A novel trinuclear titanium(IV) complex with a C3 axis along Ti1-Ti2-Ti3 containing 3-[(1H-1,2,4-triazol-1-yl)methyl]-BINOLate ligands: synthesis, structure, and reactivity

Article abstract of DOI:10.1016/j.tetasy.2006.07.043

A new modified BINOL, (S)-3-[(1H-1,2,4-triazol-1-yl)methyl]-1,1′-binaphthol, was prepared. In the presence of titanium tetraisopropoxide, this ligand showed moderate catalytic properties for the asymmetric addition of diethylzinc to aldehydes. By treating rac-3-[(1H-1,2,4-triazol-1-yl)methyl]-1,1′-binaphthol with excess titanium tetraisopropoxide, a novel trinuclear titanium(IV) complex was obtained. A C₃ axis along Ti1-Ti2-Ti3 is present in the molecule.

Full text of DOI:10.1016/j.tetasy.2006.07.043

Tetrahedron: Asymmetry 17 (2006) 2149–2153
A novel trinuclear titanium(IV) complex with a C3 axis
along Ti1–Ti2–Ti3 containing 3-[(1H-1,2,4-triazol-1-yl)methyl]-
BINOLate ligands: synthesis, structure, and reactivity
Bing Liu, Fu-Yong Jiang, Hai-Bin Song and Jin-Shan Li*
State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, PR China
Received 6 July 2006; accepted 28 July 2006
Abstract—A new modified BINOL, (S)-3-[(1H-1,2,4-triazol-1-yl)methyl]-1,10-binaphthol, was prepared. In the presence of titanium tetra-
isopropoxide, this ligand showed moderate catalytic properties for the asymmetric addition of diethylzinc to aldehydes. By treating
rac-3-[(1H-1,2,4-triazol-1-yl)methyl]-1,10-binaphthol with excess titanium tetraisopropoxide, a novel trinuclear titanium(IV) complex
was obtained. A C3 axis along Ti1–Ti2–Ti3 is present in the molecule.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
complexes have also been successfully used to catalyze
many asymmetric processes.2 Nakai3 and Chan4 reported
addition of diethylzinc to aldehydes catalyzed by chiral
titanium BINOLate complexes. Ding5 and Chan6 reported
the catalytic asymmetric addition of diethylzinc to alde-
Chiral 1,10-binaphthol (BINOL) has been successfully
applied in a wide range of catalytic asymmetric reactions
in the presence of various metals.1 Titanium BINOLate
CHO
i) 1.05 eq. nBuLi / THF
OMOM
OMOM
OMOM
OMOM
ii) DMF
MOM = CH2OCH3
4
(S)-
(S)-3
N
N
N
N
i) NaBH4 / CH3OH
ii) MsCl / Et3N
N
N
6 M HCl
OH
OH
OMOM
OMOM
iii) 1,2,4-triazole / K2CO3
(S)-1: H2L
(S)-5
Scheme 1. Synthesis of (S)-3-[(1H-1,2,4-triazol-1-yl)methyl]-1,10-binaphthol.
*
Corresponding author. Tel.: +86 22 23504230; fax: +86 22 23503627; e-mail: jinshanl@nankai.edu.cn
0957-4166/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2006.07.043

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B. Liu et al. / Tetrahedron: Asymmetry 17 (2006) 2149–2153
Figure 1. (a): The molecular structure of [Ti3L3(OPri)6] 2, (b): view along the C3 axis Ti3–Ti2–Ti1.
hydes using chiral titanium H4-BINOLate and H8-BINOL-
ate complexes, respectively. Walsh et al.7 reported in detail
the crystal structures of some titanium BINOLate and
H8-BINOLate complexes to investigate the mechanisms
of the reactions. However, only a few titanium 3- or 3,30-
substituted BINOLate complexes have been synthesized
and studied.2c,7,8 Herein, we report the synthesis of a new
3-substituted BINOL ligand (S)-3-[(1H-1,2,4-triazol-1-yl)-
methyl]-1,10-binaphthol 1 and its titanium complex [Ti3L3-
(OiPr)6Æ3CH2Cl2] 2 and the effectiveness of the ligand
(S)-1 in the titanium complex-catalyzed enantioselective
addition of diethylzinc to aldehydes.
Selected bond distances and angles are listed in Table 1.
The Ti1–Ti2 distance is 3.116(4) A. The Ti–O or Ti–N
˚
bond distances are particularly noteworthy. With regard
˚
˚
to Ti3, the three Ti3–O distances are equal to 1.757(7) A
and the three Ti3–N distances are equal to 2.288(9) A.
The situation of the Ti1–O or Ti2–O distances is fully sim-
ilar to the Ti3–O distances. The three bridging aryloxide
˚
Ti1–O distances are 2.167(7) A while the three isopropox-
˚
ide Ti1–O distances are 1.779(7) A. Likewise, the three
˚
bridging aryloxide Ti2–O distances are 2.034(6) A while
the three terminal aryloxide Ti2–O distances are
˚
1.857(6) A. At the same time, the three O–Ti3–O angles
are equal to 101.2(3)ꢁ and the three N–Ti3–N angles are
equal to 80.3(3)ꢁ. For Ti1 and Ti2 every three correspond-
ing O–Ti–O angles are also equal.
2. Results and discussion
Ligand (S)-1 was synthesized as shown in Scheme 1. The
lithium salt of (S)-2,20-bis(methoxymethyl)-1,10-binaph-
thol 3 reacted with DMF to afford (S)-3-formyl-2,20-
bis(methoxymethyl)-1,10-binaphthol 4 in 57% yield after
purification by column chromatography on silica gel.9 By
the reduction, methanesulfonylation and reaction with
1H-1,2,4-triazole, (S)-4 was transformed into (S)-5.10 After
deprotection, (S)-1 was obtained. By treating 2 equiv of tita-
nium tetraisopropoxide with rac-3-[(1H-1,2,4-triazol-1-yl)-
methyl]-BINOL, a nice C3-symmetric trinuclear titanium
complex 2 was obtained and its crystal structure was deter-
mined by X-ray diffraction.11
˚
Table 1. Selected bond distances (A) and angles (deg)
˚
Bond
Distances (A)
Bond
Angles (deg)
Ti1–Ti2
Ti1–O3
Ti1–O3A
Ti1–O3B
Ti1–O1
Ti2–O2
Ti2–O1
Ti3–O4
Ti3–N3
3.116(4)
1.779(7)
1.779(7)
1.779(7)
2.167(7)
1.857(6)
2.034(6)
1.757(7)
2.288(9)
Ti1–Ti2–Ti3
O3A–Ti1–O3
O3B–Ti1–O3
O3A–Ti1–O3B
O1–Ti1–O1A
180
100.4(3)
100.4(3)
100.4(3)
68.5(3)
96.0(2)
73.6(3)
101.2(3)
80.3(3)
118.2(10)
123.0(10)
O2A–Ti2–O2
O1A–Ti2–O1B
O4B–Ti3–O4A
N3A–Ti3–N3B
C9–C10–C11–C20
C1–C10–C11–C12
The molecule of 2 consists of a trinuclear titanium center
bonded to three 3-[(1H-1,2,4-triazol-1-yl)methyl]-BINOL-
ate ligands (Fig. 1(a)). All titanium atoms are six-coordi-
nate while the stereochemistry of the three titanium
centers are all distorted octahedral geometry. The middle
titanium (Ti2) is bonded to the six oxygens of three BINO-
Lates, among which three (O2, O2A, O2B) are terminal
and the others (O1, O1A, O1B) are bridging to Ti1. In
addition, Ti1 is still bonded to three isopropoxide groups.
Ti3 is bonded to the three nitrogens at the 4-position of
1,2,4-triazoles and three isopropoxide groups. The forma-
tion of the three Ti3–N bonds makes the whole molecule
orderliness. The crystallographic data show that there is a
C3 axis along Ti1–Ti2–Ti3 in the molecule (Fig. 1(b)).
As shown in Figure 1, the three 3-[(1H-1,2,4-triazol-1-yl)-
methyl]-BINOLate ligands are homochiral [(R)-configura-
tion]. The three-substituted naphthalene plane of one
BINOLate ligand is parallel with the unsubstituted one of
the adjacent ligand, clockwise along the Ti3–Ti2–Ti1 axis.
Every dihedral angle between the two naphthalene units is
66.9ꢁ. Additionally, the three dihedral angles of the 1,2,4-
triazole rings are all 103.0ꢁ. Therefore, the three triazole
rings can be considered as a regular propeller blade, while
the six naphthalene units can be considered as a double
propeller blade along the C3 axis.

B. Liu et al. / Tetrahedron: Asymmetry 17 (2006) 2149–2153
2151
Up until now, the asymmetric addition of diethylzinc to
aldehydes is considered as a classical test for the design
of new catalysts.12 We examined the chiral ligand
(S)-3-[(1H-1,2,4-triazol-1-yl)methyl]-1,10-binaphthol in the
enantioselective addition of diethylzinc to aldehydes.13
Instantly, 1-naphthaldehyde was taken as the substrate
for optimizing the reaction conditions. As shown in Table
2, when changing the amount of ligand from 20 mol % to
5 mol %, it led to a slight change in enantioselectivity, while
from 5 mol % to 1 mol %, led to a large decrease in enantio-
selectivity (entries 1–5). The best molar ratio of the ligand
to metal was set up to be 1–12 in the addition reaction
(entries 3, 6, and 7).
trinuclear titanium complex with the Ti1–Ti2–Ti3 axis con-
taining three 3-[(1H-1,2,4-triazol-1-yl)methyl]-1,10-BINOL-
ate ligands. We used the chiral ligand in the asymmetric
addition of diethylzinc to aldehydes to afford the corre-
sponding secondary alcohols in high yields and moderate
ee values.
4. Experimental
4.1. General
1
The H and 13C NMR spectra were recorded on a Bruker
AC-300 instrument in CDCl3 solution with TMS as the
internal standard. Optical rotations were measured on a
Perkin–Elmer 241 polarimeter. Elemental analysis was per-
formed with a Yanaco CHN Corder MT-3 elemental ana-
lyzer. All experiments, which are sensitive to moisture or
air, were carried out under argon atmosphere using stan-
dard Schlenk techniques. Diethylzinc was purchased from
Aldrich. All anhydrous solvents were purified and dried
by standard techniques just before use.
Table 2. Optimization of reaction conditions for enantioselectivity of the
addition of Et2Zn to 1-naphthaldehyde
HO
*
CHO
L*/ Ti(OiPr)4
+
Et2Zn
toluene
Entry L*
(mol %) (M/M)
L*/Ti(OiPr)4 Yielda eeb
Configurationc
(%)
(%)
1
2
3
4
5
6
7
20
10
5
3
1
1/12
1/12
1/12
1/12
1/12
1/6
97.6
76.9
80.3
76.7
69.0
41.5
71.3
44.0
S
S
S
S
S
S
S
4.2. Synthesis of (S)-3-formyl-2,20-bis(methoxymethyl)-1,10-
bi-naphthol (S)-4
93.3
96.8
100.0
94.3
93.8
96.3
To a stirred solution of MOM-protected (S)-binaphthol
(S)-3 (5.61 g, 15.1 mmol) in 60 mL of dry THF was added
n-BuLi (8.4 mL, 15.8 mmol, 1.89 M in hexane) at ꢀ78 ꢁC.
The mixture was stirred overnight at room temperature.
After cooling down to 0 ꢁC, DMF (1.4 mL, 15.8 mmol)
was added dropwise over 15 min. The mixture was then
warmed up to room temperature and stirred for further
2 h. The reaction mixture was quenched with saturated
aq NH4Cl. The solution was then extracted with ethyl ace-
tate, and the combined organic layer washed with water
and brine, and then dried over Na2SO4. After removal of
solvent, the residue was purified by column chromatogra-
5
5
1/2
a Isolated yield.
b Data were determined by GC analysis using a chiral column (Chiral
beta-DEX 120 capillary column).
c Based on the reported specific rotation (see Ref. 14).
Then, the addition of diethylzinc to a variety of aldehydes
catalyzed by the titanium complex has been studied and the
results are summarized in Table 3.
Table 3. Enantioselective addition of diethylzinc to aldehydes with the
phy (hexane/ethyl acetate 5:1) to give (S)-4 (3.75 g, 62%)
catalyst
25
as a yellow solid. Melting point: 110–112 ꢁC. ½aꢁD
¼
OH
*
O
ꢀ83:3 (c 0.4, CHCl3).
5 mol% L*/ Ti(OiPr)4
toluene
+
Et2Zn
R
H
R
4.3. Synthesis of (S)-3-[(1H-1,2,4-triazol-1-yl)methyl]-2,20-
bis(methoxymethyl)-1,10-binaphthol (S)-5
Entry
R
Yielda (%)
eeb (%)
Configurationc
1
2
3
4
5
6
7
8
9
C6H5
p-ClC6H4
p-BrC6H4
p-MeC6H4
p-MeOC6H4
p-Me2NC6H4
o-MeOC6H4
1-Naphthyl
PhCH@CH
69.0
79.6
83.3
64.7
89.3
77.2
90.5
96.8
89.1
69.2
70.3
67.3
68.1
61.7
70.4
66.4
76.7
72.4
S15
S16
S17
S18
S18
S19
S20
S14
S21
To a solution of (S)-3-formyl-2,20-bis(methoxymethyl)-
1,10-binaphthol (S)-4 (3.77 g, 9.4 mmol) in methanol
(50 mL) and THF (50 mL) was added NaBH4 (0.45 g,
11.7 mmol) at 0 ꢁC. After 30 min saturated aq NH4Cl
was added and the reaction mixture concentrated. The res-
idue was extracted with ethyl acetate (50 mL · 3). The
combined organic layer was washed with brine (50 mL)
and dried over Na2SO4. Solvent was removed under
reduced pressure and the crude product was directly used
in the next reaction without purification. The solution of
the crude product (1.78 g, 4.4 mmol) in ethyl acetate
(50 mL) was cooled to 0 ꢁC. To this solution, MsCl
(0.70 mL, 8.8 mmol) and Et3N (2.50 mL, 17.6 mmol) were
added successively. After 1 h, the reaction mixture was fil-
tered and the filtrate concentrated to dryness. The obtained
pale-yellow oil was dissolved in 100 mL of acetone. 1H-
a Isolated yield.
b Data were determined by GC analysis using a chiral column (Chiral
beta-DEX 120 capillary column).
c Based on the reported optical rotation.
3. Conclusion
In conclusion, we have synthesized (S)-3-[(1H-1,2,4-triazol-
1-yl)methyl]-1,10-binaphthol and a novel C3-symmetric

2152
B. Liu et al. / Tetrahedron: Asymmetry 17 (2006) 2149–2153
1,2,4-Triazole (0.30 g, 4.4 mmol) and anhydrous K2CO3
(0.61 g, 4.4 mmol) were added successively. The reaction
mixture was refluxed for 7 h. The precipitate was filtered
off and the solvent was removed under reduced pressure.
The residue was chromatographed (hexane/ethyl ace-
tate = 1:1) to afford compound (S)-5 (1.14 g, 2.5 mmol)
7.15 (m, 2H), 7.03 (m, 2H), 5.30 (s, 2H), 4.65 (m, 1H),
4.37 (m, 1H), 3.99 (d, J = 13.72 Hz, 1H), 3.45 (d, J =
13.82 Hz, 1H), 1.20 (d, J = 6.13 Hz, 1H), 1.17 (d,
J = 6.06 Hz, 2H), 0.90 (d, J = 6.10 Hz, 3H), 0.67 (d,
J = 6.07 Hz, 3H), 0.57 (d, J = 6.10 Hz, 3H).
in 57% yield as
C27H25N3O4 (Mr = 455.51): C, 71.19; H, 5.53; N, 9.22.
a white solid. Anal. Calcd for
4.6. A typical procedure for the asymmetric addition
of diethylzinc to aldehydes
Found: C, 71.21; H, 5.55, N, 9.01. Melting point: 109–
25
110 ꢁC. ½aꢁD ¼ ꢀ56:6 (c 1.4, CH2Cl2). 1H NMR
Titanium tetraisopropoxide (0.18 mL, 0.6 mmol) was
added to a solution of (S)-1 (0.018 g, 0.05 mmol) in 3 mL
of toluene at room temperature. The reaction mixture
was stirred for 30 min followed by the addition of diethyl-
zinc (2.59 M in hexane, 1.16 mL) with continuous stirring
for 15 min. The solution was cooled to 0 ꢁC and 1-naphth-
aldehyde (0.14 mL, 1 mmol) was added via syringe. The
reaction mixture was filtered through Celite to remove
the insoluble material and the filtrate was extracted with
3 · 20 mL ethyl acetate. The combined organic layers were
then dried over MgSO4. The residue was purified by col-
umn chromatography on silica gel to afford 1-napthhyl-1-
propanol as a light yellow liquid. The enantiomeric excess
of the products was determined by GC on a Chiral beta-
DEX 120 capillary column.
(300 MHz, CDCl3) d: 8.24 (s, 1H), 8.03 (s, 1H), 7.98 (d,
J = 9.12 Hz, 1H), 7.88 (d, J = 8.11 Hz, 1H), 7.83 (d,
J = 8.16 Hz, 1H), 7.72 (s, 1H), 7.59 (d, J = 9.08 Hz, 1H),
7.35–7.42 (m, 2H), 7.23–7.30 (m, 2H), 7.10–7.18 (m, 2H),
5.72 (dd, J = 15.04 Hz, 2H), 5.09 (dd, J = 7.02 Hz, 2H),
4.57 (d, J = 5.70 Hz, 1H), 4.44 (d, J = 5.72 Hz, 1H), 3.16
(s, 3H), 3.10 (s, 3H). 13C NMR (75 MHz, CDCl3) d:
152.8, 152.1, 151.2, 143.3, 134.2, 133.7, 130.7, 130.3,
129.7, 129.5, 128.1, 128.0, 127.0, 126.9, 125.8, 125.6,
125.2, 124.3, 119.7, 116.3, 99.5, 94.8, 57.1, 56.0, 50.2.
4.4. Synthesis of (S)-3-[(1H-1,2,4-triazol-1-yl)methyl]-1,1-
binaphthol (S)-1
(S)-5 (1.14 g, 2.5 mmol) was dissolved in the mixed solvent
of methanol/dichloromethane (30 mL/30 mL). At 0 ꢁC
HCl (6 M, 1.6 mL) was added dropwise. The reaction mix-
ture was stirred at room temperature for 3 h and the sol-
vent removed under reduced pressure. The residue was
extracted with ethyl acetate (50 mL). The extract was
washed with water, satd NaHCO3, and brine in turn. After
drying over Na2SO4 and removal of solvent, compound
(S)-1 (0.85 g, 2.3 mmol) was obtained in 90% yield as a
white solid. Anal. Calcd for C23H17N3O2 (Mr = 367.40):
Acknowledgements
We thank the National Natural Science Foundation of
China (Grant No. 20372037) for funding this project.
References
C, 75.19; H, 4.66; N, 11.44. Found: C, 74.64; H, 5.12; N,
25
12.04. Melting point: 150–153 ꢁC. ½aꢁD ¼ ꢀ29:3 (c 0.3,
1. (a) Pu, L. Chem. Rev. 1998, 98, 2405; (b) Chen, Y.; Yekta, S.;
Yudin, A. K. Chem. Rev. 2003, 103, 3155; (c) Kocˇovsku´, P.;
Vyskocˇil, S.; Smrcˇina, M. Chem. Rev. 2003, 103, 3213; (d)
Brunel, J. M. Chem. Rev. 2005, 105, 857.
CH2Cl2). 1H NMR (300 MHz, CDCl3) d: 8.23 (s, 1H),
7.96 (d, J = 8.90 Hz, 1H), 7.85 (m, 3H), 7.78 (s, 1H), 7.39
(m, 3H), 7.29 (m, 2H), 7.14 (d, J = 8.08 Hz 1H), 7.05
(d, J = 8.26 Hz 1H), 5.55 (dd, J = 14.69 Hz, 2H). 13C
NMR (75 MHz, CDCl3) d: 152.9, 151.5, 150.7, 143.5,
133.8, 133.4, 131.5, 131.3, 129.4, 129.0, 128.5, 128.5,
128.0, 127.4, 124.7, 124.5, 124.1, 124.0, 123.5, 118.1,
113.2, 110.9, 49.7.
2. (a) Rosini, C.; Franzini, L.; Raffaelli, A.; Salvadori, P.
Synthesis 1992, 503; (b) Posner, G. H.; Dai, H.; Bull, D. S.;
Lee, J. K.; Eydoux, F.; Ishihara, Y.; Welsh, W.; Pryor, N.;
Petr, S. J. J. Org. Chem. 1996, 61, 671; (c) Mikami, K.; Ueki,
M.; Matsumoto, Y.; Terada, M. Chirality 2001, 13, 541; (d)
Moore, D.; Pu, L. Org. Lett. 2002, 4, 1855; (e) Gao, G.;
Moore, D.; Xie, R.-G.; Pu, L. Org. Lett. 2002, 4, 4143; (f) Xu,
M.-H.; Pu, L. Org. Lett. 2002, 4, 4555; (g) Moore, D.; Huang,
W. S.; Xu, M. H.; Pu, L. Tetrahedron Lett. 2002, 4, 8831; (h)
Lu, G.; Li, X. S.; Chan, W. L.; Chan, A. S. C. Chem.
Commun. 2002, 172; (i) Matsukawa, S.; Mikami, K. Tetra-
hedron: Asymmetry 1995, 6, 2571; (j) Lu, G.; Li, X. S.; Chen,
G.; Chan, W. L.; Chan, A. S. C. Tetrahedron: Asymmetry
2003, 14, 449.
3. Mori, M.; Nakai, T. Tetrahedron Lett. 1997, 38, 6233.
4. Zhang, F. Y.; Yip, C. W.; Cao, R.; Chan, A. S. C.
Tetrahedron: Asymmetry 1997, 8, 585.
5. Shen, X.; Guo, H.; Ding, K. L. Tetrahedron: Asymmetry
2000, 11, 4321.
6. Zhang, F. X.; Chan, A. S. C. Tetrahedron: Asymmetry 1997,
8, 3651.
7. (a) Davis, T. J.; Balsells, J.; Carroll, P.; Walsh, P. J. Org. Lett.
2001, 3, 699; (b) Waltz, K. M.; Carroll, P.; Walsh, P. J.
Organometallics 2004, 23, 127; (c) Balsells, J.; Davis, T. J.;
Carroll, P.; Walsh, P. J. J. Am. Chem. Soc. 2002, 124, 10336.
4.5. Synthesis of titanium complex 2
Under an argon atmosphere compound rac-1 (0.410 g,
1.12 mmol) was suspended in dichloromethane (10 mL).
To this suspension was added the solution of titanium
isopropoxide (0.634 g, 2.23 mmol) in dichloromethane
(10 mL) dropwise. The reaction mixture became clear deep
red. After stirring at room temperature for 6 h, solvent and
isopropanol were evaporated. Recrystallization of the
resulting solid by dissolving it in dichloromethane at room
temperature yielded X-ray quality red crystals of [Ti3L3-
(OiPr)6Æ3CH2Cl2] in 76% yield (0.53 g, 0.28 mmol). Calcd
for C90H93N9Cl6Ti3O12 (Mr = 1849.13): C, 58.46; H, 5.07;
N, 6.81. Found: C, 59.27; H, 4.62, N, 7.26. Melting point:
1
>240 ꢁC dec H NMR (300 MHz, CDCl3) d: 8.24 (s, 1H),
8.20 (s, 1H), 7.91 (d, J = 8.07 Hz, 1H), 7.86 (d,
J = 8.13 Hz, 1H), 7.55 (s, 1H), 7.39 (s, 1H), 7.33 (m, 3H),

B. Liu et al. / Tetrahedron: Asymmetry 17 (2006) 2149–2153
2153
8. Guo, Q. S.; Song, H. B.; Li, J. S. Z. Anorg. Allg. Chem. 2006,
632, 721.
L. J. P.; Zheng, J.; Yudin, A. K. Org. Lett. 2000, 2, 3433; (c)
Guo, Q. S.; Liu, B.; Lu, Y. N.; Jiang, F. Y.; Song, H. B.; Li, J.
S. Tetrahedron: Asymmetry 2005, 16, 3667; (d) Guo, Q. S.;
Lu, Y. N.; Liu, B.; Xiao, J.; Li, J. S. J. Organomet. Chem.
2006, 691, 1282.
9. (a) Kitajima, H.; Aoki, Y.; Ito, K.; Katsuki, T. Chem. Lett.
1995, 1113; (b) Bougauchi, M.; Watanabe, S.; Arai, T.; Sasai,
H.; Shibasaki, M. J. Am. Chem. Soc. 1997, 119, 2329.
10. (a) Matsunaga, S.; Das, J.; Roel, J.; Vogl, E. M.; Yamamoto,
N.; Iida, T.; Yamaguchi, K.; Shibasaki, M. J. Am. Chem. Soc.
2000, 122, 2252; (b) Kozlowski, M. C.; DiMauro, E. F.
Organometallics 2002, 21, 1451.
14. Williams, D. R.; Fromhold, M. G. Synlett 1997, 523.
15. Soai, K.; Watanabe, M. Tetrahedron: Asymmetry 1991, 2,
97.
16. Watanabe, M.; Araki, S.; Butsugan, Y.; Uemura, M. J. Org.
Chem. 1991, 56, 2218.
11. Crystallographic
data
for
titanium
complex
2:
C90H93Cl6N9O12Ti3, formula weight 1849.13, Cubic, Pa-3,
17. Chaloner, P. A.; Perena, S. A. R. J. Chem. Soc., Perkin Trans.
1 1991, 2731.
18. Ishizaki, M.; Fujita, K.; Shimamoto, M.; Hoshino, O.
Tetrahedron: Asymmetry 1994, 5, 411.
19. Ramon, D. J.; Yus, M. Tetrahedron: Asymmetry 1997, 8,
2479.
20. Smaardijk, A.; Wynberg, H. J. Org. Chem. 1987, 52, 135.
21. Sato, T.; Gotoh, Y.; Wakabayshi, Y.; Fujisawa, T. Tetra-
hedron Lett. 1983, 24, 4123.
3
˚
˚
a = b = c = 26.408(6) A, a = b = c = 90ꢁ, V = 18417(7) A ,
Z = 8, Dcalcd = 1.334 g/cm3, T = 294.2 K, l(Mo Ka) =
0.491 mmꢀ1, R1 (wR2) = 0.1138 (0.2777), crystal dimensions
0.20 · 0.18 · 0.10 mm. (CCDC 292400).
12. Dave, R.; Sasaki, N. A. Tetrahedron: Asymmetry 2006, 17,
388.
13. (a) Dai, W. M.; Zhu, H. J.; Hao, X. J. Tetrahedron:
Asymmetry 2000, 11, 2315; (b) Chen, Y.; Yekta, S.; Martyn,