Iodination of activated aromatic compounds using sodium peroxodisulfate and iodine: An efficient way to iodinate alkylated calix[4]arenes

Article abstract of DOI:10.1055/s-2007-1000826

A simple method for the iodination of activated arenes, using molecular iodine and sodium peroxodisulfate as the oxidant, is presented. The reaction is conducted in the presence of catalytic amounts of tetramethylammonium iodide as a phase-transfer catalyst in acetonitrile. For non-polar substances, which are not soluble in pure acetonitrile such as calix[4]arenes bearing long alkyl chains, a modified reaction is introduced. In this case the phase-transfer catalyst is changed to methyltriphenylphosphonium peroxodisulfate. Chloroform as a cosolvent mediates solubility. Furthermore, we show that the slightly basic conditions obtained upon the addition of sodium bicarbonate have a beneficial effect on the yield. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-1000826

1
10
PAPER
Iodination of Activated Aromatic Compounds Using Sodium Peroxodisulfate
and Iodine: An Efficient Way to Iodinate Alkylated Calix[4]arenes
O
xidative Iodinatio
l
n of
A
a
renes
U
sin
f
Sodium Pero
G
xodisulfate and Iod
.
ine Barton, Jochen Mattay*
Organische Chemie I, Universität Bielefeld, Universitätsstr. 25, 33501 Bielefeld, Germany
Fax +49(521)1066417; E-mail: oc1jm@uni-bielefeld.de
Received 19 July 2007; revised 8 October 2007
Dedicated to Professor Paul G. Rasmussen
3
f
H PW O in CH Cl , I2 or KI/sodium percarbonate
3
12 40
2
2
Abstract: A simple method for the iodination of activated arenes,
using molecular iodine and sodium peroxodisulfate as the oxidant,
is presented. The reaction is conducted in the presence of catalytic
3g
(
Na CO ·3H O ), I /tetrabutylammonium peroxodisul-
fate in MeCN, and MeCN or CH Cl , and I /methyl-
amounts of tetramethylammonium iodide as a phase-transfer cata- triphenylphosphonium peroxodisulfate (1) in MeCN. In
2 3 2 2 2
3
h
3i
2
2
2
3
j
lyst in acetonitrile. For non-polar substances, which are not soluble a primary experiment we successfully applied the last
in pure acetonitrile such as calix[4]arenes bearing long alkyl chains,
a modified reaction is introduced. In this case the phase-transfer cat-
alyst is changed to methyltriphenylphosphonium peroxodisulfate.
a) using only a catalytic amount (5%) of the non-commer-
Chloroform as a cosolvent mediates solubility. Furthermore, we
show that the slightly basic conditions obtained upon the addition of
method to the cone calix[4]arene-tetra-n-propylether (2).
In this paper we present improvements of this method by
cially available reagent methyltriphenylphosphonium
peroxodisulfate (1) and b) showing that the addition of so-
dium bicarbonate raises the activity of the system. Fur-
thermore, we report on a new method of oxidative
iodination of activated arenes utilising solely commercial-
ly available and cheap reagents. In this new protocol, cat-
alytic amounts of tetramethylammonium iodide are
employed as a phase-transfer catalyst in acetonitrile at
sodium bicarbonate have a beneficial effect on the yield.
Key words: calixarenes, phase-transfer catalysis, iodination, oxi-
dative halogenation, peroxides
The standard method for iodination at the wide rim of
calix[4]arenes, which are alkylated at the phenolic oxy-
gen, involves silver(I) trifluoroacetate and iodine in re-
8
0 °C. The oxidant is sodium peroxodisulfate and molec-
ular iodine serves as the source of iodine.
1
a–f
fluxing chloroform. This reaction is usually fast (1 h)
and gives high yields (69–95%). However, we observed
that over-iodination easily occurred in the case of
calix[4]arenes adopting the cone conformation. The over-
iodination took place even if only a small excess of re-
agents were used to ensure conversion of all four aromatic
rings. This was indicated by MALDI-TOF-MS or ESI-
MS, which showed masses corresponding to calix[4]are-
nes iodinated five times. Because of the over-iodination
and the costs of silver(I) trifluoroacetate, we looked for al-
ternative routes to iodinate calix[4]arenes. Procedures
published in the last years reporting aromatic iodination
For complete iodination of calix[4]arenes, it is advanta-
geous that all reacting molecules, i.e. the starting material
as well as the mono-, di- and triiodinated calix[4]arenes,
are soluble in the reaction medium. Therefore, methods
using methanol as solvent were ruled out. We chose the
reaction using I –methyltriphenylphosphonium peroxo-
2
3j
disulfate (1), because it is conducted in boiling acetoni-
trile. Applied to calix[4]arene 2, we obtained the four-fold
iodinated calix[4]arenetetra-n-propylether as indicated by
MALDI-MS. However, for 1.0 g of substrate 2 (6.7 mmol
of aromatics), 5.0 g of reagent 1 were needed. This mass
relation was not only unsatisfying in terms of atom effi-
ciency but also complicated the purification process. An-
other disadvantage was the preparation of 1; although it
was easily generated by mixing methyltriphenylphospho-
nium bromide and sodium peroxodisulfate in water
2
a
include the use of NIS/ZrCl in CH Cl , NIS in ionic liq-
4
2
2
2
b
2c
uids,
ICl/In(OTf)3 in MeCN–CHCl3,
I /O /
2 2
2
d
H PV Mo O in MeCN, I /Fe(NO ) /H PW O in
5
2
10 40
2
3 3
3
12 40
2f
2
e
CH Cl , I /Bi(NO ) /BiCl /air in MeCN or CH Cl , I /
2
2
2
3 3
3
2
2
2
silfen (silica supported ferric nitrate nonahydrate) in
2
g
(
Equation 1), it had to be dried in a desiccator under vac-
CH Cl or I /ortho-periodic acid in 95% EtOH under
2
2
2
®
2h
uum, which required several exchanges of sicapent for
the large amount of material necessary.
microwave irradiation or by conventional heating.
A
number of recent publications describe the use of a peroxo
compound for the oxidative iodination of arenes, NaI/
3
a
®
3b
MePPh3+ Br– (aq) + Na2S2O8
(MePPh3)+2(S2O8)2– ↓ (1) + 2 NaBr (aq)
Ce(OH) O H in SDS–H O, NH I/Oxone in MeOH,
3
2
®
2
4
3c
KI/Oxone in MeOH, KI/benzyltriphenylphosphonium
peroxomonosulfate in MeCN, KI/30% H O /H SO in
MeOH, KI or I /polyvinylpyrrolidone supported H O /
Equation 1
3
d
2
2
2
4
3
e
2
2
2
In a first step to improve the reaction, we were successful-
ly able to regenerate 1 in situ simply by using sodium per-
oxodisulfate directly in the reaction mixture. As a model
system we chose anisole (Scheme 1).
SYNTHESIS 2008, No. 1, pp 0110–0114
x
x
.
x
x
.2
0
0
7
Advanced online publication: 07.12.2007
DOI: 10.1055/s-2007-1000826; Art ID: T11107SS
©
Georg Thieme Verlag Stuttgart · New York

PAPER
Oxidative Iodination of Arenes Using Sodium Peroxodisulfate and Iodine
111
Na2S2O8
–
2 NaHSO4
I
(MePPh )+ (S O )
2–
2 MePPh3+ HSO –
4
2
+
2
+
3
2
2
8
1
OMe
OMe
Scheme 1
We found that catalytic amounts of 1 (5 mol%) led to the position by a methyl group slowed down the reaction, but
formation of 4-iodoanisole in a yield of 54% within four full conversion of 4-methylanisole to 2-iodo-4-methylani-
hours (Table 1, entry 2). In a second step, we examined sole was achieved after raising the reaction time to 21
the effect of inorganic bases since protons were liberated hours (entries 6 and 7). The optimized reaction conditions
during the reaction. Sodium carbonate inhibited the reac- were applied in order to iodinate a calix[4]arene alkylated
tion entirely, whereas the less basic reagents sodium bi- with dodecyl chains (3). On a 2 g scale a yield of 86%
carbonate and disodium hydrogen phosphate both (entry 10) was obtained (Scheme 2).
increased the reactivity to a similar extent. With sodium
bicarbonate, 93% of 4-iodoanisole and 7% of diionidated
product were detected (Table 1, entry 2). In order to ren-
In order to improve the reaction conditions, in a second
approach we tried to avoid the use of reagent 1 complete-
ly. Though it has recently been reported that the tetrabu-
der the reaction media suitable for calix[4]arenes that are
tylammonium ion was a sufficiently potent phase-transfer
not soluble in pure acetonitrile, e.g. calix[4]arenes alkylat-
ed with long non-polar residues, we added chloroform as
a cosolvent. As shown in Table 1, reactions in solvent
mixtures with up to 30% chloroform gave 4-iodoanisole
in yields greater than 90% within four hours if sodium bi-
carbonate was present (entries 3 and 4). Blocking the para
3h,i
catalyst in iodinations employing peroxodisulfate, the
reagent tetrabutylammonium peroxodisulfate still had to
be prepared. Hence, we used the tetramethylammonium
cation as a counterion for the peroxodisulfate anion with
an in situ approach similar to that described above. We
chose inexpensive tetramethylammonium iodide as the
a
Table 1 Iodination of Arenes with 5 mol% (MePh P) S O as Phase-Transfer Catalyst
3
2
2
8
b
b
Entry
1c
Substrate
Anisole
Time (h)
Solvent
MeCN
MeCN
Yield (%) Yield (%) with NaHCO
3
4
4
14 para
0
2
54
93 para
7
disub.
3
4
MeCN–CHCl , 85:15
38
99 para
3
1
disub.
4
5
4
4
MeCN–CHCl , 70:30
27
24
12
–
91 para
82 para
55
3
MeCN–CHCl , 55:45
3
MeCN–CHCl , 40:60
3
6
7
8
4-Methylanisole
4
4
4
MeCN
90d
MeCN–CHCl , 70:30
–
68d
3
o-Xylene
MeCN
–
30 para
1
3 ortho
9
21
MeCN
–
70 para
2
5
5 ortho
disub.
1
0
Calix[4]arenetetra-dodecylether (3)
24
MeCN–CHCl , 70:30
–
86e
3
a
b
c
d
e
Solvent (5 mL/mmol arene), I (1 equiv), Na S O (95 mol%), (MePh P) S O (5 mol%), 80 °C oil bath, argon balloon.
2
2
2
8
3
2
2
8
GC yields are referenced to an internal standard (bromobenzene).
Without (MePPh ) S O .
3
2
2
8
1
00% yield after 21 h.
Yield of isolated product.
Synthesis 2008, No. 1, 110–114 © Thieme Stuttgart · New York

1
12
O. G. Barton, J. Mattay
PAPER
Scheme 2
source of the cation and were delighted to see that 20 Table 2 Iodination of Arenes with 20 mol% NMe I as Phase-Trans-
4
mol% catalyst enabled iodination of the test compound fer Catalysta
anisole (Scheme 3).
b
Entry Substrate
Time (h) Yield (%)
I
Na2S2O8, I2,
1
2
Anisole
4
91 para
93 para
NMe4I (20 mol%)
21
7
disub.
MeCN, 80 °C
OMe
OMe
3
4-Methylanisole
4
34
Scheme 3
4
21
64
5c
6
Calix[4]arene-tetrapropylether (2) 21
[82]
39 para
As summarised in Table 2, this new procedure involving
cheap and commercially available reagents can be used to
iodinate a range of electron-rich aromatic compounds in
good yields. Highly active anisole (entry 1) was iodinated
in 91% yield within four hours, and 7% of the diiodinated
product was observed after 21 hours (entry 2).
Calix[4]arenetetra-n-propylether (2), in which the posi-
tions ortho to the directing propoxy group are blocked, re-
acted within 21 hours in 82% yield without over-
iodination (Scheme 4, entry 5). However, for complete
conversion it was necessary to add some chloroform after
Phenol
2
1
0 ortho
7
4
80 para
1
2
8 ortho
disub.
8
9
0
1
2
3
4
5
p-Cresol
4
21
4
39
95
1
1
1
1
1
1
4-Nitroaniline
Acetanilide
Mesitylene
93
4
80 para
71
1
2 hours of reaction. Notably, the same result could not be
achieved starting the reaction with a solvent mixture. Sim-
ple trituration with methanol was adequate for purifica-
tion.
4
21
21
21
100 [92]
d
Toluene
67 [53]
I
I
I
I
Na2S2O8, I2
o-Xylene
72 para
16 ortho
NMe4I (20 mol%)
1
1
6
7
p-Xylene
21
21
64
MeCN, 12 h
O
O O
O
O
O O
O
+
CHCl3, 9 h
0 C
Biphenyl
62 para
7 ortho
8
1
8
Fluorene
21
21
21
43 para
5 para
0
8
2 %
Scheme 4
19
Naphthalene
Brombenzene
2
0
Our method exhibited only moderate regioselectivity in
some cases. Highly active phenol gave ~20% o-iodination
entries 6 and 7) and reactions of all weakly activated
compounds with free ortho positions, i.e. toluene, o-xy-
lene and biphenyl, led to corresponding byproducts (en-
tries 14, 15 and 17). Moderately activated compounds
such as 4-nitroaniline (entry 10) and acetanilide (entry 11)
gave good yields of 93% and 80%, respectively, after four
hours. Weakly activated mesitylene was cleanly convert-
a
MeCN (5 mL/mmol arene), I (1 equiv), Na S O (1 equiv), NMe I
2
2
2
8
4
(
20 mol%), 80 °C oil bath, under air.
(
b
GC yields are referenced to an internal standard (bromobenzene).
Yield of isolated products are shown in brackets.
c
CHCl (1 mL/mmol arene) was added after 12 h.
Ratio of p- and o-isomers was 1.9:1 (determined by H NMR).
3
d
1
Synthesis 2008, No. 1, 110–114 © Thieme Stuttgart · New York

PAPER
Oxidative Iodination of Arenes Using Sodium Peroxodisulfate and Iodine
113
ed on a 20 mmol scale into iodomesitylene in 92% isolat- IR (neat): 3048, 2913, 2847, 1562, 1455, 1378, 1192, 1161, 991,
–
1
9
1
66, 858, 838, 719, 531, 501 cm .
ed yield after 21 hours of reaction (entry 13). Activated
aromatics with blocked para positions i.e. 4-methylani-
sole (entry 3) and p-cresol (entry 8), reacted considerably
slower than the corresponding unblocked compounds.
H NMR (500 MHz, CDCl ): d = 6.97 (s, 8 H), 4.26 (d, J = 13.2 Hz,
H), 3.81 (t, J = 7.5 Hz, 8 H), 3.03 (d, J = 13.2 Hz, 4 H), 1.84–1.81
m, 8 H), 1.32–1.25 (m, 72 H), 0.86 (t, J = 6.9 Hz, 12 H).
3
4
(
Non-activated naphthalene (entry 19) showed almost no 13C NMR (125 MHz, CDCl
): d = 156.4 (q), 137.1, 136.8 (q), 88.1
q), 75.5, 32.0, 30.4, 30.1, 29.94, 29.89, 29.81, 29.79, 29.74, 29.4,
6.2, 22.7, 14.1.
MS (MALDI-TOF): m/z = 1624 [M + Na]+.
3
(
2
reactivity (5% product after 21 h) and deactivated com-
pounds, i.e. chloro- and bromobenzene, did not react un-
der these conditions.
Anal. Calcd for C H I O : C, 57.00; H, 7.30. Found: C, 56.91; H,
In summery, we have developed two methods for the ox-
idative iodination of activated arenes using sodium per-
oxodisulfate as an oxidant. We have shown that alkylated
calix[4]arenes were suitable substrates and these were io-
dinated in good yields and excellent purity.
76 116 4
4
7
.17.
Oxidative Iodination with 20% Tetramethylammonium Iodide;
General Procedure (Table 2)
For reactions analysed by GC, bromobenzene (171 mg, 1.00 mmol)
was added to the reaction mixture as an internal standard and the
workup procedure was completed as described in the general proce-
dure for Table 1.
Melting points were measured in open capillaries with a Büchi
B-540 melting point apparatus and are uncorrected. IR spectra
were recorded using attenuated total reflectance (ATR) on a Nicolet
The aromatic compound (4.00 mmol) was combined with I
(1.02 g,
2
1
4
.00 mmol), tetramethylammonium iodide (161 mg, 0.800 mmol)
3
80 FT-IR spectrometer equipped with a diamond ATR crystal. H
13
and C NMR spectra were recorded on a Bruker DRX 500 spec-
trometer, chemical shifts were calibrated to the residual proton and
carbon resonance of the solvent (CDCl ; d = 7.24 ppm, d = 77.00
and sodium peroxodisulfate (952 mg, 4.00 mmol) in MeCN (20
mL). The mixture was heated to 80 °C for the indicated time, then
cooled to r.t. and subsequently poured into H O (50 mL) containing
2
3
H
C
ppm). GC/MS were recorded on a Shimadzu GC 17A/QP 5050A
equipped with a capillary column 5MS (Hewlett–Packard). MAL-
DI-TOF mass spectra were obtained with a PerSeptive Biosystems
Voyager-DE spectrometer using 2,5-dihydroxybenzoic acid as ma-
trix. Elemental analyses were determined with a Perkin–Elmer 240
instrument. Analytical TLC was performed on silica-gel 60 F254
coated plates (Merck) and flash column chromatography on silica-
40% sodium bisulfite solution (2.4 mL, 12 mmol). The mixture was
extracted with Et O (50 mL) (containing 25 vol% CH Cl in case of
2
2
2
calix[4]arene 2). The organic layer was washed with H O (3 × 50
2
mL) and brine (50 mL), dried over MgSO and concentrated in vac-
4
uo.
5
,11,17,23-Tetraiodocalix[4]arene-25,26,27,28-tetra-n-propyl-
gel MN60, 40–63 mm (Macherey–Nagel). CHCl and MeCN were
ether (Table 2, Entry 5)
3
Calix[4]arene-25,26,27,28-tetra-n-propylether (2; 1.48 g, 2.50
mmol) was dissolved in MeCN (50 mL) and reacted as described
dried over 4Å and 3Å molecular sieves, respectively; all other re-
agents were reagent grade quality and used as received from com-
mercial suppliers. Calix[4]arenes 2 and 3 were prepared according
to the literature.4
above. After 12 h of reaction, CHCl (10 mL) was added and the
3
a,b
crude product was purified by crystallisation (MeOH–CH Cl ) to
2
2
afford the pure product that was dried under high vacuum.
Oxidative Iodination with 5 mol% Methyltriphenylphosphoni-
um Peroxodisulfate (1); General Procedure (Table 1)
Yield: 2.26 g (82%); very slightly yellow solid; mp 303.5 °C (Lit.1c
2
90–291 °C).
The aromatic compound (4.00 mmol) was combined with I (1.02 g,
2
IR (neat): 3047, 2957, 2922, 2871, 1561, 1451, 1384, 1194, 1163,
4
.00 mmol), methyltriphenylphosphonium peroxodisulfate (1; 149
mg, 0.200 mmol, 0.05 equiv) and sodium peroxodisulfate (905 mg,
.80 mmol, 0.95 equiv) in a mixture of MeCN and CHCl (various
–
1
1
002, 993, 960, 862, 836, 527, 510 cm .
1
3
H NMR (500 MHz, CDCl ): d = 6.98 (s, 8 H), 4.27 (d, J = 13.2 Hz,
3
3
ratios, 20 mL) containing bromobenzene (171 mg, 1.00 mmol) as an
internal standard. The mixture was heated to 80 °C for the indicated
time. In order to determine the GC-yield, a small portion of the mix-
ture was partitioned between CHCl (0.70 mL) and H O (0.70 mL)
4 H), 3.78 (t, J = 7.5 Hz, 8 H), 3.03 (d, J = 13.2 Hz, 4 H), 1.88–1.81
(m, 8 H), 0.94 (t, J = 7.4 Hz, 12 H).
13
C NMR (125 MHz, CDCl ): d = 156.4 (q), 137.1, 136.8 (q), 88.1
3
3
2
(
q), 77.02, 30.3, 23.0, 10.2.
containing a few drops of a 40% sodium bisulfite solution to deco-
MS (MALDI-TOF): m/z = 1118 [M + Na]+.
lourise the mixture. The organic layer was washed with H O (2 × 70
2
mL) and brine (70 mL) and submitted to GC analysis.
Anal. Calcd for C H I O : C, 43.82; H, 4.04. Found: C, 43.87; H,
4
0
44
4
4
3
.96.
5
,11,17,23-Tetraiodocalix[4]arene-25,26,27,28-tetra-n-dode-
cylether (Table 1, Entry 10)
I2 (2.54 g, 10.0 mmol), methyltriphenylphosphonium peroxodisul-
fate (1; 373 mg, 0.499 mmol) and sodium peroxodisulfate (2.26 g,
Iodomesitylene (Table 2, Entry 13)
Obtained from mesitylene (2.40 g, 20.0 mmol) as described above.
The crude product was purified by short column chromatography
9
2
.50 mmol) were added to a stirred suspension of calix[4]arene-
5,26,27,28-tetra-n-dodecylether (3; 2.74 g, 2.50 mmol) in MeCN
(silica gel, cyclohexane) and dried under high vacuum.
2
f
Yield: 4.55 g (92%); colourless solid; mp 30 °C (Lit. 30–31 °C,
(
35 mL) and CHCl (15 mL). The mixture was heated to 80 °C for
3
3j
3
0–32 °C ).
2
4 h, cooled to r.t., poured into H O (200 mL) containing 40% so-
2
dium bisulfite solution (10 mL, 13 g, 51 mmol) and stirred for 10
GC/MS (EI, 70 eV): m/z (%) = 373 (12), 372 (100), 246 (10), 245
(51), 186 (17), 127 (12), 122 (5), 119 (11), 118 (58), 117 (72), 116
(23), 115 (85), 103 (20), 102 (19).
min. After extraction with CHCl (200 mL), the organic layers were
3
washed with H O (2 × 200 mL) and brine (100 mL), dried over
2
MgSO and concentrated in vacuo. Column chromatography (sili-
4
ca-gel; cyclohexane–CHCl , 80:20) yielded the product after drying
Iodination of Toluene (Table 2, Entry 14)
3
under high vacuum at 80 °C for 1 h.
Obtained from toluene (1.84 g, 20.0 mmol) as described above. The
crude product was purified by short column chromatography (silica
Yield: 3.44 g (86%); colourless solid; mp 53 °C.
Synthesis 2008, No. 1, 110–114 © Thieme Stuttgart · New York

1
14
O. G. Barton, J. Mattay
PAPER
gel, cyclohexane) and dried under vacuum to afford a mixture of
- and 4-iodotoluene. The ratio of the two regiomers (1:1.9) was
(2) (a) Zhang, Y.; Shibatomi, K.; Yamamoto, H. Synlett 2005,
2837. (b) Yadav, J. S.; Reddy, B. V. S.; Reddy, P. S. R.;
Basak, A. K.; Narsaiah, A. V. Adv. Synth. Catal. 2004, 346,
77. (c) Johnsson, R.; Meijer, A.; Ellervik, U. Tetrahedron
2
1
determined by integration of the H NMR signal of the methyl
groups.5
2
005, 61, 11657. (d) Branytska, O. V.; Neumann, R. J. Org.
Yield: 2.31 g (53%); colourless oil.
Chem. 2003, 68, 9510. (e) Jafarzadeh, M.; Amani, K.;
Nikpour, F. Can. J. Chem. 2005, 83, 1808. (f) Wan, S.;
Wang, S. R.; Lu, W. J. Org. Chem. 2006, 71, 4349.
(g) Tilve, R. D.; Alexander, V. M.; Khadilkar, B. M.
Tetrahedron Lett. 2002, 43, 9457. (h) Sosnowski, M.;
Skulski, L. Molecules 2005, 10, 401.
1
H NMR (500 MHz, CDCl ): 4-iodotoluene; d = 7.55 (d, J = 8.16
3
Hz, 2 H), 6.92 (d, J = 8.16 Hz, 2 H), 2.28 (s, 3 H).
1
H NMR (500 MHz, CDCl ): 2-iodotoluene; d = 7.79 (d, J = 8.16
3
Hz, 1 H), 7.23–7.22 (m, 2 H), 6.87–6.83 (m, 1 H), 2.41 (s, 3 H).
(
3) (a) Firouzabadi, H.; Iranpoor, N.; Garzan, A. Adv. Synth.
Catal. 2005, 347, 1925. (b) Mohan, K. V. V. K.; Narender,
N.; Kulkarni, S. J. Tetrahedron Lett. 2004, 45, 8015.
Acknowledgment
This work was supported by the Deutsche Forschungsgemeinschaft
(
c) Narender, N.; Srinivasu, P.; Kulkarni, S. J.; Raghavan, K.
(
DFG). We thank Bayer Industry Services for the gift of chemicals.
V. Synth. Commun. 2002, 32, 2319. (d) Hajipour, A. R.;
Adibi, H. J. Chem. Res., Synop. 2004, 294. (e) Iskra, J.;
Stavber, S.; Zupan, M. Synthesis 2004, 1869. (f) Pourali, A.
R.; Ghanei, M. Chin. J. Chem. 2006, 24, 1077.
O.G.B. thanks Thomas Geisler for performing some of the experi-
ments and Dr. Tina Kasper for discussing the manuscript.
(
(
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Synthesis 2008, No. 1, 110–114 © Thieme Stuttgart · New York