn-
thesis 1988, 645; (e) Narasaka, K. Synthesis 1991, 1; (f)
Noyori, R. Chem. Soc. Rev. 1989, 18, 187; (g) Kaufmann,
D.; Boese, R. Angew. Chem., Int. Ed. Engl. 1990, 29, 545.
. (a) Sanders, C. J.; Gillespie, K. M.; Bell, D.; Scott, P. J.
Am. Chem. Soc. 2000, 122, 7132; (b) Gillespie, K. M.;
Crust, E. J.; Deeth, R. J.; Scott, P. Chem. Commun. 2001,
Acknowledgements
We thank the State Key Project of Basic Research
Project 973) (No. G2000048007) and the National
Natural Science Foundation of China for financial sup-
port (20025206). We also thank the Inoue Photochiro-
genesis Project (ERATO, JST) for chemical reagents.
7
8
(
785.
. The utilization of ligand 1 in the asymmetric cyclopropa-
nation of olefins has been reported before. However, the
synthetic details and physical data have not been
reported. Please see: Suga, H.; Fudo, T.; Ibata, T. Synlett
References
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