A simple and versatile method for the hydroiodination of alkenes and alkynes using I2 and Et3SiH in the presence of copper(II)

Article abstract of DOI:10.1016/S0040-4039(02)01335-7

The reagent system CuO·HBF₄/I₂/Et₃SiH generates in situ hydrogen iodide which regioselectively adds to alkenes and alkynes. The mild nature of this system tolerates the presence of different groups on the unsaturated compound.

Full text of DOI:10.1016/S0040-4039(02)01335-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 6111–6112
A simple and versatile method for the hydroiodination of alkenes
and alkynes using I and Et SiH in the presence of copper(II)
2
3
Pedro J. Campos,* B a´ rbara Garc ´ı a and Miguel A. Rodr ´ı guez*
Departamento de Qu ´ı mica, Universidad de La Rioja, Grupo de S ´ı ntesis Qu ´ı mica de La Rioja, Unidad Asociada al C.S.I.C,
Madre de Dios, 51, 26006 Logro n˜ o, Spain
Received 2 July 2002; accepted 3 July 2002
Abstract—The reagent system CuO·HBF /I /Et SiH generates in situ hydrogen iodide which regioselectively adds to alkenes and
4
2
3
alkynes. The mild nature of this system tolerates the presence of different groups on the unsaturated compound. © 2002 Elsevier
Science Ltd. All rights reserved.
The classical synthesis of alkyl iodides from alkenes and
hydrogen iodide often leads to low yields and side
reactions due to uncontrollable iodine liberation. Con-
the addition was carried out under several reaction
conditions. The highest yield was obtained by stirring
the mixture at −30°C for 3 h (Scheme 2 and Table 1).
1
sequently, several alternative approaches to hydroiodi-
2
nation have been developed:
chlorotrimethyl
The regioisomer obtained corresponds to
a
3
4
silane/sodium iodide/water, iodine/alumina, borane5-
Markovnikov addition of hydrogen iodide, which indi-
N,N-diethylaniline complex/iodine/acetic acid,
cates that this reagent should be generated in situ in the
6
+
iodotrimethyl silane/alumina and aluminium triiodide/
water. However, the use of iodotrimethylsilane (or its
course of the reaction from I and Et SiH. This hypoth-
3
7
esis was confirmed when we performed the reaction
using ethyl acrylate as the starting alkene, under the
same experimental conditions, since ethyl 3-iodopropi-
precursor) does not tolerate groups such as ester or
8
acetals, and other reagents are not easy to manipulate.
13
onate was formed (Table 1, entry 2). The latter result
also indicates that our method tolerates an ester group,
which could be also verified using 4-acetoxystyrene
(entry 3).
We have previously reported the iodofunctionalization
of different unsaturated systems with a mixture of
iodine and a solution of CuO·HBF (which resulted
4
from admixture of copper(II) oxide and aqueous tetra-
9,10
fluoroboric acid) in the presence of nucleophiles.
The
To check whether the reagent system could be used for
halogen-containing products, p-chlorostyrene was
treated with CuO·HBF /I /Et SiH, giving 1-iodo-1-(p-
sole example described using triethylsilane as reagent
leads to the hydroiodination of cyclohexene in excellent
yield (Scheme 1) but the usefulness of this procedure to
obtain alkyl iodides is far from having been sufficiently
explored. Since all reagents are commercially available
and can be manipulated without any special caution,
we found it of interest to investigate this addition
reaction with a range of alkenes and alkynes. We report
here our results in this field.
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3
chlorophenyl)ethane in 61% yield (entry 4).
1
1
Treatment of styrene with a dehydrated suspension of
CuO·HBF and iodine in anhydrous CH Cl afforded
1
Scheme 1.
Scheme 2.
4
2
2
1
2
-iodo-1-phenylethane as the main product. In order
to establish an optimum condition for hydroiodination,
*
0
Corresponding authors. Tel.: +34 941 299650; fax: +34 941 299621;
e-mail: pedro.campos@dq.unirioja.es
040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01335-7

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P. J. Campos et al. / Tetrahedron Letters 43 (2002) 6111–6112
Table 1. Reaction of CuO·HBF /I /Et SiH to alkenes and
In conclusion, we have developed a mild method for
the regioselective hydroiodination of alkenes and alky-
nes based on common reagents. Further studies to
extend the scope of this reaction are in progress.
4
2
3
a
alkynes
Acknowledgements
This work was supported by Spanish MCyT/FEDER
(
0
BQU2001-1625) and Universidad de La Rioja (API-
1/B07). One of us (B.G.) would like to thank the
Comunidad Aut o´ noma de La Rioja (Spain) for a fel-
lowship.
References
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. (a) Barluenga, J.; Rodr ´ı guez, M. A.; Campos, P. J.;
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(
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Chem. Soc., Perkin Trans. 1 1990, 2807.
1
1
0. We have also reported one example of hydroiodination
with IPy BF : Barluenga, J.; Gonz a´ lez, J. M.; Campos, P.
2
4
J.; Asensio, G. Angew. Chem., Int. Ed. Engl. 1985, 24,
19.
1. The aqueous solution of CuO·HBF was evaporated at
3
4
−
2
reduced pressure (10 mmHg and 50–60°C) to constant
weight (see Ref. 9). To avoid the water of crystallization
present in copper(II) tetrafluoroborate, silica gel can be
added prior to dryness.
Next, we investigated the addition of hydrogen iodide
to a number of alkynes. The results are also summa-
rized in Table 1. We found that the procedure afforded
a-iodostyrene, resulting from a mono hydroiodination
of phenylacetylene (entry 5). In a similar reaction,
12. Some polymeric material was obtained and the product
needed to be purified by column chromatography on
silica gel.
1-phenyl-1-propyne gave a mixture of (E)- and (Z)-1-
iodo-1-phenyl-1-propene (65 and 35%, respectively,
13. Comparing the regiochemistry obtained for the reactions
with styrene and ethyl acrylate, a mechanism involving a
radical addition can be discarded.
entry 6). These a-iodostyrenes are relevant reagents in
1
4
organic synthesis. The reaction with propargyl alcohol
(
entry 7) and ethyl propiolate (entry 8) illustrates other
14. For a recent application, see: Chan, P. W. H.; Kamijo, S.;
Yamamoto, Y. Synlett 2001, 910.
examples of the mildness of the reaction.