Electrophilic cyclization of buta-1,3-diynylarenes: Synthesis of precursors of (z)-3-ene-1,5-diyne systems fused to heterocycles

Article abstract of DOI:10.1055/s-0030-1259547

A simple, convenient, and promising strategy for the synthesis of 2-ethynyl-3-iodo-benzothiophenes, -benzofurans, and -indoles based on electrophilic cyclization of easily available ortho-functionalized (buta-1,3-diynyl)arenes was developed. The unique potential of using these compounds as starting materials for the synthesis of enediyne systems, containing thiophene, furan, and pyrrole units is demonstrated. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0030-1259547

LETTER
517
Electrophilic Cyclization of Buta-1,3-diynylarenes: Synthesis of Precursors of
(Z)-3-Ene-1,5-diyne Systems Fused to Heterocycles
T
owards Enediyne
a
Systems
v
t
ia Elec
t
a
rophilic Cy
l
clizatio
i
n
of
D
a
iacetylenes A. Danilkina,a Stefan Bräse,*b Irina A. Balova*a
a
Saint-Petersburg State University, Department of Organic Chemistry, Universitetskiy pr. 26, 198504, Saint-Petersburg,
Russian Federation
Fax +7(812)4286939; E-mail: irinabalova@yandex.ru
Karlsruhe Institute of Technology, Campus South, Institute of Organic Chemistry, Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany
Fax +49(721)6088581; E-mail: braese@kit.edu
b
Received 9 November 2010
with dihalosubstituted heteroarenes,10 which are not wide-
ly accessible. Meanwhile, heterocycles possessing an ene-
diyne system are promising objects for the medicinal
chemistry as analogues of naturally occurred enediyne an-
Abstract: A simple, convenient, and promising strategy for the
synthesis of 2-ethynyl-3-iodo-benzothiophenes, -benzofurans, and
-indoles based on electrophilic cyclization of easily available ortho-
functionalized (buta-1,3-diynyl)arenes was developed. The unique
potential of using these compounds as starting materials for the syn- tibiotics, which display strong antineoplastic activity.11
thesis of enediyne systems, containing thiophene, furan, and pyrrole
Herein we report for the first time the electrophilic cy-
units is demonstrated.
clization of ortho-buta-1,3-diynylthiophenol, -aniline,
Key words: electrophilic cyclization, alkynes, heterocycles, ene-
and -phenol derivatives, which led to the formation of
diynes
benzannulated 2-ethynyl-3-iodo-S,N,O-five-membered
heterocycles. Despite the fact that, Pd-, Cu-, and base-cat-
alyzed cyclizations of buta-1,3-diynylaniline and buta-
Electrophilic cyclization of ethynylarenes is well known
1,3-diynylphenol derivatives are convenient methods for
as an efficient method for the synthesis of fused haloge-
the synthesis of 2-ethynylindoles and 2-ethynylbenzo-
nated heterocycles,1 including 3-iodobenzothiophenes,1d,2
furans,12 no data has been reported about application of
-benzofurans,1b,c,i,3 and -indoles.1e,4 These compounds are
the electrophilic cyclization for the producing of this type
of great interest for the synthesis of a wide variety of
of heterocycles, having both ethynyl and halogen moi-
heterocyclic compounds with special biological activity5
eties.
and physical properties.6
First of all, a series of ortho-buta-1,3-diynylthiophenol
1a–d, -phenol 1g–i, and N,N-dimethylaniline derivatives
1e,f were obtained as the starting materials. Compounds
1a–d,g–i were prepared from corresponding ortho-iodo-
While the cyclization of ortho-substituted ethynylarenes
was investigated in details, there are only a few examples
of iodocyclization of buta-1,3-diynyl derivatives. Thus,
symmetrically1b,7 and asymmetrically1b substituted 1,4-di-
thiophenol or -phenol derivatives and buta-1,3-diynes by
arylbutadiynes underwent a double cyclization to give
Sonogashira coupling13a using procedure developed in our
symmetrical and asymmetrical bisheterocyclic com-
group recently.13b N,N-Dimethylaniline derivatives 1e,f
pounds. The formation of 4-iodo-3-ethynylisocoumarine
were synthesized by methylation of corresponding ortho-
was also detected as an intermediate of double cycliza-
buta-1,3-diynylaniline derivatives13b,c with MeI.
tion.1b
It was found that ortho-buta-1,3-diynylthioanisole deriva-
tives 1a–c can be efficiently converted into 2-ethynyl-3-
iodobenzothiophenes 2a–c by using of iodine in aceto-
Recently, we demonstrated the Richter-type cyclization of
ortho-(alka-1,3-diynyl)arenediazonium salts to be a short
route to 3-alkynyl-4-halocinnolines.8 Aiming at the devel-
nitrile at room temperature (Scheme 1, Table 1, entries 1–
opment of a general and efficient approach towards halo-
3).
ethynylheterocycles, as direct precursors of enediyne
I
systems, fused to a heterocyclic core, we reasoned that
such compounds may be accessed via electrophilic cy-
R2
R2
clization of ortho-functionalized buta-1,3-diynyarenes. It
should be noted that there is no general method to con-
struct (Z)-3-ene-1,5-diyne system attached to a variety of
heterocycles. Reported syntheses of such systems usually
include transformation of functional groups to the ethynyl
moieties9 or double cross-coupling of terminal acetylenes
R1
X
X
2
E
and/or
I
I
R2
1
X
Cl
E = I2, ICl
3
SYNLETT 2011, No. 4, pp 0517–0520
x
x.
x
x.
2
0
1
1
Advanced online publication: 11.02.2011
DOI: 10.1055/s-0030-1259547; Art ID: G33910ST
© Georg Thieme Verlag Stuttgart · New York
Scheme 1 Electrophilic cyclization of ortho-buta-1,3-diynylthio-
phenol (X = S), -aniline (X = NMe), and -phenol (X = O) derivatives.
For R1, R2, see Table 1.

518
N. A. Danilkina et al.
LETTER
It should be noted that cyclization of trimethylsilyl deriv- 2g in a poor yield (entry 8). Treatment of anisole 1g with
ative 1d under the same conditions gave the mixture of si- a more active electrophilic agent (iodine monochloride, 2
lylated and desilylated products 2d and 2d¢ in a molar equiv) in dichloromethane led to the formation of byprod-
ratio of 4.5:1 (entry 4).14 Unfortunately, complete separa- uct 3g with an iodochlorinated triple bond (entry 9). In the
tion of this mixture by column chromatography could not case of an equimolar ratio of reagents a mixture of 2g and
be achieved due to the close retention times of compounds 3g was detected by TLC and GC-MS monitoring. O-Ben-
2d and 2d¢. However, it was possible to isolate the silylat- zylated ortho-dodeca-1,3-diynylphenole 1h with iodine
ed compound 2d in 30% yield. When the reaction was did not undergo cyclization even at 70 °C in acetonitrile at
carried out in dry dichloromethane (r.t., 3 h) without treat- all, which is in accordance with the known leaving-group
ment of the reaction mixture with aqueous Na2S2O3 solu- activities in electrophilic cyclization-type reactions.1h
tion at the end, a mixture of 2d and 2d¢ with the molar Nevertheless, we found that the use of iodine monochlo-
ratio 23:114 was obtained (entry 5). Treatment of this mix- ride in acetonitrile is favorable for selective cyclization of
ture with K2CO3 in MeOH (r.t., 5 h) gave 2-ethynyl-3-io- O-benzylated derivative 1h. In this case 2-ethynylbenzo-
dobenzothiophene 2d¢ in 50% yield. It should be noted, furane 2g was isolated in 49% yield (entry 10).
that this compound is extremely interesting as a substrate
However, when we attempted to use iodine monochloride
in acetonitrile for the cyclization of ortho-dodeca-1,3-di-
ynylanisole (1i), the iodochlorination of the triple bond in
for the synthesis of cyclododeca-1,5,9-triene-3,7,11-
triyne derivatives.15
Cyclization of aniline derivatives 1e,f did not proceed in the 3-iodo-2-decynylbenzofurane proceeded smoothly to
acetonitrile at room temperature and required a higher yield the benzofurane 3i with iodochlorinated triple bond
temperature due to the lower nucleophilicity of dimethy- (entry 11).16
lamino group compared to methylthio group. Thus,
Thus we demonstrated that benzannulated five-mem-
cyclization of N,N-dimethylamino-ortho-buta-1,3-diynyl-
bered-S,N,O-heterocycles, possessing both ethynyl moi-
anilines 1e,f proceeded smoothly at 40 °C (entries 6 and
ety and iodine atom, can be directly accessed via
electrophilic cyclization of the corresponding functional-
ized ortho-buta-1,3-diynylarenes. The ability of ortho-
7) to give 2-ethynyl-3-iodoindole derivatives 2e,f in good
yields.
With regard to the synthesis of 2-ethynyl-3-iodobenzofu- buta-1,3-diynylthiophenol, -aniline, and phenol deriva-
ran derivatives, we showed that iodocyclization of ortho- tives to undergo electrophilic cyclization is in accordance
(4-phenylbuta-1,3-diynyl)anisole (1g) with 1 equivalent with the relative nucleophilicity of the functional groups
of iodine in acetonitrile at 40 °C gave the desired product and decreases among S > N > O.
Table 1 Synthesis of Compounds 2 and 3
Entry
Substrate
Conditionsa
Product, yield (%)b
1
X
S
S
S
S
R1
R2
R2
219
3
–
–
–
–
1
2
3
4
1a
1b
1c
1d
Me
Me
Me
Me
Ph
A
A
A
A
Ph
2a 83
C8H17
(CH2)2OH
TMS
C8H17
(CH2)2OH
2b 84
2c20 67
TMS
H
2d 61
2d¢ 13
5
1d
S
Me
TMS
B
TMS
H
2d 66
2d¢ 4
–
6
7
1e
1f
NMe
NMe
O
Me
Me
Me
Me
Bn
Ph
C
C
D
E
F
Ph
2e 75
–
C8H17
Ph
C8H17
Ph
2f 88
–
8
1g
1g
1h
1i
2g 16
–
9
O
Ph
Ph
2g traces
2g 49
3g 59c
3g traces
3i 38c
10
11
O
Ph
Ph
O
Me
C8H17
F
C8H17
2i traces
a Conditions A: I2 (1 equiv), MeCN, r.t., 3 h. Conditions B: I2 (1 equiv), dry CH2Cl2, r.t., 3 h. Conditions C: I2 (1 equiv), MeCN, 40 °C, 5 h.
Conditions D: I2 (1 equiv), MeCN, 40 °C, overnight. Conditions E: ICl (1 equiv), CH2Cl2, r.t., overnight, then ICl (1 equiv), r.t., 1 h. F: ICl (1
equiv), MeCN, r.t., overnight, then ICl (0.5 equiv), r.t., 3 h.
b All yields are given for individual compounds after purification by column chromatography; yields of 2d and 2d¢ (entries 4, 5) were calculated
in accordance to the molar ratio of 2d and 2d¢ (see ref. 14), which was determined from 1H NMR spectra of mixtures.
c Position of iodine and chlorine atoms was determined according to HMBC experiment.
Synlett 2011, No. 4, 517–520 © Thieme Stuttgart · New York

LETTER
Towards Enediyne Systems via Electrophilic Cyclization of Diacetylenes
519
Encouraged by the successful development of iodocy- which are precursors of various enediyne systems fused to
clization toward 3-ethynyl-2-iodoheterocycles we turned heterocyclic core.
our attention to the synthesis of enediyne systems. There
The three-step methodology described herein enables the
are a few reported examples of enediynes fused to
construction of asymmetrically substituted enediyne sys-
thiophene,1b,9,17 pyrrole,18 and furan rings,9 and only few
tems with absolute regiocontrol. We also demonstrated
known compounds with different substituents attached to
that these substituents may contain such functional groups
the triple bonds18a,b because of the lack of methods for
as OH and TMS, which is very important for further ene-
diyne modifications.
their synthesis.
So, the approach towards benzannulated 2-ethynyl-3-
iodo-S,N,O-five-membered heterocycles described above
should open a simple way for the synthesis of a variety of
Acknowledgment
N. A. Danilkina is grateful to the DAAD foundation for financial
support. I.B. and N.D. acknowledge Saint-Petersburg State Univer-
sity for a research grant 12.38.14.2011.
enediynes systems containing heterocyclic rings and dif-
ferent substituents attached to the triple bonds.
To explore this opportunity we synthesized several ene-
diyne systems using the Sonogashira coupling protocol in
the presence of Pd(PPh3)4 as a catalyst and diisopropanol-
amine (DIPA) as a base. All enediynes 4a–i were isolated
in moderate to good yields without optimization of the
reaction conditions (Scheme 2, Table 2).
References and Notes
(1) (a) Larock, R. C. In Acetylene Chemistry; Diederich, F.;
Stang, P. J.; Tykwinski, R. R., Eds.; Wiley-VCH:
Weinheim, 2005, 51–99. (b) Mehta, S.; Larock, R. C.
J. Org. Chem. 2010, 75, 1652; and references cited therein.
(c) Manarin, F.; Roehrs, J. A.; Brandão, R.; Nogueira,
C. W.; Zeni, G. Synthesis 2009, 4001. (d) Cho, C.-H.;
Neuenswander, B.; Larock, R. C. J. Comb. Chem. 2010, 12,
278. (e) Worlikar, S. A.; Neuenswander, B.; Lushington,
G. H.; Larock, R. C. J. Comb. Chem. 2009, 11, 875.
(f) Cho, C.-H.; Neuenswander, B.; Lushington, G. H.;
Larock, R. C. J. Comb. Chem. 2009, 11, 900. (g) Manarin,
F.; Roehrs,
R3
I
R3
R2
R2
i
X
X
2
4
J. A.; Gay, R. M.; Brandao, R.; Menezes, P. H.; Nogueira,
C. W.; Zeni, G. J. Org. Chem. 2009, 74, 2153. (h) Mehta,
S.; Waldo, J. P.; Larock, R. C. J. Org. Chem. 2009, 74,
1141. (i) Cho, C.-H.; Neuenswander, B.; Lushington, G. H.;
Larock, R. C. J. Comb. Chem. 2008, 10, 941.
Scheme 2 Synthesis of benzothiophene-, indole-, and benzofuran-
containing enediyne systems. Reagents and conditions: (i) Pd(PPh3)4,
CuI, Ph3P, DMF, DIPA, 50 °C, overnight.
(2) (a) Yue, D.; Larock, R. C. J. Org. Chem. 2002, 67, 1905.
(b) Flynn, B. L.; Verdier-Pinard, P.; Hamel, E. Org. Lett.
2001, 3, 651. (c) Yue, D.; Larock, R. C. Tetrahedron Lett.
2001, 42, 6011.
(3) (a) Arcadi, A.; Cacchi, S.; Fabrizi, G.; Marinelli, F.; Moro,
L. Synlett 1999, 1432. (b) Yue, D.; Yao, T.; Larock, R. C.
J. Org. Chem. 2005, 70, 10292. (c) Okitsu, T.; Nakazawa,
D.; Taniguchi, R.; Wada, A. Org. Lett. 2008, 10, 4967.
(4) (a) Barluenga, J.; Trincado, M.; Rubio, E.; Gonzalez, J. M.
Angew. Chem. Int. Ed. 2003, 42, 2406. (b) Amjad, M.;
Knight, D. W. Tetrahedron Lett. 2004, 45, 539. (c) Yue, D.;
Larock, R. C. Org. Lett. 2004, 6, 1037. (d)Yue, D.;Yao, T.;
Larock, R. C. J. Org. Chem. 2006, 71, 62.
(5) (a) Wei, S.; Coleman, R. S.; Lowary, T. L. Org. Biomol.
Chem. 2009, 7, 3709. (b) Santin, E. P.; Khanwalkar, H.;
Voegel, J.; Collette, P.; Mauvais, P.; Gronemeye, H.;
de Lera, A. R. ChemMedChem 2009, 4, 780. (c) Yang,
L.-Y.; Chang, C.-F.; Huang, Y.-C.; Lee, Y.-J.; Hu, C.-C.;
Tseng, T.-H. Synthesis 2009, 1175. (d) Bang, H. B.; Han,
S. Y.; Choi, D. H.; Yang, D. M.; Hwang, J. W.; Lee, H. S.;
Jun, J.-G. Synth. Commun. 2009, 39, 506.
(6) (a) Zhou, Y.; Liu, W.-J.; Ma, Y.; Wang, H.; Qi, L.; Cao, Y.;
Wang, J.; Pei, J. J. Am. Chem. Soc. 2007, 129, 12386.
(b) Kobayashi, T.; Hasegawa, Y. US 2005258398, 2005.
(7) Barluenga, J.; Trincado, M.; Rubio, E.; Gonzalez, J. M.
Angew. Chem. Int. Ed. 2003, 42, 2406.
Table 2 Synthesis of Enediynes 4
Entry Substrate
Acetylene
R3
Product Yield (%)
2
X
S
S
S
S
S
S
R2
421
1
2
3
4
5
6
7
8
9
2a
2a
2a
2b
2b
2c
2f
Ph
C6H13
(CH2)3OH
TMS
4a
4b
4c
4d
71
72
83
65
59
63
76a
47
69
Ph
Ph
C8H17
C8H17
Ph
4-MeOC6H4 4e
(CH2)2OH TMS
4f22
4g
4h
4i
NMe C8H17
Ph
2g
O
O
Ph
Ph
C6H13
TMS
2g
a Reaction was carried out at 40 °C.
In summary, for the first time the electrophilic cyclization
of ortho-buta-1,3-diynylthiophenol, -aniline, and -phenol
derivatives was accomplished to give benzannulated 3-
iodo-2-ethynylheterocycles. This is a promising and di-
rect approach towards heterocyclic compounds possess-
ing iodine and ethynyl moiety at neighboring atoms,
(8) (a) Vinogradova, O. V.; Sorokoumov, V. N.; Vasylevsky,
S. F.; Balova, I. A. Tetrahedron Lett. 2007, 48, 4907.
(b) Vinogradova, O. V.; Sorokoumov, V. N.; Balova, I. A.
Tetrahedron Lett. 2009, 50, 6358.
Synlett 2011, No. 4, 517–520 © Thieme Stuttgart · New York

520
N. A. Danilkina et al.
LETTER
and extracted with CH2Cl2 (3 × 7 mL). The combined
organic layers were washed with H2O, dried over anhyd
Na2SO4, and concentrated under reduced pressure to yield
the crude product, which was purified by column
chromatography on silica gel using pentane (for 2a,b,d,e,g)
or cyclohexane–EtOAc (2c,f) as the eluent.
(9) (a) Sahu, B.; Namboothiri, I. N. N.; Persky, R. Tetrahedron
Lett. 2005, 46, 2593. (b) Sahu, B.; Muruganantham, R.;
Namboothiri, I. N. N. Eur. J. Org. Chem. 2007, 2477.
(10) (a) Kim, C.-S.; Russell, K. C. J. Org. Chem. 1998, 63, 8229.
(b) Kumarasinghe, E. S.; Peterson, M. A.; Robins, M. J.
Tetrahedron Lett. 2000, 41, 8741.
(11) For recent reviews, see: (a) Jones, G. B.; Fouad, F. S. Curr.
Pharm. Des. 2002, 8, 2415. (b) Maretina, I. A.; Trofimov,
B. A. Russ. Chem. Rev. 2006, 75, 825. (c)Shao,R.-G. Curr.
Mol. Pharm. 2008, 1, 50.
(12) (a) Fiandanese, V.; Bottalico, D.; Marchese, G.; Punzi, A.
Tetrahedron 2008, 64, 53. (b) Fiandanese, V.; Bottalico, D.;
Marchese, G.; Punzi, A. Tetrahedron 2008, 64, 7301.
(13) (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron
Lett. 1975, 16, 4467. (b) Balova, I. A.; Sorokoumov, V. N.;
Morozkina, S. N.; Vinogradova, O. V.; Knight, D. W.;
Vasilevsky, S. F. Eur. J. Org. Chem. 2005, 882. (c) Liang,
Y.; Tao, L.-M.; Zhang, Y.-H.; Li, J.-H. Synthesis 2008,
3988.
(14) Relative molar ratio of 2d and 2d¢ was determined by
1H NMR analysis of the integral intensity of the signals of
acetylene hydrogen atom (d = 3.74 ppm) of 2d¢, TMS group
(d = 0.32 ppm) of 2d and multiplet signals of aromatic
hydrogen atoms (d = 7.38–7.50 and 7.67–7.76 ppm) of 2d
and 2d¢ (CDCl3, 400 MHz, TMS as reference).
(15) (a) Sooloki, D.; Kennedy, V. O.; Tessier, C. A.; Youngs,
W. J. Synlett 1990, 427. (b) Sooloki, D.; Bradshaw, J. D.;
Tessier, C. A.; Youngs, W. J. Organometallics 1994, 13,
451.
(20) Selected Data for 2c
Mp 73–75 °C. IR (neat): n = 3124 (OH), 2927 (CH), 2222
(C≡C), 1449, 1427, 1370, 1326, 1294, 1243, 1192, 1158,
1062, 1031, 1016, 983, 938, 914, 849, 831, 747, 721, 707
cm–1. 1H NMR (400 MHz, CDCl3): d = 2.01 (t, J = 6.5 Hz, 1
H), 2.83 (t, J = 6.1 Hz, 2 H), 3.88–3.93 (m, 2 H), 7.38–7.46
(m, 2 H), 7.67–7.72 (m, 2 H). 13C NMR (100 MHz, CDCl3):
d = 24.4, 60.8, 87.6, 96.9, 122.1, 125.0, 125.7, 126.1, 126.4,
138.6, 140.3 (two signals are overlapping with each other).
MS (EI, 70 eV): m/z (%) = 328.0(100) [M]+, 296.9 (66)
[M – CH2OH]+, 171.0(31), 139.1 (5) 126.1 (14). HRMS:
m/z calcd for C12H9OSI: 327.9419. Found: 327.9418. Anal.
Calcd for C12H9OSI: C, 43.92; H, 2.76; S, 9.77. Found: C,
43.85; H, 2.69; S, 9.61.
(21) General Procedure for the Synthesis of Enediyne
Systems 4
To a stirred solution of 2-ethynyl-3-iodo heterocyle 2 (0.1
mmol) in DMF (2 mL), the alkyne (0.2 mmol), Pd(PPh3)4 (5
mol%), Ph3P (10 mol%), and DIPA (0.4 mmol) were added.
The reaction vial was evacuated and flushed with Ar several
times. After that 15 mol% of CuI was added, the reaction vial
was then sealed and flushed with Ar. The reaction mixture
was allowed to stir at 40–50 °C (see Table 2) overnight.
After cooling, the reaction mixture was poured into the sat.
aq solution of NH4Cl and extracted with CH2Cl2 (3 × 10
mL). The combined organic layers were washed two times
with H2O, dried over anhyd Na2SO4, and concentrated under
reduced pressure to yield the crude product, which was
purified by column chromatography on silica gel using
pentane (for 4a,c,d,h,i) or cyclohexane–EtOAc (for 4b,e–g)
as the eluent.
(16) It was determined by TLC that O-benzyl-2-(dodeca-1,3-
diynyl)phenol reacts with ICl in MeCN in similar way giving
benzofuran 3i with iodochlorinated triple bond.
(17) Ebata, H.; Miyazaki, E.; Yamamoto, T.; Takimiya, K. Org.
Lett. 2007, 9, 4499.
(18) (a) Barluenga, J.; Fananas-Mastral, M.; Andina, F.; Aznar,
F.; Valdes, C. Organometallics 2008, 27, 3593.
(b) Kitagaki, S.; Katoh, K.; Ohdachi, K.; Takahashi, Y.;
Shibata, D.; Mukai, C. J. Org. Chem. 2006, 71, 6908.
(c) Shvartsberg, M. S.; Vasilevskii, S. F.; Prihod’ko, T. A.
Izv. Acad. Nauk SSSR, Ser. Khim. 1982, 11, 2524.
(19) General Procedure for Electrophilic Cyclization of
ortho-Buta-1,3-diynylthiophenol, -Aniline, and -Phenol
Derivatives Using I2
(22) Selected Data for 4f
IR (film on KBr): n = 3358 (OH), 3061 (CH), 2958 (CH),
2897 (CH), 2223 (C≡C), 2149 (C≡C), 1458, 1433, 1349,
1317, 1249, 1216, 1160, 1081, 1046, 976, 938, 896, 843,
729, 687, 642 cm–1. 1H NMR (400 MHz, CDCl3): d = 0.32
(s, 9 H), 2.02 (t, J = 6.7 Hz, 1 H), 2.83 (t, J = 6.1 Hz, 2 H),
3.85–3.90 (m, 2 H), 7.38–7.45 (m, 2 H), 7.70–7.72 (m, 1 H),
7.83–7.85 (m, 1 H). 13C NMR (100 MHz, CDCl3): d = 0.1,
24.5, 60.8, 75.8, 97.5, 97.7, 101.5, 122.0, 122.8, 123.3,
125.1, 126.1, 127.3, 138.0, 138.5. MS–FAB: m/z
(%) = 299.1 (61) [M+ + H], 298.1 (100) [M+]. HRMS:
m/z calcd for C17H18OSSi: 298.0848; found: 298.0845.
To an Ar flushed solution of corresponding o-(buta-1,3-
diynyl)arene 1 (0.2 mmol) in MeCN (3 mL), a solution of
iodine (0.2 mmol, 0.051 g,) in MeCN (2 mL) was added
dropwise. The reaction mixture was stirred at corresponding
temperature up to disappearance of starting material
according to TLC monitoring (see Table 1). Then, the
reaction mixture was diluted with 5% aq solution of Na2S2O3
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