J. S. Yada6 et al. / Tetrahedron Letters 43 (2002) 4679–4681
4681
functional groups. As is evident from Table 1 the acid
sensitive protecting groups are compatible with
CeCl3·7H2O–NaI in acetonitrile at ambient tempera-
ture. The cleavage proceeds smoothly and rapidly in
commercial grade acetonitrile containing 1.5% of water
which promotes the hydrolysis of thioacetals. Finally,
we have examined the possibility of CeCl3·7H2O func-
tioning catalytically or at least, in less than stoichiomet-
ric amounts. However, the best results were obtained
using an equimolar ratio of CeCl3·7H2O–NaI. In the
absence of NaI, the deprotection by CeCl3 alone in
acetonitrile at ambient temperature took longer to
achieve complete conversion. This clearly indicates that
the addition of 1 equiv. of NaI is crucial in the depro-
tection to obtain high yields of products.13
7. (a) Fuji, K.; Ichikawa, K.; Fujitha, E. Tetrahedron Lett.
1978, 18, 3561; (b) Emerson, D. W.; Winberg, H. Tetra-
hedron Lett. 1971, 11, 3445; (c) Mehta, G.; Uma, R.
Tetrahedron Lett. 1996, 37, 1897; (d) Karimi, B.; Seradj,
H.; Tabae, M. H. Synlett 2000, 1798.
8. (a) Mandai, T.; Takeshita, M.; Kawada, M.; Otera, J.
Chem. Lett. 1984, 1259; (b) Nishide, K.; Yokota, K.;
Nakamura, D.; Sumiya, T.; Node, M. Tetrahedron Lett.
1993, 34, 3425.
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3553; (b) Vedejs, E.; Fuchs, P. L. J. Org. Chem. 1971, 36,
366; (c) Ho, T. L.; Ho, H. C.; Wong, C. M. J. Chem.
Soc., Chem. Commun. 1972, 791.
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Eur. J. Org. Chem. 1999, 15.
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Torregiani, E. Synlett 1998, 209; (b) Bartoli, G.; Bellucci,
M. C.; Bosco, M.; Cappa, A.; Marcantoni, E.; Sambri,
L.; Orregiani, E. J. Org. Chem. 1999, 64, 5696; (c)
Marcantoni, E.; Nobili, F.; Bartoli, G.; Bosco, M.; Sam-
bri, L. J. Org. Chem. 1997, 62, 4183.
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toli, G.; Bosco, M.; Sambri, L. J. Org. Chem. 2001, 66,
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In summary, this paper describes a method for the
selective hydrolysis of 1,3-oxathio- and dithioacetals
using a cheap and readily available reagent system that
operates under neutral conditions thereby leaving acid-
and base-labile protecting groups intact. The high levels
of chemoselectivity in this process combined with the
simple methodology, high yields and ready availability
of reagents will facilitate a wider use of oxathio- and
dithioacetal protecting groups in organic synthesis.
Acknowledgements
B.V.S. and K.S.R. thank the CSIR, New Delhi for the
award of a fellowship.
13. Experimental procedure: A mixture of oxathio- or
dithioacetal (5 mmol), CeCl3·7H2O (5 mmol) and sodium
iodide (5 mmol) in acetonitrile (10 mL) was stirred at
reflux temperature for an appropriate time (Table 1).
After complete conversion, as indicated by TLC, the
reaction mixture was diluted with water (25 mL) and
extracted with ethyl acetate (2×20 mL). The combined
organic layers were washed with brine, dried over anhy-
drous Na2SO4 and concentrated in vacuo, and the result-
ing product was purified by column chromatography on
silica gel (Merck, 100–200 mesh, ethyl acetate–hexane,
1:9) to afford the parent carbonyl compound. Spectro-
scopic data 1e: 1H NMR (CDCl3): l 1.18 (s, 9H), 3.20
(m, 2H), 3.60 (s, 3H), 3. 85 (m, 1H), 4.45 (m, 1H), 5.85 (s,
1H), 6.60 (d, 1H, J=8.0 Hz), 6.78 (dd, 1H, J=2.7, 8.0
Hz), 6.90 (d, 1H, J=2.7 Hz), 7.28–7.42 (m, 6H), 7.65–
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1
7.78 (m, 4H). 2e: H NMR (CDCl3): l 1.18 (s, 9H), 3.60
(s, 3H), 6.60 (d, 1H, J=8.0 Hz), 7.18 (dd, 1H, J=2.7, 8.0
Hz), 7.24 (d, 1H, J=2.7 Hz), 7.30–7.41 (m, 6H), 7.65–
1
7.78 (m, 4H), 9.78 (s, 1H). 1k: H NMR (CDCl3): l 1.75
(s, 3H), 1.80 (s, 3H), 3.30 (m, 2H), 3.50 (m, 2H), 4.45 (dd,
2H, J=1.8, 10.3 Hz), 5.45 (m, 1H), 5.60 (s, 1H), 6.80 (d,
2H, J=8.0 Hz), 7.40 (d, 2H, J=8.0 Hz). 2k: 1H NMR
(CDCl3): l 1.75 (s, 3H), 1.80 (s, 3H), 4.45 (dd, 2H,
J=1.8, 10.3 Hz), 5.45 (m, 1H), 6.90 (d, 2H, J=8.0 Hz),
7.80 (d, 2H, J=8.0 Hz), 9.85 (s, 1H).