Formation of new alkynyl(phenyl)iodonium salts and their use in the synthesis of phenylsulfonyl indenes and acetylenes http://www.mdpi.org

Article abstract of DOI:10.3390/10101340

The preparation of phenylsulfonyl indene derivatives and phenylsulfonyl-acetylenes from readily available alkynyl(phenyl)iodonium tetrafluoroborates and triflates was investigated using phenylsulfinate as nucleophile.

Full text of DOI:10.3390/10101340

Molecules 2005, 10, 1340–1350
molecules
ISSN 1420-3049
http://www.mdpi.org
Formation of New Alkynyl(phenyl)iodonium Salts and Their
Use in the Synthesis of Phenylsulfonyl Indenes and Acetylenes
Alexandros E. Koumbis *, Christos M. Kyzas, Antri Savva and Anastasios Varvoglis *
Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece. Tel.:
(
+30)-2310-997839, Fax: (+30)-2310-997679.
*
Authors to whom correspondence should be addressed; e-mails: akoumbis@chem.auth.gr;
anvar@chem.auth.gr
Received: 31 March 2005 / Accepted: 27 July 2005 / Published: 31 October 2005
Abstract: The preparation of phenylsulfonyl indene derivatives and phenylsulfonyl-
acetylenes from readily available alkynyl(phenyl)iodonium tetrafluoroborates and triflates
was investigated using phenylsulfinate as nucleophile.
Keywords: Indene, alkynyl(phenyl)iodonium salt, sulfinate, carbene, rearrangement.
Introduction
Among the various known hypervalent iodine species alkynyliodonium salts represent an
interesting class of compounds regarding their applications in organic synthesis [1-9]. Their major
subgroup comprises a multitude of stable alkynyl(aryl)iodonium salts (1, Scheme 1) [9]. Since the first
preparation of a labile alkynyl(aryl)iodonium salt [10] and the isolation of the first stable one [11] their
reactivity patterns have been thoroughly studied. It is nowadays well established that 1 are, among
other things, excellent partners for Michael-type conjugate additions as well as dienophiles in Diels-
Alder reactions and dipolarophiles in 1,3-dipolar cycloadditions [9]. The great tendency of 1 to react
with nucleophiles via conjugate addition is a result of the highly electrophilic nature of the β-
acetylenic carbon. The subsequent fate of the initially formed iodonium ylide 2 depends on the
reaction conditions (Scheme 1). Thus, reaction with a proton donor will yield an alkenyliodonium ion
3, whereas carbene 4 is formed via iodobenzene elimination. This carbene then either inserts
intramolecularly into any suitable bond available (mainly a C-H bond from either R or Nu) to produce
five-membered ring systems 5 and 6 or rearranges to give a new alkyne 7. By employing C-, O-, N-

Molecules 2005, 10
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and S-nucleophiles [6-9,12] several substituted cyclopentenes [13], cyclopentenones [14] or hetero-
cyclic derivatives such as pyrroles [15], indoles [16], thiazoles [17] and benzofurans [12,18] have been
obtained. Sulfinate anions in particular were used as nucleophiles in the construction of cyclopentenes
[13,19-20] and cyclopentenones [14]. Herein we wish to report our latest results concerning the
additions of benzenesulfinate to alkynyl(phenyl)iodonium salts in order to obtain indene and (or)
alkyne derivatives.
Scheme 1.
Nu
R
Nu
R
IPh
H
Nu
H
R C C IPh X
C C IPh
C C
-X
1
2
3
-
PhI
Nu
Nu
Nu
C C
R C C Nu
R
R
R
5
6
4
7
Results and Discussion
The required alkynyl(phenyl)iodonium salts, 11 and 13, were prepared from the corresponding
o-substituted phenyliodides 8a-c [21-22] (Scheme 2). These were first converted to arylalkynes 9 in
very good yields through a Sonogashira reaction [23-24]. Some of the corresponding desilylated
products 10 were also obtained in these reactions. Arylalkynes 9 were then treated first with
3 2 4
iodosylbenzene in the presence of BF ·OEt [25] and subsequently with aqueous NaBF [26-27] to
produce tetrafluoroborates 11. The Zefirov reagent 12 [28] was also used to prepare the triflate
analogues 13 directly from the same intermediates 9 [29-30].
Scheme 2.
IPh BF4
.
1
. PhIO, BF OEt , CH Cl
3
2
2
2
2
. NaBF , H O
4
2
X
R
I
1
1
TMSA, Pd(Ph P) Cl ,
3
2
2
CuI, Et NH
OTf OTf
2
R
R
IPh OTf
I
I
Ph
O
Ph
8
a R = Me
9 X = TMS
10 X = H
1
2
b R = Et
CH Cl
2
2
c R = CH OMe
2
R
1
3
1
-Bromonaphthalene (14) was similarly used to prepare the corresponding iodonium salts (Scheme
). First the major Sonogashira reaction product 15 was obtained from 14, along with some of the
desilylated product 16. Compound 15 then furnished 1-alkynyl(naphthyl)iodonium tetrafluoroborate
17) and the triflate analogue 18 upon reaction with iodosylbenzene/NaBF or the Zefirov reagent,
3
(
4

Molecules 2005, 10
1342
respectively. We did not try to isolate and characterize all these iodonium salts (assumed to be
reasonably stable) since they could be successfully employed in their reactions with benzenesulfinate
without any further purification.
Scheme 3.
IPh BF4
.
X
1. PhIO, BF OEt , CH Cl
3
2
2
2
2
. NaBF , H O
4 2
Br
1
7
TMSA, Pd(Ph P) Cl ,
IPh OTf
3
2
2
CuI, Et NH
2
1
4
15 X = TMS
1
6 X = H
1
2, CH Cl2
2
1
8
Tetrafluoroborate 11a reacted first with PhSO
(see also Figure 1). This reaction (entry 1) furnished in moderate yield the indene derivatives 19a
and 20a as an inseparable mixture, along with the rearrangement product, phenylsulfonylacetylene
1a. The observations that 19a and 20a could not be separated (although they have slightly different R
2
Na according to the general scheme shown in Table
1
2
f
values) and that they were always obtained in the same ratio (ca. 5:1) from several runs points to the
existence of an equilibrium between them. Thus, indene 20a, initially formed from 23a through
carbene insertion to the C-H of methyl group, partially isomerized to the more stable 19a (Scheme 4).
3 2 2
Indeed, addition of Et N to a solution of 19a and 20a in CH Cl did not alter this equilibrium and only
slow decomposition was observed after prolonged stirring (two weeks) at room temperature [31].
Next we explored the reactivity of 11b which, in contrast with 11a, yielded a single phenylsulfonyl
indene derivative, 19b, accompanied again by the acetylene sulfone 21b (entry 3). It is assumed that in
this case the carbene insertion product 20b was irreversibly isomerized to 19b (Scheme 4). Generally,
the sulfone group lacks the ability to participate in conjugation, therefore indenes 19, in which
conjugation with the aromatic ring is possible, are favored. One would expect that, concerning 20b, the
introduction of an extra methyl group, would lead to a less favorable 1,3-H shift system (in
comparison with the 19a-20a pair). However, from the experimental results it becomes apparent that
this is not the case. Due probably to steric factors, this shift is not reversible and once 20b is
isomerized to 19b the indene system is locked. Another plausible explanation could be that alkene 19b
is thermodynamically more stable since the conjugated double bond is trisubstituted.
The same reactions were also investigated employing the corresponding triflates 13a and 13b
(
entries 2 and 4, Table 1). Product distributions were similar to those obtained from tetrafluoroborates,
but reaction mixtures were easier to resolve and the phenylsulfonylindenes were isolated in higher
yields. Additionally, although not completely rationalized, annulation was slightly favored over
rearrangement.

Molecules 2005, 10
1343
Figure 1.
SO Ph
SO Ph
2
SO Ph
SO Ph
2
2
2
R
R
R
2
1a R = Me
b R = Et
c R = CH OMe
1
9a R = H
20a R = H
b R = Me
2
2
b R = Me
2
c R = OMe
Table 1.
IPh X
IPh X
or
PhSO Na,
CH Cl2
2
Ring Product (A) + Rearrangement Product (B)
2
R
X = BF or OTf
Entry Substrate
Ring type products (A)
Rearrangement type products (B)
a
1
2
3
4
5
6
7
8
11a
13a
11b
13b
11c
13c
17
19a + 20a (32%, 5:1)
21a (26%)
21a (26%)
21b (26%)
21b (20%)
-
19a + 20a (44%, 5:1)
19b (40%)
19b (51%)
-
-
-
-
-
22 (15%)
22 (16%)
18
a
All yields refer to isolated products (overall from the corresponding halides), unless
otherwise mentioned. For details see the Experimental section.
We sought next to explore the reactivity of methoxy iodonium salts 11c and 13c (entries 5 and 6),
but these substrates yielded very complex reaction mixtures with PhSO Na, which after
2
chromatographic separations did not furnish any of the expected methoxy analogues 19c and 21c [32].
The situation was not improved when the reaction with the nucleophile was performed at lower
temperatures. The different reactivity behavior of 11c and 13c might be due to an interaction of the
ether oxygen with the initially formed carbene [33] and it is possible that in our case this kind of
insertion does not lead to stable products.

Molecules 2005, 10
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Scheme 4.
SO Ph
SO Ph
2
2
C-H insertion
R = Me
1,3-H shift
SO Ph
2
1
:
5
2
0a
SO Ph
19a
SO Ph
2
2
R
2
3a R = Me
b R = Et
C-H insertion
R = Et
1,3-H shift
Me
0b
Me
2
19b
Carbene insertion to an aromatic C-H bond is another feasible reaction pathway [34-37], but none
of the reactions with 11 and 13 we investigated produced such derivatives. In order to check this
reactivity pattern phenylsulfinate addition to the naphthyl iodonium salts 17 and 18 was examined,
3
since these substrates lack the possibility of insertion to an sp C-H, but these derivatives gave only the
rearrangement product 22 in low yield upon nucleophile addition (entries 7 and 8).
Conclusions
In this article we have presented an investigation of the reactivity patterns of some new
alkynyl(phenyl)iodonium tetrafluoroborates and triflates upon addition of phenylsulfinate. The
preparation of indene and phenylsulfonyl acetylene derivatives was accomplished in moderate to good
yields depending on the exact reaction conditions and substrates involved. Further exploration of this
kind of iodonium salts could lead to a general scheme for the synthesis of such systems.
Acknowledgements
We thank Prof. John K. Gallos for his suggestions and comments.
Experimental
General
All reagents are commercially available and were used without further purification unless otherwise
mentioned. Solvents were dried by standard methods. The progress of the reactions was checked by
thin layer chromatography (TLC) on Merck silica gel 60F254 glass plates (0.25 mm). Column
1
13
chromatography was performed with Merck silica gel 60 (0.063–0.200 mm). The H- and C-NMR
spectra were recorded at 300 and 75 MHz, respectively, on a Bruker 300 AM spectrometer, with
tetramethylsilane (TMS) as internal standard. High-resolution mass spectra (HRMS) were obtained on
a VG ZAB-ZSE mass spectrometer under fast-atom bombardment (FAB) conditions with nitrobenzyl
alcohol (NBA) as the matrix or on an IONSPEC FTMS spectrometer (matrix-assisted laser-desorption
ionization, MALDI) with 2,5-dihydroxybenzoic acid (DHB) as matrix.

Molecules 2005, 10
1345
General procedure for the preparation of 2-aryl-trimethylsilylacetylenes 9 and 15 [23-24]
Aryl halides 8 or 14 (20 mmol) were dissolved in Et
Trimethylsilylacetylene (TMSA, 2.36 g, 24 mmol), Pd(Ph
.2 mmol) were then added successively and the mixture was left under vigorous stirring for 5 h at
2
NH (80 mL) under an inert atomsphere.
3
)
2
Cl (0.28 g, 0.4 mmol) and CuI (40 mg,
2
0
room temperature. The solvent was evaporated and hexane (50 mL) was added to the residue. After
stirring for 1 h the supernatant solution was collected and concentrated to a volume of ca. 10 mL. This
was chromatographed on a silica gel column (hexane eluent) to afford 2-aryltrimethylsilylacetylenes 9
and 15 and the corresponding desilylated by-products 10 and 16 in this order.
Trimethyl(2-o-tolylethynyl)silane (9a). Obtained from 8a (3.42 g, 91%). This compound had identical
physical and spectra data with those reported in the literature [38].
1
1
-Ethynyl-2-methylbenzene (10a). Obtained from 8a (120 mg, 5%); H-NMR (CDCl
3
) δ: 7.51 (d, J =
1
3
7
3
.9 Hz, 1H), 7.26-7.19 (m, 2H), 7.16 (t, J = 7.9 Hz, 1H), 2.53 (s, 1H), 2.50 (s, 3H); C-NMR (CDCl )
+
9 9
δ: 140.1, 132.7, 131.4, 129.8, 125.0, 121.7, 81.8, 81.4, 18.2; HRMS m/e Calc. for C H [(M+H) ]:
117.0704. Found: 117.0707.
1
[
2-(2-ethylphenyl)ethynyl]trimethylsilane (9b). Obtained from 8b (3.65 g, 90%); H-NMR (CDCl
3
)
δ: 7.43 (d, J = 7.3 Hz, 1H), 7.25 (d, J = 4.3 Hz, 1H), 7.20 (t, J = 6.1 Hz), 1H), 7.12 (t, J = 7.3 Hz, 1H),
1
3
2
1
2
.81 (q, J = 7.3 Hz, 2H), 1.24 (t, J = 7.3 Hz, 3H), 0.26 (s, 9H); C NMR (CDCl
3
) δ: 146.7, 132.4,
+
28.7, 127.9, 125.5, 122.2, 103.9, 97.7, 27.7, 14.6, -0.1; HRMS m/e Calc. for C13
03.1256. Found: 203.1257.
H
19Si [(M+H) ]:
1
1
-Ethyl-2-ethynylbenzene (10b). Obtained from 8b (105 mg, 4%); H-NMR (CDCl
3
) δ: 7.50 (d, J = 7.5
Hz, 1H), 7.26-7.20 (m, 2H), 7.12 (t, J = 7.3 Hz, 1H), 2.89 (s, 1H), 2.79 (q, J = 7.3 Hz, 2H), 1.24 (t, J =
1
3
7
.3 Hz, 3H); C-NMR (CDCl
3
) δ: 142.3, 132.8, 128.8, 127.8, 125.5, 121.5, 82.0, 81.3, 27.2, 15.7;
+
HRMS m/e Calc. for C10
H11 [(M+H) ]: 131.0861. Found: 131.0879.
[2-[2-(Methoxymethyl)phenyl]ethynyl]trimethylsilane (9c). Obtained from 8c (4.17 g, 96%). This
compound had been previously prepared following the same procedure [39].
1
-Ethynyl-2-(methoxymethyl)benzene (10c). Obtained from 8c (60 mg, 2%). This compound had
identical physical and spectra data identical with those reported in the literature [39].
Trimethyl[2-(naphthalen-5-yl)ethynyl]silane (15). Obtained from 14 (3.90 g, 87%). This compound
had been previously prepared using the corresponding iodide as starting material according to the same
1
procedure [40]. H-NMR (CDCl
3
) δ: 8.41 (d, J = 8.3 Hz, 1H), 7.87 (d, J = 7.0 Hz, 1H), 7.85 (d, J = 7.2
Hz, 1H), 7.76 (d, J = 7.3 Hz, 1H), 7.63 (t, J = 7.8 Hz, 1H), 7.55 (t, J = 7.3 Hz, 1H), 7.44 (t, J = 7.8 Hz,
1
3
1
H), 0.40 (s, 9H); C-NMR (CDCl
20.8, 103.1, 99.4, 0.01.
3
) δ: 133.4, 133.1, 130.8, 129.0, 128.2, 126.8, 126.3, 126.2, 125.1,
1

Molecules 2005, 10
1346
1
-Ethynylnaphthalene (16). Obtained from 14 (150 mg, 5%). This compound had physical and spectra
data identical with those reported in the literature [41-42].
General procedure for the preparation of tetrafluoroborates 11 and 17 [26-27]
PhIO (3.52 g, 16 mmol) [25] and BF
trimethylsilylacetylenes 9 or 15 (10 mmol) in dry CH
inert atmosphere at room temperature for 4 h. Then a solution of NaBF
mL) was added and the resulting two phase system was vigorously stirred for 15 min at room
temperature. The organic layer was collected, the aqueous one was extracted with CH Cl (25 mL) and
the combined organic phases were dried over MgSO . Filtration of the drying agent afforded a solution
3
·OEt
2
(2 mL, 16 mmol) were added to a solution of 2-aryl-
Cl (40 mL) and the mixture was stirred under an
(5.5 g, 50 mmol) in H O (20
2
2
4
2
2
2
4
of crude tetrafluoroborates 11 and 17, which were used in the next step without further purification.
General procedure for the preparation of triflates 13 and 18 [29-30]
2 2
A solution of 2-aryltrimethylsilylacetylenes 9 or 15 (10 mmol) in dry CH Cl (10 mL) was added
dropwise to a previously prepared solution of the Zefirov reagent (12, ca. 7 mmol) in dry CH
2
Cl
2
[28]
o
at 0 C. The reaction mixture was allowed to stir for 1 h at the same temperature to provide a solution
of crude triflates 13 and 18, which was used in the next step without further purification.
General procedure for the nucleophilic addition of sodium benzenesulfinate to iodonium salts
Sodium benzenesulfinate (1.8 g, 11 mmol) was added to a solution of the above mentioned
solutions of tetrafluoroborates or triflates (ca. 10 mmol) and the mixture was stirred under an inert
atmosphere for 1 h. Then CH
organic phase was dried over MgSO
by column chromatography (silica gel) using as eluent a 1/10 mixture of ethyl acetate and hexane.
2
Cl
2
2
(30 mL) and H O (20 mL) were added and after extraction the
4
. Evaporation of the solvent yielded a residue which was purified
1
-(Phenylsulfonyl)-1H-indene (19a) and 3-(phenylsulfonyl)-1H-indene (20). Prepared from either 11a
(
820 mg, 32% overall from 9a) or 13a (1.13 g, 44% overall from 9a), these compounds were obtained
1
as an inseparable mixture (ratio ca. 5:1). 19a: H-NMR (CDCl
3
) δ: 7.91 (bd, J = 7.5 Hz, 1H), 7.50-
7
.43 (m, 3H), 7.31-7.23 (m, 4H), 7.12 (bd, J = 7.9 Hz, 1H), 6.77 (d, J = 5.5 Hz, 1H), 6.47 (d, J = 5.5
1
3
Hz, 1H), 5.07 (s, 1H); C-NMR (CDCl
3
) δ: 144.3, 143.4, 137.4, 135.5, 133.5, 129.1, 129.0, 127.9,
+
1
2
1
27.8, 126.3, 125.7, 121.6, 73.5; HRMS (for the mixture) m/e Calc. for C15
H
13
O
2
S [(M+H) ]:
1
57.0636. Found: 257.0640. 20: H-NMR (CDCl ) δ: 8.06 (d, J = 7.9 Hz, 2H), 7.73 (d, J = 7.3 Hz,
3
H), 7.63-7.43 (m, 3H, partially obscured), 7.30-7.25 (m, 3H, obscured), 7.00 (bs, 1H), 3.61 (bs, 2H).
1
1
1
1
1
2
-(2-o-Tolylethynylsulfonyl)benzene (21a). Prepared from either 11a (670 mg, 26% overall from 9a) or
1
3a (510 mg, 20% overall from 9a). H-NMR (CDCl
3
) δ: 8.09 (d, J = 7.3 Hz, 2H), 7.70 (t, J = 7.3 Hz,
H), 7.63 (t, J = 8.0 Hz, 2H), 7.47 (d, J = 7.3 Hz, 1H), 7.36 (t, J = 7.3 Hz, 1H), 7.22 (d, J = 8.0 Hz,
1
3
H), 7.18 (t, J = 7.3 Hz, 1H); C-NMR (CDCl
3
) δ: 142.2, 142.0, 133.8, 132.8, 131.3, 129.8, 129.2,
+
27.9, 127.1, 115.7, 93.1, 88.9, 20.2; HRMS m/e Calc. for C15
57.0633.
H
13
O
2
S [(M+H) ]: 257.0636. Found:

Molecules 2005, 10
1347
3
-Methyl-1-(phenylsulfonyl)-1H-indene (19b). Prepared from either 11b (1.08 g, 40% overall from 15)
1
or 13b (1.375 g, 51% overall from 15). H-NMR (CDCl
3
) δ: 7.83 (bd, J = 7.9 Hz, 1H), 7.46 (d, J = 7.9
Hz, 2H), 7.43 (t, J = 7.3 Hz, 1H), 7.33-7.28 (m, 2H), 7.23 (t, J = 7.9 Hz, 2H), 7.04 (bd, J = 7.9 Hz,
1
3
1
1
2
H), 6.11 (bs, 1H), 4.97 (bs, 1H), 1.94 (s, 3H); C-NMR (CDCl
3
) δ: 146.4, 145.5, 135.9, 135.0, 133.3,
+
29.0, 128.8, 127.6, 126.1, 125.4, 122.4, 119.4, 72.3, 12.7; HRMS m/e Calc. for C16
71.0793. Found: 271.0797.
H
15
O
2
S [(M+H) ]:
1
-[2-(2-Ethylphenyl)ethynylsulfonyl]benzene (21b). Prepared from either 11b (760 mg, 26% overall
1
from 9b) or 13b (700 mg, 20% overall from 9b); H-NMR (CDCl
3
) δ: 8.09 (d, J = 8.1 Hz, 2H), 7.69 (t,
J = 7.1 Hz, 1H), 7.60 (t, J = 6.8 Hz, 2H), 7.48 (d, J = 7.8 Hz, 1H), 7.39 (t, J = 7.5 Hz, 1H), 7.26 (bs,
1
3
1
1
3
H), 7.19 (t, J = 7.4 Hz, 1H), 2.69 (q, J = 7.8 Hz, 2H), 1.38 (t, J = 7.8 Hz, 3H); C-NMR (CDCl ) δ:
48.6, 134.0, 133.4, 133.3, 131.8, 129.3, 128.4, 127.3, 126.0, 122.5, 94.3, 72.4, 27.6, 14.8; HRMS m/e
+
Calc. for C16
H
15
O
2
S [(M+H) ]: 271.0793. Found: 270.0792.
1
1
7
-(2-(Phenylsulfonyl)ethynyl)naphthalene (22). Prepared from either 17 (440 mg, 15% overall from
1
5) or 18 (465 mg, 16% overall from 15); H-NMR (CDCl
3
) δ: 8.77 (d, J = 8.2 Hz, 1H), 8.12 (d, J =
.0 Hz, 1H), 8.10 (d, J = 8.0 Hz, 2H), 8.00 (d, J = 7.1 Hz, 1H), 8.06 (d, J = 7.3 Hz, 1H), 7.81 (t, J = 7.7
Hz, 1H), 7.86 (t, J = 7.3 Hz, 1H), 7.62 (t, J = 7.5 Hz, 2H), 7.42 (t, J = 7.7 Hz, 1H), 7.39 (t, J = 7.3 Hz,
1
3
1
1
2
H); C-NMR (CDCl
3
) δ: 134.5, 134.2, 134.0, 132.0, 131.9, 130.2, 128.6, 128.5, 127.1, 126.3, 124.7,
+
24.5, 124.1, 120.5, 98.3, 72.6; HRMS m/e Calc. for C18
93.0633.
H
13
O
2
S [(M+H) ]: 293.0636. Found:
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2
2
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1
3
3
1
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3
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Sample availability: Contact the authors.
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