Nucleophilic vinylic substitutions of (Z)-(2-aroyloxyvinyl)phenyl- λ3-iodanes with tetrabutylammonium halides: Vinylic S N2 reactions and ligand coupling on iodine(III)

Article abstract of DOI:10.1016/j.tetlet.2005.01.101

Treatment of (Z)-(β-benzoyloxyvinyl)phenyl-λ³- iodanes, readily prepared from ethynyl(phenyl)(tetrafluoroborato)- λ³-iodane via stereoselective Michael-type addition of benzoic acids in methanol in the presence of sodium benzoates, with tetrabutylammonium halides in THF at 65°C results in a vinylic S_N2 reaction to give the inverted (E)-β-benzoyloxyvinyl halides in high yields.

Full text of DOI:10.1016/j.tetlet.2005.01.101

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 1863–1866
Nucleophilic vinylic substitutions of
(Z)-(2-aroyloxyvinyl)phenyl-k3-iodanes with tetrabutylammonium
halides: vinylic SN2 reactions and ligand coupling on iodine(III)
Masahito Ochiai,* Yoshio Nishi and Masaya Hirobe
Faculty of Pharmaceutical Sciences, University of Tokushima, 1-78 Shomachi, Tokushima 770-8505, Japan
Received 15 December 2004; revised 14 January 2005; accepted 20 January 2005
Abstract—Treatment of (Z)-(b-benzoyloxyvinyl)phenyl-k3-iodanes, readily prepared from ethynyl(phenyl)(tetrafluoroborato)-k3-
iodane via stereoselective Michael-type addition of benzoic acids in methanol in the presence of sodium benzoates, with tetrabutyl-
ammonium halides in THF at 65 ꢀC results in a vinylic SN2 reaction to give the inverted (E)-b-benzoyloxyvinyl halides in high
yields.
ꢁ 2005 Elsevier Ltd. All rights reserved.
(E)-(b-Alkylvinyl)phenyl-k3-iodanes smoothly undergo
an unusual vinylic SN2 reaction under mild conditions
to give (Z)-vinylic compounds with exclusive inversion
of configuration.1–3 Hyper-nucleofugality of the phen-
yl-k3-iodanyl group is responsible for the unique vinylic
SN2 reaction.4 Nucleophiles that undergo vinylic SN2
reactions with (E)-(b-alkylvinyl)phenyl-k3-iodanes in-
volve halides,1 dialkyl sulfides and selenides,2a phospho-
roselenoates,5a dithiocarbamates,5b carboxylic acids,6
amides,7 and thioamides.8
n-C8H17
n-Bu4NCl
rt
Cl
n-C8H17
Ph
I
BF4
1
ClO4
Ph
n-Bu4NCl
rt
n-C8H17
I
n-C8H17
2
In a marked contrast, vinylic SN2 reactions of (Z)-iso-
mers of b-alkylvinyl-k3-iodanes have never been re-
ported. In fact, (Z)-1-decenyl-k3-iodane 2 does not
undergo vinylic SN2 displacement by the reaction with
excess amounts of tetrabutylammonium chloride in
dichloromethane at room temperature, but instead the
reaction affords 1-decyne quantitatively. On the other
hand, (E)-vinyl-k3-iodane 1 affords the inverted (Z)-1-
chlorodec-1-ene under the conditions in a high yield
(Scheme 1).1a Stereoelectronically preferred anti b-elim-
ination and/or a-elimination-1,2-rearrangement se-
quence will be responsible for the exclusive formation
of 1-decyne. The attempted vinylic SN2 reactions of 2
by using less basic nucleophiles such as dimethyl sulfide,
Scheme 1.
dibutyl selenide, dibutyl telluride, acetic acid, N,N-
dimethylformamide, and N,N-dimethylthioformamide
were found to be fruitless and all of these reactions pro-
duced 1-decyne. We are pleased to report that (Z)-(b-
aroyloxyvinyl)phenyl-k3-iodanes 3 undergo a vinylic
SN2 displacement by the reaction with tetrabutylammo-
nium halides.
The required (Z)-(b-benzoyloxyvinyl)phenyl-k3-iodanes
3 were directly prepared from the commercially avail-
able
ethynyl(phenyl)(tetrafluoroborato)-k3-iodane9
through a facile Michael-type addition of benzoic acids
(Scheme 2).10 Exposure of the ethynyl-k3-iodane to ex-
cess amounts of benzoic acid in the presence of sodium
benzoate (0.2 equiv) in methanol results in stereoselec-
tive Michael-type addition of benzoic acid at room
Keywords: Vinylic SN2 reaction; Hypervalent; Iodane; Ligand cou-
pling; Michael-type addition.
*
Corresponding author. Tel.: +81 88 633 7281; fax: +81 88 633
9504; e-mail: mochiai@ph.tokushima-u.ac.jp
0040-4039/$ - see front matter ꢁ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.01.101

1864
M. Ochiai et al. / Tetrahedron Letters 46 (2005) 1863–1866
ArCO2H (9 equiv)
ArCO2Na (0.2 equiv)
With the decreased concentration of n-Bu4NCl (0.01 M)
BF4
Ph
in refluxing THF, however, (Z)-isomer 5a as well as (Z)-
vinyl iodide 6a (Ar = Ph) were produced as minor prod-
ucts (entry 2). Larger amounts of these by-products were
obtained in the reaction with 0.001 M of n-Bu4NCl.
These results clearly indicate the existence of the com-
peting reaction pathway other than vinylic SN2 process
and the competing pathway becomes significant at lower
concentration of nucleophiles. In the nucleophilic substi-
tution of 3a with n-Bu4NBr and n-Bu4NI, similar con-
centration-dependent product profiles were observed,
as shown in Table 1. Thus, 0.1 M of n-Bu4NBr gave a
99:1 mixture of (E)- and (Z)-vinyl bromides, 4b and 5b
(Ar = Ph, X = Br), while an increased amount of (Z)-
isomer 5b was produced in the reaction using 0.001 M
of n-Bu4NBr (entries 4 and 6). Under the conditions,
no isomerization of these vinyl bromides 4b and 5b
was observed.
I
BF4
ArCO2
I
MeOH, rt
then aq NaBF4
Ph
3
3a: Ar = Ph, 3b: Ar = p-MeC6H4, 3c: Ar = p-ClC6H4
Scheme 2.
temperature yielding (Z)-(b-benzoyloxyvinyl)(phenyl)-
(tetrafluoroborato)-k3-iodane (3a) in a 76% yield as col-
orless needles, after ligand exchange by the reaction with
an aqueous NaBF4 solution. A small vicinal coupling
constant (J = 4.3 Hz) between the vinylic protons in
1H NMR indicates trans conjugate addition of benzoic
acid. p-Methyl 3b (66%) and p-chloro-k3-iodanes 3c
(66%) were also prepared.11
When a solution of k3-iodane 3a (4.7 · 10À4 M) and n-
Bu4NCl (0.1 M) in THF was heated under reflux for
4.5 h in nitrogen, the inverted (E)-b-benzoyloxyvinyl
chloride (4a) (Ar = Ph, X = Cl) was obtained in 55%
yield along with the formation of iodobenzene (84.6%)
(Table 1, entry 1). The substitution is exclusively stereo-
selective and the formation of the retained (Z)-isomer 5a
(Ar = Ph, X = Cl) was not detected at all. Interestingly,
detailed product analyses showed no evidences for the
formation of ethynyl benzoate, which was expected to
be produced by anti b- and/or a-elimination of 3a.12
The observed exclusive inversion of configuration in this
nucleophilic vinylic substitution is compatible with the
vinylic SN2 mechanism.
A vinylic SN2 reaction will be a major reaction course in
the nucleophilic substitution of (Z)-(b-benzoyloxyvinyl)-
k3-iodanes 3a with n-Bu4NX, which probably competes
with a ligand coupling reaction on iodine(III),13 as
shown in Scheme 3. Very rapid ligand exchange on iodi-
ne(III) in 3a with halides will produce the isomeric
vinyl(halo)-k3-iodanes 7 and 8 via addition–elimination
sequence involving the intermediacy of tetracoordinated
species.14 Both halo-k3-iodanes 7 and 8 equilibrate each
other through rapid pseudorotation on iodine(III)15 and
undergo a vinylic SN2 reaction to give the inverted (E)-
vinyl halides 4. Solvent-coordinated vinyliodonium ions
may participate in part in the vinylic SN2 reaction.1 The
Table 1. Nucleophilic substitutions of (Z)-(b-benzoyloxyvinyl)phenyl-k3-iodanes 3 with tetrabutylammonium halides in THF at 65 ꢀC under
nitrogena
BF4
ArCO2
ArCO2
n-Bu4NX
X
ArCO2
I
+
+
PhI
Ph THF, 65 °C
X
4
5: X = Cl, Br
6: X = I
3
Entry
3
n-Bu4NX
Product (yield (%))b
Ratio
X (M)
4
5
6
PhI
5:6
4:(5+6)
1
3a
3a
3a
3a
3a
3a
3a
3a
3b
3b
3b
3c
3c
3c
Cl (0.1)
55.0
61.1
42.0
98.4d
95.9d
72.4
77.4
71.7
96.2d
90
––
––
84.6
86.5
64.0c
95.5
94.9e
79.0e
75.4
77.8
85
75.8f
60.6e
68.2
70.5
52.4e
100:0
90:10
57:43
98:2
2
Cl (0.01)
Cl (0.001)
Br (0.1)
1.9
4.8
28:72
20:80
62:38
46:54
39:61
3
6.2
1.0d
1.9d
10.9
––
24.9
0.6d
2.2d
16.7
6.6
4
5
Br (0.01)
Br (0.001)
I (0.1)
96:4
72:28
92:8
6
7
8
I (0.01)
Br (0.1)
––
11.3
2.3d
6.5
86:14
96:4
9
1.5d
3.5
39:61
35:65
37:63
10
11
12
13
14
Br (0.01)
Br (0.001)
Br (0.1)
90:10
75:25
100:0
91:9
74.6
100
9.3
16.1
––
Br (0.01)
Br (0.001)
90.5
67.6
4.6
15.0
4.9
17.4
48:52
46:54
68:32
a [k3-Iodane 3] = 0.42–0.47 mM, reaction time = 2.5–7 h.
b GC yields.
c PhCl (2%) was obtained.
d 1H NMR yields.
e PhBr (1–3%) was obtained.
f PhBr (6%) was obtained.

M. Ochiai et al. / Tetrahedron Letters 46 (2005) 1863–1866
1865
4
the other hand, para-methyl substituent in 3b decreased
the ratios of 5:6 (compare entries 4–6 with 9–11).
n-Bu4NX
n-Bu4NX
PhCO2
SN2
In conclusion, we found the first example of vinylic SN2
reaction of (Z)-vinyl-k3-iodanes with n-Bu4NX yielding
the inverted (E)-vinyl halides. The reaction competes
with ligand coupling on iodine(III).
X
X
n-Bu4NX
PhCO2
I
I
3a
Ph
Ph
7
8
LCAr
LCv
References and notes
1. (a) Ochiai, M.; Oshima, K.; Masaki, Y. J. Am. Chem. Soc.
1991, 113, 7059; (b) Okuyama, T.; Takino, T.; Sato, K.;
Ochiai, M. J. Am. Chem. Soc. 1998, 120, 2275; (c)
Okuyama, T.; Takino, T.; Sato, K.; Oshima, K.; Imam-
ura, S.; Yamataka, H.; Asano, T.; Ochiai, M. Bull. Chem.
Soc. Jpn. 1998, 71, 243.
2. For reviews of nucleophilic vinylic substitutions of 1-
alkenyl(phenyl)-k3-iodanes, see: (a) Ochiai, M. J. Organo-
met. Chem. 2000, 611, 494; (b) Okuyama, T. Rev.
Heteroat. Chem. 1999, 21, 678; (c) Pirkuliev, N. Sh.; Brel,
V. K.; Zefirov, N. S. Russ. Chem. Rev. 2000, 69, 105; (d)
Koser, G. F. In The Chemistry of Halides, Pseudo-halides
and Azides, Supplement D2; Patai, S., Rappoport, Z., Eds.;
Wiley: New York, 1995; Chapter 21.
3. For intramolecular SN2 reactions of vinyl halides, see: (a)
Shiers, J. J.; Shipman, M.; Hayes, J. F.; Slawin, A. M. Z.
J. Am. Chem. Soc. 2004, 126, 6868; (b) Ando, K.;
Kitamura, M.; Miura, K.; Narasaka, K. Org. Lett. 2004,
6, 2461.
4. (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, 1999; Chapter 12.
+
+
6a
PhX
5 or 6a
PhI
Scheme 3.
competing ligand coupling on aromatic ipso carbon
atom (LCAr) of 7 produces (Z)-vinyl iodide 6a and halo-
benzenes, while that on vinylic carbon atom (LCV) of 8
affords (Z)-vinyl halides 5 or 6a with retention of config-
uration and iodobenzene.
The results shown in Table 1 clearly indicate that the ra-
tios of the vinylic SN2 reaction to the ligand coupling on
iodine(III), 4:(5 + 6), decrease with the decreasing con-
centration of halide nucleophiles. These tendencies
probably reflect the differences in the reaction order with
respect to halide nucleophiles, that is, second-order in
the vinylic SN2 reaction while first order in the ligand
coupling.
Although a detailed mechanism of ligand coupling on
iodine(III) has remained obscure,16 it seems reasonable
to assume that the reaction of 3a with n-Bu4NCl and
n-Bu4NBr yielding (Z)-vinyl iodide 6a and (Z)-vinyl ha-
lides (Cl, Br) 5 probably proceeds via partially polarized
transition states, 9 for LCAr and 10 for LCV (Scheme
4).14 A closely related transition state structure for the
vinylic ligand coupling LCV has been proposed by ab
initio MO (MP2) calculations of the reaction of
chloro(divinyl)-k3-iodane.16a The presence of an elec-
tron-withdrawing para-chlorine on the b-benzoyloxy
group in 3c may stabilize a partial negative charge devel-
oped on the b-vinylic carbon atom in the LCV transition
state. This type of substituent effect could not be anti-
cipated in the transition state of LCAr. These arguments
are in good agreement with our experimental results,
which show larger ratios of 5:6 in the reaction of 3c than
that of 3a (compare entries 5 and 6 with 13 and 14). On
5. (a) Yan, J.; Chen, Z.-C. Tetrahedron Lett. 1999, 40, 5757;
(b) Yan, J.; Chen, Z.-C. Synth. Commun. 1999, 29,
2867.
6. Okuyama, T.; Ochiai, M. J. Am. Chem. Soc. 1997, 119,
4785.
7. Ochiai, M.; Yamamoto, S.; Sato, K. Chem. Commun.
1999, 1363.
8. Ochiai, M.; Yamamoto, S.; Suefuji, T.; Chen, D.-W. Org.
Lett. 2001, 3, 2753.
9. Ethynyl(phenyl)(tetrafluoroborato)-k3-iodane was pur-
chased from Tokyo Kasei Kogyo Co. Ltd, Japan.
10. Ochiai, M.; Kitagawa, Y.; Yamamoto, S. J. Am. Chem.
Soc. 1997, 119, 11598.
11. A typical experimental procedure for synthesis of (Z)-(b-
benzoyloxyvinyl)phenyl-k3-iodanes 3: To a mixture of
(650 mg,
ethynyl(phenyl)(tetrafluoroborato)-k3-iodane
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–hexane by decant-
ation. The crude product was dissolved in dichlorometh-
ane and the solution was vigorously shaken with a
saturated aqueous NaBF4 solution two times. The organic
layer was filtered and concentrated under aspirator
vacuum to give (Z)-(b-benzoyloxyvinyl)phenyl-k3-iodane
3a (690 mg, 76%). Recrystallization from dichlorometh-
ane–hexane gave colorless needles: mp 124.5–125.5 ꢀC; IR
X
PhCO2
I
LCAr
+
6a
7
8
PhX
PhI
δ-
9
X
LCV
PhCO2
I
(KBr) 1757, 1621, 1100–1000, 732 cmÀ1
;
1H NMR
+
5
Ph
δ-
(400 MHz, CDCl3): d 6.68 (d, J = 4.3 Hz, 1H), 7.43 (t, J =
7.8 Hz, 2H), 7.54 (t, J = 7.8 Hz, 2H), 7.58 (t, J = 7.8 Hz,
1H), 7.69 (t, J = 7.8 Hz, 1H), 8.01 (d, J = 7.8 Hz, 2H), 8.08
(d, J = 7.8 Hz, 2H), 8.19 (d, J = 4.3 Hz, 1H); HRMS
10
Scheme 4.

1866
M. Ochiai et al. / Tetrahedron Letters 46 (2005) 1863–1866
(FAB) m/z calcd for C15H12O2I [(MÀBF4)+] 350.9882.
Reactions with Heteroatomic Compounds; Pergamon:
Oxford, 1998.
14. Ochiai, M. In Topics in Current Chemistry; Wirth, T., Ed.;
Springer: Berlin, 2003; Vol. 224, pp 5–68.
15. Ochiai, M.; Takaoka, Y.; Masaki, Y.; Nagao, Y.; Shiro,
M. J. Am. Chem. Soc. 1990, 112, 5677.
16. (a) Okuyama, T.; Yamataka, H. Can. J. Chem. 1999, 77,
577; (b) Martin-Santamaria, S.; Carroll, M. A.; Carroll, C.
M.; Carter, C. D.; Pike, V. W.; Rzepa, H. S.; Widdowson,
D. A. Chem. Commun. 2000, 649; (c) Grushin, V. V. Acc.
Chem. Res. 1992, 25, 529.
Found: 350.9905. Anal. Calcd for C15H12O2BF4I: C,
41.14; H, 2.76. Found: C, 40.98; H, 2.81.
12. Treatment of (Z)-(b-benzoyloxyvinyl)-k3-iodane 3a with
diisopropylethylamine (1.2 equiv) in dichloromethane at
room temperature under argon afforded ethynyl benzoate
in 89% yield.
13. (a) Oae, S.; Uchida, Y. Acc. Chem. Res. 1991, 24, 202; (b)
Ochiai, M.; Oshima, K.; Masaki, Y. Chem. Lett. 1994,
871; (c) Okuyama, T.; Takino, T.; Sato, K.; Ochiai, M.
Chem. Lett. 1997, 955; (d) Finet, J. P. Ligand Coupling