Improving alkynyl(aryl)iodonium salts: 2-anisyl as a superior aryl group

Article abstract of DOI:10.1039/c4ob00556b

The majority of alkynyl(aryl)iodonium salts reported in the literature are derived from iodobenzene. This article describes the effects of varying this iodoarene building block on the synthesis, reactivity and stability of these salts. Two procedures to synthesize a variety of known and novel alkynyl(aryl)iodonium tosylates directly from the iodoarene are reported. In the reactions of these salts, those derived from 2-iodoanisole gave superior results than the others tested in every reaction. Isothermal microcalorimetry indicated that these novel salts were significantly more stable and less prone to decomposition than all of the other derivatives. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ob00556b

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Improving alkynyl(aryl)iodonium salts: 2-anisyl as a
superior aryl group†
Cite this: Org. Biomol. Chem., 2014,
12, 4156
David J. Hamnett and Wesley J. Moran*
The majority of alkynyl(aryl)iodonium salts reported in the literature are derived from iodobenzene. This
article describes the effects of varying this iodoarene building block on the synthesis, reactivity and stabi-
lity of these salts. Two procedures to synthesize a variety of known and novel alkynyl(aryl)iodonium tosy-
lates directly from the iodoarene are reported. In the reactions of these salts, those derived from
2-iodoanisole gave superior results than the others tested in every reaction. Isothermal microcalorimetry
indicated that these novel salts were significantly more stable and less prone to decomposition than all of
the other derivatives.
Received 13th March 2014,
Accepted 6th May 2014
DOI: 10.1039/c4ob00556b
www.rsc.org/obc
Introduction
Interest in hypervalent iodine chemistry has surged in recent
years with new iodine(III) and iodine(V) compounds being
reported regularly alongside novel reactions using these
species.1 There are two main types of hypervalent organo-
iodine compounds: those with one carbon ligand and those with
two. Compounds with one carbon ligand include iodobenzene
diacetate (also called diacetoxyiodobenzene or phenyliodide
diacetate) and Dess–Martin periodinane. Generally, these types
of hypervalent iodine compounds are powerful oxidants.
Hypervalent iodine compounds with two carbon ligands are
commonly called iodonium salts and these include diaryliodo-
nium salts, alkenyl(aryl)iodonium salts and alkynyl(aryl)iodo-
nium salts. These compounds are not strong oxidants.
Iodonium salts are increasingly popular reagents in organic
synthesis because of the range of useful reactivities that they
exhibit.2 The most investigated iodonium salts are the diarylio-
donium salts, which can, in principal, donate either of their
aryl groups in reactions with nucleophiles (Scheme 1).3
Whereas, in general, alkynyl(aryl)- and alkenyl(aryl)iodonium
salts only donate the alkyne or alkenyl groups respectively.
This means that the aryl group is, essentially, a spectator
group in these two types of iodonium salts. However, the effect
of changing this spectator group on the reactivity of these salts
has not been studied. Indeed, the majority of research with
these two types of salts has been with those derived from iodo-
benzene.4 Cyclic species such as triisopropylsilylethynyl-1,2-
Scheme 1 General reactivities of iodonium salts with nucleophiles
highlighting the “spectator” role of the aryl iodide in alkenyl(aryl)- and
alkynyl(aryl)iodonium salts.
benziodoxol-3(1H)-one (TIPS-EBX) are known, but these have
only been reported in alkynylation reactions.5
Results and discussion
We identified two different reactions from the literature that
alkynyl(aryl)iodonium salts undergo and decided to compare
and contrast the effect of varying the aryl moiety on the reac-
tion outcomes. The two reactions were (i) conjugate addition
of a nucleophile followed by carbene formation and rearrange-
ment to generate a new alkyne6 and (ii) conjugate addition of a
nucleophile followed by carbene formation and intramolecular
1,5-insertion into a C–H bond (Scheme 2).7
Department of Chemistry, University of Huddersfield, Queensgate, Huddersfield
HD1 3DH, UK. E-mail: w.j.moran@hud.ac.uk
†Electronic supplementary information (ESI) available: Characterization data
and copies of 1H and 13C NMR spectra. CCDC 940260. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c4ob00556b
Our first challenge was to prepare the requisite alkynyliodo-
nium salts necessary for this study. There are several synthetic
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Table 1 Synthesis of alkynyl(aryl)iodonium tosylates with electron-
donating aryl substituentsa
Scheme 2 Two reactions of alkynyl(aryl)iodonium salts.
methods available; however, as alluded to earlier, their effec-
tiveness with regards to preparing salts from different aryl
iodides has not been reported. We elected to use the method
reported by Merritt and Olofsson for direct formation of the
salts from terminal alkynes and aryl iodides using 3-chloroper-
benzoic acid and 4-toluenesulfonic acid in dichloromethane.8
This procedure was only reported for the preparation of salt 1a
but its simplicity makes it an attractive method. However, our
attempts to make pure samples of derivatives by this method
failed in most cases, with the major impurity being the
hydroxy(tosyloxy)aryliodine(III) compound. In 2012, Bouma
and Olofsson published a new protocol using alkynyl boro-
nates instead of terminal alkynes and the authors stated that
this was a general route to high purity salts.9 Other methods
have been reported which also require initial preparation of
the corresponding alkynyl silanes,10 borons11 or stannanes.12
We wished to develop the method using terminal alkynes as
this is more direct and atom efficient.
During our study, we noted that aryl iodides bearing elec-
tron-donating substituents behaved differently to those with
electron-withdrawing groups; therefore, we optimized reaction
conditions for these derivatives separately. For aryl iodides
with electron-donating substituents, slow addition of the
oxidant over several hours to the reaction mixture at 0 °C pro-
vided high purity iodonium salts upon crystallization from the
reaction mixture (Table 1). This slow addition of the oxidant to
a cold solution of the other components was found to effec-
tively inhibit thermal decomposition of the intermediate
iodine(III) species formed during this process. Additionally, by
using an excess of the alkyne it was found, as expected, that
the amount of the major hydroxy(tosyloxy)aryliodine(III)
a Yields are for pure isolated compounds.
impurity was reduced, leading to products of higher purity and
in superior yield. If necessary, recrystallization effectively
removed any trace impurities.
For aryl iodides with electron-withdrawing substituents, the
hydroxy(tosyloxy)iodine(III) species were first prepared in situ
and then treated with the alkyne to generate the iodonium
salts in high purity after crystallization from the reaction
mixture (Table 2). Where the conditions reported by Merritt
and Olofsson were applied to the synthesis of these aryl
iodides it was found that the material obtained was of very low
purity; as little as 50%. We assume, therefore, that the pres-
ence of electron withdrawing substituents reduces the rate of
formation of the alkynyliodonium salts from the corres-
ponding hydroxy(tosyloxy)iodine(III) species and that the low
purities were a consequence of incomplete reactions. By
forming the hydroxy(tosyloxy)iodine(III) species first, we reduce
the amount of time for thermal decomposition of the product
alkynyliodonium salts, while an excess of the alkyne results in
further gains in both the yield and purity of the product alky-
nyliodonium salts obtained. Again, any impurities present
could be removed by recrystallization, but this was rarely
necessary. All of the alkynyliodonium salts synthesised could
be stored indefinitely at −20 °C.
With these salts in hand, the addition–rearrangement reac-
tion with sodium phenylsulfinate was investigated (Table 3).6
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Table 2 Synthesis of alkynyl(aryl)iodonium tosylates with electron-
withdrawing aryl substituentsa
Fig. 1 X-ray crystal structure of 1b.
insights into salt 1b a single crystal X-ray structure was
obtained (Fig. 1).13 This iodonium salt exists as a dimer in the
solid state with the bond angles and lengths around the
methoxy substituent being distorted somewhat suggesting
some coordination to the I(III) center. The C(–I)–C–O bond
angle is 116.62° compared to 120.83° for the C(–I)–C–H bond
angle. Likewise, the C(–I)–C(–O)–C bond angle is 117.93° and
the C(–I)–C(–H)–C bond angle is 118.27°. The distance
between the iodine and oxygen atoms is 3.029 Å, which is
reasonable for a van der Waals interaction. Recently, Zhdankin
and co-workers demonstrated the synthesis and chemistry of
iodonium ylides with ortho-alkoxy groups bound to the aryl
ring.14 The reported crystal structure shows similar distortions
around the I(III) center and the ortho-n-propoxy oxygen I(III) dis-
tance is reported as 2.978 Å. The authors note that these
species display superior solubility and reactivity in comparison
with their phenyl analogs.
a Yields are for pure isolated compounds.
Table 3 Addition–rearrangement reaction
Entry
R
Salt
Yielda (%)
1
2
3
4
5
6
7
8
H
1a
1b
1c
1d
1e
1f
81 (74)
90 (83)
49
53
44
73
88
79
2-OMe
3-OMe
4-OMe
2-NO2
3,5-diMe
4-Me
The addition–C–H insertion reaction was investigated next
(Table 4).7 In our hands, this reaction proved difficult with
only 12% yield being achieved with salt 2a (entry 1). However,
the 2-methoxy salt 2b once again proved to be superior and
1g
1h
4-Cl
a Yields are an average of three runs and were determined by 1H NMR
analysis of the crude reaction mixtures with reference to a standard.
Yields of isolated compounds are given in parentheses.
Table 4 Addition/C–H insertion reaction
The iodobenzene derived salt 1a worked well delivering an
average of 81% yield over three runs, with 74% yield of isolated
compound (entry 1). The 2-methoxy derivative 1b provided a
better yield of 90%, with 83% yield of isolated compound
(entry 2) whereas the 3- and 4-methoxy derivatives 1c and 1d
both led to diminished yields (entries 3 and 4). This suggests
that the improvement in yield for 1b is not due to electronic
effects. Indeed, 1b appeared to show increased solubility com-
pared to 1c and 1d. The nitro derivative 1e was a poor perfor-
mer (entry 5), whereas m-xylyl derivative 1f delivered 73%
product, p-tolyl 1g gave a superior 88% and 4-chloro 1h was
similar to parent 1a with 79%.
Entry
R
Salt
Yielda (%)
1
2
3
4
5
6
H
2a
2b
2c
2d
2e
2f
12 (5)
51 (46)
32
10
<5
2-OMe
3-NO2
4-NO2
3,5-diMe
4-Cl
32
a Yields are an average of three runs and were determined by 1H NMR
analysis of the crude reaction mixtures with reference to a standard.
These results suggest that 2-iodoanisole is the best “specta-
tor” group of those tested in this reaction. To get further Yields of isolated compounds are given in parentheses.
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Table 5 Effect of counterion on overall yield
Table 6 Conversion of silylalkyne 7 to sulfone 3 without isolation of
the alkynyliodonium salt 1
Entry
MX
Overall yielda (%)
Entry
Ar
Overall yielda (%)
1
2
3
4
5
6
NaBF4
LiOTf
NaOTs
NaOMs
NaNO3
NaPF6
50 (36)
47
45
37
46
1
2
3
4
5
6
Ph
50 (36)
96b (87)
38
48
49
2-MeOC6H4
2-NO2C6H4
3,5-diMeC6H3
4-MeC6H4
4-ClC6H4
48
62
a Yields are an average of three runs and were determined by 1H NMR
analysis of the crude reaction mixtures with reference to a standard.
Yields of isolated compounds are given in parentheses.
a Yields are an average of three runs and were determined by 1H NMR
analysis of the crude reaction mixtures with reference to a standard.
Yields of isolated compounds are given in parentheses. b First stage of
the iodonium salt formation performed at −78 °C.
51% yield of product was obtained (entry 2). The other salts
provided low amounts of products, with xylyl derivative 2e
furnishing <5% (entry 5).
Table 7 Conversion of silylalkyne 8 to cyclopentene 10 without iso-
lation of the alkynyliodonium salt 9
In order to investigate the effect of the counterions on reac-
tion yields, alkynyl(phenyl)iodonium salts were prepared from
trimethyl(phenylethynyl)silane by reaction with iodoso-
benzene followed by treatment with aqueous solutions of a variety
of lithium or sodium salts. The crude products were directly
treated with sodium benzenesulfinate to effect the addition–
rearrangement process (Table 5). The product 3 was formed in
up to 50% yield from 7 (entry 1). The yields for the different
salts were very close, with only a 5% difference, apart from for
the mesylate which was 13% lower than the best (entry 4).
This process was then repeated but with variation of the
iodosoarene and the tetrafluoroborate counterion was used
(Table 6). The different iodosoarenes required were syn-
thesized by hydrolysis of the corresponding iodoarene di-
acetates with 3 M NaOH solution.15 Yields varied from 0–92%
for this process and the products were insoluble polymeric
solids. Upon running the test reaction, a 50% overall yield of 3
was obtained for the phenyl parent and 36% yield was isolated
(entry 1). The 2-iodosoanisole appeared to decompose upon
addition of the Lewis acid at room temperature, therefore the
Lewis acid was added dropwise at −78 °C to the solution of
silylalkyne 7 and 2-iodosoanisole. The reaction mixture was
then warmed to room temperature and the aqueous NaBF4
solution added. Addition of the NaSO2Ph to this salt at room
temperature led to addition/insertion occurring in a remark-
able 96% overall yield (entry 2). The other iodosoarenes tested
gave moderate yields.
Entry
Ar
Overall yielda (%)
1
2
3
4
5
6
Ph
30 (22)
71b (64)
35
57
54
2-MeOC6H4
2-NO2C6H4
3,5-diMeC6H3
4-MeC6H4
4-ClC6H4
46
a Yields are an average of three runs and were determined by 1H NMR
analysis of the crude reaction mixtures with reference to a standard.
Yields of isolated compounds are given in parentheses. b First stage of
the iodonium salt formation performed at −78 °C.
running the reaction, a 30% overall yield of 10 was obtained
for the phenyl parent (entry 1). The 2-iodoanisole derivative
gave a superior 71% yield, 64% isolated, which was substan-
tially better than all the other derivatives tested (entry 2). This
result is particularly notable for a non-activated aliphatic C–H
insertion reaction occurring at room temperature. A small
In a similar fashion, the addition–insertion reaction was
investigated starting from the silane 8 but without isolation
of the intermediate alkynyliodonium salt 9 (Table 7). Upon
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Conclusions
We have developed two new modified procedures for the
preparation of alkynyl(aryl)iodonium tosylates directly from
iodoarenes and terminal acetylenes. We have also demon-
strated that the reactivity of alkynyl(aryl)iodonium salts vary
considerably depending on which aryl iodide they are derived
from.16 Thus, the aryl iodide is not merely a spectator group
but has a profound impact on the reactivity. Importantly, the
stability of the iodine(III) species has been shown to be critical
for achieving high yields. Of those tested, 2-iodoanisole has
been shown to be the optimum choice as it provided augmen-
ted yields of products in subsequent reactions compared to
other derivatives. It is expected that the use of 2-iodoanisole
derived alkynyl(aryl)iodonium salts, and other iodine(III)
species, will deliver superior results in other reactions.14
Fig. 2 IMC data for three alkynyl(aryl)iodonium salts in the solid state at
30 °C.
Experimental
General methods
1H NMR spectra were recorded at 400 MHz. Chemical shifts
are reported in ppm from tetramethylsilane with the solvent
resonance as the internal standard (CDCl3: 7.26 ppm). 13C
NMR were recorded with complete proton decoupling. Chemi-
cal shifts are reported in ppm from tetramethylsilane with the
solvent as the internal standard (CDCl3: 77.4 ppm). Mass spec-
trometry (m/z) was performed in ESI mode, with only mole-
cular ions being reported. Infrared (IR) spectra νmax are
reported in cm−1. Petroleum ether refers to the fraction boiling
at 40–60 °C. All purchased reagents were used as received
without further purification. All reactions were performed
under a N2 atmosphere.
Fig. 3 IMC data for three alkynyl(aryl)iodonium salts in 1,2-dichloro-
ethane at 30 °C.
Preparation of alkynyl(aryl)iodonium salts with electron-
donating substituents. To a solution of iodoarene (4.90 mmol,
1 equiv.), TsOH·H2O (0.93 g, 4.90 mmol, 1 equiv.) and an aryl
alkyne (9.80 mmol, 2 equiv.) in CH2Cl2 (25 mL) at 0 °C, was
added m-CPBA (70–75% purity, 1.22 g, 4.90 mmol, 1 equiv.)
slowly over a period of 1 hour. The resulting solution was
slowly warmed to room temperature and stirred for 24 h after
which it was reduced to half volume (approx. 12 mL) in vacuo
at ambient temperature. Diethyl ether (12 mL) was added to
this solution in a dropwise manner, with gentle swirling. The
resulting homogeneous solution was again reduced to half
volume in vacuo at ambient temperature, upon which time
crystals started to be formed. Over a period of one hour,
diethyl ether (75 mL) was added with gentle swirling, and the
resulting suspension was allowed to stand for 1 h. The precipi-
tate was filtered, washed with diethyl ether and dried under
vacuum, yielding the product as a powder. Analytically pure
material was obtained by recrystallization in CH2Cl2 and ether.
Preparation of alkynyl(aryl)iodonium salts with electron-
donating substituents. To a solution of iodoarene (4.90 mmol,
1 equiv.), TsOH·H2O (0.93 g, 4.90 mmol, 1 equiv.) in CH2Cl2
(25 mL) was added m-CPBA (70–75% purity, 1.22 g, 4.90 mmol,
1 equiv.) in one portion. The solution was allowed to stir for
amount of the 1,2-rearrangement product was also formed in
this reaction (<20%).
In order to rationalize these results, we decided to analyze
the alkynyl(aryl)iodonium salts by isothermal microcalori-
metry (IMC). Holding the samples for seven days at 30 °C
under an air atmosphere both as solids (Fig. 2) and in solution
(Fig. 3) led to rapid decomposition of all of the salts apart
from the 2-iodoanisole derivative. This salt was unchanged
after seven days, whereas the others decomposed within
minutes. This remarkable stability is postulated to arise from
coordination of the oxygen atom to the iodine(III) centre (vide
supra) as the corresponding 4-iodoanisole derivative rapidly
decomposed, suggesting that simple electronic effects are not
responsible. Assuming that this effect is also present in the
iodonium reaction intermediates, we can rationalize the
observed yields in the reactions studied by consideration of
the stabilities of the iodine(III) species and the likelihood of
their undergoing unproductive decomposition before the
desired reaction. These species are not sensitive to water or air
and no decompositions have been detected by exposing
them to daylight, although storage in the dark is
recommended.
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24 hours, upon which time an aryl alkyne (9.80 mmol, 6.3 Hz), 6.05 (s, 1H), 4.91 (s, 1H), 1.88 (s, 3H). 13C NMR
2 equiv.) was added, followed by a further 24 hours stirring. (100 MHz, CDCl3): δ 146.5, 145.6, 136.0, 135.0, 133.4, 129.1,
Removal of the volatiles in vacuo at ambient temperature 128.9, 127.8, 126.3, 125.6, 122.5, 119.5, 72.4, 12.8. HRMS: cald
yielded a residue, which was dissolved in the minimum for C16H14SO2Na [MNa]+ 293.0607; found 293.0609.
amount of CH2Cl2 and added dropwise to diethyl ether
General synthesis of (3-methylcyclopenten-1-yl)sulfonyl-
(75 mL). After 2 h, the precipitate was filtered, washed with benzene (10) from alkynylsilane (8). To a suspension of an
diethyl ether and dried under vacuum, yielding the product as iodosylarene (0.5 mmol) in CH2Cl2 (5 mL) under an inert
a powder. Analytically pure material was obtained by recrystal- atmosphere was added hex-1-yn-1-yltrimethylsilane 8 (0.046 g,
lization in CH2Cl2 and ether.
0.3 mmol), then, over a period of 5 min, boron trifluoride ethe-
General synthesis of 2-(benzenesulfonyl)ethynylbenzene (3) rate (0.5 mmol). [For 2-(iodosyl)anisole, the suspension was
from trimethyl(phenylethynyl)silane (7). To a suspension of a cooled to −78 °C and boron trifluoride was added over a
fine powder of iodosylarene (0.5 mmol) in CH2Cl2 (5 mL) period of 1 h.] The reaction was stirred for 4 h, which yielded a
under an inert atmosphere was added trimethyl(phenyl- bright yellow homogenous solution. An aqueous solution of
ethynyl)silane 7 (0.052 g, 0.3 mmol), then, over a period of sodium tetrafluoroborate (2.5 M, 1.8 mmol) was added to the
5 min, boron trifluoride etherate (0.5 mmol). [For 2-(iodosyl) mixture and the resultant emulsion was stirred vigorously for
anisole, the suspension was cooled to −78 °C and boron 15 min. The aqueous layer was separated and extracted with
trifluoride was added over a period of 1 h.] The reaction was CH2Cl2 (2 × 5 mL). The combined organic layers were washed
allowed to stir for 4 h, which yielded a bright yellow homo- with brine, dried over MgSO4, filtered and concentrated
genous solution. An aqueous solution of a sodium or lithium in vacuo at ambient temperature, yielding a viscous yellow oil,
salt (2.5 M, 1.8 mmol) was added and the resulting emulsion which was dissolved in CH2Cl2 (3 mL). To this solution was
was stirred vigorously for 15 min. The aqueous layer was separ- added benzenesulfinic acid sodium salt (0.059 g, 0.36 mmol).
ated and extracted with CH2Cl2 (2 × 5 mL). The combined The suspension was held at room temperature for 20 minutes
organic layers were washed with brine, dried over MgSO4, fil- upon which time deionized water (3 mL) was added. After an
tered and concentrated in vacuo to yield the crude alkynyl(aryl)- additional five min the aqueous layer was separated and
iodonium salts as viscous yellow oils. The crude residue was extracted with CH2Cl2 (2 × 5 mL). The combined organic layers
dissolved in CH2Cl2 (2 mL) and a solution of benzenesulfinic were washed with brine, dried over MgSO4, filtered and con-
acid sodium salt (0.019 g, 0.116 mmol) and triethylbenzyl centrated in vacuo, which yielded a yellow oil. Purification by
ammonium chloride (TEBA) (0.0024 g, 0.011 mmol) in water flash column chromatography (9 : 1 petroleum ether–ethyl
1
(1 mL) was added. The reaction mixture was stirred at room acetate) furnished a colorless oil. H NMR (400 MHz, CDCl3):
temperature for 1 hour, after which time the aqueous layer was δ 7.92 (d, 2H, J = 7.4 Hz), 7.67–7.55 (m, 3H), 6.66 (d, 1H, J =
separated and extracted with CH2Cl2 (2 × 5 mL). The combined 1.8 Hz), 3.01–2.92 (m, 1H), 2.62–2.56 (m, 1H), 2.54–2.45 (m,
organic layers were washed with water, then brine, and dried 1H), 2.30–2.22 (m, 1H), 1.59–1.53 (m, 1H), 1.11 (d, 3H, J =
over anhydrous MgSO4, filtered and concentrated in vacuo, 7.0 Hz). 13C NMR (100 MHz, CDCl3): δ 148.1, 143.5, 139.6,
which yielded a viscous yellow oil. Purification by flash 133.3, 129.1, 127.9, 40.6, 32.4, 30.4, 19.5. HRMS: cald for
column chromatography (9 : 1 petroleum ether–ethyl acetate) C12H14NaO2S [MNa]+ 245.0607; found 245.0618.
1
provided a pale yellow solid. Melting point: 70–71 °C. H NMR
(400 MHz, CDCl3): δ 8.11 (dd, 2H, J = 7.3 Hz, J = 1.3 Hz),
7.73–7.70 (m, 1H), 7.64–7.61 (m, 2H), 7.55 (dd, 2H, J = 7.1 Hz,
Acknowledgements
J = 1.3 Hz), 7.52–7.48 (m, 1H), 7.41–7.38 (m, 2H). 13C NMR
(100 MHz, CDCl3): δ 141.7, 134.1, 132.7, 131.6, 129.3, 128.7, We thank Prof. Craig Rice for assistance with the X-ray crystal
127.4, 117.8, 93.5, 85.3. HRMS: cald for C14H10NaO2S [MNa]+ structures, Mr James Rooney for assistance with the isothermal
265.0294; found 265.0303.
microcalorimetry experiments and the University of Hudders-
General synthesis of 1-benzenesulfonyl-3-methyl-indene (4) field for funding. We also thank Miss Olivia Davis for experi-
from 1-ethyl-2-ethynylbenzene(aryl)iodonium tosylates (2). To mental assistance and the Nuffield Foundation for a research
a solution of 1-ethyl-2-ethynylbenzene(aryl)iodonium tosylate 2 placement bursary.
(0.099 mmol) in CH2Cl2 (2 mL) was added benzenesulfinic
acid sodium salt (0.018 g, 0.11 mmol). The suspension was
stirred at room temperature for one hour upon which time
deionized water (2 mL) was added. After an additional 5 min
Notes and references
the aqueous layer was separated and extracted with CH2Cl2
(2 × 5 mL). The combined organic layers were washed with
brine, dried over MgSO4, filtered and concentrated in vacuo,
which yielded a yellow oil. Purification by flash column chrom-
atography (9 : 1 petroleum ether–ethyl acetate) furnished a pale
yellow liquid. 1H NMR (400 MHz, CDCl3): δ 7.77 (d, 1H, J =
6.7 Hz), 7.41–7.35 (m, 3H), 7.26–7.15 (m, 4H), 6.97 (d, 1H, J =
1 For reviews on hypervalent iodine chemistry, see:
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Y. Kita, Chem. Commun., 2009, 2073; (e) V. V. Zhdankin and
P. J. Stang, Chem. Rev., 2008, 108, 5299; (f) T. Wirth, Angew.
Chem., Int. Ed., 2005, 44, 3656; (g) D. Magdziak, S. J. Meek
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4162 | Org. Biomol. Chem., 2014, 12, 4156–4162
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