Benzyl(triphenyl)phosphonium Dichloroiodate: A New Reagent for Coiodination of Alkenes

Article abstract of DOI:10.1002/hlca.201500069

A mild, efficient, and regio- and stereoselective method for iodoalkoxylation and iodohydroxylation of olefins has been developed using benzyl(triphenyl)phosphonium dichloroiodate as iodine source. This procedure led to the corresponding iodoalkoxylated and iodohydroxylated products in moderate to excellent yields.

Full text of DOI:10.1002/hlca.201500069

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Helvetica Chimica Acta – Vol. 98 (2015)
Benzyl(triphenyl)phosphonium Dichloroiodate: A New Reagent for
Coiodination of Alkenes
by Mohammad Alikarami*a) and Mansoureh Farhadib)
a) Department of Chemistry, Ilam Branch, Islamic Azad University, Ilam, Iran
(e-mail: alikarami58@yahoo.com)
b) Department of Chemistry, Borujerd Branch, Islamic Azad University, Borujerd, Iran
A mild, efficient, and regio- and stereoselective method for iodoalkoxylation and iodohydroxylation
of olefins has been developed using benzyl(triphenyl)phosphonium dichloroiodate as iodine source. This
procedure led to the corresponding iodoalkoxylated and iodohydroxylated products in moderate to
excellent yields.
Introduction. – Iodoorganic compounds are valuable and versatile synthetic
intermediates that have found diverse applications in polymer chemistry, pharmacol-
ogy, medicine, etc. [1]. The vicinal functionalization of olefins is an important process in
synthetic organic chemistry, especially when the reaction is carried out in a regio- and
stereoselective fashion. Among the several methods found in the literature [2 – 5],
halofunctionalization [6 – 10] of alkenes towards synthetically useful substrates attract
much more attention. For example, iodoalkoxylation and iodohydroxylation of olefins
is an important transformation in organic chemistry and the resulting alkoxyiodides
and hydroxyiodides are important building blocks in organic, medicinal, as well as
industrial chemistry [11 – 17].
Iodination of alkenes is a considerably slower reaction than chlorination and
bromination, due to the low electrophilicity of I2. Activation of I2 for addition to
alkenes by modifying its electrophilicity has been achieved using transition-metal salts
[18 – 23] or oxidizing agents [24 – 27].
Other electrophilic iodinating agents commonly employed for the iodination of
organic molecules include alkyl hypoiodides [28], N-iodosaccharin, and N-iodosucci-
nimide [29 – 31], bis(pyridine)iodonium tetrafluoroborate [32][33], I2-clays [34 – 37],
hypoiodous acid [38], triiodoisocyanuric acid [39], dichloroiodoisocyanuric acid [40],
and in situ generated acyl hypoidoite using a combination of elemental I2 and hyper-
valent iodine reagents [41 – 43], to name a few.
However, most of these methods suffer from one or more disadvantages, such as use
of expensive and hazardous/toxic reagents, high reaction temperatures, long reaction
times, low yields, and tedious workup procedures, which limit their use under the aspect
of environmental benign process. Therefore, replacement of such reagents by non-
toxic, mild, selective, and easy-to-handle reagents is very desirable and represents an
important goal in the context of clean synthesis.
In our efforts towards the development of efficient procedures for coiodination of
alkenes, we report a very simple and efficient method for 1,2-iodoalkoxylation and 1,2-
ꢀ 2015 Verlag Helvetica Chimica Acta AG, Zürich

Helvetica Chimica Acta – Vol. 98 (2015)
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iodohydroxylation of alkenes in the presence of dichloroiodate salt, such as benzyl-
(triphenyl)phosphonium dichloroiodate (BTPPICl2), as an iodinated reagent under
catalyst-free conditions at room temperature.
BTPPICl2 and other dichloroiodate compounds are used as mild, efficient, and
environmentally friendly iodination reagents for iodination of aromatic compounds
[44 – 50].
Results and Discussions. – In the first stage of this study, we focused on the
coiodination of a-methylstyrene (2; 1 mmol) by BTPPICl2 (1.5 mmol) in MeOH and
MeOH/solvent (MeCN, CH2Cl2, THF, hexane, and CHCl3) as model reaction. The
yield of (2-iodo-1-methoxy-1-methylethyl)benzene (2a) in MeOH after 40 min was
95% while in MeOH/solvent after 40 min it was 40, 65, 20, 50, and 70%, respectively.
The best result in terms of solvent and yield of the desired product was obtained, when
the reaction was conducted in MeOH as solvent and with O-bearing nucleophiles. To
test the generality of this procedure, we examined the coiodination of different alkenes,
and in most cases, b-iodo ethers were achieved in good to excellent yields (Table).
Table. Coiodination of Alkenes in the Presence of BTPPICl2 and O-Bearing Nucleophiles
Entry
Alkene
R
Product
Time [min]
Yield [%]a)
1
2
3
4b)
5
6
7
8
9b)
10
11
12
13b)
1
1
1
1
2
2
2
2
2
3
3
3
3
Me
Et
iPr
H
Me
Et
iPr
Bn
H
Me
Et
iPr
H
1a
1b
1c
1d
2a
2b
2c
2d
2e
3a
3b
3c
3d
40
45
40
32
40
45
45
40
30
40
40
45
35
92
90
88
95
95
90
90
80
90
94
90
80
85
a) Yield of isolated product. b) Reaction was performed in H2O/MeCN 1 : 1.

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Helvetica Chimica Acta – Vol. 98 (2015)
As can be seen in the Table, when acyclic olefins such as styrene (1) and a-
i
methylstyrene (2) were reacted with BTPPICl2 in MeOH, EtOH, and PrOH under
optimum conditions, the corresponding 1,2-iodoalkoxy compounds, 1a – 1c and 2a – 2c,
were obtained in good to excellent yields (Entries 1 – 3 and 5 – 7). Cyclic olefins, such as
i
indene, which were reacted with the iodinating reagent in MeOH, EtOH, or PrOH
gave satisfactory yields of the corresponding b-iodoether compounds, 3a – 3c (Entries
10 – 12). Interestingly, the reaction between a-methylstyrene and BTPPICl2 in
benzylalcohol led to [(2-iodo-1-methyl-1-phenylethoxy)methyl]benzene (2d) in good
yield (Entry 8). Furthermore, this reaction was also performed in H2O and H2O/solvent
for iodohydroxylation of alkenes. The highest yields were obtained when the reaction
was carried out in H2O/MeCN. To test the generality of this procedure, we examined
the coiodination of cyclic and acyclic alkenes. The corresponding halohydrin
compounds (1d, 2e, and 3d) were achieved in good to excellent yields (Entries 4, 9,
and 13).
Most importantly, the reaction was regioselective. Only Markovnikovꢁs addition
product was obtained.
Conclusions. – In summary, we have developed a convenient route to vicinal
halohydrines and b-halo ethers from alkenes. The reaction conditions are mild, the
workup process is very simple, the reagents employed are stable, cheap, and readily
available, and, furthermore, there is no need of special techniques and conditions.
Financial support of this work from the Research Council of Islamic Azad University of Ilam is
gratefully acknowledged.
Experimental Part
General. Starting materials used in the reactions were supplied commercially from Aldrich or Merck
Chemical Co. All yields refer to isolated products. Anal. thin layer chromatography (TLC): precoated 60
F254 silica gel plates (SiO2; Merck). Column chromatography (CC): SiO2 (100 – 200 mesh). 1H-NMR
Spectra: Bruker DRX-500 MHz Avance, Bruker 400 MHz Avance, and Bruker DRX-300 MHz
spectrometer; in CDCl3 or (D6)DMSO; d in ppm rel. to Me4Si as internal standard, J in Hz.
Preparation of BTPPICl2. A soln. of benzyl(triphenyl)phosphonium chloride (10 mmol) in 10 ml of
H2O was added to an orange soln. of NaICl2 (11 mmol; prepared from 5.25% NaClO (15.6 ml), NaI
(11 mmol, 1.65 g)), and 37% HCl (22 mmol, 2.2 ml) at 08 and stirred for 30 min at r.t. The resulting
yellow precipitate was collected and washed with cooled H2O and Et2O, and dried in a desiccator to
afford a yellow solid (90%). M.p. 162 – 1648 [50].
General Procedure for Coiodination of Alkenes with BTPPICl2. To a 50-ml flask equipped with a
magnetic stirrer, BTPPICl2 (0.5 mmol) was added to a soln. of alkene (1 mmol) in ROH (2 ml) or H2O/
MeCN 1:1. The mixture was stirred at r.t. for the specified time. The progress of the reaction was
monitored by TLC. After completion, AcOEt was added, the mixture was filtered, and the org. layer was
washed with 5% aq. Na2S2O3 and dried (MgSO4). The solvent was removed in vacuo and the crude
mixture was purified by CC (AcOEt/hexane) and analyzed by 1H-NMR spectroscopy.
(2-Iodo-1-methoxyethyl)benzene (1a). Yellowish liquid [27]. 1H-NMR (400 MHz, CDCl3): 7.43 – 7.32
(m, 5 arom. H); 4.31 (dd, J ¼ 8.0, 4.8, CHÀO); 3.36 (d, J ¼ 5.2, 1 H of CH2); 3.35 (d, J ¼ 2.4, 1 H of CH2);
3.32 (s, MeO).
1
(1-Ethoxy-2-iodoethyl)benzene (1b). Yellowish liquid [51]. H-NMR (400 MHz, CDCl3): 7.32 – 7.40
(m, 5 arom. H); 4.42 (dd, J ¼ 8.0, 5.2, CHÀO); 3.50 – 3.42 (m, CH2O); 3.40 – 3.33 (m, CH2I); 1.24 (t, J ¼
7.2, Me).

Helvetica Chimica Acta – Vol. 98 (2015)
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1
[2-Iodo-1-(1-methylethoxy)ethyl]benzene (1c). Yellowish liquid [36]. H-NMR (400 MHz, CDCl3):
7.39 – 7.33 (m, 5 arom. H); 4.53 (t, J ¼ 6.4, Me2CHÀO); 3.58 (m, PhCHÀO); 3.32 (d, J ¼ 7.2, CH2); 1.24 (d,
J ¼ 6.0, Me); 1.11 (d, J ¼ 6.0, Me).
1
2-Iodo-1-phenylethanol (1d). Yellowish liquid [40]. H-NMR (400 MHz, CDCl3): 7.40 – 7.35 (m, 5
arom. H); 4.86 (d, J ¼ 8.8, CHÀO); 3.50 (d, J ¼ 3.6, 1 H of CH2); 3.44 (d, J ¼ 8.8, 1 H of CH2); 2.50 (d, J ¼
2.4, OH).
(2-Iodo-1-methoxy-1-methylethyl)benzene (2a). Yellowish liquid [52]. 1H-NMR (400 MHz, CDCl3):
7.45 – 7.29 (m, 5 arom. H); 3.53 (d, J ¼ 10.4, 1 H of CH2); 3.45 (d, J ¼ 10.4, 1 H of CH2); 3.15 (s, MeO); 1.72
(s, Me).
1
(1-Ethoxy-2-iodo-1-methylethyl)benzene (2b). Yellowish liquid [51]. H-NMR (400 MHz, CDCl3):
7.45 – 7.29 (m, 5 arom. H); 3.54 (d, J ¼ 10.4, 1 H of CH2I); 3.48 (d, J ¼ 10.4, 1 H of CH2I); 3.40 – 3.32 (m,
1 H of CH2O); 3.25 – 3.18 (m, 1 H of CH2O); 1.72 (s, Me); 1.23 (t, J ¼ 6.8, Me).
[2-Iodo-1-methyl-1-(1-methylethoxy)ethyl]benzene (2c). Yellowish liquid. 1H-NMR (400 MHz,
CDCl3): 7.50 – 7.48 (m, 2 arom. H); 7.39 – 7.31 (m, 3 arom. H); 3.60 (m, CHÀO); 3.53 (d, J ¼ 10.0, 1 H
of CH2); 3.39 (d, J ¼ 10.0, 1 H of CH2); 1.80 (s, Me); 1.19 (d, J ¼ 6.0, Me); 1.02 (d, J ¼ 6.4, Me).
[(2-Iodo-1-methyl-1-phenylethoxy)methyl]benzene (2d). Yellowish liquid. 1H-NMR (500 MHz,
CDCl3): 7.53 – 7.29 (m, 10 arom. H); 4.41 (d, J ¼ 11.2, 1 H of CH2O); 4.30 (d, J ¼ 11.2, 1 H of CH2O);
3.67 (d, J ¼ 10.4, 1 H of CH2I); 3.57 (d, J ¼ 10.4, 1 H of CH2I); 1.87 (s, Me).
1-Iodo-2-phenylpropan-2-ol (2e). Yellowish liquid [40]. 1H-NMR (400 MHz, CDCl3): 7.49 – 7.45 (m,
2 arom. H); 7.41 – 7.37 (m, 2 arom. H); 7.34 – 7.28 (m, 1 arom. H); 3.68 (d, J ¼ 10.0, 1 H of CH2); 3.64 (d,
J ¼ 10.0, 1 H of CH2); 2.39 (s, OH); 1.75 (s, Me).
2,3-Dihydro-2-iodo-1-methoxy-1H-indene (3a). Yellowish liquid [23]. 1H-NMR (500 MHz, CDCl3):
7.48 – 7.28 (m, 4 arom. H); 5.15 (d, J ¼ 3.5, CHÀO); 4.55 – 4.52 (m, CHÀI); 3.78 (dd, J ¼ 17.0, 6.8, 1 H of
CH2); 3.63 (s, MeO); 3.33 (dd, J ¼ 17.0, 4.6, 1 H of CH2).
1
1-Ethoxy-2,3-dihydro-2-iodo-1H-indene (3b). Yellowish liquid [23]. H-NMR (400 MHz, CDCl3):
7.50 – 7.31 (m, 4 arom. H); 5.19 (d, J ¼ 3.6, CHÀO); 4.49 – 4.45 (m, CHÀI); 3.93 – 3.86 (m, 1 H of CH2O);
3.81 – 3.77 (m, 1 H of CH2); 3.76 – 3.72 (m, 1 H of CH2O); 3.30 (dd, J ¼ 17.0, 4.8, 1 H of CH2); 1.28 (t, J ¼
2.4, Me).
2,3-Dihydro-2-iodo-1-(1-methylethoxy)-1H-indene (3c). Yellowish liquid [23]. 1H-NMR (400 MHz,
CDCl3): 7.40 – 7.21 (m, 4 arom. H); 5.22 (d, J ¼ 4.4, ArCHÀO); 4.37 – 4.33 (m, CHÀI); 4.14 – 4.08 (m,
Me2CHÀO); 3.69 (dd, J ¼ 16.8, 7.2, 1 H of CH2); 3.29 (dd, J ¼ 16.4, 6.4, 1 H of CH2); 1.31 (d, J ¼ 3.2, Me);
1.30 (d, J ¼ 3.6, Me).
1
2,3-Dihydro-2-iodo-1H-inden-1-ol (3d). Solid. M.p. 1128 [53]. H-NMR (400 MHz, CDCl3): 7.46 –
7.24 (m, 4 arom. H); 5.42 (t, J ¼ 6.0, CHÀO); 4.23 (m, CHÀI); 3.62 (dd, J ¼ 16.2, 7.4, 1 H of CH2); 3.33
(dd, J ¼ 16.4, 8.0, 1 H of CH2); 2.36 (d, J ¼ 6.0, OH).
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Received March 18, 2015