Efficient and mild oxidative nuclear thiocyanation of activated aromatic compounds using ammonium thiocyanate and diacetoxyiodobenzene

Article abstract of DOI:10.1081/SCC-200054770

A mild and general method for the nuclear thiocyanation of electron rich arenes has been developed by the reaction of NH₄SCN with diacetoxyiodobenzene as the oxidant. Copyright Taylor & Francis, Inc.

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Efficient and Mild Oxidative
Nuclear Thiocyanation of
Activated Aromatic Compounds
Using Ammonium Thiocyanate
and Diacetoxyiodobenzene
a
a
b
N. N. Karade , G. B. Tiwari , S. G. Shirodkar
&
b
B. M. Dhoot
a
School of Chemical Sciences, S. R. T. M. University,
Nanded, India
b
Netaji Subhash Chandra Bose College, Nanded,
India
Version of record first published: 16 Aug 2006.
To cite this article: N. N. Karade , G. B. Tiwari , S. G. Shirodkar & B. M. Dhoot
(2005): Efficient and Mild Oxidative Nuclear Thiocyanation of Activated Aromatic
Compounds Using Ammonium Thiocyanate and Diacetoxyiodobenzene, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 35:9, 1197-1201
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Synthetic Communications , 35: 1197–1201, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200054770
Efficient and Mild Oxidative Nuclear
Thiocyanation of Activated Aromatic
Compounds Using Ammonium Thiocyanate
and Diacetoxyiodobenzene
N. N. Karade and G. B. Tiwari
School of Chemical Sciences, S. R. T. M. University, Nanded, India
S. G. Shirodkar and B. M. Dhoot
Netaji Subhash Chandra Bose College, Nanded, India
Abstract: A mild and general method for the nuclear thiocyanation of electron rich
arenes has been developed by the reaction of NH
as the oxidant.
4
SCN with diacetoxyiodobenzene
Keywords: Ammonium thiocyanate, arenes, aryl thiocyanates, hypervalent iodine,
oxidation
INTRODUCTION
Aryl thiocyanates are the valuable and versatile class of organic compounds
useful for the transformations of the thiocyanato group into various sulfur
[1]
functional groups as well as in the synthesis of sulfur-containing hetero-
[2]
cycles. The synthesis of aryl thiocyanates is usually accomplished by the
chemical oxidation of thiocyanate anion using heavy metal oxidants such as
[
3–5]
[6]
[7]
MnO , Pb(OAc) , CuSO ,
CuBr -Al O ,
NaBO3,
and cerric
ammonium nitrate. The other methods for aryl thiocyanate preparation
2
4
4
2
2 3
[8]
Received in India December 30, 2004
Address correspondence to N. N. Karade, School of Chemical Sciences, S. R. T. M.
University, Nanded 431 606, India. Fax: þ91 (2462) 229245; E-mail: nnkarade@
rediffmail.com

1198
N. N. Karade et al.
Scheme 1.
[9]
utilizes polymer-supported thiocyanogen ion, and the procedures based upon
[10]
the reaction of NBS with alkali metal thiocyanates. Recently, the reaction of
[
11]
N-bromosulphonamides with thiocyanate anion has been used for aromatic
electrophilic thiocyanation reactions. The thiocyanation of selected substrates
such as phenols and phenol ethers using thiocyanating agents such as
[
12]
[13]
Me SiNCS
and Pb(SCN)2
PhICl , respectively, has been previously reported. It was surprising that inex-
in combination with PhI(OCOCF ) and
3 2
3
2
pensive and readily available NH SCN as a thiocyanating agent has not been
4
utilized. In this article, we report the thiocyanation of electron-rich arenes by
using NH SCN coupled with DIB as an oxidant (Scheme 1).
4
RESULTS AND DISCUSSION
Initially, we examined the model thiocyanation reaction of hydroquinone
dimethyl ether (1 mmol) with NH SCN (3 mmol) in acetonitrile. When DIB
4
(1.1 mmol) was added to this stirred reaction mixture, immediately the
solution turned yellow and the thiocyanation product was obtained in 82%
yield.
The mechanism of the reaction may involve the initial nucleophilic
attack of thiocyanate anion on the fairly electrophilic DIB 3, through a pheno-
[
14]
menon of ligand exchange
to form the intermediate 4. The overwhelming
[15]
tendency of intermediate 4 to expel iodobenzene is expected to generate the
rather unstable thiocyanogen 5 required for aromatic electrophilic thiocyan-
ation reaction (Scheme 2).
A variety of aromatic compounds including methoxybenzenes and hetero-
aromatics were successfully thiocyanated by using the DIB and NH SCN
4
(Table 1). The electron density on the aromatic ring was shown to have
considerable effect on the yield of thiocyanation reaction. Highly activated
Scheme 2.

Thiocyanation of Activated Aromatic Compounds
1199
Table 1. Electrophilic thiocyanation of activated aromatic substrates using NH SCN
4
a
and DIB
b
Yield
(%)
Entry
1
Substrate
Product
mp (lit) (8C)
[
11]
89
41 (33–44)
2
86
Oil
[
13]
3
4
82
79
68 (68–69)
[
13]
106 (106–107)
5
6
7
73
74
78
Oil
[
[
13]
11]
48 (49–50)
72 (73–74)
8
9
72
69
Oil
91
a
3
All the reactions were carried out in CH CN solvent at room temperature and stirred
for 2 h.
b
Isolated yields after chromatography.

1200
N. N. Karade et al.
methoxybenzenes (entries 1–6) underwent thiocyanation in good yields. It is
noteworthy that only para substitution products are formed in the case of
anisole (entry 1). The heteroaromatics such as thiophene (entry 8) and
N-methyl indole yield thiocyanation products in moderate yields. The
reaction of phenol and indole with the DIB/NH SCN combination gave a
4
number of products. This may be attributed to the facile oxidation of phenols
14]
and amines with DIB.
[
In summary, we have found that aryl thiocyanates can be synthesized in
high yields under mild conditions using readily available, inexpensive, eco-
friendly, and recyclable DIB in combination with ammonium thiocyanate.
EXPERIMENTAL
General Procedure
To a solution of aromatic substrate (1 mmol), NH SCN (3 mmol) in aceto-
4
nitrile (10 ml) was added diacetoxyiodobenzene (1.1 mmol). The reaction
mixture was magnetically stirred for 2 h at room temperature. The progress
of the reaction was monitored by TLC. After completion of the reaction,
water (10 ml) was added and extracted with CH Cl (2 ꢀ 10 ml). The
2
2
combined organic extract was dried over anhydrous sodium sulphate, concen-
trated in vacuo, and chromatographed to give the thiocyanated product.
ACKNOWLEDGMENT
We are thankful to UGC, New Delhi, India, for financial assistance.
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