Facile synthesis of iodonium salts by reaction of organotrifluoroborates with p-iodotoluene difluoride

Article abstract of DOI:10.1055/s-2007-966031

A simple and easy method for the synthesis of various iodonium salts was developed, and involves the reaction of potassium organotrifluoroborates with p-iodotoluene difluoride under mild conditions. The one-pot synthesis of a (Z)-(2-fluoroalkenyl)iodonium

Full text of DOI:10.1055/s-2007-966031

1542
PAPER
Facile Synthesis of Iodonium Salts by Reaction of Organotrifluoroborates with
p-Iodotoluene Difluoride
S
ynthesis of Iodonium
a
S
alts
f
rom
s
O
rganotri
a
fluoroborat
n
es ori Yoshida,* Kanako Osafune, Shoji Hara
Division of Chemical Process Engineering, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan
Fax +81(11)7066557; E-mail: myoshida@eng.hokudai.ac.jp
Received 9 February 2007; revised 16 March 2007
within 15 minutes at room temperature to afford 3a in
Abstract: A simple and easy method for the synthesis of various io-
good yield (Table 1, entry 1). A solvent screen found ace-
tonitrile to be a suitable solvent for this reaction (Table 1,
donium salts was developed, and involves the reaction of potassium
organotrifluoroborates with p-iodotoluene difluoride under mild
entries 1–3). Attempted optimization of reaction tempera-
ture gave no improvement in the yield of 3a (Table 1, en-
tries 3–5). Finally, we successfully obtained 3a in 95%
yield by tuning the substrate concentration in acetonitrile
to 0.05 molar (Table 1, entry 7); a higher substrate con-
centration resulted in a decrease in the yield of 3a
(Table 1, entry 6).
conditions. The one-pot synthesis of a (Z)-(2-fluoroalkenyl)iodo-
nium salt from an alkynyltrifluoroborate was also carried out.
Key words: alkenes, alkynes, arenes, boron, iodine
Hypervalent iodine(III) compounds, especially alkynyl-,
alkenyl-, or diaryliodonium salts, are known as useful re-
agents for a number of organic syntheses, since phe-
nyliodanyl is an excellent leaving group.1,2 Generally,
they are synthesized by reaction of organometals, such as
organostannanes,3 organosilanes,4 or organoboranes,5
with aryl–iodine(III) compounds (ArIX2). However, the
reaction of organosilanes or organoboranes with ArIX2
generally needs activation with acids,6 and the use of or-
ganostannanes sometimes causes handling problems, due
to its high toxicity. Therefore, it would be worthwhile to
develop an easier and safer method for the synthesis of io-
donium salts. Recently, potassium organotrifluoroborates
Table 1 Optimization of the Reaction Conditions with 1aa
C10H21
C10H21
2
BF3–K+
Solvent
CH2Cl2
acetone
MeCN
MeCN
MeCN
MeCN
MeCN
I(p-Tol)BF4
1a
3a
Entry
Concn of 1a Temp
Yieldb (%)
1
2
3
4
5
6
7
0.1
0.1
0.1
0.1
0.1
0.2
0.05
r.t.
66
89
90
82
89
83
95
r.t.
r.t.
–
(RBF3 K+) have been employed instead of organoboronic
40 °C
0 °C
r.t.
acids or esters in organic synthesis, since organotrifluo-
roborates have many advantages with regard to handling
and reactivity compared to the other organoboranes.7 Or-
ganotrifluoroborates are readily obtainable from the cor-
responding organoboronic acids, and some of them are
commercially available.8 We were interested in the nu-
cleophilicity of organotrifluoroborates,9 and planned to
synthesize the iodonium salts 3 by reaction of organotri-
fluoroborates 1 with p-iodotoluene difluoride (2),10 which
is known as a mild and safe oxidizing reagent (Scheme 1).
r.t.
a Reagents and conditions: 1a (1 mmol), 2 (1 mmol), 15 min.
b Isolated yield of 3a.
The scope of this iodonium salt synthesis was studied with
various organotrifluoroborates (Table 2). Under these re-
action conditions, alkynyltrifluoroborate 1b prepared
from propargyl alcohol was converted into iodonium salt
3b in 83% yield (Table 2, entry 1). The reaction with po-
tassium (E)-trifluoro(hex-1-enyl)borate (1c) as starting
material gave a better result at –20 °C than at room tem-
perature (Table 2, entries 2 and 3). Under the same reac-
tion conditions, potassium (E)-trifluoro(styryl)borate (1d)
and the internal alkenyltrifluoroborate potassium (4-tert-
butylcyclohex-1-enyl)trifluoroborate (1e) provided the
corresponding alkenyliodonium salts 3d and 3e in 82%
and 69% yields, respectively (Table 2, entries 4 and 5).
Then, the reactions of aryltrifluoroborates giving diaryl-
iodonium salts were investigated. The reaction of potassi-
um trifluoro(phenyl)borate (1f) with 2 proceeded well at
60 °C to give (4-methylphenyl)(phenyl)iodonium tetra-
To optimize reaction conditions, potassium dodec-1-ynyl-
trifluoroborate (1a) was employed as a starting material to
give dodec-1-ynyl(4-methylphenyl)iodonium tetrafluo-
roborate (3a) (Table 1). To our delight, the reaction of 1a
with one equivalent of 2 in dichloromethane was complete
F
I
Me
–
BF4
I+
F
2
R
BF3–K+
R
Me
1
3
Scheme 1
SYNTHESIS 2007, No. 10, pp 1542–1546
x
x.
x
x
.
2
0
0
7
Advanced online publication: 02.05.2007
DOI: 10.1055/s-2007-966031; Art ID: F03107SS
© Georg Thieme Verlag Stuttgart · New York

PAPER
Synthesis of Iodonium Salts from Organotrifluoroborates
1543
Bu
fluoroborate (3f) in 60% yield, although the reaction was
sluggish at room temperature (Table 2, entry 6). To study
the substituent effect, p-methyl- (1g), p-methoxy- (1h),
and p-chloro-substituted (1i) trifluoro(phenyl)borates
were used as starting materials (Table 2, entries 7–9).
These results confirmed that an electron-donating group
increases the reactivity of organotrifluoroborate 1 towards
2, while an electron-withdrawing group decreases it. The
reaction of the hetaryltrifluoroborate potassium trifluo-
(a)
3c
B(Oi-Pr)2
4
48%
C10H21
(b)
1a
C10H21
I(Ph)BF4
5, 78%
+
AcO
I(Ph)BF4
6, 5%
Scheme 2 Reagents and conditions: (a) 1. 2 (1.0 equiv), MeCN
ro(5-methyl-2-thienyl)borate (1j) proceeded smoothly at (0.05 M), –20 °C, 15 min; 2. aq NaBF4; (b) 1. PhI(OAc)2 (1.0 equiv),
MeCN (0.05 M), r.t., 15 min; 2. aq NaBF4.
room temperature to give the thienyliodonium salt 3j in
88% yield (Table 2, entry 10). Thus, it was found that a
variety of organotrifluoroborates 1 react with 2 without
the requirement of the addition of acids to give iodonium
salts 3 in good yields.
A possible reaction mechanism for 1a is presented in
Scheme 3. At first, nucleophilic attack of the alkynyl
group on 1a occurs at the iodine(III) atom of 2 to give an
alkynyliodonium fluoride along with potassium tetrafluo-
roborate. Then, ligand exchange at the iodine atom gives
alkynyliodonium tetrafluoroborate 3a, which is more sta-
ble than the fluoride salt.1e
Table 2 Synthesis of 3b–j
Entry Borate R
Conditions
Yielda
(%)
1
1
2
1b
1c
1c
1d
1e
1f
C≡CCH2OBn
(E)-CH=CHBu
(E)-CH=CHBu
(E)-CH=CHPh
r.t., 15 min
r.t., 15 min
83
69
73
82
69
60
67
83
65
88
C10H21
BF3–K+
F
1a
BF4–K+
F
I
C10H21
I
F
3a
3
–20 °C, 15 min
–20 °C, 15 min
– KF
4
2
Me
Me
5
4-tert-butylcyclohex-1-enyl –20 °C, 15 min
Scheme 3
6
Ph
60 °C, 6 h
7
1g
1h
1i
Tol
60 °C, 2 h
To carry out the iodonium salt synthesis more effectively,
we employed relatively electronegative iodoarene
difluorides10 in the reaction of 1b (Scheme 4); however,
the yields of the alkynyliodonium salts 7 and 8 were lower
than in the reaction with 2, because of decomposition of
alkynyliodonium salts 7 and 8.
8
PMP
60 °C, 15 min
60 °C, 15 h
r.t., 15 min
9
p-ClC6H4
10
1j
5-methyl-2-thienyl
a Isolated yield of 3.
Ar-IF2 (1.0 equiv)
BnO
1b
I(Ar)BF4
Ar = Ph: 7, 69%
Ar = p-ClC6H4: 8, 62%
Next, we attempted the reactions of diisopropyl hexenyl-
boronate (4) with 2, and of alkynyltrifluoroborate 1a with
iodobenzene diacetate, to investigate if these reactions
proceed without activation by acids (Scheme 2). Alkenyl-
boronate 4 reacted with 2 in the absence of acids; howev-
er, the yield of alkenyliodonium salt 3c from 4 was only
48%, while alkenyltrifluoroborate 1c gave 3c in 73%
yield, as shown in Table 2. On the other hand, the reaction
of alkynyltrifluoroborate 1a with iodobenzene diacetate
also proceeded without the addition of acids; however, a
mixture of alkynyliodonium salt 5 (78%) and (2-acetoxy-
alkenyl)iodonium salt 6 (5%) was obtained,11 while the
reaction between 1a and 2 afforded only alkynyliodonium
salt 3a in 95% yield (see Table 1). These investigations
confirmed that both of these reactions, between 4 and 2
and between 1a and iodobenzene diacetate, could be car-
ried out without activation by acids. However, it revealed
that the combination of an organotrifluoroborate and 2 is
essential for various iodonium salts to be obtained in good
yields.
MeCN (0.05 M), r.t., 15 min
Scheme 4
We previously reported the synthesis of (Z)-(2-fluoroalk-
enyl)iodonium salts in good yields by Michael-type addi-
tion of the fluoride anion to alkynyliodonium salts when
aqueous hydrogen fluoride was used.12 However, hydro-
gen fluoride addition to (phenylethynyl)iodonium salt 9
resulted in a low yield of (Z)-(2-fluoro-2-phenyleth-
enyl)iodonium salt 11 (Scheme 5), because of the low sta-
bility of 9. Therefore, we attempted a one-pot synthesis
of (Z)-(2-fluoro-2-phenylethenyl)(4-methylphenyl)iodo-
nium tetrafluoroborate (10) from potassium (phenyleth-
ynyl)trifluoroborate (1k) to evaluate our iodonium salt
synthesis (Scheme 5). First, alkynyltrifluoroborate 1k
was prepared from phenylacetylene in 67% yield by a
published procedure (Scheme 5).8a Then, the reaction of
1k with 2 was carried out in acetonitrile at room tempera-
ture. After 15 minutes, without prior isolation of the (phe-
Synthesis 2007, No. 10, 1542–1546 © Thieme Stuttgart · New York

1544
M. Yoshida et al.
PAPER
0 °C. The mixture was warmed to r.t. and stirred for 30 min. Evap-
oration of the mixture at 40 °C gave a crude product, which was,
then, dissolved in hot acetone. After hot filtration and evaporation,
pure 1e was obtained.
nylethynyl)iodonium salt, 10 equivalents of 20% aqueous
hydrogen fluoride was added to the reaction vessel, and
the reaction mixture was stirred at 60 °C for 16 hours.
This gave us (fluoroalkenyl)iodonium salt 10 in 55% yield
from phenylacetylene (82% yield from 1k). By our previ-
ous method, (fluoroalkenyl)iodonium salt 11 was synthe-
sized in 43% yield from 9, which had been prepared in
48% yield from phenylacetylene; this gave 11 in a total
yield of only 21% from phenylacetylene (Scheme 5).
When hydrogen fluoride addition proceeded without prior
Yield: 2.19 g (45%); mp >300 °C.
IR (KBr): 2966, 2912, 2871, 2834, 1703, 1647, 1469, 1433, 1364,
1246, 1234, 1193, 1165, 1050, 1018, 976, 918, 897, 826, 811 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 0.75–0.96 (m, 10 H), 1.04–
1.11 (m, 1 H), 1.57–1.67 (m, 2 H), 1.73–1.84 (m, 2 H), 1.99–2.05
(m, 1 H), 5.44 (s, 1 H, H-2).
isolation of 9, only a complex mixture resulted, and the 13C NMR (100 MHz, DMSO-d6): d = 24.4, 27.1 (3 C), 28.3, 30.7,
32.0, 44.3, 122.5.
formation of 11 was not observed. Thus, we improved the
yield of the (Z)-(2-fluoro-2-phenylethenyl)iodonium salt
HRMS–FAB: m/z [M – K]– calcd for C10H17BF3: 205.1375; found:
205.1382.
by using a one-pot synthesis via alkynyltrifluoroborate.
Potassium Dodec-1-ynyltrifluoroborate (1a)
Mp >300 °C.
1. BuLi
2. B(OMe)
Ph
Ph
F
1. 2, MeCN
Ph
I(p-Tol)BF4
IR (KBr): 2956, 2921, 2852, 2189, 1469, 1146, 1126, 968, 721
cm–1.
1H NMR (400 MHz, DMSO-d6): d = 0.85 (t, J = 6.7 Hz, 3 H, 12-H),
1.21–1.35 (m, 16 H), 1.94–1.98 (m, 2 H, 3-H).
13C NMR (100 MHz, DMSO-d6): d = 13.9, 18.9, 22.1, 28.5, 28.8 (2
C), 29.05, 29.08 (2 C), 31.3, 88.8 (m, 1 C).
HRMS–FAB: m/z [M – K]– calcd for C12H21BF3: 233.1688; found:
233.1694.
3. aq KHF2
67%
2. aq HF
82%
BF3–K+
1k
10
55% from
phenylacetylene
Ph
Ph
F
Ph-I=O, aq HBF4
20% aq HF
CHCl3
I(Ph)BF4
cat. HgO, CH2Cl2
48%
9
11
I(Ph)BF4
43%
21% from
phenylacetylene
Scheme 5
Potassium [3-(Benzyloxy)prop-1-ynyl]trifluoroborate (1b)
Mp >300 °C.
In summary, we successfully synthesized alkenyl-, alky-
nyl-, and diaryliodonium salts in good yields by reaction
of the corresponding organotrifluoroborates with p-iodo-
toluene difluoride. A (phenylethynyl)iodonium salt was
also synthesized by this method, and was used for a
Michael-type addition of hydrogen fluoride without prior
isolation of the alkynyliodonium salt. By this one-pot syn-
thesis, (Z)-(2-fluoro-2-phenylethenyl)iodonium salt was
obtained in good yield.
IR (KBr): 3061, 3032, 2874, 2854, 2229, 1497, 1454, 1405, 1383,
1367, 1353, 1255, 1207, 1114, 963, 731, 695 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 4.02 (s, 2 H, 3-H), 4.48 (s, 2
H, H-5), 7.28–7.37 (m, 5 H, Ph).
13C NMR (100 MHz, DMSO-d6): d = 58.0, 70.0, 84.7 (m, 1 C),
127.4, 127.6 (2 C), 128.2 (2 C), 138.2.
HRMS–FAB: m/z [M – K]– calcd for C10H9BF3O: 213.0699; found:
213.0692.
Potassium (4-Methylphenyl)trifluoroborate (1g)
Mp 293–294 °C.
IR spectra were recorded on a JASCO FT/IR-410 instrument. The
1H NMR (400 MHz), 19F NMR (376 MHz), and 13C NMR (100
MHz) spectra were recorded on a JEOL JNM-A400II FT NMR
spectrometer and the chemical shifts d are relative to TMS (1H, 13C)
and CFCl3 (19F). The high-resolution mass spectra were measured
on a JEOL JMS-700TZ, JMS-FABmate, or JMS-HX110 instru-
ment. Melting points were measured on a Yanagimoto micro melt-
ing point apparatus and are uncorrected. Alkynyltrifluoroborates
1a, 1b, and 1k were prepared by literature procedures.8a Alkenyltri-
fluoroborates 1c and 1d were synthesized from the corresponding
alkenylboronic acids,8b which were prepared from hex-1-yne13a and
phenylacetylene.13b Aryltrifluoroborates 1f–i were prepared by lit-
erature procedures.8b Potassium trifluoro(5-methyl-2-thienyl)borate
(1j) was purchased from Aldrich. p-Iodotoluene difluoride (TolIF2,
2) is commercially available from Aldrich. The spectral data of
1c,14a 1d,13b 1f,8b,14b 1g,14b 1i,8a 1k,14c 3f,15 and 3i15 have been report-
ed previously.
IR (KBr): 3040, 3016, 2982, 2924, 2867, 1663, 1613, 1387, 1233,
1200, 1022, 973, 923, 809 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 2.20 (s, 3 H, CH3), 6.88 (d,
J = 7.6 Hz, 2 H), 7.19 (d, J = 7.6 Hz, 2 H).
13C NMR (100 MHz, DMSO-d6): d = 21.0, 127.0 (2 C), 131.3 (m, 2
C), 133.0, 159.4.
HRMS–FAB: m/z [M – K]– calcd for C7H7BF3: 159.0593; found:
159.0588.
Dodec-1-ynyl(4-methylphenyl)iodonium Tetrafluoroborate
(3a); Typical Procedure
TolIF2 (2) (256 mg, 1 mmmol) was dissolved in anhyd MeCN (20
mL) in a Teflon PFA vessel. Borate 1a (272 mg, 1 mmol) was add-
ed, and the mixture was stirred for 15 min at r.t. Then the mixture
was poured into 5% aq NaBF4 (30 mL) and extracted with CH2Cl2
(3 × 20 mL). The combined organic phase was dried (MgSO4) and
concentrated under reduced pressure. The residue was dissolved in
a little CH2Cl2 (2 mL), followed by the addition of a large quantity
of hexane (40 mL). The upper clear part was removed by decanta-
tion, and the remaining viscous oil was washed with hexane. Final-
ly, complete removal of the solvent under reduced pressure gave 3a.
Potassium (4-tert-Butylcyclohex-1-enyl)trifluoroborate (1e)
To a soln of 4-tert-butyl-1-chlorocyclohexene16 (3.45 g, 20 mmol)
in anhyd Et2O (80 mL) was added (MeO)3B (4.2 mL, 40 mmol) and
Na cuttings (3.00g, 130 mmol) at r.t. After the mixture had stirred
for 3 d at r.t., excess Na was removed by decantation. To the result-
ing soln was slowly added aq KHF2 (12.5 g, 40 mL, 160 mmol) at
Synthesis 2007, No. 10, 1542–1546 © Thieme Stuttgart · New York

PAPER
Synthesis of Iodonium Salts from Organotrifluoroborates
1545
Yield: 447 mg (95%); mp 42 °C.
IR (paraffin): 2187, 1465, 1377, 1060, 986, 803, 720 cm–1.
1H NMR (400 MHz, CDCl3): d = 0.88 (t, J = 6.4 Hz, 3 H, H-12),
1.22–1.35 (m, 14 H), 1.54–1.61 (m, 2 H, H-4), 2.44 (s, 3 H,
C6H4CH3), 2.62 (t, J = 7.1 Hz, 2 H, H-3), 7.33 (d, J = 8.6 Hz, 2 H),
7.93 (d, J = 8.6 Hz, 2 H).
2.60–2.71 (m, 2 H), 6.98–7.00 (m, 1 H, H-2), 7.32 (d, J = 8.4 Hz, 2
H), 7.87 (d, J = 8.4 Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 21.5, 26.9 (3 C), 27.2, 31.8, 32.2,
35.2, 41.9, 104.3, 119.0, 133.3 (2 C), 135.8 (2 C), 144.1, 147.2.
HRMS–FAB: m/z [M – BF4]+ calcd for C17H24I: 355.0923; found:
355.0929.
13C NMR (100 MHz, CDCl3): d = 14.1, 15.9, 20.7, 21.3, 22.6, 27.5,
28.7, 28.8, 29.2, 29.3, 29.4, 31.8, 110.6, 113.2, 133.3 (2 C), 134.0
(2 C), 144.1.
Bis(4-Methylphenyl)iodonium Tetrafluoroborate (3g)
Mp 113–114 °C.
IR (KBr): 3086, 3048, 2954, 2927, 2867, 1666, 1579, 1479, 1447,
1396, 1282, 1211, 1188, 1060, 999, 801 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.33 (s, 6 H, CH3), 7.21 (d, J = 8.6
Hz, 4 H), 7.90 (d, J = 8.6 Hz, 4 H).
HRMS–FAB: m/z [M – BF4]+ calcd for C19H28I: 383.1236; found:
383.1241.
[3-(Benzyloxy)prop-1-ynyl](4-methylphenyl)iodonium Tetra-
fluoroborate (3b)
Mp 79–81 °C.
13C NMR (100 MHz, CDCl3): d = 21.7 (2 C), 109.0 (2 C), 133.6 (4
C), 135.7 (4 C), 144.3 (2 C).
IR (KBr): 3089, 3059, 3032, 2906, 2870, 2202, 1741, 1578, 1477,
1454, 1390, 1354, 1284, 1259, 1208, 1066, 905, 804, 748, 700 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.41 (s, 3 H, C6H4CH3), 4.45 (s, 2
H, H-3), 4.57 (s, 2 H, H-5), 7.29–7.33 (m, 7 H), 7.92 (d, J = 8.6 Hz,
2 H).
HRMS–FAB: m/z [M – BF4]+ calcd for C14H14I: 309.0140; found:
309.0138.
(4-Chlorophenyl)(4-methylphenyl)iodoniumTetrafluoroborate
(3i)
Mp 46–47 °C.
13C NMR (100 MHz, CDCl3): d = 21.4, 24.4, 57.9, 72.5, 106.6,
110.5, 128.2, 128.3 (2 C), 128.5 (2 C), 133.5 (2 C), 134.6 (2 C),
136.3, 144.5.
IR (KBr): 3092, 2954, 2927, 1918, 1742, 1635, 1585, 1556, 1471,
1391, 1282, 1213, 1190, 1089, 990, 803 cm–1.
HRMS–FAB: m/z [M – BF4]+ calcd for C17H16IO: 363.0246; found:
363.0245.
1H NMR (400 MHz, CDCl3): d = 2.93 (s, 3 H, C6H4CH3), 7.26 (d,
J = 8.3 Hz, 2 H), 7.39 (d, J = 8.8 Hz, 2 H), 7.88–7.93 (m, 4 H).
13C NMR (100 MHz, CDCl3): d = 21.1, 108.4, 109.1, 132.1 (2 C),
Hex-1-enyl(4-methylphenyl)iodonium Tetrafluoroborate (3c)
Oil.
132.9 (2 C), 135.3 (2 C), 136.2 (2 C), 139.3, 143.8.
HRMS–FAB: m/z [M – BF4]+ calcd for C13H11ClI: 328.9594; found:
328.9597.
IR (neat): 3086, 2959, 2932, 2872, 1631, 1584, 1483, 1463, 1397,
1283, 1210, 1065, 918, 804 cm–1.
1H NMR (400 MHz, CDCl3): d = 0.87 (t, J = 7.3 Hz, 3 H, H-6),
1.24–1.34 (m, 2 H, H-5), 1.39–1.47 (m, 2 H, H-4), 2.30–2.35 (m, 2
H, H-3), 2.43 (s, 3 H, C6H4CH3), 6.76 (d, J = 13.7 Hz, 1 H, H-1),
6.89–6.96 (m, 1 H, H-2), 7.30 (d, J = 8.5 Hz, 2 H), 7.87 (d, J = 8.5
Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 13.9, 21.7, 22.3, 30.0, 35.2, 97.1,
105.8, 133.6 (2 C), 136.0 (2 C), 144.3, 154.8.
(4-Methylphenyl)(5-methyl-2-thienyl)iodonium Tetrafluoro-
borate (3j)
Mp 105–107 °C.
IR (KBr): 3102, 2959, 2925, 2862, 1910, 1632, 1576, 1528, 1477,
1444, 1420, 1395, 1283, 1223, 1188, 1074, 934, 801 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.37 (s, 3 H, C6H4CH3), 2.59 (s, 3
H, thienyl-CH3), 6.79 (d, J = 3.9 Hz, 1 H), 7.23 (d, J = 8.4 Hz, 2 H),
7.81 (d, J = 3.9 Hz, 1 H), 7.87 (d, J = 8.4 Hz, 2 H).
HRMS–FAB: m/z [M – BF4]+ calcd for C13H18I: 301.0453; found:
301.0454.
13C NMR (100 MHz, CDCl3): d = 15.6, 21.3, 88.1, 112.3, 128.7,
133.0 (2 C), 134.1 (2 C), 142.9, 143.7, 153.9.
(4-Methylphenyl)(2-phenylethenyl)iodonium Tetrafluoro-
borate (3d)
Oil.
HRMS–FAB: m/z [M – BF4]+ calcd for C12H12IS: 314.9704; found:
314.9714.
IR (neat): 3085, 2960, 2925, 2871, 1684, 1591, 1566, 1483, 1447,
1396, 1283, 1038, 804, 731 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.39 (s, 3 H, C6H4CH3), 7.24–7.47
(m, 8 H), 7.71 (d, J = 14.2 Hz, 1 H), 7.91 (d, J = 8.4 Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 21.7, 96.6, 106.6, 128.4 (2 C),
129.3 (2 C), 131.4, 133.5 (2 C), 134.4, 136.1 (2 C), 144.2, 151.1.
[3-(Benzyloxy)prop-1-ynyl](phenyl)iodonium Tetrafluoro-
borate (7)
Mp 46–47 °C.
IR (KBr): 3090, 3062, 3030, 2925, 2858, 2186, 1724, 1561, 1500,
1456, 1377, 1077, 983, 739, 700 cm–1.
1H NMR (400 MHz, CDCl3): d = 4.48 (s, 2 H, H-3), 4.59 (s, 2 H, H-
5), 7.30–7.36 (m, 5 H), 7.54 (t, J = 8.1 Hz, 2 H), 7.68 (t, J = 7.5 Hz,
1 H), 8.06 (d, J = 7.9 Hz, 2 H).
HRMS–FAB: m/z [M – BF4]+ calcd for C15H14I: 321.0140; found:
321.0137.
13C NMR (100 MHz, CDCl3): d = 24.3, 57.9, 72.5, 107.0, 114.4,
128.2, 128.3 (2 C), 128.5 (2 C), 132.7 (2 C), 133.1, 134.5 (2 C),
136.3.
HRMS–FAB: m/z [M – BF4]+ calcd for C16H14IO: 349.0089; found:
349.0088.
(4-tert-Butylcyclohex-1-enyl)(4-methylphenyl)iodonium Tetra-
fluoroborate (3e)
Mp 75–76 °C.
IR (KBr): 3089, 3066, 2961, 2868, 1627, 1579, 1479, 1436, 1399,
1366, 1083, 1057, 1022, 801, 692 cm–1.
1H NMR (400 MHz, CDCl3): d = 0.84 (s, 9 H, t-Bu), 1.36–1.53 (m,
2 H), 1.89–1.93 (m, 1 H), 2.22–2.31 (m, 1 H), 2.42–2.48 (m, 4 H),
[3-(Benzyloxy)prop-1-ynyl](4-chlorophenyl)iodonium Tetra-
fluoroborate (8)
Mp 89–90 °C.
Synthesis 2007, No. 10, 1542–1546 © Thieme Stuttgart · New York

1546
M. Yoshida et al.
PAPER
IR (KBr): 3085, 3061, 3033, 2927, 2871, 2197, 1638, 1473, 1392,
1352, 1264, 1086, 994, 971, 809, 744, 698 cm–1.
1H NMR (400 MHz, CDCl3): d = 4.46 (s, 2 H, H-3), 4.58 (s, 2 H, H-
5), 7.30–7.33 (m, 5 H), 7.46 (d, J = 8.8 Hz, 2 H), 8.00 (d, J = 8.9 Hz,
2 H).
13C NMR (100 MHz, CDCl3): d = 25.0, 58.3, 72.9, 107.6, 111.2,
128.60, 128.64 (2 C), 128.9 (2 C), 133.0 (2 C), 136.3 (2 C), 136.6,
140.5.
(3) For recently published papers concerned with iodonium salt
synthesis, see: (a) Kitamura, T.; Inoue, D.; Wakimoto, I.;
Nakamura, T.; Katsuno, R.; Fujiwara, Y. Tetrahedron 2004,
60, 8855. (b) Zhdankin, V. V.; Koposov, A. Y.; Su, L.;
Boyarskikh, V. V.; Netzel, B. C.; Young, V. G. Jr. Org. Lett.
2003, 5, 1583.
(4) (a) Kitamura, T.; Aoki, Y.; Isshiki, S.; Wasai, K.; Fujiwara,
Y. Tetrahedron Lett. 2006, 47, 1709. (b) Klein, M.; König,
B. Tetrahedron 2004, 60, 1087. (c) Abe, T.; Yamaji, T.;
Kitamura, T. Bull. Chem. Soc. Jpn. 2003, 76, 2175.
(d) Radhakrishnan, U.; Stang, P. J. J. Org. Chem. 2003, 68,
9209. (e) Kitamura, T.; Abe, T.; Fujiwara, Y.; Yamaji, T.
Synthesis 2003, 213. (f) Ochiai, M.; Miyamoto, K.; Suefuji,
T.; Shiro, M.; Sakamoto, S.; Yamaguchi, K. Tetrahedron
2003, 59, 10153. (g) Carroll, M. A.; Pike, V. W.;
Widdowson, D. A. Tetrahedron Lett. 2000, 41, 5393.
(5) (a) Fujita, M.; Lee, H. J.; Okuyama, T. Org. Lett. 2006, 8,
1399. (b) Ochiai, M.; Miyamoto, K.; Yokota, Y.; Suefuji, T.;
Shiro, M. Angew. Chem. Int. Ed. 2005, 44, 75. (c) Abo-
Amer, A.; Adonin, N. Y.; Bardin, V. V.; Fritzen, P.; Frohn,
H.-J.; Steinberg, C. J. Fluorine Chem. 2004, 125, 1771.
(6) Benziodoxole and its acetoxy derivative can react with
alkynylboronates to afford iodonium salts in the absence of
acids; however, excess boronate and reflux temperature in
acetonitrile are required. See: Zhdankin, V. V.; Persichini, P.
J. III; Cui, R.; Jin, Y. Synlett 2000, 719.
HRMS–FAB: m/z [M – BF4]+ calcd for C16H13ClIO: 382.9700;
found: 382.9707.
One-Pot Synthesis of (Z)-(2-Fluoro-2-phenylethenyl)(4-meth-
ylphenyl)iodonium Tetrafluoroborate (10)
TolIF2 (2) (256 mg, 1 mmmol) was dissolved in anhyd MeCN (20
mL) in a Teflon PFA vessel. Borate 1k (208 mg, 1 mmol) was add-
ed, and the mixture was stirred for 15 min at r.t. Then 20% aq HF
(1.0 g, 10 mmol) was added, and the mixture was stirred for 16 h at
60 °C. The resulting soln was poured into 5% aq NaBF4 (30 mL)
and extracted with CH2Cl2 (3 × 20 mL). The combined organic
phase was dried (MgSO4) and concentrated under reduced pressure.
To the residue was added a little CH2Cl2 (2 mL), followed by the ad-
dition of a large quantity of hexane (40 mL). The upper clear part
was removed by decantation, and the remaining solid was washed
with hexane. Finally, complete removal of the solvent under re-
duced pressure gave 10.
(7) For reviews on trifluoro(organo)borates, see: (a) Molander,
G. A.; Figueroa, R. Aldrichimica Acta 2005, 38, 49.
(b) Darses, S.; Genet, J.-P. Eur. J. Org. Chem. 2003, 4313.
(8) (a) Darses, S.; Michaud, G.; Genet, J.-P. Eur. J. Org. Chem.
1999, 1875. (b) Vedejs, E.; Chapman, R. W.; Fields, S. C.;
Lin, S.; Schrimpf, M. R. J. Org. Chem. 1995, 60, 3020.
(9) (a) Batey, R. A.; Quach, T. D.; Shen, M.; Thadani, A. N.;
Smil, D. V.; Li, S.-W.; MacKay, D. B. Pure Appl. Chem.
2002, 74, 43. (b) Kerverdo, S.; Gingras, M. Tetrahedron
Lett. 2000, 41, 6053.
Yield: 342 mg (82%); mp 144–145 °C.
IR (KBr): 3114, 1629, 1575, 1496, 1477, 1449, 1287, 1190, 1083,
1038, 799, 782, 743, 694 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 2.36 (s, 3 H, C6H4CH3), 7.37
(d, J = 8.2 Hz, 2 H), 7.38–7.60 (m, 3 H), 7.74 (d, J = 7.4 Hz, 2 H),
7.90 (d, J = 37.6 Hz, 1 H, H-1), 8.04 (d, J = 8.2 Hz, 2 H).
13C NMR (100 MHz, DMSO-d6): d = 20.9, 80.6 (d, 2JC–F = 21.7 Hz,
3
1 C, C-1), 111.8, 125.9 (d, JC–F = 6.6 Hz, 2 C, o-Ph), 127.4, (d,
2JC–F = 27.8 Hz, 1 C, ipso-Ph), 129.4 (2 C), 132.5 (3 C), 135.1 (2 C),
(10) Sawaguchi, M.; Ayuba, S.; Hara, S. Synthesis 2002, 1802;
142.6, 164.5 (d, 1JC–F = 260.5 Hz, 1 C, C-2).
and references cited therein.
19F NMR (376 MHz, DMSO-d6): d = –84.2 (d, J = 37.6 Hz, 1 F,
F-2).
HRMS–FAB: m/z [M – BF4]+ calcd for C15H13FI: 339.0046; found:
339.0042.
(11) The iodonium salts 5 and 6 were obtained as an inseparable
mixture. The yields were determined by 1H NMR spectro-
scopy; for the spectral data of the (Z)-(2-acetoxyalkenyl)io-
donium salt, see: Ochiai, M.; Kitagawa, Y. J. Org. Chem.
1999, 64, 3181.
(12) (a) Yoshida, M.; Komata, A.; Hara, S. Tetrahedron 2006, 62,
8636. (b) Yoshida, M.; Hara, S. Org. Lett. 2003, 5, 573.
(13) (a) Brown, H. C.; Cambell, J. B. Jr. J. Org. Chem. 1980, 45,
389. (b) Petasis, N. A.; Yudin, A. K.; Zavialov, I. A.;
Prakash, G. K. S.; Olah, G. A. Synlett 1997, 606.
(14) (a) Bardin, V. V.; Idemskaya, S. G.; Frohn, H.-J. Z. Anorg.
Allg. Chem. 2002, 628, 883. (b) Smoum, R.; Rubinstein, A.;
Srebnik, M. Org. Biomol. Chem. 2005, 3, 941.
References
(1) For reviews on iodonium salts, see: (a) Zhdankin, V. V.;
Stang, P. J. Chem. Rev. 2002, 102, 2523. (b) Wirth, T.; Hirt,
U. H. Synthesis 1999, 1271. (c) Zhdankin, V. V.; Stang, P. J.
Tetrahedron 1998, 54, 10927. (d) Varvoglis, A.
Tetrahedron 1997, 53, 1179. (e) Stang, P. J.; Zhdankin, V.
V. Chem. Rev. 1996, 96, 1123. (f) Varvoglis, A. Synthesis
1984, 709.
(c) Molander, G. A.; Katona, B. W.; Machrouhi, F. J. Org.
Chem. 2002, 67, 8416.
(2) For books on iodonium salts, see: (a) Chemistry of
Hypervalent Compounds; Akiba, K., Ed.; Wiley-VCH:
Weinheim, 1999. (b) Varvoglis, A. The Organic Chemistry
of Polycoordinated Iodine; Wiley-VCH: Weinheim, 1992.
(15) Kasumov, T. M.; Brel, V. K.; Koz’min, A. S.; Zefirov, N. S.
Synthesis 1995, 775.
(16) Lambert, J. B.; Wang, G.-T.; Finzel, R. B.; Teramura, D. H.
J. Am. Chem. Soc. 1987, 109, 7838.
Synthesis 2007, No. 10, 1542–1546 © Thieme Stuttgart · New York