An expedient and highly selective iodination of alcohols using a KI/BF3·Et2O system

Article abstract of DOI:10.1016/S0040-4039(00)01953-5

Alkyl iodides are prepared in high yields by treatment of allylic and benzylic alcohols with an equimolar amount of KI in the presence of BF₃·Et₂O in dioxane under mild conditions.

Full text of DOI:10.1016/S0040-4039(00)01953-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 951–953
An expedient and highly selective iodination of alcohols using a
KI/BF ·Et O system
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B. P. Bandgar,* V. S. Sadavarte and L. S. Uppalla
Organic Chemistry Research Laboratory, School of Chemical Sciences, Swami Ramanand Teerth Marathwada University,
Vishnupuri, Nanded 431 606, India
Received 10 August 2000; revised 10 October 2000; accepted 2 November 2000
Abstract—Alkyl iodides are prepared in high yields by treatment of allylic and benzylic alcohols with an equimolar amount of KI
in the presence of BF ·Et O in dioxane under mild conditions. © 2001 Elsevier Science Ltd. All rights reserved.
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Alkyl iodides or bromides are often used for ionic or
radical carbon–carbon coupling reactions and can also
act as intermediates in substitution reactions, elimina-
tion reactions and rearrangements. Therefore, the con-
version of alcohols into alkyl halides is a very
important transformation in organic chemistry.
Although various methods have been reported in the
temperature within 5–30 min. Among various solvents
studied, 1,4-dioxane was found to be the solvent of
choice. The products were isolated by aqueous work-up
followed by solvent extraction and were purified by
column chromatography if necessary to afford pure
alkyl iodide (Table 1).
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literature to achieve this goal, some of these require
expensive reagents, long reaction times and tedious
reaction work-up. Other methods involve mild condi-
The reaction was found to be highly selective as only
allylic and benzylic alcohols are converted to iodides in
high yields (84–95%), whereas saturated aliphatic alco-
hols did not yield iodides even after prolonged stirring
in dioxane. The remarkable selectivity of this reaction
allowed only allylic and benzylic hydroxyls to be iodi-
nated without affecting other OH groups present in the
molecule (entries 6, 12). Furthermore, a secondary OH
group at an allylic or benzylic position could easily be
substituted by an iodide group in high yields using this
technique. As the reaction proceeds with gradual con-
sumption of BF ·Et O by the byproduct KOH, a molar
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tions and the use of iodo and bromotrimethylsilanes,
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chlorotrimethylsilane–sodium iodide and hexamethyld-
isilazane–iodine as reagents. More recently, some use-
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–12
ful reports
selective conversion of allylic and benzylic and other
primary, secondary and tertiary) alcohols into halides.
We found that the KI/BF ·Et O system was effective
have been published regarding the
(
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for this transformation and this communication deals
with the scope and limitations of this newly developed
iodination method.
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equivalent of BF ·Et O is essential in order to achieve
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complete conversion of the alcohol.
In conclusion, the highly selective, simple, mild, direct
and high yielding iodination of allylic and benzylic
alcohols using KI/BF ·Et O system in dioxane, pre-
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sented in this paper, serves as a useful synthetic entry to
valuable alkyl iodides.
A variety of allylic and benzylic alcohols were con-
verted into the corresponding iodides when treated with
a molar equivalent of KI in the presence of BF ·Et O.
Conversion of benzylic and allylic alcohols into iodides—
general procedure: The alcohol (5 mmol) was dissolved
in dry 1,4-dioxane (10 ml) to which BF ·Et O (5 mmol)
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The reaction was found to proceed smoothly at room
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and KI (5 mmol) were added and the resulting mixture
was stirred at room temperature. After the complete
conversion of alcohol to iodide (TLC) the reaction
mixture was poured into cold water and extracted with
Keywords: alcohols; iodides; BF ·Et O; selective iodination.
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*
Corresponding author. Fax: 0091-2462-29245; e-mail: upekam@
hotmail.com
0
040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)01953-5

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B. P. Bandgar et al. / Tetrahedron Letters 42 (2001) 951–953
Table 1. Conversion of alcohols to iodides using a KI/BF ·Et O system at 25°C
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a
Yields of isolated products.
b
Products are characterised by spectral and elemental analysis.13
diethyl ether (3×10 ml). The combined organic layer
Chem. Soc. 1954, 2281; (c) Rydon, H. N.; Tonge, B. L. J.
Chem. Soc. 1956, 3043.
was washed with water and brine, dried (Na SO ) and
2
4
the solvent was evaporated under reduced pressure. The
product was purified wherever necessary by column
chromatography on silica gel using hexane/ethyl acetate
2. (a) Crofts, P. C.; Downie, I. M. J. Chem. Soc. 1963,
2559; (b) Lee, J. B.; Nolan, T. J. Can. J. Chem. 1966, 44,
1331; (c) Havlock, C. R.; Melton, L. D.; Slessor, K. N.;
(
9:1) as an eluent to afford pure alkyl iodide.
Tracey, A. S. Carbohydr. Res. 1971, 16, 375; (d) Ver-
heyden, J. P. H.; Moffatt, J. G. J. Org. Chem. 1972, 37,
2
289.
Acknowledgements
3
4
. Hanessian, S.; Ponpipom, M. M.; Lavallee, P. Carbohydr.
Res. 1972, 24, 45.
. (a) Gareg, P. J.; Samuelsson, B. J. Chem. Soc., Perkin
Trans. 1 1980, 2866; (b) Garegg, P. J.; Johansson, R.;
Orthega, C.; Samuelson, B. J. Chem. Soc., Perkin Trans.
V.S.S. thanks CSIR, New Delhi for award of junior
research fellowship.
1
1982, 681.
. Jung, M. E.; Ornstein, P. L. Tetrahedron Lett. 1977,
659.
5
References
2
1. (a) Landauer, S. R.; Rydon, H. N. J. Chem. Soc. 1953,
6. Jung, M. E.; Hatfield, G. C. Tetrahedron Lett. 1978,
2
224; (b) Coe, D. G.; Landauer, S. R.; Rydon, H. N. J.
4483.

B. P. Bandgar et al. / Tetrahedron Letters 42 (2001) 951–953
953
7
. (a) Morita, T.; Yoshida, S.; Okamoto, Y.; Sakuraj, H.
Synthesis 1979, 379; (b) Olah, G. A.; Narang, S. C.;
Gupta, B. G. B.; Malhotra, R. J. Org. Chem. 1979, 44,
CDCl ): l=3.69 (s, 2H, ArCH ), 6.74 (d, 2H, Ar-H), 6.91
3
2
(d, 2H, Ar-H). Anal. calcd for C H OI (233.9809): C,
7
7
35.93; H, 2.99; I, 54.23. Found: C, 35.88; H, 3.01; I,
54.26.
1
247.
−
1
8
. Olah, G. A.; Narang, S. C.; Gupta, B. G. B.; Malhotra,
R. Angew. Chem., Int. Ed. Engl. 1979, 18, 612.
. Olah, G. A.; Hussain, A.; Singh, B. P.; Mehrotra, A. K.
J. Org. Chem. 1983, 48, 3667.
Compound 2h: IR (Neat, cm ): 699, 801, 1023, 1097,
1
1
261, 1463, 1603, 2852, 2923, 2961. H NMR (300 MHz,
9
CDCl ): l=3.75 (s, 2H, ArCH ), 7.04 (s, 3H, Ar-H).
3
2
Anal. calcd for C H OI (207.9589): C, 28.88; H, 2.40; I,
5
5
1
1
1
1
0. Mandal, A. K.; Mahajan, S. W. Tetrahedron Lett. 1985,
6, 3863.
1. Vankar, Y. D.; Rao, C. T. Tetrahedron Lett. 1985, 26,
717.
2. Classon, B.; Liu, Z.; Samuelsson, B. J. Org. Chem. 1988,
3, 6126.
3. Compound 2c: IR (Neat, cm ): 644, 711, 805, 831, 1013,
6
1.02. Found: C, 28.85; H, 2.42; I, 60.97.
2
−1
Compound 2i: IR (KBr, cm ): 699, 761, 850, 960, 1020,
1
3
210, 1300, 1451, 1493, 1602, 2730, 2850, 2963, 3010,
120. H NMR (300 MHz, CDCl ): l=2.68 (d, 3H,
2
1
3
CH ), 4.8 (q, 1H, Ar-CH), 7.1 (s, 5H, Ar-H). Anal. calcd
for C H I (232.0874): C, 41.40; H, 3.88; I, 54.68. Found:
C, 41.44; H, 3.85; I, 54.73.
Compound 2j: IR (KBr, cm ): 638, 699, 734, 919, 1027,
3
5
−
1
8
9
1
1
086, 1153, 1177, 1212, 1407, 1422, 1488, 1503, 1592,
−
1
1
901, 2910, 3010. H NMR (300 MHz, CDCl ): l=4.41
3
1
2
058, 1185, 1236, 1278, 1318, 1449, 1493, 1598, 1660,
810, 2910, 3026, 3061. H NMR (300 MHz, CDCl3):
(
s, 2H, ArCH ), 7.29 (m, 4H, Ar-H). Anal. calcd for
2
1
C H ClI (252.4342): C, 33.81; H, 2.38; Cl, 14.05; I, 50.27.
7
6
l=4.6 (s, 1H, Ar-CH), 7.15 (s, 10H, Ar-H). Anal. calcd
for C13 11I (294. 1424): C, 53.08; H, 3.74; I, 43.18.
Found: C, 53.11; H, 3.77; I, 43.21.
Found: C, 33.78; H, 2.42; Cl, 13.98; I, 50.33.
−
1
H
Compound 2d: IR (Neat, cm ): 695, 810, 835, 1090,
1
1
260, 1470, 1605, 2910. H NMR (300 MHz, CDCl3):
−
1
Compound 2k: IR (KBr, cm ): 635, 697, 810, 935, 1020,
l=3.77 (s, 3H, OCH ), 3.86 (s, 2H, ArCH ), 6.82 (d, 2H,
3
2
1
1058, 1503, 1607, 1720, 2827, 2921, 3026. H NMR (300
Ar-H), 7.07 (d, 2H, Ar-H). Anal. calcd for C H OI
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MHz, CDCl ): l=4.9 (s, 1H, Ar-CH), 7.11 (s, 5H, Ar-
H), 7.2 (s, 5H, Ar-H). Anal. calcd for C H OI
(323.0579): C, 52.05; H, 3.40; I, 39.59. Found: C, 52.11;
H, 3.38; I, 39.64.
Compound 2m: IR (KBr, cm ): 699, 755, 1031, 1130,
(
247.9919); C, 38.75; H, 3.63; I, 51.17. Found: C, 38.79;
H, 3.59; I, 51.21.
Compound 2e: IR (KBr, cm ): 630, 650, 710, 841, 934,
3
14 11
−
1
1
3
039, 1117, 1258, 1218, 1483, 1503, 1620, 2895, 3010,
−
1
1
120. H NMR (300 MHz, CDCl ): l=3.81 (s, 2H,
3
1
ArCH ), 4.7 (s, 2H, O-CH -O), 7.02 (m, 3H, Ar-H).
1451, 1499, 1598, 1653, 2851, 2827, 2921, 3033. H NMR
2
2
Anal. calcd for C H O I (254.9913): C, 37.68; H, 2.75; I,
(300 MHz, CDCl ): l=3.4 (d, 2H, CH I), 6.6 (m, 1H,
3 2
8
7
2
4
9.77. Found: C, 37.72; H, 2.78; I, 49.84.
ꢀCH), 6.8 (d, 1H, ArCH), 7.20 (s, 5H, Ar-H). Anal. calcd
−
1
Compound 2f: IR (KBr, cm ): 696, 1091, 1260, 1475,
for: C H I (245.0035): C, 44.13; H, 3.67; I, 52.21. Found:
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9
1
1
608, 2850, 2919, 3450 (br). H NMR (300 MHz,
C, 44.09; H, 3.65; I, 52.14.
.
.