1484
A. R. Hajipour et al.
PAPER
Table 3 Comparison of the Cleavage of S,S-Acetals in the Presence of Other Protecting Groups and Free Alcoholsa,b (continued)
Example
10
Cleavage reaction
30 min
r.t.
S
+ PhCH2OH
0%
Me
CHO
PhCH2CH2OH
(1 mmol)
+
Me
S
90%
(1 mmol)
a All reactions were carried out with NaNO3/silicasulfuric acid (1.2:2 molar ratio) and wet SiO2 (60% w/w) (0.5 g) in CH2Cl2 (8 mL).
b The progress of the reactions was determined by TLC/GC analysis.
c Only a trace of p-methoxybenzaldehyde was observed.
ed a mixture of p-methylphenyl-1,3-dithiolane (0.196 g, 1 mmol)
and 1,1-diacetoxy-1-(4-nitrophenyl)methane (0.253 g, 1 mmol) and
then the reaction mixture was stirred for 15 min. The progress of the
reaction was followed by TLC/GC. 4-Methylbenzaldehyde was ob-
tained in 93% yield and 1,1-diacetoxy-1-(4-nitrophenyl)methane
remained unaffected (Table 3, entry 5).
In conclusion, we have developed a simple, mild, inex-
pensive, and environmentally safe method for the depro-
tection of S,S-acetals. High yields and short reaction times
are noteworthy features of the reported method.
Products were characterized by comparison of authentic samples
(IR, 1H NMR spectrum, mp, mixed mp and co-TLC analysis) with
those obtained by literature methods5 or alternative methods of syn-
thesis. All mps were taken on a Gallenkamp melting apparatus and
Acknowledgment
We gratefully acknowledge the funding support received for this
project from the Isfahan University of Technology (IUT), IR Iran.
Further financial support from the Center of Excellence in Chemi-
stry Research (IUT) is gratefully acknowledged.
1
are uncorrected. H NMR spectra were recorded on a Varian 250
NMR Spectrometer operating at 250 MHz. The spectra were mea-
sured in CCl4 and CDCl3 relative to TMS (d = 0.00 ppm). GC anal-
ysis was run with a Shimadzu GC-14A instrument. IR spectra were
recorded on a Shimadzu 435 IR spectrophotometer. Spectra of sol-
ids were measured using KBr pellets. Silicasulfuric acid was pre-
pared according to a previously reported method.7
References
(1) Greene, T. W. Protective Groups in Organic Synthesis;
Wiley: New York, 1981.
(2) Kunz, H.; Waldmann, H. In Comprehensive Organic
Synthesis, Vol. 6; Trost, B. M.; Fleming, I., Eds.; Pergamon:
New York, 1991, 677–681.
(3) Corey, E. J.; Seebach, D. J. Org. Chem. 1966, 31, 4097.
(4) Mori, Y.; Kohchi, Y.; Suzuki, M. J. Org. Chem. 1991, 56,
631.
(5) Hajipour, A. R.; Khoee, S.; Ruoho, A. E. Org. Prep. Proced.
Int. 2003, 35, 527.
Dethioacetalization of p-Chlorophenyl-1,3-dithiolane Using
Silicasulfuric Acid/NaNO3 and Wet SiO2(60% w/w);
Typical Procedure
A mixture of p-chlorophenyl-1,3-dithiolane (0.21 g, 1 mmol), sili-
casulfuric acid (0.55 g, 2 mmol), NaNO3 (0.10 g, 1.2 mmol), wet
SiO2 (0.5 g; 60% w/w) and CH2Cl2 (5 mL) was stirred for 15 min in
a round-bottom flask. The progress of the reaction was followed by
TLC/GC. After the reaction was completed, CH2Cl2 (2 × 10 mL)
was added to the reaction mixture and after vigorous stirring the sol-
id was removed by filtration through a sintered glass funnel and
then the filtrate was transferred into a separatory funnel and washed
with NaHCO3 (5%). The organic layer was dried over anhyd
Na2SO4 and the solvent was removed under reduced pressure. The
residue was purified through a short column of silica gel (cyclohex-
ane–EtOAc, 3:1) to obtain pure p-chlorobenzaldehyde [yield: 0.12
g (88%); mp 45–47 °C].
(6) Kamal, A.; Reddy, P. S. M. M.; Reddy, R. Tetrahedron Lett.
2003, 44, 2857.
(7) (a) Hajipour, A. R.; Mirjalili, B. F.; Zarei, A.; Khazdooz, L.;
Ruoho, A. E. Tetrahedron Lett. 2004, 45, 6607.
(b) Zolfigol, M. A. Tetrahedron 2001, 57, 9509.
(8) (a) Fuji, K.; Ichikawa, K.; Fujita, E. Tetrahedron Lett. 1978,
19, 3561. (b) Zolfigol, M. A.; Mirjalili, F.; Bamoniri, A.;
Karimi Zarchi, M. A.; Zarei, A.; Khazdooz, L.; Noei, J. Bull.
Korean Chem. Soc. 2004, 25, 1414.
Dethioacetalization of p-Methylphenyl-1,3-dithiolane in the
Presence of 1,1-Diacetoxy-1-(4-nitrophenyl)methane;
Typical Procedure
To a mixture of silicasulfuric acid (0.55 g, 2 mmol), NaNO3 (0.10 g,
1.2 mmol), wet SiO2 (0.5 g; 60% w/w) and CH2Cl2 (8 mL) was add-
Synthesis 2006, No. 9, 1480–1484 © Thieme Stuttgart · New York