Dibenzo macrocyclic acetylenic sulfide and a comparable silane

Article abstract of DOI:10.1016/S0040-4039(02)00186-7

The syntheses, X-ray structures and characterization of a dibenzo macrocyclic acetylenic sulfide 4a and a comparable silane 4b are described.

Full text of DOI:10.1016/S0040-4039(02)00186-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 2079–2082
Dibenzo macrocyclic acetylenic sulfide and a comparable silane†
H. Zhang, K. T. Lam, Y. L. Chen, T. Mo, C. C. Kwok, W. Y. Wong, M. S. Wong and
Albert W. M. Lee*
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong, China
Received 29 October 2001; revised 14 January 2002; accepted 24 January 2002
Abstract—The syntheses, X-ray structures and characterization of a dibenzo macrocyclic acetylenic sulfide 4a and a comparable
silane 4b are described. © 2002 Elsevier Science Ltd. All rights reserved.
Conjugated or homoconjugated all-carbon and carbon-
rich linear or cyclic molecules continue to be of intense
interest.1 Both experimental and theoretical studies sug-
gest that these molecules may exhibit interesting elec-
tronic and optical properties. Studies of these novel
systems are also highly relevant in materials research,
particularly in the search of organic conducting and
non-linear optical materials.2 Recently, we reported the
synthesis of oligoacetylenic sulfides through an iteration
of the sulfurization and coupling reaction cycles. Linear
oligomers having up to eight acetylene units with alter-
nating sulfur atoms were prepared.3 Subsequently, the
corresponding oligoacetylenic sulfide platinum(II) com-
plexes were also synthesized and characterized.4 In this
article, we report our results on the syntheses and
characterization of the dibenzo derivatives of a cyclic
acetylenic sulfide and silane.
Initially, a stepwise approach was used in the syntheses
of the 14-membered macrocyclic systems (Scheme 1).
1,2-Diethynylbenzene (1) was prepared according to the
literature procedure.5 Mono-deprotonation of 1 with 1
equiv. of LIHMDS followed by either 0.5 equiv. of
bis(benzenesulfonyl) sulfide 26 (for sulfurization) or
dichlorodiphenylsilane (for silylation) afforded interme-
diates 3a and 3b. A repeat of the deprotonation fol-
lowed by sulfurization or silylation cycle afforded the
targeted dibenzo acetylenic sulfide 4a and silane 4b in
65 and 77% yield, respectively, after column chro-
matography. One-step preparation of compounds 4a
and 4b using 2 equiv. of base and 2 equiv. of the
sulfurization or silylation agents also yielded the desired
products. However, the yields were 50% of those of the
previous method. The dibenzoacetylenic macrocyclic
sulfide 4a is a new compound while the macrocyclic
X
X
(i)
X
1
3ab
a : X = S
b : X = Ph2Si
4a (65%)
4b (77%)
(ii)
Co(CO)3
X
(4b)
(CO)3Co
X
X
X
6ab
Scheme 1. Reagents and conditions: (i) a. LIHMDS, 0°C to rt; b. 0.5 equiv. of 2 (PhSO2SSO2Ph) or Ph2SiCl2; (ii) Co2(CO)8,
benzene.
* Corresponding author. Tel.: +852-2339-7064; fax: +852-2339-7348; e-mail: alee@hkbu.edu.hk
† This paper is dedicated to Professor Barry Sharpless on the occasion of his 60th birthday.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00186-7

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H. Zhang et al. / Tetrahedron Letters 43 (2002) 2079–2082
silane had been reported in the patent literature.7 These
dibenzo acetylenic macrocyclic compounds were fully
characterized by spectroscopic methods.8
symmetry. The sulfur analog 4a was v-shape with a
dihedral angles of 15.8°, while the silicon analog 4b was
almost planar.
The 13C NMR data showed the macrocyclic structures
to be highly symmetrical with two acetylenic sp carbon
signals and three aromatic sp2 carbon signals for the
macrocyclic ring systems. Their structures were further
confirmed by X-ray analyses (Fig. 1). The X-ray struc-
tures showed that the macrocyclic molecules have C2v
The PM3 optimized geometry of 4a was in good agree-
ment with the X-ray structure. For 4b, in contrast to the
PM3 optimized geometry (Fig. 1), the diphenyl groups
in the silane analog were approximately symmetrically
arranged above and below the dibenzo plane in the solid
state, which is presumably due to the packing effect.
Figure 1. X-Ray structures of 4a and 4b, view from top (above) and side (middle).

H. Zhang et al. / Tetrahedron Letters 43 (2002) 2079–2082
2081
The UV absorption of 4a and 4b suggested that the
degree of conjugation between the acetylene units
across the heteroatoms is weak (Table 1). This result
was similar to that of the oligoacetylenic sulfides we
previously reported. Although the two acetylene units
in 4b lay almost in the same plane in the solid state,
according to the PM3 semi-empirical calculations, the
sulfur analog 4a exhibits a higher degree of conjugation
between the acetylene units. Consistently, the absorp-
tion maximum of the sulfur analog 4a appeared at a
slightly longer wavelength as compared to that of 4b.
Furthermore, the sulfur analog was oxidized more eas-
ily in cyclic voltammetry experiments (Table 1).
by X-ray analysis (Fig. 2). Although excess reagent was
used, only the mono-adduct could be detected. This is
not surprising because adducts 6a and 6b are already
highly strained.
The macrocyclic acetylenic silane 4b decomposed before
melting at 273°C. In contrast, the macrocyclic sulfide 4a
decomposed violently with a flash of orange light at
176°C, with the formation of black powder. Similar
dramatic thermal behavior had been reported for the
high-energy, high C/H ratio benzo-oligoalkynes.9
Both the dibenzocyclic acetylenic sulfide and silane can
be viewed as bis-enediyne structures linked together
with heteroatoms through the acetylene terminals.
Enediyne structures including 1,2-diethynylbenzene are
known to undergo Bergman cyclization to yield 1,4-
didehydrobenzene structures.10 The Bergman cycliza-
tion also constitutes the basis for the biological activity
of certain potent antitumor antibiotics.11 We envisage
The preparation of the cobalt complexes of 4a and 4b
was also carried out. Reaction with Co2(CO)8 in ben-
zene gave the mono-adducts (6a, 6b) in 96 and 19%
yield, respectively. The mono-cobalt complex 6b could
be obtained in good crystalline form after recrystalliza-
tion from CH2Cl2/hexane. Its structure was confirmed
Table 1. Results of calculations and physical measurements
umaxa/nm (mmax/104
Calcd HOMOb
(eV)
Calcd LUMOb
(eV)
Calcd energy
gap (eV)
CV-HOMOc
(eV)
CV-LUMOd
(eV)
Optical band
gapa (eV)
M−1 cm−1
)
4a 285 (3.8)
4b 275 (4.8)
−8.105
−8.855
−3.908
−3.032
4.197
5.823
−4.965
−5.045
−1.009
−0.930
3.956
4.115
a Measured in cyclohexane.
b Calculated by PM3 semi-empirical method in Mopac 6.
c Derived from the cyclic voltammetry measurements measured in Bu4NFP4/CH2Cl2 with scan rate 100 mV s−1 using SCE as a reference.
d Derived from the difference.
Figure 2. X-Ray structure of 6b.

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H. Zhang et al. / Tetrahedron Letters 43 (2002) 2079–2082
that 4a and 4b could undergo double Bergman cycliza-
tion to yield the bis-didehydrobenzene intermediate 5.
Because of the thermal instability of 4a, only 4b was
subjected to the attempted cyclization. To our disap-
pointment, the cyclization of 4b did not take place even
up to 170°C or under microwave irradiation with 1,4-
cyclohexadiene as the hydrogen atom donor.12 The
strain imposed by the double enediyne units may be too
high to forbid the cyclization. Similar observations were
also reported recently on a bis-enediyne macrocarbo-
cyclic system.13 Attempted cyclization on precursor 3b
also failed.
R. E.; Diederich, F. Angew. Chem., Int. Ed. Engl. 1999,
38, 1350–1377; (d) Diederich, F. Chem. Commun. 2001,
219–227.
3. Lee, A. W. M.; Yeung, A. B. W.; Yuen, M. S. M.;
Zhang, H.; Zhao, X.; Wong, W. Y. Chem. Commun.
2000, 75–76.
4. Zhang, H.; Lee, A. W. M.; Wong, W. Y.; Yuen, M. S. M.
J. Chem. Soc., Dalton Trans. 2000, 3675–3680.
5. (a) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagi-
hara, N. Synthesis 1980, 627; (b) Huynh, C.; Lin-
strumelle, G. Tetrahedron 1988, 44, 6337.
6. DeJong, F.; Janssen, M. J. J. Org. Chem. 1971, 36, 1645.
7. Okda, K.; Fujisaka, T.; Yamaguchi, B. Chem. Abstr.
1995, 123:84375.
In summary, dibenzo acetylenic sulfide and silane were
synthesized, with their structures confirmed by X-ray
analyses. Mono-cobalt complexes were also prepared
but attempted double Bergman cyclization of 4a failed.
Further studies of these and related macrocyclic
acetylenic systems such as formation of other metal
complexes and the thermal decomposition are in
progress.
8. Selected spectral data. 4a umax (cyclohexane)/nm, 285;
wmax (KBr)/cm−1, 2332, 2362, l (1H) (CDCl3, 270 MHz)
7.17–7.32 (m); l (13C) (CDCl3, 67.8 Hz) 75.7, 93.7, 124,
128, 131; m/z (EI): calcd 312.0066 for C20H8S2, found
312.0067. 4b umax (cyclohexane)/nm, 275; wmax (KBr)/
cm−1, 2099, 2166; l (1H) (CDCl3, 400 MHz): 7.27–7.60
(m); 7.35–7.88 (m, SiPh2); l (13C) (CDCl3, 100.57 MHz):
92.3, 106.1, 125.6, 128.0, 128.6, 130.2, 132.2, 132.3,
135.0); m/z (EI): calcd 612.1722 for C44H28Si2, found
612.1706.
Acknowledgements
9. (a) Boese, R.; Matzger, A. J.; Vollhardt, K. P. C. J. Am.
Chem. Soc. 1997, 119, 2052–2053; (b) Dosa, P. I.; Erben,
C.; Iyer, V. S.; Vollhardt, K. P. C.; Wasser, I. M. J. Am.
Chem. Soc. 1999, 121, 10430–10431; (c) Faust, R. Angew.
Chem., Int. Ed. Engl. 1998, 37, 2825–2828.
Financial support from the Hong Kong Research
Grant Council (HKBU 2048/97P) is gratefully
acknowledged.
10. (a) Bergman, R. G. Acc. Chem. Res. 1973, 6, 25–31; (b)
Choy, N.; Kim, C.; Ballestere, C.; Artigas, L.; Diez, C.;
Lichtenberger, F.; Shapiro, J.; Russell, K. C. Tetrahedron
Lett. 2000, 41, 6955–6958.
References
11. Nicolaou, K. C.; Smith, A. L. Acc. Chem. Res. 1992, 25,
497–503.
1. (a) Topics in Current Chemistry (Carbon–Rich Compounds
I); Meijere, A. de, Ed.; Springer: Berlin, 1998; Vol. 196;
(b) Topics in Current Chemistry (Carbon–Rich Compounds
II); Meijere, A. de, Ed.; Springer: Berlin, 1999; Vol. 201;
(c) Youngs, W. J.; Tessier, C. A.; Bradshaw, J. D. Chem.
Rev. 1999, 99, 3153–3180.
2. (a) Sarkar, A.; Haley, M. Chem. Commun. 2000, 1733–
1734; (b) Modern Acetylene Chemistry; Stang, P. J.;
Diederich, F., Eds.; VCH: Weinheim, 1995; (c) Martin,
12. (a) McMahon, R. J.; Halter, R. J.; Fimmen, R. L.;
Wilser, R. J.; Peebles, S. A.; Kuczkowski, R. L.; Stanton,
J. F. J. Am. Chem. Soc. 2000, 122, 939–945; (b) Thoen,
K. K.; Thoen, J. C.; Uckun, F. M. Tetrahedron Lett.
2000, 41, 4019–4024.
13. Blanchette, H. S.; Brand, S. C.; Naruse, H.; Weakley, T.
J. R.; Haley, M. M. Tetrahedron 2000, 56, 9581–9588.