Effects of stereochemistry and β-substituents on the rates of vinylic SN2 reaction of hypervalent vinyl(phenyl)-λ3- iodanes with tetrabutylammonium halides

Article abstract of DOI:10.1016/j.tet.2010.04.041

Both stereoisomers of β-(2-phenylethoxy)vinyl-λ³- iodane and (Z)-β-aroyloxyvinyl-λ³-iodane were prepared stereoselectively. These substituted vinyl-λ³-iodanes undergo nucleophilic vinylic substitutions with n-Bu₄NX (X=Cl, Br, I) under mild conditions, yielding vinyl halides. The observed inversion of configuration at the ipso vinylic carbon atom is compatible with a concerted vinylic S _N2 mechanism. Kinetic measurements indicated that the rates for vinylic S_N2 reaction of (Z)-vinyl-λ³-iodane are greater than those of the E-isomer, probably because of the higher ground state energy of the Z-isomer. Electronic effects of β-substituents of vinyl-λ³-iodanes in the vinylic S_N2 reaction are also discussed.

Full text of DOI:10.1016/j.tet.2010.04.041

Tetrahedron 66 (2010) 5819e5826
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Effects of stereochemistry and
of hypervalent vinyl(phenyl)-
b
-substituents on the rates of vinylic SN2 reaction
l
3-iodanes with tetrabutylammonium halides
,
a
a
b
a
Kazunori Miyamoto a , Takuji Okubo , Masaya Hirobe , Munetaka Kunishima , Masahito Ochiai
*
a Graduate School of Pharmaceutical Sciences, University of Tokushima, 1-78 Shomachi, Tokushima 770-8505, Japan
b Faculty of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
a r t i c l e i n f o
a b s t r a c t
Both stereoisomers of b-(2-phenylethoxy)vinyl-l b-aroyloxyvinyl-l
3-iodane and (Z)- 3-iodane were pre-
Article history:
pared stereoselectively. These substituted vinyl-l
3-iodanes undergo nucleophilic vinylic substitutions
Received 2 March 2010
Accepted 8 April 2010
Available online 24 April 2010
with n-Bu4NX (X¼Cl, Br, I) under mild conditions, yielding vinyl halides. The observed inversion of
configuration at the ipso vinylic carbon atom is compatible with a concerted vinylic SN2 mechanism.
Kinetic measurements indicated that the rates for vinylic SN2 reaction of (Z)-vinyl-l
3-iodane are greater
Keywords:
SN2 reaction
Iodine
Hypervalent
Vinyliodane
Inversion
than those of the E-isomer, probably because of the higher ground state energy of the Z-isomer. Elec-
tronic effects of
b
-substituents of vinyl-
l
3-iodanes in the vinylic SN2 reaction are also discussed.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
All of the kinetic data, the secondary isotope effects, sub-
stituent effects of the leaving groups, the solvent effects, the
pressure effects as well as stereochemistry of the substitutions
firmly establish the in-plane vinylic SN2 mechanism.3,4 Hyper-
Bimolecular nucleophilic substitution (SN2 reaction) at a vinylic
sp2 carbon atom involves the attack of a nucleophile to the
s
*
orbital of a vinylic CeL bond (L¼a leaving group) from the side
opposite the leaving group and proceeds with exclusive inversion
of configuration in a concerted manner without forming an in-
termediate. This process has been considered to be a high-energy
pathway on the basis of steric factors and of early calculations,1 and
in fact was rarely observed.2 In 1991, we reported that a nucleo-
nucleofugality of the phenyl(tetrafluoroborato)-l
3-iodanyl
group,7 being
a much better nucleofuge than superleaving
triflate,8 is responsible for the unique vinylic SN2 reaction. Dialkyl
sulfides and selenides,5b phosphoroselenoates,9a dithiocarbama-
tes,9b carboxylic acids,10 amides,11 and thioamides12 serves as
efficient nucleophiles in the vinylic SN2 reactions of vinyl-l3
iodanes 1.
-
philic vinylic substitution of (E)-
b-alkylvinyl(phenyl)(tetra-
fluoroborato)-
l
3-iodanes 1 with tetrabutylammonium halides (Cl,
To understand in depth the mechanism of bimolecular
nucleophilic substitution at a vinylic carbon atom, it is highly
desirable to compare the differences in reactivity between both
Br, and I) proceeds with complete inversion of configuration on the
vinylic ipso carbon atom even at room temperature (Scheme 1).3
This is the unambiguous example of a vinylic SN2 reaction.4e6
(E)- and (Z)-stereoisomers of vinyl-
substitution of (Z)-derivatives of -alkylvinyl-
halides, however, resulted in an exclusive formation of terminal
l
3-iodanes 1. The attempted
3-iodanes 1 with
b
l
R
n-Bu4NX
X = Cl, Br, I
Ph
R
X
alkynes, probably via facile anti b-elimination and/or a-elimina-
I
tion-1,2-rearrangement sequence.13 No evidence for the vinylic
SN2 displacement of the (Z)-isomers of 1 with halides was
observed in these reactions. The only example of vinylic SN2
FBF3
1
R = n-C8H17, Ph(CH2)3
reaction of (Z)-vinyl-
reaction of (Z)-( -aroyloxyvinyl)phenyl-
Bu4NX undergoes bimolecular nucleophilic substitution
l
3-iodanes was reported recently:13 thus,
Scheme 1. Vinylic SN2 reaction of vinyl-l
3-iodanes 1 with halides.
b
l 2 with n-
3-iodanes
a
selectively to give inverted (E)-vinyl halides. Unfortunately,
however, no methods for the synthesis of (E)-isomers of 2 are
available in the literature (Scheme 2).
* Corresponding author. Tel.: þ81 88 633 9532; fax: þ81 88 633 9504; e-mail
address: kmiya@ph.tokushima-u.ac.jp (K. Miyamoto).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.04.041

5820
K. Miyamoto et al. / Tetrahedron 66 (2010) 5819e5826
In 1988, we reported a unique method for the synthesis of (E)-
-ethoxyvinyl(phenyl)(tetrafluoroborato)-
3-iodane: the method
involves an initial Lewis acid (BF3eEt2O)-catalyzed anti ethoxy-l3
iodanation of trimethylsilylacetylene with iodosylbenzene, followed
by the protodesilylation of the resulting (E)- -trimethylsilyl-
ethoxyvinyl-
3-iodane with water in the presence of triethyl-
amine.20 The alkoxy group of (E)- 3-iodane originates
-ethoxyvinyl-
ArCO2
FBF3
Ph
n-Bu4NX
X = Cl, Br, I
ArCO2
b
l
I
-
X
2
a
b-
Scheme 2. Vinylic SN2 reaction of (Z)-vinyl-
l
3-iodanes 2.
l
b
l
Intramolecular nucleophilic substitution of 2-bromobut-2-
enylamines afforded 2-ethyleneaziridines by way of stereochemical
inversion at the vinylic carbon atom.14 Intramolecular vinylic SN2-
type reaction of vinyl halides was also reported by Narasaka
and co-workers:15 thus, vinyl halides with hydroxy, sulfonamide,
and active methine groups afforded the corresponding hetero- and
carbocycles by the exposure to a base with inversion of configu-
ration. Recently, formation of a transition state model compound
for vinylic SN2 reaction with a very short lifetime was detected by
Yamamoto and co-workers in the laser flash photolysis of vinyl
bromide derived from 1,8-dimethoxythioxanthen-9-one.16
from the ligand Et2O of Lewis acid BF3. The method was slightly
modified for the stereoselective synthesis of (E)-4 (Scheme 4).21
PhIO
BF3-O(CH2CH2Ph)2 (1 equiv)
(PhCH2CH2)2O (5 equiv)
O
TMS
TMS
(3 equiv)
Ph
Ph
CH2Cl2, rt, 15 h, N2
I
FBF3
7
O
MeOH
rt, 48 h, Ar
We report herein the stereoselective synthesis of both stereo-
Ph
Ph
isomers of
b-alkoxyvinyl-l 4
3-iodanes 4. These vinyliodanes
I
FBF3
undergo vinylic SN2 displacement by the reaction with n-Bu4NX
stereospecifically under mild conditions and the rates for these
nucleophilic substitutions are compared each other, indicating
higher reactivity of (Z)-isomer (Z)-4 than that of (E)-4 toward halide
(E)-4
Scheme 4. Stereoselective synthesis of (E)-b-alkoxyvinyl-l
3-iodane (E)-4.
nucleophiles. Effects of the
b-substituents (alkyl, alkoxy, and
Treatment of iodosylbenzene with 3 equiv of trimethylsilylacety-
lene in the presence of BF3eO(CH2CH2Ph)2 (1 equiv)22 and bis(phe-
nethyl) ether (5 equiv) in dichloromethane at room temperature
aroyloxy groups) of vinyl-
l
3-iodanes are also evaluated.
resultedinananti-selectivealkoxy-
triple bond, yielding pure (E)- -trimethylsilyl-
vinyl-
3-iodane 7 in a 26% yield as a pale yellow oil. Low yield of (E)-7
is partly due to the formation of trimethylsilylethynyl-
3-iodane 5 as
l
3-iodanationofacarbonecarbon
-(2-phenylethoxy)
2. Results and discussion
2.1. Synthesis of -alkoxyvinyl-
-(2-phenylethoxy)vinyl-l
3-iodane (Z)-4
a
b
b
l
3-iodanes
l
l
Synthetic method of (Z)-
is straightforward: it was directly prepared from the commercially
available ethynyl(phenyl)(tetrafluoroborato)-
3-iodane (3) through
anti Michael-type addition of phenethyl alcohol (Scheme 3).17 Thus,
exposure of ethynyl-
3-iodane 3 to a large excess of phenethyl alcohol
at room temperature afforded a 73% yield of (Z)- -alkoxyvinyl(phe-
nyl)(tetrafluoroborato)-
3-iodane (Z)-4 stereoselectively as colorless
crystals. Michael addition of the alcohol toward trimethylsilyl-
ethynyl-
3-iodane 5,18 accompanied by protodetrimethylsilylation,
also afforded (Z)-vinyl-
3-iodane (Z)-4 (72%) under ambient condi-
b
a by-product: the alkynyliodane 5 was selectively removed from
a crude reaction mixture by the exposure to an aqueous NaBr solution
(see Experimental), which probably produces bromo(trimethylsilyl)
acetylene through tandem Michael additionealkylidene carbene
l
rearrangement of 5.23 Under the conditions, vinyl- 3-iodane (E)-7
l
l
b
remains intact: neither Michael-type addition nor bimolecular
l
nucleophilic substitution of (E)-7 with bromide anion takes place.
Subsequentprotodesilylationofvinyl-
developed by Kunishima,21 proceeded in an exclusively stereo-
selective manner with retention of configuration and gave (E)- -(2-
phenylethoxy)vinyl-
3-iodane (E)-4 at room temperature in an 85%
l
3-iodane(E)-7 withmethanol,
l
l
b
tions. Stereochemistry of (Z)-4 was determined by the small vicinal
coupling constantof 3.3 Hz between the vinylic protons. Alkoxyvinyl-
l
yield. A large vicinal coupling constant (J¼12.9 Hz) of the vinylic
l
3-iodane (Z)-4 is rather thermally labile but complexation with
protons in (E)-4 is in a good agreement with the reported value
18-crown-6 (18C6) increases its stability in the solid state.17,19 Thus,
no decomposition was observed when the colorless prisms of 2:1
(12.5 Hz) for (E)-
To investigate the electronic effects of
vinyl-
3-iodanes in vinylic SN2 reaction, (Z)-
b-ethoxyvinyl-l
3-iodane.20
b-aroyloxy substituents of
l
3-iodane$18C6 complex 6, prepared from silyl-
l
b
-aroyloxyvinyl-l3
-
(Z)-
ethynyl-
were left standing under ambient conditions for several days.
b-alkoxyvinyl-
l
3-iodane 5 in the presence of 18C6 (0.5 equiv) in a 69% yield,
iodanes 2aed were prepared in good yields according to the
reported method (Scheme 5).13,24
Ph(CH2)2OH
rt, 5.5 h, Ar
I
FBF3
Ph
Ph
ArCO2H (9 equiv)
O
I
Ph
3
ArCO2Na (0.2 equiv)
FBF3
2
3
MeOH, rt, Ar
then aq NaBF4
(Z)-4
(Z)-4
2a: Ar = Ph, 2b: Ar = p-MeC6H4, 2c: Ar = p-ClC6H4, 2d: Ar = p-CF3C6H4
Scheme 5. Stereoselective synthesis of (Z)-2.
Ph(CH2)2OH
TMS
I
Ph
FBF3
rt, 27 h, air
5
18C6 (0.5 equiv)
Ph(CH2)2OH
rt, 47 h, Ar
2.2. Structure of vinyl-l
3-iodanes
Ph
Ph
5
18C6
O
I
X-ray crystallographic analysis of vinyl-
illustrates an asymmetric dimer structure with two independent
but closely related molecules. Each
3-iodane molecule in the di-
mer unit shows a T-shaped structure, ligated with one fluorine
l
3-iodane (Z)-4 (Fig. 1)
FBF3
2
6
l
Scheme 3. Stereoselective synthesis of (Z)-b-alkoxyvinyl-l
3-iodanes.

K. Miyamoto et al. / Tetrahedron 66 (2010) 5819e5826
5821
3.0748(15) Å or I2/F1 2.9893(13) Å, each iodane molecule adopts
a distorted square-planar arrangement around the iodine atom
with rms deviation (0.177(1) Å for I1, C1, C11, F2, and F8, or 0.041(1)
Å for I2, C17, C27, F1, and F5) from the least squares plane. Other I/F
and I/O interactions (I1/F3, I1/F6, I2/F3, I2/F6, I1/O1, and
I2/O2) are very weak and considerably deviate from the linearity
of hypervalent 3ce4e bonding.26
Figure 2 shows a similar dimeric structure of (Z)-
b-benzoyloxy-
vinyl-
l
3-iodane 2a. Two closely related molecules in the dimer unit
adopt a distorted square-planar arrangement around the iodine
atoms.
2.3. Product analysis
The results for vinylic substitution of (E)- and (Z)-b-(2-phenyl-
Figure 1. ORTEP drawing of vinyl-l
3-iodane (Z)-4. Selected bond lengths (Å) and an-
ethoxy)vinyl-
l
3-iodanes 4 with n-Bu4NX (X¼Cl, Br, and I) are
gles (deg): C1eI1 2.076(2), C11eI1 2.109(2), I1/F8 2.8969(15), I1/F2 3.0748(15),
I1/F3 3.3161(17), I1/F6 3.3798(19), I1/O1 3.1317(16), C17eI2 2.079(2), C27eI2 2.119
(2), I2/F5 2.9076(16), I2/F1 2.9893(13), I2/F6 3.298(2), I2/F3 3.3098(14), I2/O2
3.0826(18), C1eI1eC11 97.27(9), C17eI2eC27 94.80(9).
shown in Table 1. Reactions were carried out by using an excess of
n-Bu4NX (10 equiv) under heating. All of the reactions afforded
good yields of vinyl halides 8 via nucleophilic displacement at the
ipso vinylic position with halides, except for the reaction of (Z)-vi-
nyl-
noted that these substitutions predominantly proceed with in-
version of configuration at the -vinylic carbon atom of 4, which is
l
3-iodane (Z)-4 with n-Bu4NCl in THF (Table 1, entry 2). It is
a
compatible with the in-plane vinylic SN2 mechanism. In THF and
1,4-dioxane as solvents, both (E)- and (Z)-4 by the reaction with
chloride and bromide anions afforded the inverted b-(2-phenyl-
ethoxy)vinyl chloride 8a and bromide 8b with more than 97%
stereoselectivity (entries 1e6). Slightly decreased inversion of
configuration was observed in the reactions in acetonitrile (entries
7e10). Therefore, the reaction is highly stereoselective and the
overall substitutions are stereospecific. In addition, the vinylic
substitutions of (Z)-4 seem to be more rapid than those of the E-
isomer (E)-4.
Figure 2. ORTEP drawing of vinyl-l
3-iodane (Z)-2a. Selected bond lengths (Å) and
angles (deg): I1eC1 2.1084(13), I1eC7 2.0850(14), I1/F5 2.8530(8), I1/F1 2.9424(8),
I2eC16 2.1160(14), I2eC22 2.0780(14), I2/F2 2.8572(8), I2/F6 3.0691(8), C1eI1eC7
97.43(5), C16eI2eC22 96.51(5).
In contrast to the reaction of (E)-4 with chloride in THF at 65 ꢀC
(entry 1), which produced (Z)-vinyl chloride 8a selectively through
vinylic SN2 reaction, Z-isomer (Z)-4 gave regioisomeric vinyl chlo-
ride 9a as a major product (58%, entry 2), in which a chlorine atom
atom (F8 or F5) of tetrafluoroborate at an apical site of the iodine
center with a distance of I1/F8 2.8969(15) Å or I2/F5 2.9076(16)
Å and with a near linear triad, C1eI1/F8 (171.10ꢀ) or C27eI2/F5
(169.27ꢀ).25 Including an another close contact between I1/F2
is introduced at the b-vinylic carbon atom of 4. Vinyl bromide 9b
was also produced in the reaction of (Z)-4 with bromide anion,
albeit in a low yield (5%). Scheme 6 depicts a possible reaction
pathway, leading to the formation of vinyl halides 9a and 9b: the
Table 1
Nucleophilic substitutions of (E)- and (Z)-b-(2-phenylethoxy)vinyl-l
3-iodanes 4 with n-Bu4NXa
O
n-Bu4NX
O
X
X
Ph
O
Ph
+
Ph
I
Ph
(10 equiv)
FBF3
8a: X = Cl
8b: X = Br
8c: X = I
9a: X = Cl
9b: X = Br
4
Entry
l
3-Iodane
X
Solvent
Temp. (ꢀC)
Time (h)
Product, Yieldb (%)
4
8a (E/Z)
8b (E/Z)
8c (E/Z)
9a
9b
1
(E)-4
(Z)-4
(E)-4
(Z)-4
(E)-4
(Z)-4
(E)-4
(Z)-4
(E)-4
(Z)-4
Cl
Cl
Br
Br
Br
Br
Br
Br
I
THF
THF
THF
THF
1,4-Dioxane
1,4-Dioxane
CH3CN
CH3CN
CH3CN
CH3CN
65
65
65
65
65
65
81
81
81
81
72
4
24
2
67
4
36
5
74 (3:97)
d
5 (100:0)
d
5 (100:0)c
d
d
58
d
d
d
d
5c
d
1c
d
d
d
d
2
13 (100:0)c
d
3d
4
d
d
d
d
d
d
d
d
61 (3:97)
67 (97:3)
80 (<1:>99)
77 (98:2)
75 (15:85)
66 (95:5)
d
5
6
7
8
9
10
1 (100:0)
d
d
d
d
d
d
d
d
d
18
1.5
88 (11:89)
87 (96:4)
I
d
a
Initial concentration: vinyl-
Isolated yields.
NMR yields.
l
3-iodane 4, 0.01 M; n-Bu4NX, 0.1 M.
b
c
d
PhI (56%) and PhBr (2%) were obtained.

5822
K. Miyamoto et al. / Tetrahedron 66 (2010) 5819e5826
reaction probably involves a stereoelectronically preferred anti
-elimination of phenyl- -elimina-
3-iodanyl group27 and/or an
in an exclusive elimination reaction of (Z)-4 and produced ynol ether
10 in a high yield (87%), while interestingly (E)-4 was recovered
unchanged under the conditions.
b
l
a
tion-1,2-rearrangement sequence,13,28 yielding ynol ether 10. Sub-
sequent addition reaction of hydrogen chloride and bromide,
generated in situ, toward ynol ether 10 will occur in a Markovnikov
fashion to give vinyl halides 9.29 A higher yield of vinyl chloride 9a,
compared to that of vinyl bromide 9b, probably reflects the
differences in basicity between chloride and bromide anions.30,31
2.4. Kinetic measurements
Rates for nucleophilic substitutions of various kinds of
b-
substituted vinyl-
l
3-iodanes 1, 2, and 4 with tetrabutylammonium
halides were measured spectrophotometrically by monitoring the
decrease in an absorbance in the range of 250e330 nm. Pseudo-
first-order rate constants kobsd were obtained throughout each runs
and the values for 2e5 runs were averaged. Table 2 shows the values
for the observed first-order rate constants kobsd determined for the
n-Bu4NX
X = Cl, Br
O
O
HX
Ph
(Z)-4
Ph
X
PhI, HBF4
10
9a,b
reactions of vinyl-
l
3-iodanes (6ꢁ10ꢂ5 M) in acetonitrile, THF, and
Scheme 6. A possible reaction pathway for formation of 9.
1,4-dioxane, which contain an excess n-Bu4NX (0.02 M). It is noted
that the observed value of 7.9ꢁ10ꢂ4 sꢂ1 for the reaction of (Z)-4 with
n-Bu4NCl inTHFat 50 ꢀC (Table 2, entry 13) probably reflects the rate
Reaction of (E)-4 with n-Bu4NBr in THF produced (Z)-vinyl
bromide (Z)-8b (59%) and PhI (56%) as major products (entry 3).
Detailed product analysis further indicated the formation of a small
amount of (E)-8b (2%), (E)-vinyl iodide (E)-8c (5%), and PhBr (2%).
As discussed in our previous report,13 these results clearly indicate
that the vinylic SN2 reaction of (E)-4 with bromide, yielding (Z)-8b
and PhI, competes with a ligand coupling reaction on iodine(III) of
of the anti b- and/or a-elimination, as shown in Table 1 (entry 2).
Table 2
Observed rate constants for the reaction of vinyl-
l
3-iodanes with tetrabuty-
lammonium halidesa
Entry
l
3-Iodane
X
Temp. (ꢀC)
Solvent
105kobsd/sꢂ1
1
2
3
4
5
6
7
8
(E)-1b
(E)-1b
(E)-1b
(Z)-2a
(Z)-2a
(Z)-2b
(Z)-2c
(Z)-2d
(Z)-4
(Z)-4
(Z)-4
(Z)-4
(Z)-4
Br
Br
I
25
22
25
60
50
60
60
60
60
50
50
60
50
60
60
50
50
60
CH3CN
THF
CH3CN
CH3CN
THF
CH3CN
CH3CN
CH3CN
CH3CN
THF
1,4-Dioxane
CH3CN
THF
120
1040
339
13.2
79.0
13.4
12.4
10.5
42.8
227
bromo-
l
3-iodane intermediates 11 to a discernible extent (Scheme
7).32 Thus, the ligand coupling on aromatic ipso carbon atom (LCAr
)
of 11a produces (E)-vinyl iodide (E)-8c and bromobenzene, while
that on vinylic ipso carbon atom (LCv) of 11b affords (E)-vinyl bro-
mide (E)-8b with retention of configuration and iodobenzene.
Br
Br
Br
Br
Br
Br
Br
Br
I
Cl
Br
Br
Br
Br
I
9
O
O
n-Bu4NBr
10
11
12
13
14
15
16
17
18
Ph
Ph
Br
Ph
Ph
(E)-4
47.0
130
I
I
Br
11a
11b
79.0
43.0
0.794
50.3
33.9
4.68
((Z)-4)2$18C6
(E)-4
(E)-4
(E)-4
(E)-4
CH3CN
CH3CN
THF
1,4-Dioxane
CH3CN
LCAr
LCv
+
+
(E)-8c
(E)-8b
PhBr
PhI
Scheme 7. A competing ligand coupling reaction.
a
Initial concentration: vinyl-
l
3-iodane, 6ꢁ10ꢂ5 M; n-Bu4NX, 0.02 M.
b
R¼n-C8H17
.
Thioamides have been shown to be good nucleophiles in the vi-
nylic SN2 reaction of (E)- -alkylvinyl-
3-iodanes 1.12 In fact, reaction
of (Z)- -(2-phenylethoxy)vinyl-
3-iodane (Z)-4 with N,N-dime-
As shown by the previous report of Okuyama, Ochiai, and co-
workers,4a nucleophilic substitutions of the -substituted vinyl-l3
b
l
b
-
b
l
iodanes with bromide anion in THF are always faster than those in
acetonitrile. A more effective hydrogen bonding between the latter
solvent and the halide anion, leading to the reduced nucleophilicity
of the anion, will be responsible at least in part for the decreased
rates of substitutions in acetonitrile.33
thylthiobenzamide in dichloromethane (40 ꢀC/27 h) proceeded in
an exclusive inversion of configuration via SN2 displacement and
afforded (E)-S-vinylthioimidonium tetrafluoroborate (E)-12 quan-
titatively (Scheme 8). Under the conditions, (E)-4 similarly produced
inverted (Z)-imidonium salt (Z)-12 selectively, but in contrast the
yield was found to be very low (14%) and a large amount (79%) of
(E)-4 was recovered unchanged. These results again indicate lower
reactivity of (E)-4 toward vinylic SN2 reaction than that of the Z-
isomer. Highly basic methoxide ion (NaOMe/MeOH/rt/1 h) resulted
2.5. Discussion
The observed rate constants, shown in Table 2, indicate that the
vinylic SN2 reactions of (Z)-b-(2-phenylethoxy)vinyl-l
3-iodane (Z)-4
with halides (Br, I) proceed more rapidly than those of the E-isomer,
especially for the reactions in acetonitrile solution. For instance,
reactions of (Z)-4 with bromide and iodide in acetonitrile are 54 and
28 times faster than those of (E)-4, respectively (compare entries 9
and 15; 12 and 18). A similar tendency for the reactivity difference
between (Z)- and (E)-4 but to a lesser extent (kZ-4/kE-4¼4.5 and 1.4)
was observed for the vinylic substitutions with bromide in THF and
1,4-dioxane (compare entries 10 and 16; 11 and 17).
The greater reactivity of the Z-isomer (Z)-4 toward the vinylic
SN2 reactions is probably ascribed to its higher ground state energy
due to a vicinal steric interaction between sterically demanding Ph
(CH2)2O and I(Ph)BF4 groups.34,35 In other words, steric assistance36
Ph
PhC(S)NMe2 (10 equiv)
CH2Cl2, 40 °C, 27 h, N2
O
(Z)-4
(E)-4
Ph
N+Me2
S
S
-
BF4
(E)-12
PhC(S)NMe2 (10 equiv)
CH2Cl2, 40 °C, 27 h, N2
O
N+Me2
-
BF4
Ph
Ph
(Z)-12
Scheme 8. Vinylic SN2 reaction with a thioamide.

K. Miyamoto et al. / Tetrahedron 66 (2010) 5819e5826
5823
would efficiently increase the reaction rates of (Z)-4 compared to
that of (E)-4, because the vicinal steric interaction of the Z-isomer
will be attenuated to some extent in the concerted vinylic SN2
energies estimated from isodesmic reactions decrease in the order
of -Me>H> -OH>
-F.38 A similar order of substituent effects on
b
b
b
the gas-phase SN2 reaction of imidoyl chlorides XN]CHCl (X¼Me,
H, F) with chloride anion has been calculated at the G2(þ)//MP2/6-
311þG** level.6e Thus, it seems reasonable to assume that the
transition state. The b-(2-phenylethoxy) group of (E)-4 could cause
steric and electrostatic repulsions toward the incoming halide ion
in the in-plane SN2 transition state.4a The rate of nucleophilic
substitutions depends on halide anions and decreases in the order
n-Bu4NI>n-Bu4NBr (entries 1, 3, 9, 12, 15, and 18).
ability of a
of vinyl-
increase in the order
b-substituent to stabilize the vinylic SN2 transition state
l
3-iodanes by hyperconjugative and inductive effects will
-PhCO2< -Ph(CH2)2O< -n-C8H17, which is in
b
b
b
Table 2 shows that, in both acetonitrile and THF solutions,
magnitude of the observed rate constants for the reactions of vinyl-
l
good agreement with our experimental results shown in Table 2.
3-iodanes with n-Bu4NBr decreases in the order (E)-1>(Z)-4>(Z)-
3. Conclusion
2a>(E)-4 (entries 1, 9, 4, and 15 in acetonitrile; entries 2, 10, 5, and
16 in THF). These reactivity orders seem to suggest that the pres-
Both isomers of (E)- and (Z)-
4 and (Z)- -aroyloxyvinyl-
3-iodanes (Z)-2 were prepared stereo-
selectively. These -substituted vinyl-
3-iodanes undergo nucleo-
b-(2-phenylethoxy)vinyl-l
3-iodanes
ence of an inductively electron-withdrawing group at the
tion of vinyl-
3-iodanes decreases the rate of nucleophilic vinylic
substitutions.37 In fact, introduction of an electron-withdrawing p-
Cl or p-CF3 group at the
-benzoyloxy substituent of (Z)-vinyl-l3
b-posi-
b
l
l
b
l
philic vinylic substitution reactions with tetrabutylammonium
halides (Cl, Br, and I). The observed inversion of configuration at the
ipso vinylic carbon atom in the reactions is compatible with a con-
certed vinylic SN2 mechanism. Kinetic measurements indicated that
b
-
iodane (Z)-2a tends to slightly decrease the rates of nucleophilic
vinylic substitutions in acetonitrile. A linear free energy relation-
ship (
r
¼ꢂ0.15) for the substituent effects in the reaction of (Z)-2
the rates for vinylic SN2 reaction of vinyl-l
3-iodane (Z)-4 with
with bromide anion with a correlation coefficient r of 0.97 was
found between log kAr/kPh and Hammett sp constants (Fig. 3).
halides are larger than those of the E-isomer, probably because of the
higher ground state energy of (Z)-4 caused by a vicinal steric
interaction between sterically demanding Ph(CH2)2O and I(Ph)BF4
groups. The observed rate constants for the reactions of vinyl-l3
-
iodanes with n-Bu4NBr decreased in the order (E)-1>(Z)-4>(Z)-2a>
(E)-4. Since buildup of partial positive charge at the vinylic ipso
carbon atom in the transition state of the concerted vinylic SN2
reaction is expected, vinyl-l a b-substituent,
3-iodanes with
showing the more efficient hyperconjugative and inductive effects,
react faster.
4. Experimental
4.1. General information
IR spectra were recorded on PerkineElmer 1720 FT-IR spec-
trometer. 1H and 13C NMR were recorded on a JEOL JNM-AL300 or
AL400 spectrometer. Chemical shifts are reported in parts per
million (ppm) downfield from internal Me4Si. Mass spectra (MS)
were obtained on either JEOL JMS-DX 300, JEOL-SX 102A, Waters
LCT Premier, or SHIMADZU Model GCMS-QP505 spectrometer.
Melting points were determined with a Yanaco micro melting
points apparatus and are uncorrected.
Figure 3. Hammett plot of log kAr/kPh vs sp constants for the reaction of (Z)-2.
Okuyama and Yamataka reported an ab initio MO (MP2/DZþd)
calculation for the vinylic SN2 reaction of vinyl(methyl)iodonium ion
with chloride anion (Scheme 9), which indicates that the transition
state geometry of the concerted vinylic SN2 displacement is quite
loose with a small degree of CeCl bond formation (2.622 Å) and with
a large extent of CeI(III) bond cleavage (2.496 Å).6b Therefore,
a considerable positive charge will be developed at the vinylic ipso
carbon atom in the transition state. Double bond distance (1.317 Å)
becomes significantly shorter than that of the vinyl(methyl)iodo-
nium ion, probably reflecting the substantial hyperconjugative sta-
Substrates. (E)-1-Decenyl(phenyl)(tetrafluoroborato)-
(1)27 was prepared by boroneiodine(III) exchange reaction. Ethynyl
(phenyl)(tetrafluoroborato)-
3-iodane (3)18 and trimethylsilyle-
l
3-iodane
l
thynyl(phenyl)(tetrafluoroborato)-l
3-iodane (5)18 were purchased
from Tokyo Kasei Kogyo Co. Ltd.
4.2. Synthesis of
and (E)-4, and (Z)-
b
-(2-phenylethoxy)vinyl-
3-iodanes (Z)-
-(2-phenylethoxy)vinyl-l
3-iodane$18C6 2:1
l
bilization between
s
(C
beH) and
s
*
(C
aeI) orbitals, evoked by the
b
buildup of partial positive charge at the vinylic
a
-carbon atom.
complex 6
Similar MO calculations havebeen reportedfor the gas-phase vinylic
SN2 reaction of vinyl chloride with nucleophiles.6d,e
4.2.1. Reaction of ethynyl(phenyl)-
alcohol: preparation of (Z)-[ -(2-phenylethoxy)vinyl](phenyl)(tetra-
fluoroborato)-
3-iodane (Z)-(4). Ethynyl(phenyl)(tetrafluoroborato)-
3-iodane (3) (14 mg, 0.044 mmol) was dissolved in phenethyl
alcohol (1.3 mL) under argon and the solution was stirred for 5.5 h at
room temperature. Evaporation of the solvent under reduced pres-
sure, followed by repeated decantation at room temperature with
l 3 with phenethyl
3-iodane
-
b
Cl
2.622
l
H
H
H
+
H
H
H
H
Cl
1.333
2.114
-
1.317
H
1.335
Cl
l
1.729
- MeI
I Me
H
2.496
+
I Me
hexane and then with diethyl ether, gave (Z)-b-(2-phenylethoxy)vi-
Scheme 9. Calculated vinylic SN2 reaction of vinyl(methyl)iodonium ion with chloride.
nyl-l
3-iodane 4 (15 mg, 73%): colorless prisms (recrystallized from
Ab initio MO calculations indicate that, for the
vinyl cations XCH]CHþ, both the hyperconjugative effect between
(CeX) and empty 2p(Cþ) orbitals and the X inductive effect con-
trol the stability of the vinyl cations, and the vinyl stabilization
b
-substituted
dichloromethane/hexane at ꢂ20 ꢀC); mp 61e61.5 ꢀC; IR (KBr) 3120,
1614, 1285, 1150e900, 744, 706 cmꢂ1 1H NMR (400 MHz, CDCl3)
;
s
d
7.74 (d, J¼8.2 Hz, 2H), 7.55 (t, J¼7.7 Hz, 1H), 7.37 (dd, J¼8.2, 7.7 Hz,
2H), 7.33e7.19 (m, 3H), 7.15 (d, J¼7.0 Hz, 2H), 6.97 (d, J¼3.3 Hz, 1H),

5824
K. Miyamoto et al. / Tetrahedron 66 (2010) 5819e5826
5.97 (d, J¼3.3 Hz,1H), 4.38(d, J¼6.6 Hz, 2H), 2.95(d, J¼6.6 Hz, 2H);13
C
(dd, J¼8.2, 7.4 Hz, 2H), 7.35e7.17 (m, 5H), 6.11 (d, J¼12.9 Hz, 1H),
4.29 (d, J¼6.9 Hz, 2H), 3.04 (d, J¼6.9 Hz, 2H); 13C NMR (75 MHz,
NMR (75 MHz, CDCl3)
d 160.1, 136.7, 134.6, 132.3, 132.2, 129.1, 128.9,
127.6, 110.9, 76.1, 70.6, 36.0. Anal. Calcd for C16H16BF4IO: C, 43.87; H,
3.68. Found: C, 43.70; H, 3.66.
CDCl3) d 167.0, 136.9, 134.0, 132.3, 132.1, 129.0, 128.6, 126.8, 112.2,
72.8, 70.7, 35.2; HRMS (FAB, positive) calcd for C16H16IO [(MꢂBF4)þ]
351.0246, found 351.0241.
4.2.2. Reaction of trimethylsilylethynyl-l
3-iodane 5 with phenethyl
alcohol: preparation of (Z)-vinyl-
thynyl(phenyl)(tetrafluoroborato)-
l
3-iodane (Z)-4. Trimethylsilyle-
4.3. General procedure for preparation of (Z)-
(phenyl)(tetrafluoroborato)-
3-iodanes 2aed. A typical
example: (Z)-( -benzoyloxyvinyl)(phenyl)(tetrafluoroborato)-
3-iodane (2a)
b-aroyloxyvinyl
l
3-iodane (5) (60 mg, 0.16 mmol)
l
was dissolved in phenethyl alcohol (1.2 mL) and the solution was
stirred for 27 h at room temperature. After addition of dichloro-
methane (1 mL), diethyl ether (1 mL), and hexane (10 mL), the mix-
ture was allowed to stand at room temperature for 1 h. The
supernatant was removed and the residue was washed several times
with hexane and diethyl ether by decantation at room temperature to
b
l
To a mixture of ethynyl(phenyl)(tetrafluoroborato)-l
3-iodane
(3) (650 mg, 2.1 mmol), benzoic acid (2.3 g, 19 mmol), and sodium
benzoate (59 mg, 0.41 mmol) was added methanol (50 mL) at room
temperature under argon and the solution was stirred for 2 h. The
solvent was evaporated under reduced pressure. To remove excess
benzoic acid, the residue was washed several times with diethyl
ether by decantation. The crude product was dissolved in methanol
and the solution was vigorously shaken with a saturated aqueous
NaBF4 solution two times. The organic layer was filtered and con-
give l
3-iodane(Z)-4(49 mg,72%)asapaleyellowoil. Recrystallization
from dichloromethane/hexane at ꢂ20 ꢀC gave colorless prisms.
4.2.3. Reaction of trimethylsilylethynyl-
alcohol in the presence of 18C6: preparation of (Z)-vinyl-l3
iodane$18C6 2:1 complex 6. To a mixture of trimethylsilylethynyl-
3-iodane
(300 mg, 0.77 mmol) and 18-crown-6 (102 mg,
l
3-iodane 5 with phenethyl
-
l
5
centrated under aspirator vacuum to give (Z)-(
phenyl-
3-iodane 2a (690 mg, 76%). Recrystallization from di-
chloromethane/hexane gave colorless needles.13
b-benzoyloxyvinyl)
0.39 mmol) was added phenethyl alcohol (22 mL) at room tem-
perature and the solution was stirred for 47 h. After addition of
ethyl acetate (20 mL) and hexane, the reaction mixture was allowed
to stand at ꢂ20 ꢀC for 30 min to give the complex 6 (310 mg, 69%):
colorless prisms (recrystallized from dichloromethane/hexane at
ꢂ20 ꢀC); mp 90e91 ꢀC; IR (Nujol) 3130, 1610, 1232, 1150e900, 833,
l
4.3.1. (Z)-[b-(4-Methylbenzoyloxy)vinyl](phenyl)(tetrafluoroborato)-
l
3-iodane (2b). Colorless needles (recrystallized from dichloro-
methane/ether at ꢂ20 ꢀC): mp 129e130 ꢀC; IR (KBr) 1749, 1607,
736, 704 cmꢂ1
;
1H NMR (400 MHz, CDCl3)
d
7.74 (d, J¼8.0 Hz, 4H),
1150e900, 742 cmꢂ1; 1H NMR (400 MHz, CDCl3)
d
8.21 (d, J¼3.9 Hz,
7.62 (d, J¼7.0 Hz, 2H), 7.41 (dd, J¼8.0, 7.0 Hz, 4H), 7.36e7.21 (m, 6H),
7.17 (d, J¼7.3 Hz, 4H), 6.89 (d, J¼3.5 Hz, 2H), 5.93 (d, J¼3.5 Hz, 2H),
4.43 (t, J¼5.9 Hz, 4H), 3.67 (s, 24H), 3.02 (t, J¼5.9 Hz, 4H); 13C NMR
1H), 8.01 (d, J¼8.4 Hz, 2H), 7.98 (d, J¼8.4 Hz, 2H), 7.61 (t, J¼7.2 Hz,
1H), 7.45 (t, J¼8.4 Hz, 2H), 7.35 (t, J¼8.4 Hz, 2H), 6.60 (d,
J¼3.9 Hz, 1H), 2.45 (s, 3H); HRMS (FAB, positive) calcd for C16H14IO2
[(MꢂBF4)þ] 365.0039, found 365.0088. Anal. Calcd for
C16H14BF4IO2: C, 42.52; H, 3.12. Found: C, 42.29; H, 3.41.
(75 MHz, CDCl3)
d 159.6, 136.7, 134.8, 132.0, 131.8, 128.9, 128.7,
126.9, 111.4, 75.7, 71.0, 69.8, 35.9. Anal. Calcd for C44H56B2F8I2O8: C,
46.34; H, 4.94. Found: C, 46.04; H, 4.87.
4.3.2. (Z)-[b-(4-Chlorobenzoyloxy)vinyl](phenyl)(tetrafluoroborato)-
4.2.4. Preparation of (E)-[
(phenyl)(tetrafluoroborato)-
a
-trimethylsilyl-
b
-(2-phenylethoxy)vinyl]
l
3-iodane (2c). Colorless prisms (recrystallized from dichloro-
l
3-iodane (7). To a stirred solution of
methane/hexane at ꢂ20 ꢀC); mp 138e139 ꢀC; IR (KBr) 1752, 1591,
iodosylbenzene (0.18 g, 0.80 mmol), bis(phenethyl) ether (0.90 g,
4.0 mmol), and ethynyl(trimethyl)silane (0.24 g, 2.4 mmol) in
dichloromethane (6.0 mL) was added 1.0 M dichloromethane so-
lution of BF3ebis(phenethyl) ether complex (0.8 mL, 0.80 mmol) at
0 ꢀC under nitrogen and the mixture was stirred at room temper-
ature for 15 h. After addition of a cold water, the mixture was
extracted with dichloromethane four times. The combined organic
phase was washed with a cold saturated aqueous solution of NaBr
(2 mL) two times, and then with saturated aqueous solution of
NaBF4 (2 mL) four times. After filtration of the organic phase,
dichloromethane was evaporated under aspirator vacuum to give
an oil, which was washed several times with hexane by decantation
1150e900, 742 cmꢂ1; 1H NMR (400 MHz, CDCl3)
d
8.21 (d, J¼4.1 Hz,
1H), 8.06 (d, J¼8.4 Hz, 2H), 8.00 (d, J¼8.4 Hz, 2H), 7.63 (t, J¼7.7 Hz,
1H), 7.53 (d, J¼8.4 Hz, 2H), 7.47 (dd, J¼8.4, 7.7 Hz, 2H), 6.61 (d,
J¼4.1 Hz, 1H); HRMS (FAB, positive) calcd for C15H11ClIO2
[(MꢂBF4)þ] 384.9492, found 384.9492. Anal. Calcd for
C15H11BF4ClIO2$2/5H2O: C, 37.56; H, 2.48. Found: C, 37.85; H, 2.88.
4.3.3. (Z)-{
fluoroborato)-
b-[4-(Trifluoromethyl)benzoyloxy]vinyl}(phenyl)(tetra-
l
3-iodane (2d). Colorless needles (recrystallized from
dichloromethane/ether/hexane at ꢂ20 ꢀC); mp 106e107 ꢀC; IR
(KBr) 1749, 1626, 1200e950, 735 cmꢂ1 1H NMR (400 MHz, CDCl3)
;
d
8.26 (d, J¼7.9 Hz, 2H), 8.22 (d, J¼3.8 Hz,1H), 8.01 (d, J¼8.2 Hz, 2H),
at room temperature to give (E)-
ethoxy)vinyl-
3-iodane 7 (120 mg, 26%) as a pale yellow oil: IR
(neat) 3060, 1574, 1266, 1167, 1150e950, 847, 738 cmꢂ1 1H NMR
(400 MHz, CDCl3)
a
-trimethylsilyl-
b
-(2-phenyl-
7.81 (d, J¼7.9 Hz, 2H), 7.63 (t, J¼7.3 Hz, 1H), 7.47 (dd, J¼8.2, 7.3 Hz,
2H), 6.67 (d, J¼3.8 Hz, 1H); HRMS (ESI, positive) calcd for
C16H11F3IO2 [(MꢂBF4)þ] 418.9756, found 418.9731.
l
;
d
8.11 (s, 1H), 7.83 (d, J¼8.5 Hz, 2H), 7.60 (t,
J¼7.4 Hz, 1H), 7.46 (dd, J¼8.5, 7.4 Hz, 2H), 7.35e7.18 (m, 5H), 4.52 (t,
J¼7.0 Hz, 2H), 3.05 (t, J¼7.0 Hz, 2H), 0.11 (s, 9H); HRMS (ESI, posi-
tive) calcd for C19H24IOSi [(MꢂBF4)þ] 423.0641, found 423.0653.
4.4. General procedure for the reaction of (E)- and (Z)-
(2-phenylethoxy)vinyl-
3-iodanes 4 with tetrabutylammonium
halides. A typical example (Table 1, entry 3)
b-
l
4.2.5. Synthesis of (E)-[
b
-(2-phenylethoxy)vinyl](phenyl)(tetrafluoro-
To a stirred solution of (E)-vinyl-l
3-iodane (E)-4 (4.3 mg,
borato)-
l
3-iodane (E)-(4). Vinyl-
l
3-iodane 7 (120 mg, 0.21 mmol)
0.0097 mmol) in THF (1 mL) was added tetrabutylammonium bro-
mide (31 mg, 0.096 mmol) at room temperature under nitrogen and
the mixture was heated at 65 ꢀC for 24 h. After cooling, the mixture
was poured into water and extracted with pentane (5 mL). The
combined organic phase was washed with water four times, filtered,
and analyzed by GC using a capillary column of FFS ULBON HR-1
(0.25 mmꢁ50 m, 100 ꢀC, undecane as an internal standard): iodo-
benzene (56%) and bromobenzene (2%). The mixture was dried over
was dissolved in methanol (4.0 mL, 99 mmol) under argon and the
solution was stirred for 48 h at room temperature. Evaporation of
the solvent under reduced pressure, followed by repeated de-
cantation with hexane at 0 ꢀC gave (E)- -(2-phenylethoxy)vinyl-l3
b -
iodane (E)-4 (78 mg, 85%) as a pale yellow oil; IR (neat) 3092, 1586,
1160, 1130e1000, 990, 739 cmꢂ1; 1H NMR (400 MHz, CDCl3)
7.89
(d, J¼8.2 Hz, 2H), 7.65 (d, J¼12.9 Hz, 1H), 7.63 (t, J¼7.4 Hz, 1H), 7.48
d

K. Miyamoto et al. / Tetrahedron 66 (2010) 5819e5826
5825
anhydrous Na2SO4 and concentrated at 0 ꢀC under an aspirator
vacuum to give an oil. The yields of (E)- -(2-phenylethoxy)vinyl
intensity) 228 [<0.1%, Mþ
79 (19), 77 (15).
(
81Br)], 226 [<0.1%, Mþ
(
79Br)], 105 (100),
b
bromide (E)-(8b) (2%) and (E)-b-(2-phenylethoxy)vinyl iodide (E)-
(8c) (5%) were determined by integration of the 1H NMR spectrum of
the crude reaction mixture. Preparative TLC (hexane/diethyl ether,
4.5. Nucleophilic substitutions of (E)- and (Z)-
b-(2-
phenylethoxy)vinyl-
l
3-iodane 4 with thioamide.
9:1) gave (Z)-
59%) as a colorless oil: IR (neat) 3107, 2935, 1643, 1496, 1454, 1317,
1238, 1105, 750, 698 cmꢂ1 1H NMR (400 MHz, CDCl3)
7.36e7.16
b
-(2-phenylethoxy)vinyl bromide (Z)-(8b) (1.3 mg,
A representative example: reaction of (Z)-4 with N,N-
dimethylthiobenzamide
;
d
(m, 5H), 6.57 (d, J¼4.0 Hz,1H), 5.10 (d, J¼4.0 Hz,1H), 4.10 (t, J¼7.3 Hz,
To a stirred solution of (Z)-vinyl-l 4 (8.0 mg,
3-iodane
1H), 3.00 (t, J¼7.3 Hz, 1H); MS m/z (relative intensity) 228 [7%, Mþ
0.018 mmol) in dichloromethane (1.3 mL) was added N,N-dime-
thylthiobenzamide (30 mg, 0.18 mmol) at room temperature under
argon and the mixture was heated at 40 ꢀC for 27 h. After the so-
lution was concentrated under an aspirator vacuum to one-half of
its original volume, addition of hexane (5 mL) separated a pale
yellow oil, which was washed several times with hexane/diethyl
(
81Br)], 226 [7, Mþ 79Br)], 105 (100), 91 (12), 79 (20), 77 (21); HRMS
(
m/z calcd for C10H11BrO (Mþ) 225.9993, found 226.0001.
4.4.1. (E)-
IR (neat) 3101, 2925, 1620, 1496, 1454, 1387, 1317, 1176, 748,
698 cmꢂ1 1H NMR (300 MHz, CDCl3)
7.37e7.16 (m, 5H), 6.67 (d,
b-(2-Phenylethoxy)vinyl chloride (E)-(8a). A colorless oil;
;
d
ether by decantation to give (E)-S-[b-(2-phenylethoxy)vinyl]-N,N-
J¼11.3 Hz, 1H), 5.49 (d, J¼11.3 Hz, 1H), 3.90 (t, J¼6.9 Hz, 2H), 2.97 (t,
J¼6.9 Hz, 2H); MS m/z (relative intensity) 182 (2%, Mþ), 105 (100),
91 (8), 79 (14), 77 (15); HRMS (ESI, positive) calcd for C10H11ClNaO
[(MþNa)þ] 205.0396, found 205.0401.
(dimethyl)thiobenzimidonium tetrafluoroborate (E)-(12) (7.4 mg,
100%) as a pale yellow oil; IR (neat) 2947, 1616, 1601, 1496, 1288,
1100e1000, 758, 702 cmꢂ1; 1H NMR (300 MHz, CDCl3)
d 7.56e7.46
(m, 3H), 7.42e7.33 (m, 2H), 7.33e7.18 (m, 3H), 7.05 (d, J¼7.0 Hz, 2H),
6.84 (d, J¼16.1 Hz, 1H), 4.65 (d, J¼16.1 Hz, 1H), 3.80 (s, 3H), 3.72 (t,
J¼6.6 Hz, 2H), 3.47 (s, 3H), 2.76 (t, J¼6.6 Hz, 2H); HRMS (FAB, pos-
itive) calcd for C19H22NOS [(MꢂBF4)þ] 312.1422, found 312.1426.
4.4.2. (Z)-
IR (neat) 3103, 2931, 1651, 1496, 1454, 1329, 1246, 1113, 750,
700 cmꢂ1 1H NMR (400 MHz, CDCl3)
7.37e7.16 (m, 5H), 6.31 (d,
b-(2-Phenylethoxy)vinyl chloride (Z)-(8a). A colorless oil;
;
d
J¼4.0 Hz, 1H), 5.12 (d, J¼4.0 Hz, 1H), 4.09 (t, J¼7.5 Hz, 2H), 3.00 (t,
J¼7.5 Hz, 2H); MS m/z (relative intensity) 182 (2%, Mþ), 105 (100),
91 (7), 79 (2), 77 (3); HRMS (ESI, positive) calcd for C10H11ClNaO
[(MþNa)þ] 205.0396, found 205.0402.
4.5.1. (Z)-S-[
benzimidonium tetrafluoroborate (Z)-(12). A pale yellow oil; IR
(neat) 2925, 1620, 1446, 1286, 1200e950, 760, 702 cmꢂ1 1H NMR
(400 MHz, CDCl3) 7.59e7.44 (m, 3H), 7.42e7.18 (m, 7H), 6.30 (d,
J¼4.8 Hz, 1H), 4.47 (d, J¼4.8 Hz, 1H), 4.11 (t, J¼6.8 Hz, 2H), 3.82 (s,
3H), 3.46 (s, 3H), 2.98 (t, J¼6.8 Hz, 2H); HRMS (ESI, positive) calcd
for C19H22NOS [(MꢂBF4)þ] 312.1422, found 312.1407.
b-(2-Phenylethoxy)vinyl]-N,N-(dimethyl)thio-
;
d
4.4.3. (E)-
IR (neat) 3101, 2924, 1632, 1601, 1496, 1454, 1321, 1163, 749,
699 cmꢂ1 1H NMR (400 MHz, CDCl3)
7.34e7.18 (m, 5H), 6.76 (d,
b-(2-Phenylethoxy)vinyl bromide (E)-(8b). A colorless oil;
;
d
J¼11.8 Hz, 1H), 5.37 (d, J¼11.8 Hz, 1H), 3.92 (t, J¼7.0 Hz, 2H), 2.97 (t,
4.6. Reaction of (Z)-b-(2-phenylethoxy)vinyl-l
3-iodane
(Z)-4 with sodium methoxide
J¼7.0 Hz, 2H); MS m/z (relative intensity) 228 [10%, Mþ
(
81Br)], 226
[10, Mþ 79Br)], 105 (100), 79 (42), 77 (36); HRMS m/z calcd for
(
C10H11BrO (Mþ) 225.9993, found 226.0005.
To a stirred solution of (Z)-vinyl-l
3-iodane 4 (5.4 mg, 0.012 mmol)
in methanol (1 mL) was added a 0.49 M methanol solution of sodium
methoxide (25 L, 0.012 mmol) at room temperature under argon
4.4.4. (E)-
(neat) 3084, 2924,1626,1597,1456,1219,1146,1097, 750, 698 cmꢂ1
1H NMR (400 MHz, CDCl3)
1H), 5.06 (d, J¼12.5 Hz, 1H), 3.96 (t, J¼7.3 Hz, 2H), 2.98 (t, J¼7.3 Hz,
2H); MS m/z (relative intensity) 274 (10%, Mþ), 105 (100), 91 (12), 79
(30), 77 (24); HRMS m/z calcd for C10H11IO (Mþ) 273.9855, found
273.9856.
b
-(2-Phenylethoxy)vinyl iodide (E)-(8c). A colorless oil; IR
m
;
and the mixture was stirred for 1 h. The mixture was poured into
water and extracted with dichloromethane four times. The combined
organic phases were dried over anhydrous Na2SO4, filtered, and
concentrated at 0 ꢀC under an aspirator vacuum to give an oil, which
was purified by preparative TLC (hexane/ethyl acetate, 9:1) to give (2-
phenylethoxy)acetylene (10) (1.6 mg, 87%) as a colorless oil; IR (neat)
d
7.35e7.16 (m, 5H), 6.81 (d, J¼12.5 Hz,
3313, 2952, 2148, 1496, 1456, 1375, 1103, 748, 698 cmꢂ1
;
1H NMR
4.4.5. (Z)-
(neat) 3091, 2929, 1626, 496, 1454, 1309, 1221, 1097, 750, 700 cmꢂ1
1H NMR (400 MHz, CDCl3)
1H), 4.93 (d, J¼3.8 Hz, 1H), 4.13 (t, J¼7.3 Hz, 2H), 3.00 (t, J¼7.3 Hz,
2H); MS m/z (relative intensity) 274 (44%, Mþ),105 (100), 91 (13), 79
(16), 77 (17); HRMS m/z calcd for C10H11IO (Mþ) 273.9855, found
273.9856.
b
-(2-Phenylethoxy)vinyl iodide (Z)-(8c). A colorless oil; IR
(400 MHz, CDCl3) 7.37e7.29 (m, 2H), 7.29e7.18 (m, 3H), 4.26 (t,
d
;
J¼7.3 Hz, 2H), 3.08 (t, J¼7.3 Hz, 2H), 1.59 (s, 1H); MS m/z (relative in-
tensity) 146 (3%, Mþ),105 (100), 91 (66), 77 (47); HRMS (ESI, positive)
calcd for C10H9Na2O [(MꢂHþ2Na)þ] 191.0449, found 191.0458.
d
7.35e7.17 (m, 5H), 6.57 (d, J¼3.8 Hz,
4.7. Kinetic study (Table 2)
Rates for the reaction of vinyl-l
3-iodanes with tetrabuty-
4.4.6.
(neat) 3030, 2925, 2854, 1637, 1454, 1192, 1173, 1022, 698 cmꢂ1; 1H
NMR (400 MHz, CDCl3)
4.31 (d, J¼3.7 Hz, 1H), 4.05 (t, J¼7.3 Hz, 2H), 3.02 (t, J¼7.3 Hz, 2H);
MS m/z (relative intensity) 182 (12%, Mþ), 105 (100), 91 (12), 79
(28), 77 (29); HRMS (ESI, positive) calcd for C10H11ClNaO [(MþNa)þ]
205.0396, found 205.0393.
a
-(2-Phenylethoxy)vinyl chloride (9a). A colorless oil; IR
lammonium halides were measured by monitoring the decrease in
absorbance at 250e330 nm at different temperatures in the range
of 22e60 ꢀC on Shimadzu UV-160A spectrophotometer. The re-
action temperature was controlled by CPS-240A controller and
d
7.38e7.17 (m, 5H), 4.35 (d, J¼3.7 Hz, 1H),
accurate to within ꢃ0.1 ꢀC. A stock solution of vinyl-
l
3-iodanes was
prepared by weighting and dissolving in 1,4-dioxane (0.017 M) and
stored in a refrigerator at ꢂ20 ꢀC. The reaction solutions were
prepared by weighting of n-Bu4NX and dissolving in CH3CN, THF,
and 1,4-dioxane (0.02 M) at room temperature. To a solution
(3.0 mL) of n-Bu4NX in a quartz cuvette inserted in a cell com-
partment of the spectrophotometer and equilibrated at the reaction
Formation of
a-(2-phenylethoxy)vinyl bromide (9b) was
detected by 1H NMR and GC/MS, but it was too labile to be isolate.
4.4.7.
a
-(2-Phenylethoxy)vinyl bromide (9b). 1H NMR (400 MHz,
7.35e7.15 (m, 5H), 4.74 (d, J¼3.7 Hz, 1H), 4.55 (d, J¼3.7 Hz,
1H), 4.05 (t, J¼7.3 Hz, 2H), 3.02 (t, J¼7.3 Hz, 2H); MS m/z (relative
CDCl3)
d
temperature was added 10
from a microsyringe. The absorbance change was fed to a computer
mL of stock solution vinyl-l
3-iodane

5826
K. Miyamoto et al. / Tetrahedron 66 (2010) 5819e5826
7. (a) Okuyama, T.; Takino, T.; Sueda, T.; Ochiai, M. J. Am. Chem. Soc. 1995, 117,
3360; (b) Ochiai, M. In Chemistry of Hypervalent Compounds; Akiba, K., Ed.;
Wiley-VCH: New York, NY, 1999, Chapter 12.
8. Stang, P. J.; Rappoport, Z.; Hanack, M.; Subramanian, L. R. Vinyl Cations; Aca-
demic: New York, NY, 1979.
9. (a) Yan, J.; Chen, Z.-C. Tetrahedron Lett. 1999, 40, 5757; (b) Yan, J.; Chen, Z.-C.
Synth. Commun. 1999, 29, 2867.
10. Okuyama, T.; Ochiai, M. J. Am. Chem. Soc. 1997, 119, 4785.
11. Ochiai, M.; Yamamoto, S.; Sato, K. Chem. Commun. 1999, 1363.
12. Ochiai, M.; Yamamoto, S.; Suefuji, T.; Chen, D.-W. Org. Lett. 2001, 3, 2753.
13. Ochiai, M.; Nishi, Y.; Hirobe, M. Tetrahedron Lett. 2005, 46, 1863.
14. Shiers,J. J.;Shipman, M.;Hayes, J.F.;Slawin,A.M.Z.J.Am.Chem.Soc.2004,126, 6868.
15. (a) Ando, K.; Kitamura, M.; Miura, K.; Narasaka, K. Org. Lett. 2004, 6, 2461; (b)
Miyauchi, H.; Chiba, S.; Fukamizu, K.; Ando, K.; Narasaka, K. Tetrahedron 2007,
63, 5940.
NEC PC-9821V13 through an interface and processed by a pseudo-
first-order kinetics program. The reaction followed pseudo-first-
order kinetics for at least four half-lives and pseudo-first-order rate
constants kobsd were calculated.
4.8. Crystallographic data
Crystallographic data were recorded on a Rigaku RAXIS-RAPID
imaging plate diffractometer with graphite monochromated Mo KR
radiation. The data were corrected for Lorentz and polarization ef-
fects. The structure was solved by the direct methods39 and expanded
using Fourier techniques.40 The non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were included but not refined.
Neutralatom scatteringfactorsweretakenfromCromerand Waber.41
The values for the mass attenuation coefficients are those of Creagh
and Hubbel.42 All calculations were performed using the teXsan43
crystallographic software package of Molecular Structure Corp.
X-ray data for (Z)-4: C16H16BF4IO, M¼438.01, T¼93 K, triclinic
space group P-1 (No. 2), a¼10.596(3) Å, b¼12.079(3) Å, c¼14.684
16. Yamaguchi, T.; Yamamoto, Y.; Fujiwara, Y.; Tanimoto, Y. Org. Lett. 2005, 7, 2739.
17. For anti Michael-type addition of alcohols to ethynyl(phenyl)(tetra-
fluoroborato)-
l
3-iodane$18-crown-6 complex, see: Ochiai, M.; Miyamoto, K.;
Suefuji, T.; Sakamoto, S.; Yamaguchi, K. Angew. Chem., Int. Ed. 2003, 42, 2191.
18. Ochiai, M.; Ito, T.; Takaoka, Y.; Masaki, Y.; Kunishima, M.; Tani, S.; Nagao, Y.
J. Chem. Soc., Chem. Commun. 1990, 118.
19. For complexation of hypervalent organo-l
3-iodanes with 18C6, see: (a) Ochiai, M.
Chem.Record 2007, 7,12; (b)Ochiai, M.Coord.Chem.Rev. 2006, 250, 2771;(c)Ochiai,
M.;Miyamoto,K.;Yokota,Y.;Suefuji, T.;Shiro,M.Angew. Chem.,Int.Ed. 2005, 44, 75;
(d) Ochiai, M.; Suefuji, T.; Miyamoto, K.; Shiro, M. Org. Lett. 2005, 14, 2893; (e)
Ochiai, M.; Suefuji, T.; Miyamoto, K.; Tada, N.; Goto, S.; Shiro, M.; Sakamoto, S.;
Yamaguchi, K. J. Am. Chem. Soc. 2003, 125, 769; (f) Ochiai, M.; Nishi, Y.; Goto, S.;
Shiro, M.; Frohn, H. J. J. Am. Chem. Soc. 2003, 125, 15304; (g) Ochiai, M.; Miyamoto,
K.; Shiro, M.; Ozawa, T.; Yamaguchi, K. J. Am. Chem. Soc. 2003, 125, 13006.
20. Ochiai, M.; Kunishima, M.; Fuji, K.; Shiro, M.; Nagao, Y. J. Chem. Soc., Chem.
Commun. 1988, 1076.
(3) Å,
a
¼110.52(2)ꢀ,
b
¼99.34(2)ꢀ,
g
¼99.06(2)ꢀ, V¼1689.5(7) Å3,
Z¼4, Dc¼1.722 g cmꢂ3
,
m
(Mo K
a
)¼19.347 cmꢂ1. A total of 16,263
reflections were collected; 7656 were unique. R¼0.024, Rw¼0.083.
CCDC registration number 761728.
X-ray data for 2a: C15H12BF4IO2, M¼437.97, T¼153 K, triclinic
space group P-1 (No. 2), a¼10.085(5) Å, b¼11.354(6) Å, c¼14.386
21. Kunishima, M. FIU Rep. 2003, 6, 130.
22. For synthesis of BF3eO(CH2CH2Ph)2, see: Hennion, G. F.; Hinton, H. D.;
Nieuwland, J. A. J. Am. Chem. Soc. 1933, 55, 2857.
(7) Å,
a
¼100.19(4)ꢀ,
b
¼101.84(5)ꢀ,
g
¼97.10(5)ꢀ, V¼1564.8(13) Å3,
23. For Michael-type addition of bromide anion to alkynyl-l
3-iodanes, see: (a) Ochiai,
Z¼4, Dc¼1.859 g cmꢂ3
,
m (Mo Ka
)¼20.936 cmꢂ1. A total of 15,352
M.; Uemura, K.; Masaki, Y. J. Am. Chem. Soc. 1993, 115, 2528; (b) Ochiai, M.; Ku-
nishima, M.; Nagao, Y.; Fuji, K.; Shiro, M.; Fujita, E. J. Am. Chem. Soc.1986,108, 8281.
24. Ochiai, M.; Kitagawa, Y.; Yamamoto, S. J. Am. Chem. Soc. 1997, 119, 11598.
25. These I/F distances are comparable to the reported value of 3.037 Å for 4- tert-
reflections were collected; 7098 were unique. R¼0.026, Rw¼0.045.
CCDC registration number 761727.
Copies of the data can be obtained, free of charge, on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: þ44 1223
336033 or e-mail: deposit@ccdc.cam.ac.uk).
butyl-1-cyclohexenyl(phenyl)(tetrafluoroborato)-l
3-iodane. See: Ochiai, M.;
Sumi, K.; Takaoka, M.; Kunishima, M.; Nagao, Y.; Shiro, M.; Fujita, E. Tetrahedron
1988, 44, 4095.
26. (a) Alcock, N. W. Adv. Inorg. Chem. Radiochem. 1972, 15, 1; (b) Alcock, N. W.
Bonding and Structure; Ellis Horwood: Chichester, UK, 1990; (c) Starbuck, J.;
Norman, N. C.; Orpen, A. G. New J. Chem. 1999, 23, 969; (d) Macikenas, D.;
Sktzypezak-Jankun, E.; Protasiewicz, J. Angew. Chem., Int. Ed. 2000, 39, 2007; (e)
Landrum, G. A.; Hoffmann, R. Angew. Chem., Int. Ed. 1998, 37, 1887.
27. Ochiai, M.; Oshima, K.; Masaki, Y. J. Chem. Soc., Chem. Commun. 1991, 869.
28. Ochiai, M.; Takaoka, Y.; Nagao, Y. J. Am. Chem. Soc. 1988, 110, 6565.
29. For hydrobromination of ynol ethers with hydrogen bromide, see: Glazunovae,
Y.; Lutsenko, S. V.; Efmova, I. V.; Trostyanskaya, I. G.; Kazankova, M. A. Russ. J.
Org. Chem. 1998, 34, 1104.
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Re-
search (B) (JSPS).
Supplementary data
30. For pKa values of hydrogen halides, see: Vollhardt, K. P. C.; Schore, N. E. Organic
Chemistry, Structure and Function; W.H. Freeman: New York, NY, 2007.
31. For proton affinities of bromide and chloride anions, see: (a) Gronert, S. J. Am.
Chem. Soc. 1993, 115, 10258; (b) Curtiss, L. A.; McGrath, M. P.; Blaudeau, J.; Davis,
N. E.; Binning, R. C.; Radom, L. J. Chem. Phys. 1995, 103, 6104.
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Chem. Lett. 1997, 955; (d) Finet, J. P. Ligand Coupling Reactions with Heteroatom
Compounds; Pergamon: Oxford, 1998.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tet.2010.04.041. These data in-
clude MOL files and InChIKeys of the most important compounds
described in this article.
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