A facile and convenient method for deprotection of thiocarbonyls to their carbonyl compounds using oxone under aprotic and nonaqueous conditions

Article abstract of DOI:10.1080/10426500307781

The reaction of oxone as an inexpensive, stable, and commercially available reagent with thiocarbonyl compounds in refluxing acetonitrile has been studied. Primary, secondary, and tertiary thioamides and thioureas are converted to their oxo analogues efficiently. Thiono esters also are transformed to their corresponding esters, while thioketones remained intact under these conditions.

Full text of DOI:10.1080/10426500307781

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Phosphorus, Sulfur, and Silicon and the Related
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A Facile and Convenient Method for Deprotection of
Thiocarbonyls to Their Carbonyl Compounds Using
Oxone Under Aprotic and Nonaqueous Conditions
I. Mohammadpoor-Baltork a , M. M. Sadeghi a & K. Esmayilpour a
a Isfahan University , Isfahan, Iran
Published online: 27 Oct 2010.
To cite this article: I. Mohammadpoor-Baltork , M. M. Sadeghi & K. Esmayilpour (2003) A Facile and Convenient Method
for Deprotection of Thiocarbonyls to Their Carbonyl Compounds Using Oxone Under Aprotic and Nonaqueous Conditions,
Phosphorus, Sulfur, and Silicon and the Related Elements, 178:1, 61-65, DOI: 10.1080/10426500307781
To link to this article: http://dx.doi.org/10.1080/10426500307781
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Phosphorus, Sulfur and Silicon, 2003, Vol. 178:61–65
C
Copyright 2003 Taylor & Francis
1042-6507/03 $12.00 + .00
DOI: 10.1080/10426500390170327
A FACILE AND CONVENIENT METHOD FOR
DEPROTECTION OF THIOCARBONYLS TO THEIR
CARBONYL COMPOUNDS USING OXONE UNDER
APROTIC AND NONAQUEOUS CONDITIONS
I. Mohammadpoor-Baltork, M. M. Sadeghi, and K. Esmayilpour
Isfahan University, Isfahan, Iran
(Received March 2, 2002; accepted June 18, 2002)
The reaction of oxone as an inexpensive, stable, and commercially avail-
able reagent with thiocarbonyl compounds in refluxing acetonitrile
has been studied. Primary, secondary, and tertiary thioamides and
thioureas are converted to their oxo analogues efficiently. Thiono esters
also are transformed to their corresponding esters, while thioketones
remained intact under these conditions.
Keywords: Carbonyl compounds; deprotection; oxone; thiocarbonyl
compounds
INTRODUCTION
The protection and deprotection of functional groups is of vital impor-
tance in synthetic organic chemistry. The conversion of thiocarbonyls
to their corresponding carbonyl compounds is a useful transformation
in organic synthesis. A wide variety of methods and reagents such
as dimethyl selenoxide,1 diaryl selenoxide,2 t-butyl hypochlorite,3
diaryl telluroxide,4 singlet oxygen,5 bromate or iodate in alkaline
solutions,6 sodium peroxide,7 benzeneseleninic anhydride,8 dimethyl
sulfoxide/iodine,9 thiophosgene,10 NOBF4,11 m-chloroperbenzoic
acid,12 trifluoroacetic anhydride,13 soft NO+ species,14 clay sup-
ported ferric nitrate,15 p-nitrobenzaldehyde/TMSOTf,16 manganese
dioxide,17 2-nitrobenzenesulfonyl chloride/potassium superoxide,18
N-nitrosamines,19 clayfen or clayan/MW,20 and caro’s acid supported
We are thankful to the Isfahan University Research Council for the partial support
of this work.
Address correspondence to I. M. Mohammadpoor-Baltork, Department of Chemistry,
Isfahan University, Isfahan 81744, Iran. E-mail: imbaltork@sci.ui.ac.ir
61

62
I. Mohammadpoor-Baltork et al.
on silica gel21 have been used for the transformation of thiocarbonyl
compounds to their corresponding oxo analogues. However, some of
these methods are not either suitable for deprotection of primary
thioamides or encounter drawbacks such as long reaction times,
expensive or toxic reagents, and tedious work-up. Therefore, there is
still a need to introduce new methods and inexpensive reagents for
such functional group transformations.
RESULTS AND DISCUSSION
Oxone (2KHSO5 KHSO4 K2SO4) is a stable, easily handled, and com-
mercially available oxidizing agent. Recently we introduced oxone as a
convenient reagent for the selective deprotection of trimethysilyl and
tetrahydropyranyl ethers, ethylene acetals, and ketals.22 In this ar-
ticle we wish to report an efficient and inexpensive method for the
conversion of thiocarbonyls to their corresponding carbonyl compounds
with oxone under nonaqueous and aprotic conditions (Scheme 1). Sev-
eral solvents including acetonitrile, dichloromethane, chloroform, car-
bon tetrachloride, n-hexane, and tetrahydrofuran were investigated
during the course of this study. The best results were achieved using
acetonitrile.
SCHEME 1
The treatment of a series of thioamides and thioureas with oxone in
refluxing acetonitrile afforded the corresponding carbonyl compounds
in good to excellent yields (Table I, entries 1–31). Thiono esters also
were converted to esters in good yields (entries 32, 33). Under the same
reaction conditions, thioketones remained unchanged in the reaction
mixture (entries 34–37). Therefore, selective deprotection of thioamides
and thiono esters in the presence of thioketones is achievable and can
be considered as a noteworthy feature of this method.
In summary, we have introduced a convenient and selective method
for deprotection of thioamides, thioureas, and thiono esters using

Thiocarbonyl Deprotection
63
TABLE I Transformation of Thiocarbonyl Compounds to Carbonyl
Compounds with Oxone
Oxone
(equivalent)
Time
(min)
Yield
(%)a
Run
R1
R2
R3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Me
NH2
NH2
NH2
H
H
NH2
Ph
Ph
H
PhNH
Ph
PhCH2
2-MeOC6H4
2-MeC6H4
4-MeOC6H4
4-MeC6H4
4-BrC6H4
4-NO2C6H4
Ph
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
Me
Me
Et
1
10
35
30
15
25
60
30
16
15
15
15
30
35
35
25
25
35
30
35
30
25
55
35
57
27
45
40
40
45
40
75
90
98
90
95
80
97
95
90
97
98
93
95
94
78
81
90
94
92
80
77
87
80
95
93
75
70
96
95
87
82
90
1.5
1.5
1.5
1.5
2
1.5
1
1.5
1
1
1
1
1
PhNH
H2NC Sb
PhN
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
N
1
1
1
1
4-MeC6H4
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
2-ClC6H4
4-MeC6H4
Me
Me
3,5-(NO2)2C6H3
3,5-(NO2)2C6H3
Me
4-NO2C6H4
3,5-(NO2)2C6H3
3,5-(NO2)2C6H3
Ph
2-MeOC6H4
2-MeC6H4
2-ClC6H4
4-MeC6H4
1-Naphthyl
4-BrC6H4
4-NO2C6H4
Ph
2-MeC6H4
Ph
Ph
Me
Et
1
1.5
1.5
1.5
1
1
1
1
1.5
1.5
2
2
2
3
3
3
3
3
3
50
55
60
60
60
60
85
87
0
32
33
34
35
36
37
0
0
0
aIsolated yields.
bOxamide was obtained from the reaction mixture.

64
I. Mohammadpoor-Baltork et al.
oxone, an inexpensive, commercially available and nontoxic reagent.
Moreover, the selectivity of the procedure may find application in
organic synthesis.
EXPERIMENTAL
General
Thiocarbonyl compounds are either commercially available or were pre-
26
pared according to described procedures.23
Yields refer to isolated
products. All of the products were characterized by comparison of their
spectral and physical data with those of authentic samples.
Conversion of Thiocarbonyl Compounds to Their
Corresponding Carbonyl Compounds—General Procedure
In a round-bottomed flask (50 ml), a solution of thiocarbonyl com-
pound (1 mmol) in CH3CN (10 ml) was treated with oxone (1–3 mmol)
and the reaction mixture was refluxed for 10–75 min. The progress of
the reaction was monitored by TLC (eluent: CCl4/EtOAc, 4:1). The re-
action mixture was filtered and the solid material was washed with
CH3CN (15 ml). The filtrate was evaporated and the crude product was
either recrystallized from EtOH/H2O or subjected to silica gel chro-
matography using CCl4/EtOAc, 4:1 as the eluent (Table I).
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