Photochemical oxidative deprotection of 1,3-dithianes to carbonyl compounds with hydrogen peroxide (HP)

Article abstract of DOI:10.1080/10426500490422263

Regeneration of carbonyl compounds from their 1,3-dithianes were achieved using photochemical oxidation with (HP 30%) in relatively high yields. Thus, an efficient, economic and simple photochemical method for this deprotection has been demonstrated.

Full text of DOI:10.1080/10426500490422263

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Phosphorus, Sulfur, and Silicon and the Related
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PHOTOCHEMICAL OXIDATIVE DEPROTECTION OF 1,3-
DITHIANES TO CARBONYL COMPOUNDS WITH HYDROGEN
PEROXIDE (HP)
a
a
a
a
M. H. Habibi , S. Tangestaninejad , I. Mohammadpoor-Baltork & M. Montazerozohori
a
Isfahan University , Isfahan, Iran
Published online: 12 Aug 2010.
To cite this article: M. H. Habibi , S. Tangestaninejad , I. Mohammadpoor-Baltork & M. Montazerozohori (2004)
PHOTOCHEMICAL OXIDATIVE DEPROTECTION OF 1,3-DITHIANES TO CARBONYL COMPOUNDS WITH HYDROGEN PEROXIDE (HP),
Phosphorus, Sulfur, and Silicon and the Related Elements, 179:3, 597-600, DOI: 10.1080/10426500490422263
To link to this article: http://dx.doi.org/10.1080/10426500490422263
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Phosphorus, Sulfur, and Silicon, 179:597–600, 2004
Copyright ꢀC Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490422263
PHOTOCHEMICAL OXIDATIVE DEPROTECTION OF
1
,3-DITHIANES TO CARBONYL COMPOUNDS WITH
HYDROGEN PEROXIDE (HP)
M. H. Habibi, S. Tangestaninejad, I. Mohammadpoor-Baltork,
and M. Montazerozohori
Isfahan University, Isfahan, Iran
(
Received May 26, 2003; accepted September 25, 2003)
Regeneration of carbonyl compounds from their 1,3-dithianes were
achieved using photochemical oxidation with (HP 30%) in relatively
high yields. Thus, an efficient, economic and simple photochemical
method for this deprotection has been demonstrated.
Keywords: Carbonyl compound; deprotection; dithiane; hydrogen
peroxide; photochemical
The wide use of 1,3-dithianes as protecting groups for the carbonyl
functionality, and as acyl equivalents,2 has triggered the intense
search for flexible deprotection strategies. Oxidative methods are im-
portant among the other methods. Some of these methods are oxi-
1
3
4
5
6
6
dation with Cl2, Br2, I2, NCS, NBS, tert-BuOCl, and iron (III)
7
phenanthroline. Variants of oxidative methods that are based on one-
electron transfer oxidation, however, have been introduced only re-
cently, on one side with triarylamonium salts as mediators in an electro-
8
chemical oxidation, and on the other side using photoinduced electron
9
transfer in the presence of oxygen. Recently a new method for cleav-
1
0
age of the 1,3-dithianes with selecfluorTM, o-iodoxy benzoic acid in
11
DMSO containing traces of water, have been developed. In continua-
tion of our previous photochemical studies 1
2−14
we employed hydrogen
peroxide in aqueous acetonitrile (5% water) under photochemical con-
ditions for deprotection of 1,3-dithianes.
We are grateful to the University of Isfahan Research Council for the partial support
of this work.
Address correspondence to M. H. Habibi, Department of Chemistry, Isfahan Univer-
sity, Isfahan 81744, Iran.
5
97

5
98
M. H. Habibi et al.
RESULTS AND DISCUSSION
Photochemical deprotection of 1,3-dithianes was recognized by treat-
ment of substrate with HP (30%) in acetonitrile containing 5% water
for 2.5-3.5 h under irradiation at room temperature, which afforded the
corresponding carbonyl compounds (Scheme 1, Table I).
SCHEME 1
As shown in Table I, different types of dithio compounds are con-
verted to their corresponding carbonyl compounds in acetonitrile sol-
vent in the presence of UV light and in 75–92% yields. Under the same
reaction conditions, the dithio compounds bearing nitro group on the
aromatic ring were decomposed and unidentified products were pro-
duced (run 11,12).
It seems that under these conditions, hydrogen peroxide is cleaved
homolytically and produces highly oxidant OH-radical that can oxidize
dithio compounds, ultimately to corresponding carbonyl compounds.
Therefore with regard to literature,1
5,16
we propose a mechanism for
this transformation which involves stepwise oxidation of dithio com-
pounds to their disulfoxides and consequent cleavages to their parent
carbonyl compounds. On the basis of this mechanism, 3–4 eq. of the
reagents is required for the completion of the reaction (Scheme 2). It is
noteworthy that in the absence of UV-light, deprotection did not proceed
considerably even after prolonged reaction times that can be explained
due to stability of these compounds.
SCHEME 2

1
,3-Dithianes to Carbonyl Compounds
599
TABLE I Photochemical Deprotection of Various
,3-Dithianes Using HP (30%) in Acetonitrile
5% Water)
1
(
Run
R1
R2
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
9
2-MeOC6H4
4-BrC6H4
Ph
4-ClC6H4
4-PhC6H4
4-BrC6H4
4-ClC6H4
C6H13
H
Me
Ph
2.5
2.5
3
2.5
3
2.5
3
3.5
3
80
92
90
75
85
83
85
75
82
H
Me
CH2Br
Ph
H
10
–
3.5
80
1
1
1
2
3-O2NC6H4
2-O2NC6H4
H
H
0.5
0.5
Decompose
Decompose
aIsolated yields.
In summary we have introduced a simple and efficient procedure
for photochemical oxidative deprotection of 1,3-dithianes under neu-
tral condition and room temperature in good to excellent yields. This
reaction offers an interesting example of photochemical deprotection of
dithio compounds that is useful for synthetic organic photochemistry.
The advantages of this method are that it provides an economically vi-
able and efficient photochemical methodology using a readily available
reagent.
EXPERIMENTAL
General
The carbonyl derivative were prepared from corresponding car-
bonyl compounds and 1,3-propanedithiol according to the reported
1
7,18
procedure.
Conversion of 1,3-Dithianes Compounds to Their
Corresponding Carbonyl Compounds; General Procedure
To a solution of 2,2-diphenyl-1,3-dithane (133 mg, 0.5 mmol) in ace-
tonitril (20 ml) in a pyrex cell was added hydrogen peroxide (2 mmol).
The reaction cell was placed in a pyrex water bath at room temperature.

6
00
M. H. Habibi et al.
The mixture was stirred magnetically and irradiated with a 400 W high-
pressure Hg lamp for 3 h. After completion (as monitored by TLC), the
reaction mixture concentrated by evaporation under reduced pressure
and resulting crude material was purified on a silica-gel-plate (eluent:
n-hexane/diethyl ether 3:1) affording the pure product (Table I) All of
the products were characterized by elemental analysis (new products)
and comparison of their spectral (IR, H-NMR), chromatographic (TLC)
and physical data (melting and boiling points) with those of known
1
9
samples.
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