1238
H. S. Eriksen et al.
LETTER
is obtained upon treatment with diethylzinc. This ethyl
selenide was proven not to be the dominant catalytically
active species in the addition of diethylzinc to benzaldehyde
(17% yield). Furthermore, these workers also provided
NMR evidence for zinc selenolate dimers. See: Wirth, T.;
Kulicke, K. J.; Fragale, G. Helv. Chim. Acta 1996, 79, 1957.
(b) A similar observation has been made that selenoethers
derived from aliphatic amino diselenides are not
thiols 8 (49–57% ee). The polymer-supported thiobenzal-
dehyde 6b was fully recyclable without diminishing the
catalytic effectiveness in terms of enantioselectivities or
efficiencies.
Acknowledgment
catalytically productive: Braga, A. L.; Paixão, M. W.;
Lüdtke, D. S.; Silveira, C. C.; Rodrigues, O. E. D. Org. Lett.
2003, 5, 2635.
We are grateful to the EPSRC for a quota studentship (HSE) and to
the British Council and Colombian Government for a Colciencias
award (SCO).
(9) Gibson, C. L. Tetrahedron: Asymmetry 1999, 10, 1551.
(10) Kleijn, H.; Rijnberg, E.; Jastrzebski, J. T. B. H.; van Koten,
G. Org. Lett. 1999, 1, 853.
References
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(1) Present address: Departamento de Química y Biología,
Universidad del Norte, Km 5 via Puerto Colombia,
Barranquilla, Colombia.
(2) For reviews see: Pu, L.; Hong-Bin, Y. Chem. Rev. 2001, 101,
757.
(3) For reviews of soluble enantioselective catalysts see:
(a) Soai, K.; Shibata, T. In Comprehensive Asymmetric
Catalysis, Vol. 2; Jacobsen, E. N.; Pfalz, A.; Yamamoto, H.,
Eds.; Springer-Verlag: Berlin, 1999, 911–922. (b) Noyori,
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Chem., Int. Ed. Engl. 1991, 30, 46.
(15) Typical Procedure for the Synthesis of the Polymer-
Supported Thioesters 6 and 7.
To a stirred solution of [(2S)-1-(polystyrylmethyl)pyrrol-
idinyl]methanol (0.5008 g) and triphenylphosphine (0.5885
g) in anhyd toluene (10 mL) under nitrogen was added at r.t.
a solution of DEAD (0.3912 g) in toluene (1 mL). After 3–5
min thiobenzoic acid (0.3012 g) in toluene (1 mL) was
added. The resulting mixture was stirred for a further 45 h at
r.t. At the completion of this period the polymer was filtered
and rinsed with toluene, DMF and EtOH. The polymer beads
were then transferred to a soxhlet apparatus and washed with
THF for 1 d, rinsed with acetone and finally soxhlet
extracted with Et2O for 1 d. The beads were then dried in a
drying pistol (40 °C, 0.05 mmHg) for 24 h to give 0.5639 g
of polymer. IR (KBr): nmax = 1664 cm–1. Anal. Calcd: N,
2.08; S, 4.78. Found: N, 1.94; S, 3.82. Loading 1.19 mmol
S/g and an 80% conversion based on sulfur microanalysis.
(16) Yelm, K. E. Tetrahedron Lett. 1999, 40, 1101.
(17) Govindachari, T. R.; Rajagopalan, T. G.; Viswanathan, N. J.
Chem. Soc., Perkin Trans. 1 1974, 1161.
(4) For reviews of polymer-supported catalysts see: (a) Fan,
Q.-H.; Li, Y.-M.; Chan, A. S. C. Chem. Rev. 2002, 102,
3385. (b) de Miguel, Y. R.; Brulé, E.; Margue, R. G. J.
Chem. Soc., Perkin Trans. 1 2001, 3085. (c) Clapham, B.;
Reger, T. S.; Janda, K. D. Tetrahedron 2001, 57, 4637.
(5) (a) Hof, R. P.; Poelert, M. A.; Peper, N. C. M. W.; Kellogg,
R. M. Tetrahedron: Asymmetry 1994, 5, 31. (b) Fitzpatrick,
K.; Hulst, R.; Kellogg, R. M. Tetrahedron: Asymmetry 1995,
6, 1861. (c) Kang, J.; Lee, D. J. W.; Kim, J. I. Chem.
Commun. 1994, 2009. (d) Kang, J.; Kim, D. S.; Kim, J. I.
Synlett 1994, 842. (e) Masaki, Y.; Satoh, Y.; Makihara, T.;
Shi, M. Chem. Pharm. Bull. 1996, 44, 454. (f) Gibson, C. L.
Chem. Commun. 1996, 645. (g) Kang, J.; Kim, J. B.; Kim, J.
W.; Lee, D. J. Chem Soc., Perkin Trans. 2 1997, 189.
(h) Nakano, H.; Kumagai, N.; Matsuzaki, H.; Kabuto, C.;
Hongo, H. Tetrahedron: Asymmetry 1997, 8, 1391.
(i) Iwasa, K.; Hongo, H. Heterocycles 1997, 46, 267.
(j) Chelucci, G.; Berta, D.; Fabbri, D.; Pinna, G. A.; Saba,
A.; Ulgheri, F. Tetrahedron: Asymmetry 1998, 9, 1933.
(k) Aurich, H. G.; Soeberdt, M. Tetrahedron Lett. 1998, 39,
2553. (l) Kossenjans, M.; Soebert, M.; Wallbaum, S.;
Harms, K.; Martens, J.; Aurich, H. G. J. Chem Soc., Perkin
Trans. 1 1999, 2353. (m) Tseng, S.-L.; Yang, T.-K.
Tetrahedron: Asymmetry 2004, 15, 3375.
(6) For recent examples of b-amino sulfur ligands as catalysts in
the diethylzinc addition to aldehydes see: (a) Braga, A. L.;
Milani, P.; Paixão, M. W.; Zeni, G.; Rodrigues, O. E. D.;
Alves, E. F. Chem. Commun. 2004, 2488. (b) Braga, A. L.;
Vargas, F.; Silveira, C. C.; de Andrade, L. H. Tetrahedron
Lett. 2002, 43, 2335. (c) Braga, A. L.; Appelt, H. R.;
Schneider, P. H.; Rodrigues, O. E. D.; Silveira, C. C.;
Wessjohann, L. A. Tetrahedron 2001, 57, 3291. (d)Jimeno,
C.; Moyano, A.; Pericàs, M. A.; Riera, A. Synlett 2001,
1152.
(18) Typical Procedure for the Enantioselective Addition of
Diethylzinc to Benzaldehyde Catalysed by Polymer-
Supported Catalysts 6–8.
Diethylzinc (1.87 mL of a 1 M solution in hexane, 1.87
mmol) was added to a stirred solution of the catalyst (0.024
mmol, 0.048 mmol, or 0.096 mmol based on sulfur content)
in anhyd toluene (5 mL) under a nitrogen atmosphere. After
stirring at r.t. for 2 h the solution was cooled to –27 °C
whereupon, freshly distilled benzaldehyde (0.937 mmol)
was added and the resulting solution was stirred at 0 °C.
After stirring for 19 h at this temperature additional
diethylzinc was added (1.87 mL, 1.87 mmol) and the
mixture stirred for a further 46 h at 0 °C. At the completion
of this period there was no starting aldehyde, so HCl was
added (1 M, 3 mL). The aqueous phase was extracted with
CH2Cl2 (3 ꢀ 10 mL) and dried over Na2SO4. Evaporation of
the solvent and silica column chromatography (hexane–
EtOAc, 88:12) afforded (R)-(+)-1-phenyl-1-propanol as a
colourless oil. 1H NMR (CDCl3): d = 0.9 (t, 3 H, CH2CH3,
J = 7.4 Hz), 1.65–2.00 (m, 3 H, CH2CH3, J = 7.4 Hz, OH),
4.60 (t, 1 H, CHOH, J = 6.6 Hz), 7.30–7.40 (m, 5 H, ArCH).
The ee was determined by HPLC using a DAICEL chiralcel
OB column with 3% i-PrOH in hexane (flowrate: 0.5 mL/
min); tR = 25 min for the S-isomer and 31 min for the R-
isomer.
(7) For examples of the lower catalytic effectiveness of b-amino
thioethers over the corresponding disulfides see: Braga, A.
L.; Appelt, H. R.; Schneider, P. H.; Silveira, C. C.;
Wessjohann, L. A. Tetrahedron: Asymmetry 1999, 10, 1733.
(8) (a) In related amino aryl diselenides, Wirth et al. have
unequivocally established that an ethyl selenide (45% yield)
(19) Itsuno, S.; Fréchet, J. M. J. J. Org. Chem. 1987, 52, 4140.
(20) Sung, D. W.; Hodge, P.; Stratford, P. W. J. Chem. Soc.,
Perkin Trans. 1 1999, 1463.
Synlett 2005, No. 8, 1235–1238 © Thieme Stuttgart · New York