A facile deprotection of dithioacetals by FeCl3/KI

Article abstract of DOI:10.1081/SCC-120016345

Carbonyl compounds were regenerated from corresponding dithioacetals via refluxing with FeCl₃/KI and methanol as a solvent.

Full text of DOI:10.1081/SCC-120016345

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A Facile Deprotection of Dithioacetals by FeCl3/KI
Subhash P. Chavan a , Priti B. Soni a , Ramesh R. Kale a & K. Pasupathy a
a Division of Organic Chemistry: Technology , National Chemical Laboratory , Pune, India
Published online: 17 Aug 2006.
To cite this article: Subhash P. Chavan , Priti B. Soni , Ramesh R. Kale & K. Pasupathy (2003) A Facile Deprotection of
Dithioacetals by FeCl3/KI, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 33:6, 879-883, DOI: 10.1081/SCC-120016345
To link to this article: http://dx.doi.org/10.1081/SCC-120016345
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 6, pp. 879–883, 2003
A Facile Deprotection of
Dithioacetals by FeCl3/KI
*
Subhash P. Chavan, Priti B. Soni, Ramesh R. Kale, and
K. Pasupathy
Division of Organic Chemistry: Technology,
National Chemical Laboratory, Pune, India
ABSTRACT
Carbonyl compounds were regenerated from corresponding
dithioacetals via refluxing with FeCl3/KI and methanol as a solvent.
Key Words: FeCl3; KI; Dithioacetals.
Dithioacetals are frequently used to protect carbonyl compounds in
the course of total syntheses and hence several systems[1] have
been reported for their deprotection. Some of them include use of transi-
tionmetals (Hg 2þ, Ce4þ, Tl3þ).[2–4] However most of these methods
*Correspondence: Subhash P. Chavan, Division of Organic Chemistry:
Technology, National Chemical Laboratory, Pune 411008, India; Fax: þ91-20-
5893614; E-mail: spchavan@dalton.ncl.res.in.
879
DOI: 10.1081/SCC-120016345
Copyright & 2003 by Marcel Dekker, Inc.
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880
Chavan et al.
involve use of toxic, corrosive oxidants in stoichiometric amounts at
elevated temperatures. In connection with our interest in exploring the
utility of FeCl3 we have recently demonstrated the unique efficiency of
FeCl3 to function both as a Lewis acid[5] in catalyzing ionic Diels–Alder
reactions as well as an oxidising agent[6] ineffecting iodoetherification
and iodolactonisation. Our interest in developing methods for deprotec-
tionof oxathioacetals [7,8] and dithioacetals[9] encouraged us to investigate
the reactionwith oen equivalent of FeCl
3/KI. It was surmised that
FeCl3/KI combination could serve as an excellent reagent as the source
of iodonium ion/iodine. These in turn would react with dithioacetal
thereby making it a better leaving group, thus helping in regeneration
of carbonyl compounds. Recent report on utility of FeCl3 by Kamal et
al.[10] for deprotectionof dithioacetals prompts us to disclose our find-
ings. Although the reaction reported by Kamal et al. is efficient, FeCl3
has to be used ina very large excess. This becomes really unattractive
especially whenit has to be used ona large scale. Hereinwe report that
dithioacetals are efficiently deprotected in the presence of FeCl3 and KI in
very short time (Sch. 1).
It is interesting to note that the reaction does not proceed with either
FeCl3 (1 eq) or KI (1 eq) alone. After considerable trials it was concluded
that combination of FeCl3 and KI in the ratio 1:1 is required for clean
transformation. The reaction is fast and the product is isolated by
a simple aqueous workup.
A
wide variety of dithiolanes derived from ketones and
aldehydes were shown to undergo facile deprotection under these
conditions (Table 1). Both dithiolanes as well as dithiane (Entries 7 and
8
respectively) were deprotected with equal ease. The starting
materials[11–15] and the products, all previously known compounds
were identified by comparision of their physical and spectroscopic data
with literature data.
Scheme 1.

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Deprotection of Dithioacetals by FeCl3/KI
881
Table 1. Deprotectionof dithioacetals by FeCl /KI.
3
Time (hr)
3
Entry
1
Dithioacetal
Product
Yield (%)
90
2
3
4
3
91a
90
4
5
3
3
91
91
6
7
11
7
87b
89
8
6
89
9
10
11
5.5
7
90
91
6
92c
12
4
88
aM.p. ¼ 106ꢀC (lit.[16] M.p. ¼ 106–106.5ꢀC).
bbased onrecovery of the starting material.
cM.p. ¼ 49ꢀC (lit.[17] M.p. ¼ 49–50ꢀC).

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882
Chavan et al.
[18]
Inconclusionthe present protocol
therefore should find widespread utility in organic synthesis.
is efficient, nonhazardous, and
ACKNOWLEDGMENT
The authors PBS, RRK and KP thank CSIR, New Delhi for
financial support. Funding from CSIR, New Delhi under YSA (SPC)
scheme is gratefully acknowledged.
REFERENCES
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3743.
3. Ho, T.L.; Ho, H.C.; Wong, C.M. J. Chem. Soc. Chem. Commun.
1972, 791.
4. Lipshutz, B.H.; Moretti, R.; Crow, R. TetrahedronLett. 1989,
30, 15.
5. Chavan, S.P.; Sharma, A.K. Synlett. 2001, 667.
6. Chavan, S.P.; Sharma, A.K. Tetrahedron Lett. 2001, 42, 4923.
7. Ravindranathan, T.; Chavan, S.P.; Varghese, J.P. J. Chem. Soc.
Chem. Commun. 1994, 1937.
8. Chavan, S.P.; Soni, P.; Kamat, S.K. Synlett. 2001, 1255.
9. Ravindranathan, T.; Chavan, S.P.; Tejwani, R.B.; Varghese, J.P.
J. Chem. Soc. Chem. Commun. 1991, 1750.
10. Kamal, A.; Laxman, E.; Reddy, P.S.M.M. Synlett, 2000, 1476 and
references cited therein.
11. Saraswathy, G.V.; Sankararaman, S. J. Org. Chem. 1994, 59, 4665.
12. Lindsey, J.S.; Prathapan, S.; Johnson, T.E.; Wagner, R.W.
Tetrahedron 1994, 50, 8941.
13. Nickon, A.; Rodriguer, A.D.; Shirhatti, V.; Ganguly, R. J. Org.
Chem. 1985, 50, 4218.
14. Hoppmann, A.; Weyerstahl, P.; Zummack, W. Liebigs Ann. Chem.
1977, 1547.
15. Jnaneshwara, G.K.; Barhate, N.B.; Sudalai, A.; Deshpande, V.H.;
Wakharkar, R.D.; Gajare, A.S.; Shingare, M.S.; Sukumar, R.
J. Chem. Soc. PT-I, 1998, 965.
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Deprotection of Dithioacetals by FeCl3/KI
883
18. General Procedure: A mixture of dithioacetal of p-methoxy
benzaldehyde (212 mg, 1 mmol), FeCl3 (162 mg, 1 mmol) and KI
(166 mg, 1 mmol) was refluxed inmethanol. Progress of the reaction
was monitored by TLC. After the completion of the reaction,
methanol was removed under reduced pressure and residue was
extracted inether. The ether extract was dried over anhydrous
Na2SO4 and the organic layer was filtered. Evaporation of the
solvent under reduced pressure furnished pure anisaldehy-
de (122 mg, 90%). IR (film, cmꢁ1) : n ¼ 3009, 2739, 1684, 1578,
1
1511, 1461. H NMR (CDCl3, 200 MHz): d ¼ 3.89 (s, 3H), 7.01 (d,
J ¼ 8.7 Hz, 2H), 7.85 (d, J ¼ 8.7 Hz, 2H), 9.90 (s, 1H). 13C NMR
(CDCl3, 50 MHz): d ¼ 190.6, 164.4, 131.7, 129.7, 114.1, 55.3.
Received inthe USA February 21, 2002

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