2
864
M. R. Rohman et al. / Tetrahedron Letters 51 (2010) 2862–2864
I -Al O
3
References and notes
2
2
I
R1
R1
1. (a) Kocienski, P. J. Protecting Groups; Thieme: New York, 1994; (b) Greene, T. W.;
S
I--I--Al
O
S
2
3
+
I-Al O
Wuts, P. G. M. Protective Groups in Organic Synthesis, 2nd ed.; John Wiley: New
York, 1991; (c) Pearson, A. J.; Roush, W. J. In Hand Book of Reagents for Organic
Synthesis, 1st ed.. In Activating Agents and Protecting Groups; John Wiley: New
York, 1999.
R2
R2
2
3
O
O
5
SI
SI R1
1
H O R
2
+
O
O
2. (a) Page, P. C. B.; van Niel, M. B.; Prodger, J. C. Tetrahedron 1989, 45, 7643; (b)
Guanti, G.; Banfi, L.; Brusco, S.; Riva, R. Tetrahedron Lett. 1993, 34, 8549.
3. (a) Corey, E. J.; Ericson, B. W. J. Org. Chem. 1971, 36, 3553; (b) Corey, E. J.; Bock,
M. G. Tetrahedron Lett. 1975, 2643.
HO
R2
R2
6
Scheme 2.
4. (a) Haroutounian, S. A. Synthesis 1995, 39; (b) Barton, D. H.; Cussons, R. N. J.; Ley,
S. V. J. Chem. Soc., Chem. Commun. 1977, 751.
ried out in water using I
2
–Al
2
O
3
(30 mol %) as described for the
5. (a) Fuji, K.; Ichikawa, K.; Fujita, E. Tetrahedron Lett. 1978, 3561; (b) Emerson, D.
W.; Wynberg, H. Tetrahedron Lett. 1971, 3445; (c) Rabindranathan, T.; Chavan, S.
P.; Dantale, S. W. Tetrahedron Lett. 1995, 36, 2285; (d) Rabindranathan, T.;
Chavan, S. P.; Tejwani, R. B.; Vargese, J. P. J. Chem. Soc., Chem. Commun. 1991,
1750; (e) Rabindranathan, T.; Chavan, S. P.; Tejwani, R. B.; Vargese, J. P. J. Chem.
Soc., Chem. Commun. 1994, 1937; (f) Nishide, K.; Yokata, K.; Nakamura, D.;
Sumiya, T.; Node, M.; Ueda, M.; Fuji, K. Tetrahedron Lett. 1993, 34, 3425; (g)
Karimi, B.; Seradj, H.; Tabaei, M. H. Synlett 2000, 1798.
deprotection of 1,3-oxathiolanes to their carbonyl functionalities
with slight variation in time and yields (Table 2). In either case,
it was noticed that the cleavage of 1,3-dithiolane to the parent
carbonyl compounds require slightly longer reaction time as
compared to the corresponding 1,3-oxathiolane derivatives. It
is noteworthy to mention that no iodination (for entries 1h–j)
takes place either at the double bond or allylic position. Signif-
icantly, the protecting groups such as benzyl and acetyl (entries
6. (a) Khalizadeh, M. A.; Hosseini, A.; Shokrollahzadeh, M.; Halvagar, M. R.;
Ahmadi, D.; Mohannazadeh, F.; Tajbkhsh, M. Tetrahedron Lett. 2006, 47, 3525;
(
b) Pagni, R. M.; Kabalka, G. W.; Boothe, R.; Gaetano, K.; Stewart, L. J.; Conaway,
R.; Dial, C.; Gray, D.; Larson, S.; Luidhardt, T. J. Org. Chem. 1988, 53, 4477; (c)
Ganguly, N. C.; Barik, S. K. Synthesis 2009, 1393; (d) Mondal, E.; Sahu, P. R.; Bose,
G.; Khan, A. T. J. Chem. Soc., Perkin Trans. 1 2002, 1026.
2
c and 2d) remain unaffected under the experimental condi-
tions. The work-up procedure includes the filtration of the reac-
tion mixture through a Celite bed followed by extraction and
evaporation under reduced pressure to obtain the corresponding
carbonyl compounds in high yield. However, in some cases col-
umn purification was required to obtain the desired compound
in pure form. All the deprotected carbonyl compounds were
7.
(a) Firouzabadi, H.; Iranpoor, N.; Hazarkhani, H. J. Org. Chem. 2001, 66, 7527; (b)
In A Hand Book of Fine Chemicals and Laboratory Equipments; 2000–2001; p. 917
8. Typical deprotection protocol; Method A: A mixture of freshly prepared catalyst
iodine (0.30 mmol) adsorbed on neutral alumina (750 mg)] and 2-(p-
hydroxyphenyl)-1,3-oxathiolane (1a) (198.31 mg, 1.00 mmol) in ethanol
900 L) was stirred for 10 min at room temperature. Then water (100 L)
[
(
l
l
was added and the reaction mixture was allowed to stir for additional 2 min.
The completion of the reaction was monitored by TLC. The reaction mixture was
fully characterized by IR and 1H NMR and by comparison with
the spectra of the authentic samples.9
filtered through
10 mL Â 3). The organic layer was separated and washed with sodium
bisulfite (5% aqueous solution), water (10 mL) and brine (10 mL). The organic
layer was dried over anhydrous Na SO , filtered and evaporated in vacuo to
a Celite bed and washed thoroughly with ethyl acetate
(
The deprotection of various 1,3-oxathiolanes and 1,3-dithiol-
anes into the corresponding carbonyl compounds can be ex-
plained as follows: alumina polarizes the iodine molecule and
2
4
obtain a crude solid mass, which was triturated with hexane to give the desired
compound (3a) as a light yellow solid (117.23 mg, 96%) in pure form.
Method B: A mixture of freshly prepared catalyst [iodine (0.40 mmol) adsorbed
on neutral alumina (1g)] and 2-(p-hydroxyphenyl)-1,3-oxathiolane (1a)
it acts as an activating agent to produce a strongly electrophilic
+
species. The I+ species react with the soft nucleophilic sulfur
I
(
198.31 mg, 1.00 mmol) was stirred for 20 min at room temperature. Then
atom of the dithiolane as well as oxathiolane to form the corre-
sponding iodosulfonium complex (5), which is finally hydrolyzed
with water to give the corresponding carbonyl compounds, as
depicted in Scheme 2.
In this study, we have devised a simple and environmentally
benign protocol for the regeneration of the parent carbonyl
compounds from their corresponding 1,3-oxathiolanes and 1,3-
water (1 mL) was added and the reaction mixture was allowed to stir for
additional 15 min. The completion of the reaction was monitored by TLC. The
reaction mixture was diluted with ethyl acetate (10 mL) and filtered through a
Celite bed. The organic layer was separated and washed with sodium bisulfite
(
5% aqueous solution), water (10 mL) and brine (10 mL). The organic layer was
dried over anhydrous Na SO , filtered and evaporated in vacuo to obtain a
crude solid mass, which was triturated with hexane to give the desired
compound (3a) 1 as light yellow solid (113.57 mg, 93%) in pure form.
Compound (3a) H NMR (400 MHz, CDCl ): d = 6.94 (d, 2H, J = 8.4 Hz, ArH),
.77 (d, 2H, J = 8.8 Hz, ArH), 9.79 (s, 1H, CHO). C NMR (100 MHz, CDCl
2
4
a
3
dithiolanes by using I
2
–Al
2
O
3
. In addition, these methodologies
13
7
3
):
are compatible in the presence of other protecting groups such
as acetyl, benzyl, allyl and also provide good yield for enolizable
ketones. Due to its operational simplicity, this environment
friendly procedure is expected to have wider applicability for
conversion of various 1,3-oxathiolanes and 1,3-dithiolanes to the
corresponding carbonyl functionalities.
d = 116.02, 128.92, 132.61, 163.31, 191.71. IR (KBr): 2925, 2854, 1669, 1601,
À1
1456, 1288, 1217, 1161, 834 cm . Light yellow solid. Mp 114–116 °C (lit. mp
7b
1
17–119 °C).
Spectroscopic data for compound (3h): 1H NMR (400 MHz, CDCl
J = 5.2 Hz, –OCH –CH@CH ), 5.46–5.33 (m, 1H, –OCH –CH@CH
1H, –OCH –CH@CH ) 7.02 (d, 2H, J = 8.8 Hz, ArH), 7.84 (d, 2H, J = 8.7 Hz, ArH),
9.
3
): d = 4.64 (d, 2H,
), 6.11–6.01 (m,
2
2
2
2
2
2
3
1
9
1
8
3
.89 (s, 1H, CHO). C NMR (100 MHz, CDCl ): d = 69.00, 114.99, 118.39, 130.01,
31.98, 132.26, 163.59, 190.85. IR (Neat): 1695, 1603, 1506, 1265, 1168, 1004,
À1
40 cm . Light yellow liquid.
1
Acknowledgements
Compound (3j) H NMR (400 MHz, CDCl
3
): d = 2.02–1.99 (m, 3H, –CH@CH–CH
), 6.89–6.80 (m, 1H, –CH@CH–CH ), 9.47(d, 1H,
J = 8 Hz, CHO). C NMR (100 MHz, CDCl ): d = 18.70, 134.59, 154.24, 194.13. IR
Neat): 2975, 2934, 1705, 1655, 1444, 1380, 1292, 1219, 1142, 1101, 969,
3
),
6
.15–6.09 (m, 1H, –CH@CH–CH
3
3
13
3
M.R.R. thanks the UGC for support under the Special Assistance
Program and SAIF, NEHU for providing analytical supports.
(
À1
899 cm . Viscous liquid.