(1.0 mL) was added 4-dimethylaminopyridine (5.4 mg, 0.044 mmol) and
acetic anhydride (225 mg, 2.2 mmol), and the mixture was stirred for 3 h
at room temperature. Usual work up and purification by column chromato-
graphy (silica gel, hexane/ethyl acetate 97:3) gave syn-2b (64 mg, 93% ee)
and anti-2b (87 mg, 88% ee).
‡ Crystal data for syn-2b: C17H23NO4S, M = 337.43, (0.31 × 0.18 ×
0.08 mm), orthorhombic, P212121 (#19), a = 8.23(1), b = 9.09(2),
c = 22.54(4) Å, = 90, V = 1689(4) Å3, = 1.871 mm, Z = 4, 31284
reflections measured, 2909 unique (Rint = 0.058). Final
R indices
[I > 3(I)]: R = 0.066, Rw = 0.068. CCDC reference number 241332. See
.cif or other electronic format.
1 (a) D. Hoppe and O. Zschage, Angew. Chem., Int. Ed. Engl., 1989, 28,
69–71; (b) D. Hoppe, F. Hintze and P. Tebben, Angew. Chem., Int. Ed.
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2 (a) For reviews see: P. Beak, A. Basu, D. J. Gallagher, Y. S. Park and
S. Thayumanavan, Acc. Chem. Res., 1996, 29, 552–560; (b) P. O’Brien,
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462–463.
Fig. 1 Chem 3D structure derived from the X-ray crystallography of
syn-2b.
In order to clarify whether the reaction proceeds through
a dynamic thermodynamic resolution14 or a dynamic kinetic
resolution pathway,15 we examined Beak’s test using an insufficient
amount of the electrophile.2a The reaction of lithiated 1 with
benzaldehyde in the presence of (−)-sparteine afforded syn-2b and
anti-2b with 93 and 88% ee, respectively, after acetylation (Table 1,
entry 1). On the other hand, when 0.1 eq. of benzaldehyde was used,
syn-2b and anti-2b were formed in 74 and 78% ee, respectively.
These enantioselectivities were lower in comparison with those of
the corresponding isomers obtained in the reaction with 1.3 eq. of
benzaldehyde (Scheme 2). These results suggest that the reaction
proceeds through a dynamic thermodynamic resolution pathway.
5 L. Colombo, M. D. Giacomo, G. Brusotti and G. Delogu, Tetrahedron
Lett., 1994, 35, 2063–2066.
6 L. Colombo, M. D. Giacomo, G. Brusotti and E. Milano, Tetrahedron
Lett., 1995, 36, 2863–2866.
7 (a) R. E. Gawley, Q. ZhangandA. T. McPhail, Tetrahedron:Asymmetry,
2000, 11, 2093–2106; (b) R. E. Gawley, S. A. Campagna, M. Santiago
and T. Ren, Tetrahedron: Asymmetry, 2002, 13, 29–36; (c) C. Gaul and
D. Seebach, Org. Lett., 2000, 2, 1501–1504; (d) C. Gaul, K. Schärer
and D. Seebach, J. Org. Chem., 2001, 66, 3059–3073; (e) C. Gaul,
P. I. Arvidsson, W. Bauer, R. E. Gawley and D. Seebach, Chem. Eur.
J., 2001, 7, 4117–4125; (f) C. Gaul and D. Seebach, Helv. Chim. Acta,
2002, 85, 772–787.
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865–868; (b) K. Tomioka, M. Sudani, Y. Shinmi and K. Koga, Chem.
Lett., 1985, 329–332.
9 N. Kise, T. Urai and J. Yoshida, Tetrahedron: Asymmetry, 1998, 9,
3125–3128.
Scheme 2
In summary, lithiated N-Boc-thiazolidine serves as a new
chiral formyl anion equivalent affording highly enantiomerically
pure products, which could be converted to optically active 1,2-
ethanediols.
10 For a review of enantioselective reactions of -thio carbanions, see:
T. Toru and S. Nakamura, In Organolithiums in Enantioselective Syn-
thesis; D. M. Hodgson, ed.; Springer: Berlin, 2003; vol. 5, pp. 177–216.
See also: (a) S. Nakamura, R. Nakagawa, Y. Watanabe and T. Toru,
Angew. Chem., Int. Ed., 2000, 39, 353–355; (b) S. Nakamura,
R. Nakagawa, Y. Watanabe and T. Toru, J. Am. Chem. Soc., 2000, 122,
11340–11347; (c) S. Nakamura, A. Furutani and T. Toru, Eur. J. Org.
Chem., 2002, 1690–1695; (d) S. Nakamura, T. Kato, H. Nishimura and
T. Toru, Chirality, 2004, 16, 86–89; (e) S. Nakamura, T. Ogura, L. Wang
and T. Toru, Tetrahedron Lett., 2004, 45, 2399–2402.
11 S. Nakamura, Y. Ito, L. Wang and T. Toru, J. Org. Chem., 2004, 69,
1581–1589.
12 (a) B. T. Cho and Y. S. Chun, Tetrahedron: Asymmetry, 1999, 10, 1843–
1846; (b) T. Tsujigami, T. Sugai and H. Ohta, Tetrahedron: Asymmetry,
2001, 12, 2543–2549.
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research
(no. 11650890) from the Ministry of Education, Science, Sports
and Culture of Japan and an NIT research promotion program. We
thank Dr Shinya Kusuda, Ono Pharmaceutical Co., Ltd, for the
X-ray crystallographic analysis.
Notes and references
† Typical procedure for the reaction of N-Boc-thiazolidine 1 with benzal-
dehyde: A 1.46 M solution of n-BuLi (0.49 mL, 0.72 mmol) in hexane was
added to a solution of 1 (114 mg, 0.60 mmol) in toluene (1.0 mL) at −78 °C.
The mixture was stirred for 10 min and then a solution of (−)-sparteine
(169 mg, 0.72 mmol) in toluene (0.4 mL) was added. After the reaction
mixture was stirred for 1 h, benzaldehyde (83 mg, 0.78 mmol) was added
and the reaction mixture was stirred for an additional 30 min. Saturated
aqueous NH4Cl was added and the aqueous layer was extracted with CH2Cl2.
The combined organic extracts were washed with brine, dried over Na2SO4
and concentrated under reduced pressure to leave a residue, which was puri-
fied by column chromatography (silica gel, hexane/ethyl acetate 90:10) to
give 2a (131 mg, 74%). To a solution of 2a (131 mg, 0.44 mmol) in pyridine
13 For example, the vicinal coupling constants are 4.2 Hz for syn-2b and
6.6 Hz for anti-2b.
14 P. Beak, D. R. Anderson, M. D. Curtis, J. M. Laumer, D. J. Pippel and
G. A. Weisenburger, Acc. Chem. Res., 2000, 33, 715–727.
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1995, 68, 36–56; (b) R. S. Ward, Tetrahedron: Asymmetry, 1995, 6,
1475–1490; (c) S. Caddick and K. Jenkins, Chem. Soc. Rev., 1996,
447–456; (d) H. Pellissier, Tetrahedron, 2003, 59, 8291–8327.
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 1 6 8 – 2 1 6 9
2 1 6 9