Selective iodination of alcohols with NaI/Amberlyst 15 in acetonitrile

Article abstract of DOI:10.1055/s-2004-815445

A simple and effective procedure for conversion of primary, secondary, allylic and benzylic alcohols into the corresponding iodides is described using NaI/Amberlyst 15 in acetonitrile at room temperature. Selective conversion of benzylic alcohols in the presence of saturated alcohols into the corresponding benzylic iodides is achieved under these conditions.

Full text of DOI:10.1055/s-2004-815445

LETTER
635
Selective Iodination of Alcohols with NaI/Amberlyst 15 in Acetonitrile
S
M
elective Iodination of
a
A
lcohols w
h
ith NaI/Am
b
m
erlyst 15 in
A
ceton
o
itrile od Tajbakhsh,* Rahman Hosseinzadeh,* Zahra Lasemi
Department of Chemistry, Mazandaran University, Babolsar, Iran
Fax +98(11252)42029; E-mail: tajbaksh@umz.ac.ir
Received 15 September 2003
hydroxyl groups into iodides are of increasing importance
to overcome such difficulties.
Abstract: A simple and effective procedure for conversion of pri-
mary, secondary, allylic and benzylic alcohols into the correspond-
ing iodides is described using NaI/Amberlyst 15 in acetonitrile at We report herein an exceedingly mild preparation of io-
room temperature. Selective conversion of benzylic alcohols in
dides from alcohols by the use of a NaI/Amberlyst 15 sys-
the presence of saturated alcohols into the corresponding benzylic
tem in acetonitrile at room temperature (Scheme 1).
iodides is achieved under these conditions.
Key words: iodination, Amberlyst 15, benzylic alcohol, saturated
alcohol, iodides
Scheme 1
Halogen-containing compounds are very useful interme-
diates in organic synthesis. They react with nucleophiles
1
such as amines or alkoxides to give the corresponding The results of the iodination reactions are summarized in
substituted products and can be lithiated to introduce elec- Table 1. The data indicate that iodination of a variety of
2
trophiles via a halogen–lithium exchange reaction. Alkyl allylic or benzylic and saturated primary or secondary al-
iodides or bromides are widely used for ionic and radical cohols occurs using a NaI/Amberlyst 15 system in aceto-
carbon-carbon coupling reactions, and also act as interme- nitrile at room temperature. The iodination of benzyl
diates in substitution, elimination and rearrangement reac- alcohol was selected for optimization of the reaction con-
tions. The most common precursors to alkyl halides are ditions. It was observed that when benzyl alcohol was
alcohols. Therefore, the conversion of alcohols into alkyl treated with NaI without Amberlyst 15, no change took
iodides is a frequently used functional group transforma- place, implying that Amberlyst 15 plays an important role
3
tion. Although alkyl iodides are less stable than the cor- in this reaction. This was further confirmed when other
responding chloride or bromide, and iodine is the most solid supports such as SiO , Al O , Zeolite HY, Mont-
2
2
3
expensive of the common halogens, they are far more morillonite K10 and Montmorillonite KSF were em-
reactive than the other halides, and in some cases iodides ployed. Treatment of benzyl alcohol with NaI/SiO , NaI/
2
4
are the only reactive halides.
Al O and NaI/Montmorillonite K10 gave the corres-
2 3
ponding iodide in low yield (Table 1, entries 2–4). Under
the same conditions, NaI/Zeolite HY and NaI/Mont-
morillonite KSF gave benzyl iodide in 40% and 60% yield
respectively (Table 1, entries 5 and 6). We have also ex-
amined the effect of solvent in this reaction. When benzyl
alcohol reacted with NaI/Amberlyst 15 in various solvents
such as acetonitrile, ethyl acetate, chloroform, dioxane,
dichloromethane and THF, we found that the reaction pro-
ceed most rapidly and give optimal yields in acetonitrile.
A number of synthetic methods for transformation of al-
cohols into iodides has been developed during the past
5
–8
two decades. Some methods involve mild conditions
9
and the use of iodotrimethylsilane, bromotrimethylsi-
1
0
11
lane, chlorotrimethylsilane-sodium iodide, hexameth-
1
2
13
yldisilazane-iodine, P I in CS , N,N-diethylaniline-
borane-I2, CeCl ·7H O/NaI system, sodium iodide
over KSF-clay under microwave irradiation, and KI/
H SO supported on natural kaolinitic clay under micro-
2
4
2
1
4
15
3
2
1
6
2
4
1
7
wave irradiation as reagents. More recently, some useful Benzyl alcohol with NaI/Amberlyst 15 provided benzyl
reports have been published regarding the selective con- iodide in excellent yield (Table 1, entry 1).24 We have
version of allylic, benzylic and other (primary, secondary tested various benzylic alcohols with both electron-donat-
and tertiary) alcohols into halides.18–22 However, some of ing and electron-withdrawing groups on the aryl ring
these suffer from drawbacks, which include the use of tox- (Table 1, entries 8–14) and have observed that, as expect-
ic and/or hazardous materials, reagents that are not com- ed, the reaction is slightly accelerated by an electron-do-
mercially available, long reaction times, low yields and nating group (Table 1, entry 13). Certainly, the
tedious work-up procedures. As such mild and efficient substitution of the electron-withdrawing group onto the
methods that can be used to promote the transformation of aromatic ring retards the transformation (Table 1, entry
1
4), while, no significant difference in reactivity was ob-
served when performing the reaction with substituents
such as Cl, OH, and OMe groups at the ortho and meta
positions (Table 1, entries 8–11). In the case of primary
alcohols the conversion into the corresponding iodides
SYNLETT 2004, No. 4, pp 0635–0638
Advanced online publication: 29.01.2004
DOI: 10.1055/s-2004-815445; Art ID: D23203ST
0
9.
0
3.
2
0
0
4
©
Georg Thieme Verlag Stuttgart · New York

6
36
M. Tajbakhsh et al.
LETTER
requires longer reaction times (Table 1, entry 18). Like- served that the attack of the iodide ion on primary allylic
wise, secondary alcohols such as cyclohexanol and 5- alcohols does not involve allylic rearrangement (Table 1,
nonanol were also converted into the corresponding alkyl entries 15 and 16); whereas displacement of allylic alco-
iodides (Table 1, entries 19 and 20). Furthermore, under hols containing a terminal double bond gave iodides
the same reaction conditions, allylic alcohols formed al- accompanied by allylic rearrangement (Table 1, entry 17).
lylic iodides, usually not available commercially due to
their rapid decomposition during storage. It has been ob-
Table 1 Conversion of Alcohols into Alkyl Iodides Using NaI/Amberlyst15a
Entry
1
Substrate
Reagent
Productb
Time
1 h
Yield (%)c
95f
NaI, Amberlyst 15, r.t.d
2
3
4
5
6
NaI, SiO , r.t.
4 h
5 h
4 h
3 h
3 h
20
10
10
40
60
2
NaI, Al2O3, r.t.
NaI, Montmorillonite K10, r.t.
NaI, ZeolitheHY, r.t,
Montmorillonite KSF, r.t.
7
8
NaI, Amberlyst 15, r.t.
NaI, Amberlyst 15, r.t.
N.r.e
5 h
–
50 min
95
9
NaI, Amberlyst 15, r.t.
NaI, Amberlyst 15, r.t.
NaI, Amberlyst 15, r.t.
1 h
88f
90
1
1
0
1
75 min
1 h
87f
1
2
NaI, Amberlyst 15, r.t.
1 h
90f
Synlett 2004, No. 4, 635–638 © Thieme Stuttgart · New York

LETTER
Selective Iodination of Alcohols with NaI/Amberlyst 15 in Acetonitrile
637
a
Table 1 Conversion of Alcohols into Alkyl Iodides Using NaI/Amberlyst15 (continued)
Entry
Substrate
Reagent
Productb
Time
Yield (%)c
98
1
1
1
3
4
5
NaI, Amberlyst 15, r.t.
45 min
NaI, Amberlyst 15, r.t.
NaI, Amberlyst 15, r.t.
3.5 h
60f
90
50 min
1
1
6
7
NaI, Amberlyst 15, r.t.
NaI, Amberlyst 15, r.t.
50 min
45 min
90
90
1
1
2
8
9
0
NaI, Amberlyst 15, r.t.
NaI, Amberlyst 15, r.t.
NaI, Amberlyst 15, r.t.
10 h
10 h
10 h
80f
80f
80f
a
All reactions were carried out at r.t. with alcohol/NaI (1:1) molar ratio.
All Products were characterized spectroscopically (IR, H NMR, GC) and showed physical and spectral data in accordance with their expected
b
1
structure and by comparison with authentic samples.
c
Yields refer to pure isolated products. All starting materials were commercially available.
Room temperature.
No reaction.
Purified by column chromatography.
d
e
f
Chemoselective iodination of benzylic alcohols was car- In conclusion, the present study for the conversion of al-
ried out in the presence of saturated alcohols as well as cohols into iodides, shows that our method represents a
phenols. The results are shown in Table 2.
valuable alternative to those reported in the literature.
Table 2 Selective Synthesis of Benzyl Iodides
Entry
1
Substrate
Product
Time (h)
2
Yield (%)a
Benzyl acohol
Heptanol
Benzyl iodide
95
00
98
00
60
00
95
00
1-Iodoheptane
2
3
4-Methoxybenzylalcohol
4-Methoxybenzyl-iodide
5-Iodononan
2
4
5
5
-Nonanol
4-Nitrobenzyl alcohol
Cyclohexanol
4-Nitrobenzyl iodide
Cyclohexyl iodide
2-Hydroxybenzyl iodide
4
2-Hydroxybenzyl alcohol
Phenol
n.r.b
a
1
23,25,
Yields of pure isolated product; products are characterized spectroscopically (IR, H NME, GC) and by comparison with authentic samples.
No reaction.
b
Synlett 2004, No. 4, 635–638 © Thieme Stuttgart · New York

6
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M. Tajbakhsh et al.
LETTER
Acknowledgment
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Financial support of this work from the Research Council of
Mazandaran University is gratefully acknowledged.
(
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(
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Krief, A. Tetrahedron Lett. 1979, 1801.
14) Reddy, C. K.; Periasamy, M. Tetrahedron Lett. 1989, 30,
5663.
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Synlett 2004, No. 4, 635–638 © Thieme Stuttgart · New York