Chemistry Letters 2000
335
Lipski, M. A. Hilfinker, and S. G. Nelson, J. Org. Chem., 62,
4566 (1997). i) T. Mukaiyama, A. Kagayama, and I. Shiina,
Chem. Lett., 1998, 1107. ). j) A. Gansäuer and D. Bauer, J. Org.
Chem., 63, 2070 (1998). k) M. Bandini, P. G. Cozzi, S.
Morganti, and A. Umani-Ronchi, Tetrahedron Lett., 40, 1997
(1999). l) S. Matsubara, Y. Hashimoto, T. Okano, and K.
Utimoto, Synlett, 1999, 1411.
a) TiCl2(thf)2: J. J. Eisch, X. Shi, and J. Lasota, Z. Naturforsch.,
50b, 342 (1995). b) TiCl3: A. Clerici and O. Porta, Tetrahedron
Lett., 23, 3517 (1982); A. Clerici, L. Clerici and O. Porta,
Tetrahedron Lett., 37, 3035 (1996). c) Cp2TiCl: M. C. Barden
and J. Schwartz, J. Am. Chem. Soc., 118, 5484 (1996). d)
Cp2TiPh: Y. Yamamoto, R. Hattori, and K. Itoh, Chem.
Commun., 1999, 825.
3
4
5
D. Gordon and M. G. H. Wallbridge, Inog. Chim. Acta, 111, 77
(1986).
Preparation of 1: To a solution of TiCl4 (0.76 g, 4.0 mmol) in a
mixed solvent of CH2Cl2 (1.6 mL) and THF (6.5 mL) was gradu-
ally added TMEDA (1.2 mL, 8.0 mmol) at 0 °C. After stirring at
25 °C for 20 min, zinc powder (Merck, < 60 µm, assay min 95%)
(0.30 g, 4.5 mmol) and a catalytic amount of PbCl2 (6.5 mg,
0.023 mmol) were both added in one portion. The color of the
reaction mixture changed to dark blue, and the reaction mixture
was then additionally stirred for 30 min. The resulting suspen-
sion was centrifuged to remove inorganic materials. Hexane (6.0
mL) was added to the dark blue supernatant and stored at –20 °C
overnight. Complex 1 (1.36 g, 99% yield) was obtaind as blue
crystals: mp 129—133 °C (dec); ESR (solid, 25 °C): g = 1.9502.
IR (nujol/CsI): 861, 356, 328, 296 cm–1. UV/vis (THF): λ max
(ε), 659(13), 416(11) nm. Anal. Calcd for C10H24Cl3N2OTi: C,
35.05; H, 7.07; N, 8.18%. Found: C, 34.85; H, 7.07; N, 8.09%.
K. Takai, T. Kakiuchi, Y. Kataoka, and K. Utimoto, J. Org.
Chem., 59, 2668 (1994).
6
7
viously reported titanium mediated intermolecular pinacol cou-
pling of aromatic aldehydes.2a–e,k,3b,c,16 For example, the yield
was 80% (Entry 4), compared to that for the TiCl3 in CH2Cl2
system.3b The reaction in toluene proceeded rapidly; the alde-
hyde was completely consumed within 1 h, although the yield
decreased to 83% (Entry 5). On the other hand, protic solvents
led to low stereoselectivities (Entries 6—8).
The coupling reaction of functionalized aromatic aldehydes
also proceeds in high yields with excellent diastereoselectivi-
ties. The corresponding diols were obtained without losses of
ether (Entries 9—11), halide (Entries 14 and 15), cyano (Entry
16), and ester groups (Entry 17) bound to the aromatic rings.
Although 1-dodecanal, an aliphatic aldehyde, was completely
consumed when reacted with 1 within 24 h at 25 °C, many
unidentified products were detected and no trace of the cou-
pling product was observed.
R. J. H. Clark, J. Lewis, D. J. Machin, and R. S. Nyholm, J.
Chem. Soc., 1963, 379.
8
9
B. J. Hathaway and D. G. Holah, J. Chem. Soc., 1965, 537.
Measurement was made on a Rigaku AFC5R diffractometer at
the X-ray Laboratory of Okayama University. Crystallographic
calculation was performed on SGI workstation at Venture
Business Laboratory, Graduate School of Okayama University.
Crystallographic Data for 1: C10H24Cl3N2OTi, fw = 342.57, mon-
oclinic, space group, P21/n (No. 14), a = 11.00(1) Å, b =
12.372(9) Å, c = 12.356(8) Å, β = 101.47(6)°, V = 1648(2) Å3, Z
= 4; dcalcd = 1.380 g cm–1, 3936 reflections, 2θmax = 55.0°,
2θ–ω scan, 25 °C), R1 = 0.124 (all data) and wR2 = 0.205 (all
data) for 154 variables.
10 S. Hosmane, Y. Wang, H. Zhang, K.-J. Lu, J. A. Maguire, T. G.
Gray, K. A. Brooks, E. Waldhör, W. Kaim, and R. K. Kremer,
Organometallics, 16, 1365 (1997).
11 J. W. Pattiasina, H. J. Heeres, F. van Bolhuis, A. Meetsma, J. H.
Teuben, and A. L. Spek, Organometallics, 6, 1004 (1987).
12 J. J. H. Edema, R. Duchateau, S. Gambarotta, R. Hynes, and E.
Gabe, Inorg. Chem., 30, 154 (1991).
13 R. D. Shannon, Acta Cryst., A32, 751 (1976).
14 P. Sobota, J. Utko, S. Szafert, and K. Szczegot, J. Chem. Soc.,
Dalton Trans, 1997, 679.
15 Typical procedure is described for the coupling reaction of ben-
zaldehyde mediated by 1. To a solution of 1 (0.69 g, 2.0 mmol) in
THF (10 mL) was added dropwise a solution of benzaldehyde
(0.11 g, 1.0 mmol) in THF (1 mL). After being stirred at 25 °C for
24 h, the reaction mixture was quenched by adding dilute aq.
H2SO4. The organic layer was separated and the products were
extracted with ether. The crude products obtained were subjected to
column chromatography (ethyl acetate–hexane, 1 : 3) to give 1,2-
diphenyl-1,2-ethanediol (0.10 g, 92% yield, dl / meso = >99 / <1).
16 For some other transition metal mediated stereoselective coupling
of aromatic aldehydes, see: a) V: T. Hirao, B. Hatano, Y.
Imamoto, and A Ogawa, J. Org. Chem., 64, 7665 (1999). b) Nb:
J. Szymoniak, J. Besançon, and C. Moïse, Tetrahedron, 48, 3867
(1992).
The detailed pathway for the formation of 1 from TiCl4
and the mechanism of the pinacol coupling reaction mediated
by 1 is currently under investigation.
We thank Dr. Chiaki Ishii, Faculty of Engineering, Chiba
University, for measurement of the ESR spectra of 1.
References and Notes
1
Recent Reviews: a) T. Hirao, Synlett, 1999, 175. b) M.
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2
17 J. H. Stocker, D. H. Kern, and R. M. Jenevein, J. Org. Chem., 33,
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