1466
V. Gembus et al.
LETTER
(5) General Procedure for the Preparation of Silyl Ethers
1a–m
OTs
2a 91%
OTMS
MeCN, r.t.,
TsF (1 equiv)
1a
+
To a solution of 3-phenylpropanol (139 mg, 1 mmol) and
Et3N (120 mg, 1.1 mmol) in CH2Cl2 (5 mL) was added
TMSCl (115 mg, 1.05 mmol). The mixture was stirred at r.t.
overnight. The solvent was removed under reduced pressure
and the residue was diluted with pentane (10 mL). Simple
filtration through a short pad of Celite® provided silyl ether
1a in 93% yield which could be used in the silyl ether
exchange reaction without further purification.
+
DBU (20 mol%)
then HCl hydrolysis
3 92%
1f
HO
()5
TMSO
MeCN, r.t.,
TsF (1 equiv)
()5
+
OTMS
1b
OTs
2b 90%
(6) For other examples in nucleophilic catalysis in which DBU
is superior to other amine bases, see: (a) Aggarwal, V. K.;
Mereu, A. Chem. Commun. 1999, 2311. (b) Shieh, W.-C.;
Dell, S.; Repič, O. J. Org. Chem. 2002, 67, 2188.
(c) Yeom, C.-E.; Kim, H. W.; Lee, S. Y.; Kim, B. M. Synlett
2007, 146. (d) Murtagh, J. E.; McCooey, S. H.; Connon, S.
J. Chem. Commun. 2005, 227.
+
DBU (20 mol%)
OR
1j or 1k
R = TES, TBDMS
recovered 1j or 1k
Scheme 3 Examples of selective direct tosylation of silyl ethers
(7) DBU (Sigma-Aldrich) and p-toluenesulfonyl fluoride 97%
TsF (1 equiv), DBU (1 equiv)
(Acros Organics) were used as received.
OTMS
MeCN, r.t.
(8) (a) Olah, G. A.; Narang, S. C.; Gupta, B. G. B.; Malhotra, R.
J. Org. Chem. 1979, 44, 1247. (b) Morita, T.; Okamoto, Y.;
Sakurai, H. J. Chem. Soc., Chem. Commun. 1978, 874.
(c) Morita, T.; Okamoto, Y.; Sakurai, H. Tetrahedron Lett.
1978, 2523. (d) Olah, G. A.; Narang, S. C. Tetrahedron
1982, 38, 2225.
1l
90%
4
OTMS
TsF (1 equiv), DBU (1 equiv)
MeCN, r.t.
BocHN
CO2Me
BocHN
CO2Me
81%
(9) General Procedure for the Interconversion of Silyl
Ethers 1a–m
1m
5
To a solution of TMS ether 1a (209 mg, 1 mmol) and TsF
(179 mg, 1 mmol) in MeCN (2 mL) was added DBU (30 mL,
0.2 mmol). The mixture was stirred for 4 h at r.t. followed by
addition of H2O (4 mL). The aqueous phase was extracted
with EtOAc (3 × 10 mL). The combined organic layers were
washed with H2O (10 mL) and brine (10 mL). After drying
(MgSO4) and concentration under vacuum, the residue was
chromatographed on SiO2 (cyclohexane–Et2O, 9:1)
affording tosylate 2a (278 mg, 96% yield).
Scheme 4 Examples of tandem interconversion–elimination reac-
tions
making possible interconversion of TMS ethers in the
presence of an additional TES or TBDMS ether. A high
selectivity was also observed between primary and sec-
ondary ethers.
(10) Spectral Data for Tosylate 2h
Acknowledgment
1H NMR (300 MHz, CDCl3): d = 7.77 (d, 2 H, J = 8.3 Hz),
7.51 (d, 1 H, J = 7.5 Hz), 7.36 (d, 2 H, 8.3 Hz), 7.29 (t, 1 H,
J = 7.5 Hz), 7.21 (t, 1 H, J = 7.5 Hz), 6.86 (d, 1 H, J = 7.5
Hz), 4.58 (s, 2 H), 2.61 (s, 1 H), 2.48 (s, 3 H). 13C (75 MHz,
CDCl3): d = 146.9, 145.9, 134.6, 132.2, 130.3, 130.0, 128.8,
128.5, 127.6, 122.3, 59.6, 21.8. IR (KBr): nmax = 3392, 1597,
1487, 1453, 1371, 1192, 1179, 1156, 1089, 1040.
Spectral Data for Tosylate 2d
We thank the CNRS, the région Haute-Normandie and the CRI-
HAN for financial and technical support.
References and Notes
(1) (a) Selected recent references: Greene, T. W.; Wuts, P. G. M.
Protective Groups in Organic Synthesis, 3rd ed.; Wiley:
New York, 1999. (b) Kim, J.-G.; Jang, D. O. Synlett 2007,
2501. (c) Kazemi, F.; Massah, A. R.; Javaherian, M.
Tetrahedron 2007, 63, 5083. (d) Comagic, S.;
1H NMR (300 MHz, CDCl3): d = 7.66 (d, 2 H, J = 8.3 Hz),
7.35–7.17 (m, 7 H), 5.20–5.18 (m, 1 H), 4.93–4.89 (m, 1 H),
4.28–4.15 (m, 2 H), 2.43 (s, 3 H), 1.41 (s, 9 H). 13C (75 MHz,
CDCl3): d = 155.0, 145.0, 137.8, 132.4, 129.9, 128.8, 128.0,
127.9, 126.6, 80.1, 71.6, 28.3, 21.7. IR (KBr): nmax = 3383,
1690, 1525, 1361, 1172, 1097, 1052, 964. Mp 123–124 °C.
Spectral Data for Tosylate 2i
Schirrmacher, R. Synthesis 2004, 883.
(2) Selected recent references: (a) Honda, T.; Kaneda, K.
J. Org. Chem. 2007, 72, 6541. (b) Prasad, K. R.;
Chandrakumar, A. J. Org. Chem. 2007, 72, 6312. (c) Ojika,
M.; Kigoshi, H.; Yoshida, Y.; Ishigaki, T.; Nisiwaki, M.;
Tsukada, I.; Arakawa, M.; Ekimoto, H.; Yamada, K.
Tetrahedron 2007, 63, 3138. (d) Watanabe, H.; Mori, N.;
Itoh, D.; Kitahara, T.; Mori, K. Angew. Chem. Int. Ed. 2007,
46, 1512. (e) Lawhorn, B. G.; Boga, S. B.; Wolkenberg, S.
E.; Boger, D. L. Heterocycles 2006, 70, 65.
1H NMR (300 MHz, CDCl3): d = 9.13 (d, 1 H, J = 6.0 Hz),
8.22 (t, 1 H, J = 7.7 Hz), 7.80 (d, 1 H, J = 7.7 Hz), 7.72 (t, 1
H, J = 6.9 Hz), 7.59 (d, 2 H, J = 8.1 Hz), 7.04 (d, 2 H, J = 8.1
Hz), 4.96 (t, 2 H, J = 7.7 Hz), 3.44 (t, 2 H, J = 7.7 Hz), 2.43–
2.35 (m, 2 H), 2.27 (s, 3 H). 13C (75 MHz, CDCl3): d = 158.4,
144.9, 144.1, 142.4, 139.2, 128.7, 126.0, 125.9, 124.6, 59.4,
32.5, 21.7, 21.4. IR (KBr): nmax = 3434, 1628, 1505, 1190,
1129, 1039, 1012, 812, 691, 571. Mp 120–121 °C. All other
synthesized compounds are in accordance with the literature
data.
(3) Movassagh, B.; Shokri, S. Z. Naturforsch., B: Chem. Sci.
2005, 60, 763.
(4) Poisson, T.; Dalla, V.; Papamicaël, C.; Dupas, G.; Marsais,
F.; Levacher, V. Synlett 2007, 381.
(11) Polystyrene-bound DBU (1.15 mmol/g loading, 1% cross-
linked with DVB) was purchased from Aldrich.
Synlett 2008, No. 10, 1463–1466 © Thieme Stuttgart · New York