Y. Xu et al. / Tetrahedron Letters 49 (2008) 3634–3637
3637
OP
R2
Acknowledgments
OH
R2
R1
R1
TBPA
We are grateful for the generous financial support by
NSFC (QT program, No. 20572037), NCET-05-0879,
and Gansu Science Foundation (3ZS051-A25-004).
1. P = TBS
2. P = THP
References and notes
TBPA
TBPA
OH
R2
OP
R2
1. (a) Greene, T. W.; Wuts, P. G. M. Protective Groups in
Organic Synthesis, 4rd ed.; John Wiley & Sons: New York, 2007;
p 89; (b) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 4rd ed.; John Wiley & Sons: New York, 2007; p 59.
2. Corey, E. J.; Venkateswarlu, A. J. Am. Chem. Soc. 1972, 94, 6190.
3. Corey, E. J.; Jones, G. B. J. Org. Chem. 1992, 57, 1028.
4. (a) Tanemura, K.; Suzuki, T.; Horaguchi, T. J. Chem. Soc., Perkin
Trans. 1 1992, 2997; (b) DuttaGupta, A.; Singh, R.; Singh, V. K.
Synlett 1996, 69; (c) Sabitha, G.; Syamala, M.; Yadav, J. S. Org. Lett.
1999, 1, 1701.
5. (a) Lee, A. S. Y.; Yeh, H. C.; Tsai, M. H. Tetrahedron Lett. 1995, 36,
6891; (b) Maiti, G.; Roy, S. C. Tetrahedron Lett. 1997, 38, 187; (c)
Jaume, F.; Carme, S.; Jaume, V. Tetrahedron Lett. 1998, 39, 327; (d)
Wang, M. J.; Li, C.; Yin, D. L.; Liang, X. T. Tetrahedron Lett. 2002,
43, 8727; (e) Crouch, R. D. Tetrahedron 2004, 60, 5833; (f) Khan, A.
T.; Islam, S.; Choudhury, L. H.; Ghosh, S. Tetrahedron Lett. 2004, 45,
9617.
R1
R1
ROP
ROH
Scheme 1. The plausible mechanism.
When entry 17 was tested, we found that the THP ether
was partially cleaved at the same time. So, we wondered
whether this reagent could be applied for the deprotection
of the THP ethers. Thus, several THP ethers were prepared
and subjected to these reaction conditions and the results
are summarized in Table 3. The reactions proceeded
smoothly and the corresponding alcohols were obtained
in high yields within 2–3 h. However, we noticed that the
THP ether of cholesterol could not be deprotected even
after long reaction times, due to the poor solubility in
methanol. But replacing methanol as the solvent with a
1:1 mixture of methanol and CHCl3 allowed the reaction
to proceed at a satisfactory rate and in high yield (entry
5). Interestingly, THP ether of phenol could be cleaved in
a short time (entry 9).
The plausible mechanism of the reaction is proposed
(Scheme 1). A single electron transfer process may be
involved.
In conclusion, we have developed a simple, inexpensive,
and mild procedure for the cleavage of TBS and THP
ethers which will have a wide scope in view of the tremen-
dous usefulness in organic synthesis.
6. Schmidt, W.; Steckhan, F. Chem. Ber. 1980, 113, 577.
7. (a) Dapperheld, S.; Steckhan, E.; Brinkhaus, K.-H. G.; Esch, T. Chem.
Ber. 1991, 124, 2557; (b) Bell, F. A.; Ledwith, A.; Sherrington, D. C. J.
Chem. Soc. 1969, 2719; (c) Jia, X. D.; Da, Y. X.; Yang, C. X.; Yang,
L.; Liu, Z. L. Tetrahedron Lett. 2008, 49, 1786.
8. General procedure: TBPAþÅSbCl6 (0.05 mmol) was added to
a
ꢀ
solution of TBS or THP ether (1 mmol) in methanol (5 mL). The
resulting mixture was stirred at room temperature and monitored by
TLC. After the reaction was complete, the mixture was diluted with
water (5 mL) and extracted with CH2Cl2 (10 mL ꢁ 3). The organic
extracts were collected, washed with brine and dried with anhydrous
Na2SO4. When the solvent was removed in vacuum, the residue was
purified by column chromatography on silica gel to afford the
corresponding alcohol or phenol.
9. (a) Crouch, R. D. Tetrahedron 2004, 60, 5833; (b) Nelson, T. D.;
Crouch, R. D. Synthesis 1996, 1031.