Simple and highly efficient method for the deprotection of allyl ethers using dimethylsulfoxide-sodium iodide

Article abstract of DOI:10.1080/00397910701459548

A simple and highly efficient method for deprotection of allyl ethers has been developed using dimethylsulfoxide-sodium iodide (catalytic amount). This method is inexpensive, has simple reaction conditions, has an easy workup procedure, proceduces excellent yields (60-99%), and is effective for several structurally varied allyl ethers. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701459548

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Simple and Highly Efficient Method for
the Deprotection of Allyl Ethers Using
Dimethylsulfoxide–Sodium Iodide
M. Nagaraju a , A. Krishnaiah a & Hari Babu Mereyala a
a Organic Chemistry Division II , Indian Institute of Chemical Technology ,
Hyderabad, India
Published online: 09 Aug 2007.
To cite this article: M. Nagaraju , A. Krishnaiah & Hari Babu Mereyala (2007) Simple and Highly
Efficient Method for the Deprotection of Allyl Ethers Using Dimethylsulfoxide–Sodium Iodide, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:15,
2467-2472, DOI: 10.1080/00397910701459548
To link to this article: http://dx.doi.org/10.1080/00397910701459548
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Synthetic Communicationsw, 35: 2467–2472, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701459548
Simple and Highly Efficient Method for the
Deprotection of Allyl Ethers Using
Dimethylsulfoxide–Sodium Iodide
M. Nagaraju, A. Krishnaiah, and Hari Babu Mereyala
Organic Chemistry Division II, Indian Institute of Chemical Technology,
Hyderabad, India
Abstract: A simple and highly efficient method for deprotection of allyl ethers has
been developed using dimethylsulfoxide–sodium iodide (catalytic amount). This
method is inexpensive, has simple reaction conditions, has an easy workup
procedure, proceduces excellent yields (60–99%), and is effective for several struc-
turally varied allyl ethers.
Keywords: allyl ethers, deprotection, sodium iodide
Protection and deprotection of functional groups play important roles in
organic transformations.[1] Developing a simple and efficient method for
this purpose is an equally important and challenging task to organic
chemists. In general, protection of hydroxy groups as ethers and esters is
often employed in organic synthesis. However, ethers are preferred over
esters because of their stability in acidic and basic conditions. The allyl
functional is a choice candidate in such guarding groups popularly used
in carbohydrate and peptide chemistry.[2,3] The classical procedure for
removal of allyl protection involves a two-step sequence, where the allyl
group is first isomerized to the corresponding propenyl function with a
strong base t-BuOK[4] or a metal catalyst such as Pd/C, (Ph3P)RhCl, or
Received December 7, 2006
Address correspondence to A. Krishnaiah, Organic Chemistry Division II, Indian
Institute of Chemical Technology, Hyderabad, India. E-mail: krishnu@iict.res.in
2467

2468
M. Nagaraju, A. Krishnaiah, and H. B. Mereyala
[Ir(COD)(PMePh2)2]PF6,[5–8] followed by conversion of the propenyl group
into free alcohol. Recently, several newer methods are well documented in
the literature for the removal of allyl protection using number of reagents
such as ZrCl4/NaBH4,[9] TiCl4-n-Bu4NI,[10] Ti(O-i-Pr)4,[11] PdCl2/CuCl2/
[14]
DMF-H2O/O2,[12] DDQ,[13] CeCl3 7H2O-NaI,
tetrabutylammonium per-
.
oxydisulfate,[15] and p-TSA.[16] Very recently, an efficient method for the
deprotection of allyl esters using dimethylsulfoxide–iodine reagent
appeared in the literature.[17] However, most of these methods suffer from
unsatisfactory yields, cost, toxicity of the reagents, and the necessity for
anhydrous conditions. Based on literature reports and our continuous
interest in perfluoroalkyl 2(1H)pyridones[18–20] (entries 1–6), where it was
necessary to remove the allyl protection, reactions were attempted with p-
TSA and DMSO-I2 independently. In this instance, p-TSA did not give any
product, whereas DMSO-I2 could effect the deprotection after several hours
of heating but in very low yields. Therefore, an alternate method was
required to cleave the allyl protection in 2(1H) pyridones. To this end, we
have developed a novel and efficient method for allyl deprotection using
dimethylsulfoxide–sodium iodide reagent (Scheme 1) and extended it to
several other allyl ethers. However, allyl derivatives of amino acids and
sugars when subjected to deprotection could not give the desired products.
The benzyl, methyl, and tert-butyl protecting groups (entries 14–16) were
quite stable in these reaction conditions. The results pertaining to this very
important transformation are tabulated (Table 1). Several experiments were
conducted with varied reaction temperatures, and we observed that 1308C is
ideal for the reaction. This method could also regenerate the 2(1H)
pyridones from their N-allyl pyridones (entries 4–6) and hydrolyze the
2-O-acetamido pyridines (entries 12 and 13) in quantitative yield (Scheme 2).
In conclusion, this method provides an effective deallylation procedure
for a variety of allylethers and N-allyl compounds and could hydrolyze the
2-O-acetamido pyridines. The advantages of this method include that it has
simple reaction conditions, easy workup procedure, and high yields, active
functional groups remain intact; and it is compatible with several structural
varied allyl ethers.
EXPERIMENTAL
The allyl compounds were prepared by the reported method and were
subjected to deprotection.
Scheme 1.

Deprotection of Allyl Ethers
2469
Table 1. Deprotection of allyl ethers
Entry
1
Substrate
Product
Time (h)
1
Yield (%)
99
2
3
4
3
3
98
66
93
3(1/2)
5
6
4
4
66
60
7
8
4
4
99
71
9
4
82
(continued)

2470
M. Nagaraju, A. Krishnaiah, and H. B. Mereyala
Table 1. Continued
Entry
10
Substrate
Product
Time (h)
4
Yield (%)
89
11
12
4
4
92
99
13
4
98
14
15
No reaction
No reaction
16
No reaction
Typical Procedure
To a solution of allyl ether (entry 1, 500 mg, 1.6 mmol) in DMSO (3 ml),
sodium iodide (20 mg) was added and the mixture was heated to 1308C for
1–4 h. The progress of the reaction was monitored by thin-layer
Scheme 2.

Deprotection of Allyl Ethers
2471
chromatography (TLC). After completion of the reaction, the reaction mixture
was allowed to cool to room temperature and poured onto crushed ice. The
separated solid was filtered and dried (430 mg, 99% yield). In the case of
entries 7 and 9, it was extracted into ethyl acetate and worked up with brine
to isolate the products.
Data
3-Cyano-4-trifluoromethyl-6-phenyl-2(1H) pyridone (1). IR (KBr): 3350,
1
2225, 1675, 1250, 1170 cm21. H NMR (DMSO-d6, 200 MHz): d 6.82 (1H,
s, H-5); 7.46–7.65 (3H, m, Ar-H); 7.78–7.82 (2H, m, Ar-H).
3-Cyano-4-trifluoromethyl-6-methyl-2(1H) pyridone (5). IR (KBr): 3325,
1
2250, 1675, 1210, 1175 cm21. H NMR (DMSO-d6): d 2.02 (3H, s, -CH3);
6.54 (1H, s, H-5).
ACKNOWLEDGMENTS
We are thankful to the director of IICT for encouragement and financial
support under the NMITLI program.
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