Mild, Efficient, and greener dethioacetalization protocol using 30% hydrogen peroxide in catalytic combination with ammonium iodide

Article abstract of DOI:10.1080/00397911.2010.502995

A simple, mild, efficient, and expedient greener dethioacetalization protocol employing a catalytic amount of nontoxic ammonium iodide (10mol%) in combination with 30% hydrogen peroxide as terminal oxidizer is revealed. The reagent accomplished facile deprotection of 1,3-dithianes and dithiolanes of activated aromatic substrates in an aqueous medium in the presence of sodium dodecylsulfate (SDS) at room temperature under virtually neutral conditions. Deactivated and sterically encumbered substrates, which are otherwise reluctant to cleave under aqueous micellar conditions, were expeditiously cleaved in good to excellent yields in acetic acid. The method is tolerant, with several acid-sensitive protecting groups, such as tert-butyldiphenylsilyl (TBDPS) ether, aryl acetate, NHBoc, and NHBn, and with further oxidation of oxidation-prone activated benzaldehydes and furyl aldehydes. A tentative mechanism of hypoiodous acid-mediated catalytic cleavage is proposed.

Full text of DOI:10.1080/00397911.2010.502995

This article was downloaded by: [University of West Florida]
On: 29 December 2014, At: 12:41
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Mild, Efficient, and Greener
Dethioacetalization Protocol Using
30% Hydrogen Peroxide in Catalytic
Combination with Ammonium Iodide
a
a
Nemai C. Ganguly & Pallab Mondal
a
Department of Chemistry , University of Kalyani , Kalyani , India
Published online: 14 Jun 2011.
To cite this article: Nemai C. Ganguly & Pallab Mondal (2011) Mild, Efficient, and Greener
Dethioacetalization Protocol Using 30% Hydrogen Peroxide in Catalytic Combination with Ammonium
Iodide, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 41:16, 2374-2384, DOI: 10.1080/00397911.2010.502995
To link to this article: http://dx.doi.org/10.1080/00397911.2010.502995
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“
Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

1
Synthetic Communications , 41: 2374–2384, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.502995
MILD, EFFICIENT, AND GREENER
DETHIOACETALIZATION PROTOCOL USING 30%
HYDROGEN PEROXIDE IN CATALYTIC COMBINATION
WITH AMMONIUM IODIDE
Nemai C. Ganguly and Pallab Mondal
Department of Chemistry, University of Kalyani, Kalyani, India
GRAPHICAL ABSTRACT
Abstract A simple, mild, efficient, and expedient greener dethioacetalization protocol
employing a catalytic amount of nontoxic ammonium iodide (10 mol%) in combination with
3
0% hydrogen peroxide as terminal oxidizer is revealed. The reagent accomplished facile
deprotection of 1,3-dithianes and dithiolanes of activated aromatic substrates in an aqueous
medium in the presence of sodium dodecylsulfate (SDS) at room temperature under virtually
neutral conditions. Deactivated and sterically encumbered substrates, which are otherwise
reluctant to cleave under aqueous micellar conditions, were expeditiously cleaved in good
to excellent yields in acetic acid. The method is tolerant, with several acid-sensitive protecting
groups, such as tert-butyldiphenylsilyl (TBDPS) ether, aryl acetate, NHBoc, and NHBn,
and with further oxidation of oxidation-prone activated benzaldehydes and furyl aldehydes.
A tentative mechanism of hypoiodous acid–mediated catalytic cleavage is proposed.
Keywords Ammonium iodide; dethioacetalization; 1,3-dithianes; 30% hydrogen peroxide;
sodium dodecylsulfate (SDS)
INTRODUCTION
The carbonyl functionality is ubiquitous in naturally occurring multifunctional
as well as synthetic targets. The protection and deprotection of this synthetically flex-
ible group at appropriate stages is often required in multistep synthetic sequences.
Among the host of carbonyl protecting groups currently available, 1,3-dithianes
[1]
and 1,3-dithiolanes are particularly useful in view of their easy accessibility and
stability under acidic as well as basic conditions. Apart from these useful features,
[
aldehyde 1,3-dithianes are excellent acyl anion equivalents that are widely utilized
2]
Received March 12, 2010.
Address correspondence to Nemai C. Ganguly, Department of Chemistry, University of Kalyani,
Kalyani 741235, WB, India. E-mail: nemai_g@yahoo.co.in
2
374

DETHIOACETALIZATION WITH H
2
O
2
AND NH
4
I
2375
for C-C bond-formation reactions. However, regeneration of the parent carbonyl
compound from these procarbonyl derivatives is often not facile and requires harsh
reaction conditions with attendant side reactions.
[
3]
The traditional HgCl -mediated dethioacetalization method or those subse-
2
[
quently developed utilizing heavy-metal salts such as AgNO =AgClO -I , AgNO3-
4]
2
4 2
[
5]
þ3
[6a]
NCS, Tl salts, SeO2,
[6b]
[7]
or volatile CH3I suffer from significant limitations,
primarily because of environmental concerns arising from stoichiometric or excess
use of reagents and the resulting waste generation. Notwithstanding the availability
of a good number of cleavage protocols, a contemporary concern for development
[
8]
of clean chemical processes triggered a resurgence of interest in this area. Several
[
9]
hypervalent iodine compounds including bis(trifluoroacetoxy)-iodobenzene (BTI),
[11]
[10]
Dess–Martin periodinane (DMP),
and o-iodoxybenzoic acid (IBX)
have been
employed as dethioacetalization reagents for their environmentally benign nature
and mild oxidizing property. However, these methods involve stoichiometric or excess
use of reagents. Replacement of existing stoichiometric methods by catalytic ones uti-
lizing nontoxic mild reagents is one of the major goals of green chemistry. To this end,
we felt that reagents that generate iodonium ion or its equivalent are attractive candi-
dates for dethioacetalization. Iodonium ion is a competent thiophile, and we surmised
that mild electrophilicity of the iodonium ion, in contrast to its chloronium and bro-
monium ion counterparts, combined with the sluggish and reversible nature of inher-
ently weak C-I bond-formation reactions, would allow selective dethioacetalization in
preference to ring iodination, even for activated aromatic substrates. Utilization of a
catalytic amount of ammonium iodide with 30% hydrogen peroxide is hitherto unex-
plored for this purpose and constitutes a green approach because aqueous hydrogen
peroxide is a safe, environmentally friendly terminal oxidizer that produces water as
the only by-product of oxidation, thereby minimizing waste at source. Ammonium
iodide is a readily available nontoxic nonmetal iodide source that can be oxidized with
aqueous hydrogen peroxide without addition of catalyst or mineral acid and is inex-
pensive, particularly when used in catalytic amounts. Stereoselective iodoacetoxyla-
[
12]
[13]
tion of protected glycals and aromatic iodination
using NH I-H O -Ac O=AcOH and NH I-H O -AcOH respectively. In our continu-
have been recently reported
4
2
2
2
4
2
2
ing efforts to develop greener synthetic protocols exploiting 30% aqueous hydrogen
14]
[
peroxide or its solid equivalents as terminal oxidizer, we became interested in
employing a catalytic amount of ammonium iodide in combination with 30% H O
for cleavage of 1,3-dithianes and allied S,S-acetals. Interestingly, commercial 30%
2
2
H O is fairly acidic because of the presence of acid stabilizers, and one such sample
2
2
used by us exhibited a pH of 2.9. The addition of 0.1 millimolar solution of NH I in
4
5
mL of water provided a near-neutral solution of pH 7.1. Previous reports of acti-
vation of the iodonium ion in iodofunctionalization of alkenes by anionic surfactant
[15]
sodium dodecylsulfate (SDS) prompted us to choose an aqueous micellar route to
solubilization of organic substrates for the current initiative.
RESULTS AND DISCUSSION
Initial exploratory experiments using 2-(3,4-methylenedioxyphenyl)-1,3-dithiane
1) as the model substrate showed that neither 30% H O nor 20 mol% NH I alone was
(
effective as a cleaving reagent under aqueous micellar conditions (Table 1).
2 2 4

2376
N. C. GANGULY AND P. MONDAL
a
Table 1. Optimization of cleavage conditions of 2-(3,4-methylenedioxyphenyl)-1,3-dithiane (1) with
NH I and 30% aqueous H
4
2 2
O
b
Yield of carbonyl
compound (%)
NH
4
I
Entry (mol%)
30% H
(mL)
2
O
2
Reaction
time (min=h)
Solvent (mL), additive
1
2
3
4
5
6
7
8
9
—
20
5
1
—
H
H
H
H
H
H
H
H
2
2
2
2
2
2
2
2
O (5 mL) SDS (0.4 mmol)
O (5 mL) SDS (0.4 mmol)
O (5 mL) SDS (0.4 mmol)
O (5 mL) SDS (0.4 mmol)
O (5 mL) SDS (0.4 mmol)
O (5 mL) SDS (0.2 mmol)
O (5 mL) SDS (0.4 mmol)
O (5 mL) SDS (0.2 mmol)
8 h
10 h
No reaction
No reaction
0.50
1.0
1 h
30 min
1 h
90
95
85
98
96
93
97
5
10
10
10
20
10
0.25
0.50
0.50
0.25
0.50
15 min
15 min
45 min
15 min
3 2
CH COOH (1.5 mL) H O (0.5 mL)
a
Deprotections were carried out on a 1-millimolar scale at room temperature; amount of reagents=
solvents refer to per mmol of substrate.
b
Refers to isolated yield upon chromatography.
The attempted deprotection of 1 with 10 mol% of NaI or KI along with 30%
H O (0.5 mL, ꢀ4.5 mmol) under similar conditions also proved abortive. A catalytic
2
2
combination of 10 mol% of NH I with 30% H O (0.5 mL, ꢀ4.5 mmol) in water
4
2
2
(5 mL) containing SDS (0.2 mmol) was found to be the optimized cleavage condition
an released 3,4-methylenedioxybenzaldehyde (piperonal) from 1 within 15 min with a
yield of 98%. Comparable efficient deprotection was also observed with identical
amounts of NH I and 30% H O in glacial acetic acid (1.5 mL). We preferred an
4
2
2
aqueous medium that allowed cleavage under virtually neutral conditions without
compromising expediency and efficiency. To demonstrate the utility, generality
and functional group compatibility of the method, a wide assortment of S,S-acet-
[
16]
als was reacted under these conditions. It worked well for electron-rich aromatic
aldehydes, ketones, and nonactivated dithianes (Table 2).
However, thioacetals derived from deactivated benzaldehydes (entries 12, 22
and 24) and sterically congested 1,3-dithiolane of camphor (entry 21) were relatively
reluctant in an aqueous medium. Gratifyingly, switching over to an acetic acid
medium led to faster cleavage with vast improvement in yields for these substrates.
A substantial rate differential of cleavage of activated and nonactivated aromatic sub-
strates in an aqueous medium offered scope for preferential deprotection of former in
a mixture. A competition experiment performed with a mixture consisting of 1 mmol
each of 1,3-dithiane, 2-nitrobenzaldehyde, and 4-hydroxy-3-methoxybenzaldehyde
(vanillin) under optimized conditions for 20 min resulted in near-quantitative iso-
lation of vanillin and unreacted dithiane of the former. Nonactivated dithianes and
[
8g]
dithiolanes are reported to be quite reluctant to cleave under oxidative conditions.
To our satisfaction, glucose pentaacetate dithiane (entry 17) as well as 1,3-dithiolane
of 2-hydroxybenzaldehyde (entry 20) underwent smooth cleavage in H O-SDS. The
2
tolerance of acid-sensitive phenol-protecting tert-butyldiphenylsilyl (TBDPS) ether,
aryl acetate, NHBoc, and NHBn groups and generality of the protocol are advan-
tageous features, adding further synthetic value to the method. Notably, bis(trifluoro-
acetoxy)-iodobenzene (BTI)-mediated deprotection of a 1,3-dithiane bearing a
TBDPS ether group was accompanied by removal of the latter moiety and olefin

DETHIOACETALIZATION WITH H
2
O
2
AND NH
4
I
2377
Table 2. Deprotection of S,S-acetals using a catalytic amount of NH
4 2 2
I and 30% H O
a
b
Yield of the carbonyl compound (%)
Entry
1
Substrate
Reaction time
15 min
98
2
3
40 min
95
10 min
ꢀ100
4
2 h
98
5
6
10 min
20 min
98
ꢀ100
7
8
30 min
97
80
1 h
(
Continued )

2378
N. C. GANGULY AND P. MONDAL
Table 2. Continued
a
b
Yield of the carbonyl compound (%)
Entry
9
Substrate
Reaction time
30 min
ꢀ100
1
0
1
45 min
85
1
2 h
98
30
(
i) 4 h
ii) 1 h
1
2
3
c
(
95
d
97
1
30 min
d
14
15
16
20 min
1 h
98
ꢀ100
15 min
98
1
1
7
8
15 min
20 min
96
95
(
Continued )

DETHIOACETALIZATION WITH H
2
O
2
AND NH
4
I
2379
Table 2. Continued
a
b
Yield of the carbonyl compound (%)
Entry
Substrate
Reaction time
19
1 h
96
2
0
1
30 min
98
60
(
i) 8 h
ii) 1 h
2
c
(
95
(i) 2 h
ii) 10 min
75
98
22
c
(
23
30 min
95
2
4
4
1.5 h
94
30
(i) 6 h
ii) 1.5 h
2
c
(
98
(
Continued )

2380
N. C. GANGULY AND P. MONDAL
Table 2. Continued
a
b
Yield of the carbonyl compound (%)
Entry
Substrate
Reaction time
d
2
5
6
20 min
98
d
96
2
30 min
a
Reaction conditions: NH
substrate, rt.
4
I (10 mol%), 30% H
O
2 2
(0.5 mL), H
2
O (5 mL), SDS (0.2 mmol) per mmol of
b
Refers to isolated yield after chromatographic purification; the carbonyl products are known
compounds that showed physical and spectral features in good agreement with those reported in the
[
18a]
literature.
c
4 2 3 2 2
Reaction conditions: NH I (10 mol%) in H O (0.5 mL), CH COOH (1.5 mL), 30% H O (0.5 mL) per
mmol of substrate, rt.
d
Yield was assessed from 2,4-dinitrophenylhydrazone derivative.
[9]
isomerization, due to the release of potent trifluoroacetic acid as a by-product dur-
ing the cleavage process. No undesired overoxidized by-product was formed even for
oxidation-prone phenolic and furyl aldehydes (entries 3, 5, 6, 19, and 25). Absence of
any product arising from acid-catalyzed cyclization of geranial after its release (entry
1
superior to an earlier protocol developed by us based on iodine-H O -SDS
6) further attests to the mildness of the cleaving system. The current method is
14c]
[
in
2
2
water in terms of yield and reaction time. For example, 1,3-dithiane of piperonal
and vanillin (entries 1 and 3) were deprotected in 98% and ꢀ100% yields within 15
and 10 min respectively with the current reagent in an aqueous medium, whereas
the same substrates required 0.5 and 1 h (yield 95% each) respectively with I -H O -
2
2
2
SDS in water. The deprotection reaction can be tuned by appropriate selection of
the reaction medium as demonstrated by removal of deactivated thioacetals, such
as 1,3-dithianes of 2- and 4-nitrobenzaldehyde in acetic acid in 1 h and 10 min (95%
and 98%) respectively.
Regarding the mechanistic scenario of cleavage, formation of a pale, greenish
yellow solution upon addition of 30% H O to aqueous NH I solution is suggestive
of in situ generation of hypoiodous acid (Eq. 1, Scheme 1).
2
2
4
It is a stronger iodonium ion equivalent than molecular I owing to its highly
2
reactive nature. Although HOI undergoes fast pH-sensitive disproportionation into
17]
[
I and HIO , particularly above pH 9 (Eq. 2),
þ
it is a weak acid (pKa 10.7), and
5% of I species exist in the form of HOI at pH below 9.5. It is plausible that
2
3
9
4 2 2
Scheme 1. Generation of iodonium ion equivalent in NH I-H O solution.

DETHIOACETALIZATION WITH H
2
O
2
AND NH
4
I
2381
4 2 2
Scheme 2. Tentative catalytic cycle for the cleavage of 1,3-dithianes with NH I-H O .
HOI, usually elusive in aqueous solution, is intercepted by highly nucleophilic sulfur
as soon as it is generated to form an aquo-labile sulfonium ion intermediate, paving
the cleavage process. Formation of a stronger iodonium ion equivalent in the form of
acetylhypoiodite in acetic acid (Eq. 3) coupled with improved solubility of the
substrate accounts for better results for deactivated substrates in acetic acid. An anal-
[
13]
ogous species has been suggested as intermediate in oxyiodination with the same
reagent. A tentative catalytic cycle for the cleavage process is delineated in Scheme 2.
CONCLUSION
We have developed a mild catalytic dethioacetalization method based on
ammonium iodide catalyst and 30% H O at room temperature, which is useful in
2
2
an aqueous medium in the presence of SDS for activated aromatic substrates. Acetic
acid is the preferred medium for cleavage of reluctant deactivated aromatics and
sterically hindered substrates. The mildness, operational simplicity, high throughput,
and generality of the protocol combined with its green features make it an attractive
alternative to existing methods.
EXPERIMENTAL
Representative Procedure for the Cleavage of 2-(3,4-Methylenediox-
yphenyl)-1,3-dithiane (1) with NH I–30% H O in Aqueous Micellar
Medium
4
2
2
Compound 1 (256 mg, 1.06 mmol), was added to a stirred aqueous solution of
NH I (15.6 mg, 0.107 mmol) containing SDS (5 mL H O, 59 mg, ꢀ0.2 mmol), and
4
2

2382
N. C. GANGULY AND P. MONDAL
then 30% H O (0.5 mL, 4.5 mmol), was added slowly as the mixture assumed a pale,
2
2
greenish yellow coloration. It was thoroughly stirred for 15 min at rt when thin-layer
chromatography (TLC) showed complete disappearance of the starting material.
Addition of 5% sodium thiosulfate solution (5 mL) to the reaction mixture followed
by extraction with EtOAc (2 ꢁ 5 mL), washing the combined organic extract with
water (3 mL), drying (Na SO ), and removal of solvent gave a concentrated extract.
2
4
It was filtered through a short pad of silica gel (60–120 mesh, Spectrochem, India)
using EtOAc–light petrol (1:10) as eluent to furnish piperonal (157 mg, 98%); mp
ꢂ
[18a]
ꢂ
3
6–37 C (EtOAc–light petrol) (lit.
38 C).
Representative Procedure for the Cleavage of 2-(2-Nitrophenyl)-1,3-
dithiane (12) with NH I–30% H O in Glacial Acetic Acid
4
2
2
Glacial acetic acid (1.5 mL) and then 12 (259 mg, 1.08 mmol) were added to a
stirred solution of NH I (15.7 mg, 0.108 mmol) in water (0.5 mL). This was followed
4
by slow addition of 30% H O (0.5 mL, 4.5 mmol), and the mixture was stirred for
2
2
1 h at rt (TLC monitoring). A solution of 5% sodium thiosulfate solution (5 mL)
was added to quench the reaction, which was followed by extraction of the reaction
mixture with EtOAc (2 ꢁ 5 mL). The combined organic extract was washed with
saturated NaHCO solution (2 ꢁ 3 mL) and water (2 ꢁ 2 mL) and then dried
3
(Na SO ). Removal of the solvent gave concentrated extract that was filtered
2 4
through a short pad of silica gel (60–120 mesh, Spectrochem, India) eluting with
EtOAc–light petrol (1:49) to furnish 2-nitrobenzaldehyde (154 mg, 95%); mp
ꢂ
[18a]
ꢂ
4
2–44 C (lit.
41–43 C).
ACKNOWLEDGMENTS
One of the authors (P. M.) is thankful to the Council of Scientific and
Industrial Research, India, for financial assistance by way of a research fellowship.
We thankfully acknowledge the facilities provided by the Department of Science
and Technology–Funding for Infrastructure in Science and Technology and the Uni-
versity Grants Commission, SAP programs, government of India, to the Department
of Chemistry, University of Kalyani.
REFERENCES
1
2
3
4
. Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 3rd ed.; John Wiley
and Sons: New York, 1999; pp. 333–344.
. Seebach, D. Methods of reactivity umpolung. Angew Chem., Int. Ed. Engl. 1979, 18,
2
39–258.
. Burghardt, T. E. Developments in the deprotection of thioacetals. Sulfur Chem. 2005, 26,
11–427.
4
. Nishide, K.; Yokota, K.; Nakamura, D.; Sumiya, T.; Node, M.; Ueda, M.; Fuji, K. A new
entry for the deprotection of monothioacetals and dithioacetals: Silver nitrite-iodine
system. Tetrahedron Lett. 1993, 34, 3425–3428.
5. Corey, E. J.; Ericson, B. W. Oxidative hydrolysis of 1, 3-dithiane derivatives to carbonyl
compounds using N-halosuccinimide reagents. J. Org. Chem. 1971, 36, 3553–3560.

DETHIOACETALIZATION WITH H
2
O
2
AND NH
4
I
2383
6. (a) Jones, P. S.; Ley, S. V.; Simkins, N. S.; Whittle, A. J. Total synthesis of the insect
antifeedant a jugarin I and degradation studies of related clerodane diterpene. Tetrahedron
1986, 42, 6519–6534; (b) Haroutounian, S. A. Selenium(IV) oxide mediated cleavage of
1,3-dithiolanes: A convenient method of dedithioacetalization. Synthesis 1995, 39–40.
7
8
. Fetizon, M.; Jurion, M. Aldehydes and ketones from thioacetals. J. Chem. Soc., Chem.
Commun. 1972, 382–383.
. (a) Varma, R. S.; Saini, R. K. Solid state dethioacetalization using clayfen. Tetrahedron
Lett. 1997, 38, 2623–2624; (b) Gupta, N.; Sonu; Kad, G. L.; Singh, J. Acidic ionic liquid
4
[bmim]HSO : An efficient catalyst for acetalization and thioacetalization of carbonyl com-
pounds and their subsequent deprotection. Catal. Commun. 2007, 8, 1323–1328; (c) Desai,
M. V.; Pore, D. M.; Tamhankar, B. V.; Jaghav, S. A.; Wadgaonkar, P. P. An efficient
deprotection of dithioacetals to carbonyls using Oxone-KBr in aqueous acetonitrile.
Tetrahedron Lett. 2006, 47, 8559–8561; (d) Kamal, A.; Reddy, P. S. M. M.; Rajasekhar
Reddy, D. An efficient catalytic deprotection of thioacetals employing bismuth triflate:
Synthesis of pyrrolo[2,1-c][1,4] benzodiazepines. Tetrahedron Lett. 2003, 44, 2857–2860;
(
e) Bandgar, B. P.; Kasture, S. P. Natural kaolinitic clay: A remarkable reusable solid
catalyst for the selective cleavage of thioacetals without solvent. Green. Chem. 2000,
54–156; (f) Barhate, N. B.; Shinde, P. D.; Mahajan, V. A.; Wakharkar, R. D. A con-
venient oxidative demasking of 1,3-dithiolanes and dithianes to carbonyl compounds with
TBHP. Tetrahedron Lett. 2002, 43, 6031–6033; (g) Oksdath-Mansilla, G.; Pen ory, A. B.
1
˜ ˜
en
´
Simple and efficient deprotection of 1,3- dithianes and 1,3-dithiolanes by copper(II) salts
under solvent-free conditions. Tetrahedron Lett. 2007, 48, 6150–6154.
. Stork, G.; Zhao, K. A simple method of dethioacetalization. Tetrahedron Lett. 1989, 30,
9
287–290.
10. Langville, N. F.; Dakin, L. A.; Panek, J. S. A mild, chemoselective protocol for the
removal of thioketals and thioacetals mediated by Dess–Martin periodinane. Org. Lett.
2003, 5, 575–578.
1
1. (a) Nicolaou, K. C.; Mathison, C. J. N.; Montagnon, T. o-Iodoxybenzoic acid (IBX) as a
viable reagent in the manipulation of nitrogen- and sulfur-containing substrates: Scope,
generality, and mechanism of IBX-mediated amine oxidation and dithiane deprotections.
J. Am. Chem. Soc. 2004, 126, 5192–5201; (b) Krishnaveni, N. S.; Surendra, K.;
Nageshwar, Y. V. D.; Rao, K. R. Mild and efficient hydrolysis of aromatic thioacetals=
thioketals using o-iodoxybenzoic acid (IBX) in the presence of b-cyclodextrin in water.
Synthesis 2003, 2295–2297.
1
1
1
2. Gammon, D. W.; Kinfe, H. H.; Devos, D. E.; Jacobs, P. A.; Sels, B. F. A simple, efficient
alternative for highly stereoselective iodohydroxylation of protected glycals. Tetrahedron
Lett. 2004, 45, 9533–9536.
3. Narender, N.; Reddy, K. S. K.; Krishna Mohan, K. V. V.; Kulkarni, S. J. Eco-friendly
oxyiodination of aromatic compounds using ammonium iodide and hydrogen peroxide.
Tetrahedron Lett. 2007, 48, 6124–6128.
4. (a) Ganguly, N. C.; Datta, M. Mild and eco-friendly oxidative cleavage of 1,3- dithianes and
1
,3-dithiolanes with a catalytic amount of hydrobromic acid and hydrogen peroxide: Syn-
ergetic effect of bromonium ion equivalent and hydrogen peroxide. J. Chem. Res., Synop.
005, 218–221; (b) Ganguly, N. C.; Datta, M. Eco-friendly solid-state oxidative deprotec-
2
tion of 1,3-dithianes and 1,3-dithiolanes using ammonium persulfate on wet montmorillon-
ite K-10 clay support under microwave irradiation. Synlett 2004, 659–662; (c) Ganguly,
N. C.; Barik, S. K. A facile, catalytic deoximation method using potassium bromide and
ammonium heptamolybdate in the presence of hydrogen peroxide in an aqueous medium.
Synthesis 2008, 425–428; (d) Ganguly, N. C.; Barik, S. K. A facile mild deprotection
protocol for 1,3-dithianes and 1,3-dithiolanes with 30% hydrogen peroxide and iodine cata-
lyst in aqueous micellar system. Synthesis 2009, 1393–1399; (e) Ganguly, N. C.; Nayek, S.;

2384
N. C. GANGULY AND P. MONDAL
Barik, S. K. A convenient mild catalytic deprotection of oximes to carbonyl compounds
with hydrogen peroxide and iodine catalyst in aqueous acetonitrile. Synth. Commun.
2009, 39, 4053–4061.
1
1
5. Cerritelli, S.; Chiarini, M.; Cerichelli, G.; Capone, M.; Marsili, M. Supramolecular assem-
blies as promoters of iodohydrin formation. Eur. J. Org. Chem. 2004, 623–630.
6. 1,3-Dithianes, 1,3-dithiolanes, and other thioacetals=ketals were prepared following
literature procedures: (a) Hatch, R. P.; Shringarpure, J.; Weinreb, S. M. Studies on total
synthesis of the olivomycins. J. Org. Chem. 1978, 43, 4172–4177; (b) Marshall, J. A.;
Belletire, J. L. Heterolytic fragmentation of 1,3-dithianyl tosylates. Tetrahedron Lett.
1971, 12, 871–874.
1
7. (a) LeBlond, C. R.; Rossen, K.; Gortsema, F. P.; Zavialov, I. A.; Cianciosi, S. J.;
Andrews, A. T.; Sun, Y. Harvesting short-lived hypoiodous acid for efficient diastereose-
R
lective iodohydroxylation in Crixivan synthesis. Tetrahedron Lett. 2001, 42, 8603–8606;
(
b) Lengyel, I.; Epstein, I. R.; Kustin, K. Kinetics of iodine hydrolysis. Inorg. Chem. 1993,
2, 5880–5882; (c) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th ed.;
John Wiley & Sons, 1988.
3
18. (a) Vogel, A. I. A Textbook of Practical Organic Chemistry, 3rd ed.; ELBS and Longman
Group Ltd.: London, 1973; (b) Miranda, R.; Osnaya, R.; Gardu n˜ , R.; Delgado, F.;
´
Alvarez, C.; Salmon, M. A general alternative to obtain S,S-acetals using taff, a bentonitic
clay, as the catalyst. Synth. Commun. 2001, 31, 1587-1597; (c) Khan, A. T.; Mondal, E.;
Ghosh, S.; Islam, S. A simple and practical synthetic protocol for acetalisation, thioaceta-
lisation, and transthioacetalisation of carbonyl compounds under solvent-free conditions.
Eur. J. Org. Chem. 2004, 9, 2002–2009.