Polyyne cyclization to form carbon cages: [16.16.16](1,3,5)cyclophanetetracosayne derivatives C60H6 and C60Cl6 as precursors to C60 fullerene

Article abstract of DOI:10.1016/S0040-4020(01)00250-2

[16.16.16](1,3,5)Cyclophanes fused by six [4.3.2]propellatriene units, which would serve as precursors to cage polyyne C₆₀H₆ and its perchloro derivative C₆₀Cl₆, respectively, were prepared. In the negative mode laser desorption mass spectra of the cyclophanes, the polyyne anions C₆₀H₆^- and C₆₀Cl₆^- were detected. Moreover, size-selective formation of C₆₀⁺ as well as C₆₀^- was also observed, indicating the possible polyyne cyclization mechanism to form the fullerene cage.

Full text of DOI:10.1016/S0040-4020(01)00250-2

TETRAHEDRON
Pergamon
Tetrahedron 57 ,2001) 3629±3636
Polyyne cyclization to form carbon cages:
[16.16.16]ꢀ1,3,5)cyclophanetetracosayne derivatives C60H6 and
C60Cl6 as precursors to C60 fullerene
Yoshito Tobe,a,p Nobuko Nakagawa,a Jun-ya Kishi,a Motohiro Sonoda,a Koichiro Naemura,a
Tomonari Wakabayashi,b Tadamasa Shidab and Yohji Achibac
aDepartment of Chemistry, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
bDivision of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
cDepartment of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan
Received 29 September 2000; accepted 21 November 2000
AbstractÐ[16.16.16],1,3,5)Cyclophanes fused by six [4.3.2]propellatriene units, which would serve as precursors to cage polyyne C60H6
and its perchloro derivative C60Cl6, respectively, were prepared. In the negative mode laser desorption mass spectra of the cyclophanes, the
polyyne anions C60H62 and C60Cl62 were detected. Moreover, size-selective formation of C601 as well as C602 was also observed, indicating
the possible polyyne cyclization mechanism to form the fullerene cage. q 2001 Elsevier Science Ltd. All rights reserved.
C60 and some higher fullerenes are produced by arc-
vaporization of graphite1 and are readily available from
commercial sources.2 However, it is still important to
synthesize fullerenes in a rational manner based on organo-
chemical transformations, because it would be possible to
manipulate carbon cages in size-selective and structure-
de®ned manner. It would also be possible to encapsulate
transition metals into the cage leading to the yet discovered
endohedral transition-metallofullerenes,3 which are of
tremendous interest as new materials. In this respect, inten-
sive studies have been conducted toward the designed
synthesis of C60. The ®rst attempts were conducted by
Chapman's group4 well before the ®rst observation of
C60,5 which was followed by several different approaches.
However, despite the numerous efforts, the controlled
chemical synthesis of fullerenes as well as that of endo-
hedral metallofullerenes has not been achieved yet.
cyclic aromatic hydrocarbons exempli®ed by corannulene
can be prepared ef®ciently without using the FVP
technique,7 this strategy will become more powerful than
before. As an alternative approach to synthesize C60
from molecules already possessing sixty carbon atoms, a
twisted C60H30 hydrocarbon, benzo[1,2-e:3,4-e0:5,6-
e00]tribenzo[l:l0:l00]triacephenanthrylene ,2), which repre-
sents a developed diagram of C60, was prepared.8 Partial
dehydrogenation of 2 took place in the matrix-assisted
laser-desorption ionization ,MALDI) time-of-¯ight ,TOF)
mass spectroscopy down to C60H101 but complete dehydro-
1
genation to C60 was not observed.8a A mechanistically
different approach from sixty-carbon-containing molecules,
utilizing cyclization of highly reactive three-dimensional
polyynes, was investigated by the groups of Rubin9 and
ours,10 which is the topic of this report.11
Although the mechanism has not been clari®ed,12 it has been
proposed that monocyclic carbon clusters, called cyclo[n]-
carbons,13 are likely to play a key role during the early
stages of the fullerene formation.14 Inspired by this
One of the most potential approaches to the rational synthe-
sis of C60 is to build up six-membered rings around ®ve-
membered rings by intramolecular C±C bond formation
under high-temperature pyrolytic conditions ,FVP), leading
to the formation of bowl-shaped molecules called `bucky-
bowls' or `fullerene fragments'.6 Scott and Rabideau have
developed this method extensively. To date, the largest
known fullerene fragment is C36H12 ,1) synthesized by
Scott.6e,f In view of the recent ®ndings that curved poly-
Keywords: fullerene; cyclization; cyclophanes.
Corresponding author. Tel.: 181-6-6850-6225; fax: 181-6-6850-6229;
e-mail: tobe@chem.es.osaka-u.ac.jp
p
1
2
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020,01)00250-2

3630
Y. Tobe et al. / Tetrahedron 57 32001) 3629±3636
[2+2]
Polyyne
Cycloreversion
Cyclization
R
R
R
R
R
— 6 (C9H10)
— 3 R2
R
R
R
R
R
R
R
C60
3a R = H
3b R = Cl
5a R = H
5b R = Cl
Scheme 1. Proposed formation of C60 from propellane-annelated cyclophanes 5a and b by [212] cycloreversion followed by polyyne cyclization of three-
dimensional polyynes 3a and b. Only one of the diastereomers of 5a and b is shown for clarity reasons.
proposal, Rubin proposed recently a new route to fullerene
synthesis involving cyclization of reactive polyynes.15 Thus
the reactive cage polyyne C60H6 ,3a) would isomerize to the
most stable icosahedral structure of Ih symmetry by forming
the ®ve- and six-membered rings with the loss of hydrogen
atoms, like the cascade rearrangement of C10H16 hydro-
carbons called `adamantane rearrangement'.16 As an initial
step to the synthesis of 3a, Rubin prepared C60H18 ,4) which
contained two double bonds in each polyyne bridge. In the
ion cyclotron resonance ,ICR) mass spectrum ,negative
ments ,indane). We also report the observation of C60 ions in
the positive and negative modes of the laser desorption mass
spectra of 5a and b, an indication of the polyyne cyclization
mechanism for the fullerene formation ,Scheme 1).
According to the semi-empirical calculations on the AM1
level,17 cage polyyne 3a has a heat of formation of
1341 kcal/mol which is about 500 kcal/mol larger than
that of the known 1,2,33,41,42,50-hexahydrofullerene
,DHf0 ,AM1)ˆ847.6 kcal/mol) prepared by dissolving
metal reduction of C60.18 Although the bond angles of
each sp carbon atom of 3a ,169.8±170.38) are not severely
distorted, the total strain for 48 sp carbon atoms must be
tremendous. Moreover, the individual polyyne chain of 3a
can be envisioned as a diaryl-substituted hexadecaoctayne
whose parent compound has been shown to lie on the iso-
lation limit of the linear polyynes.19 These data suggest that
compound 3a must be too reactive for isolation at room
temperature. It is also worth noting that 3a is a member of
polyyne-bridged cyclophanes proposed recently as a new
family of strained cyclophanes.20
2
mode) of 4, partial dehydrogenation down to C60H14 was
observed,15a suggesting the possibility of complete dehydro-
genation of C60H6 ,3a) to C60. As an extension of our
strategy to generate highly reactive polyynes by [212]
cycloreversion of [4.3.2]propellatriene derivatives,13e we
report here the preparation of a stable hydrocarbon pre-
cursor 5a, C60H6,Ind)6, and its perchlorinated derivative
5b, C60Cl6,Ind)6, which would form cage polyynes C60H6
or C60Cl6, respectively, by extrusion of six aromatic frag-
H
H
H
The precursors 5a and b were synthesized by oxidative
dimerization of the corresponding tris,propellane)-substi-
tuted benzene derivatives 9b and d which were obtained
by hetero coupling of appropriate tris,bromoethynyl)-
benzenes 8a and c with unsymmetrically substituted di-
alkynylpropellatriene 7b ,Scheme 2). In order to prepare
7b, the protective group of the known monoalkynylated
propellatriene 6a13e was changed to the more readily
removable triisopropylsilyl group by deprotection followed
by reprotection to give 6b. Introduction of the second
alkynyl group was achieved ef®ciently by the Sonogashira-
type reaction using the recently reported P,t-Bu)3 ligand,21
and subsequent selective deprotection of the trimethylsilyl
group of 7a afforded monoprotected diyne 7b. Pd-catalyzed
hetero coupling of 7b with tris,bromoethynyl)benzene
,8a)9a under the protocol reported by Vasella22 afforded
1,3,5-tris,propellanylethynyl)benzene 9a in 67% yield.
After removal of the triisopropylsilyl group, oxidative
coupling of 9b was performed under high dilution condi-
tions to yield 5a as a mixture of diastereomers23 in
70% yield. In order to prepare the chloro derivative 5b,
H
H
H
3a
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
4

Y. Tobe et al. / Tetrahedron 57 32001) 3629±3636
3631
R2
R1
R
Cl
b
R2
6a R=CMe2OH
6b R=Si(i-Pr)3
7a R1=Si(i-Pr)3, R2=SiMe3
7b R1=Si(i-Pr)3, R2=H
c
a
f
e
5a, 5b
R2
R1
R1
R2
R1
R1
R1
R2
R2
R1
R2
8a R1=H, R2=Br
8b R1=Cl, R2=SiMe3
8c R1=Cl, R2=Br
9a R1= H, R2=Si(i-Pr)3
9b R1=R2=H
9c R1=Cl, R2=Si(i-Pr)3
9d R1=Cl, R2=H
d
Scheme 2. ,a) ,i) KOH, benzene, re¯ux, 91%; ,ii) BuLi, THF, 08C, then CF3SO3Si,i-Pr)3, rt, 99%; ,b) ,CH3)3SiCuCH, Pd,PhCN)2, CuI, P,t-Bu)3, NH,i-Pr)2,
THF, 508C, 85%; ,c) K2CO3, MeOH±THF, rt, 96%; ,d) NBS, AgNO3, 67%; ,e) Pd2,dba)3´CHCl3, CuI, 1,2,2,6,6-pentamethylpiperidine, benzene, rt, 67% for
9a, 39% for 9c; ,f) ,i) Bu4N1F2, THF, rt, ,ii) Cu,OAc)2, pyridine, rt, 70% for 5a, 29% for 5b. Only one of the diastereomers of 9a±d is shown for clarity
reasons.
1,3,5-trichloro-2,4,6-triiodobenzene24 was converted to
tris,trimethylsilyl)ethynyl derivative 8b under the normal
Sonogashira conditions, which was converted to the
bromoethynyl derivative 8c by treatment with NBS and
silver ,I) nitrate. Hetero coupling22 of 8c with the propellane
unit 7b gave 9c in 38% yield. After deprotection to 9d,
oxidative coupling of 9d gave 5b in 29% yield.23 Solutions
of 5a and b are rather sensitive to room light; when a
benzene solution of 5a was allowed to stand under a ¯uor-
escent light for a few days, several unidenti®ed products
were detected by HPLC but no indane was detected.
While the hydrocarbon 5a was quite stable in the dark, the
chloro derivative 5b decomposed gradually even when it
was stored in a refrigerator.25
result represents one of few examples of size-selective
formation of C60 cluster,14c because no larger cluster such
as C70 was detected.
It was reported that perchlorinated polycyclic aromatic
compounds served as good precursors to produce carbon
cluster ions by electron impact induced fragmentation.28
In this respect, we expected that the chloro derivative 5b
would serve as a better precursor to C60 cation although our
ionization conditions were different from those reported. As
shown in Fig. 1b, the positive mode LDTOF mass spectrum
of 5b exhibits a strong peak of C601. The most important
feature of the spectrum is that the S/N ratio is much
improved from that of the spectrum of 5a. The formation
of C601 is facilitated by the electron capture by the chlorine
atoms, as supported by the observation of a strong peak of
Cl2 in the negative mode spectrum in Fig. 2b. As in the case
of 5a, neither the parent peak nor C60Cl61 can be detected.
In addition to the fragmentation down to C501 due to the C2
loss, ions up to C1201 were observed which might be formed
by an ion-molecule reaction of C60 and the subsequent frag-
mentation of the dimeric cluster ion.
Laser desorption time-of-¯ight ,LDTOF) mass spectra of 5a
and b were measured using liquid paraf®n as a matrix and
the third harmonic of an Nd:YAG laser ,355 nm, typically
3 MW/cm2 with
a 7 ns duration) for simultaneous
desorption and ionization. Fig. 1a shows the positive
mode laser desorption mass spectrum of hydrocarbon 5a.
A prominent peak due to C60 formed by the loss of eight
1
indane fragments and six hydrogen atoms is observed,
although the signal to noise ratio of the spectrum is not
large. Neither the parent peak ,m/z 1434) nor C60H6 ,m/z
The negative mode LDTOF mass spectrum of 5a is shown
in Fig. 2a. In contrast to the positive mode spectrum, the
negative mode spectrum exhibits peaks due to C60H6 and
1
2
726) can be detected. It has been well-documented that, in
general, carbon cluster cations generated by the laser
desorption method are thermally highly excited, and, as a
result, fragmentation due to C2 loss is frequently observed.26
C60H6,Ind)2 at m/z 726 and 844, respectively, though the
parent peak is not detected. It has been documented that the
internal temperature of negative ions is much lower than
those of positive ions, and the negative ions represent better
structures and populations of neutral species.29 Conse-
quently, it is reasonable to assume that the polycyclic
cage structure of 3a remains intact in the C60H6 anion
observed. Fig. 2a also shows a small peak due to C60
anion. Judging from the isotope distribution of the C60
anion, there seems to be no intermediate species between
1
The internal temperature of thermally excited C60 was
estimated to be as high as 2300±3000 K.27 Since such C2
loss down to C50 is indeed observed in the positive mode
1
spectrum of 5a, indicating that the internal temperature of
the C60 is considerably high, it is hard to deduce whether
1
the structure of the C60 cation retains the Ih symmetry of
fullerene or not. However, it should be pointed out that this

3632
Y. Tobe et al. / Tetrahedron 57 32001) 3629±3636
Figure 1. Positive mode laser desorption time-of-¯ight mass spectra of: ,a)
5a and ,b) 5b.
Figure 2. Negative mode laser desorption time-of-¯ight mass spectra of: ,a)
5a and ,b) 5b.
2
2
C60H6 and C60 like C60H52, C60H42, and so on. This
means that the dehydrogenation takes place simultaneously
to the drastic skeletal isomerization, leading to the forma-
tion of a fullerene-like structure. Similar results were
reported by Rubin for the FT-ICR mass spectrum of a
precursor having cyclobutenedione units which exhibited
six chlorine atoms would give an additional internal energy
,,18 eV) to the molecule being able to heat it up to the
temperature above ,1200 K which would be suf®ciently
high for the skeletal isomerization to form icosahedral C60.30
Although there is no evidence on the mechanism of the
fullerene formation from the precursors 5a and b or 3a
and b, it is tempting to propose possible mechanisms.
Taking into account the proposed mechanism of the conver-
sion of cyclo[30]carbon into C60, we can speculate a
mechanism shown in Scheme 3 involving intramolecular
cyclizations between the polyyne chains of 3a and b to
form the requisite ®ve- and six-membered rings of the full-
erene structure. The polyyne chains in the transition state
geometry A of Scheme 3 do not seem too much constrained
with regard to the bending, while the top and bottom
benzene rings are twisted by 3008 to each other. There are
two other possible geometries B and C. Although the twist
angle of the benzene rings ,1208) in both B and C is smaller
than that of A, these transition states seem to be highly
strained because they have one or two small angle,s) in a
polyyne chain.
C60H62 and C60 more clearly than 5a.9
2
Fig. 2b shows the negative mode LDTOF mass spectrum of
5b. While the parent peak is not detected, the fragments
2
from C60Cl6,Ind)4 down to C60Cl6 are clearly seen due
2
to the successive loss of the indane fragments. A small peak
due to C60 was also detected. However, since the inter-
2
2
mediate ions such as C60Cl5 and C60Cl4 are observed,
2
2
2
the elimination of chlorine atoms from C60Cl6 to C60 is
likely to take place stepwise, in contrast to the negative
mode spectrum of 5a. Since the bonding energy of a
C±Cl bond ,,3.1 eV) is lower than that of a C±H bond
,,3.9 eV), the elimination of a chlorine atom takes place
more easily than the case of hydrogen. It may occur even
when the internal temperature of the precursory C60Cl6
molecule is not so high. However, the successive loss of

Y. Tobe et al. / Tetrahedron 57 32001) 3629±3636
3633
a
b
b
b
a
b
b
b
a
C60
A
b
a
c
c
a
b
b
a
c
C
B
Scheme 3. Schlegel diagrams A, B and C of the transition state geometries for possible cyclization mechanisms of three-dimensional polyynes 3a or b to C60
fullerene. Filled circle denotes an sp2 carbon bearing a hydrogen or chlorine atom. Lower case a, b and c in the hexagons indicate the six-membered rings being
formed by a [412] transition state of butadiyne and benzene ,a) or acetylene ,b) and a 6p electrocyclic transition state ,c).
In the transition state geometry A of Scheme 3, there are
nine six-membered rings that are to be formed by formal
[412] cycloaddition between a butadiyne fragment ,4p)
and a benzene or an acetylene moiety ,2p) as indicated by
the hexagons a and b, respectively, in the Schlegel diagram
of A. Similarly, the geometry B has six [412] hexagons ,a
and b) and three 6p hexatriyne units ,as indicated c) that
would form six-membered rings by an electrocyclic reac-
tion. It has been demonstrated by Johnson, both theoreti-
cally and experimentally, that [412] cycloaddition of
butadiyne with ethylene or acetylene required high activa-
tion energy although the reaction was feasible.31 These
results may be related to the observation that C60 produced
by the laser furnace method from graphite is best formed
when the medium gas temperature is 700±900 K.30 Accord-
ingly, it is reasonable to assume that the polyyne cyclization
of Scheme 3 would not occur at ambient temperature.
Indeed, in contrast to the photodecomposition of 5a by the
visible light irradiation described above, photolysis of 5a in
benzene solution with a low-pressure mercury lamp at room
temperature resulted in the formation of indane ,ca. 50%
yield by the 1H NMR spectrum), indicating the formation of
polyyne chains at least partially. However, only uncharac-
terized polymeric materials were obtained and no C60 was
detected by HPLC. Though attempts to perform ¯ash
vacuum pyrolysis of 5a were not successful so far owing
to its low volatility, works in the preparative scale fragmen-
tation of 5a and b are under way.
present work marks a step forward toward designed
synthesis of fullerenes.
1. Experimental
1.1. General
1H NMR ,400, 300 or 270 MHz) and 13C NMR ,100.5, 75 or
67.5 MHz) spectra were recorded on a JEOL JNM-AL-400,
a Varian Mercury-300 or a JEOL JNM-GSX-270 spectro-
meter at 308C. IR spectra were recorded as a KBr disk or a
neat ®lm on a JASCO FTIR-410 spectrometer. UV±Vis
spectra were recorded on a Hitachi 220A spectrometer. EI
and FAB mass spectral analyses were performed on a JEOL
JMS-DX303HF spectrometer. LDTOF mass spectra were
obtained on a home-built spectrometer equipped with an
Nd:YAG laser ,355 nm, typically 3 MW/cm2 with a 7 ns
duration).13d Elemental analyses were carried out with a
Perkin±Elmer 2400II analyzer. Preparative HPLC separa-
tion was undertaken with a JAI LC-908 chromatograph
using 600 mm£20 mm JAIGEL-1H and 2H GPC columns
with CHCl3 as an eluent.
1.1.1. 10-Chloro-11-[ꢀtriisopropylsilyl)ethynyl][4.3.2]-
propella-2,4,10-triene ꢀ6b).
A
mixture of 13.1 g
,50.2 mmol) of 6a13e and 13.3 g ,85%, 201 mmol) of
powdered KOH in 600 mL of benzene was degassed by
three freeze±thaw cycles. The mixture was heated at 908C
for 1 h while benzene was slowly distilled out under nitro-
gen. After being cooled, the mixture was diluted with water
and the organic phase was separated, which was washed
successively with saturated NaHCO3 solution and saturated
NaCl solution ,brine) and dried over MgSO4. Removal of
the solvent followed by ¯ash chromatography gave 9.23 g
,91%) of 10-chloro-11-ethynyl[4.3.2]propella-2,4,10-triene
In summary, we prepared stable precursors 5a and b having
[4.3.2]propellatriene units to cage polyyne C60H6 ,3a) and
its perchloro derivative C60Cl6 ,3b) and succeeded in the
2
2
observation of C60H6 and C60Cl6 in their negative mode
laser desorption mass spectra. Size-selective formation of
1
2
C60 as well as C60 was also observed, particularly with
remarkable clarity in the positive mode mass spectrum of
5b, indicating the possible polyyne cyclization mechanism
to form the fullerene cage. Although the preparative scale
formation of C60 is yet to be achieved, we believe the
1
as a colorless oil. H NMR ,CDCl3) d 5.76±5.96 ,m, 4H),
3.15 ,s, 1H), 1.93±2.02 ,m, 2H), 1.34±1.67 ,m, 2H), 1.15±
1.28 ,m, 2H); 13C NMR ,CDCl3) d 132.2 ,s), 128.5 ,d),

3634
Y. Tobe et al. / Tetrahedron 57 32001) 3629±3636
127.3 ,d), 125.1 ,s), 122.7 ,d), 121.7 ,d), 82.4 ,s), 73.3 ,d),
59.5 ,s), 55.7 ,s), 32.1 ,t), 31.5 ,t), 18.4 ,t); IR ,neat) 3293,
,d), 98.24 ,s), 98.20 ,s), 82.2 ,s), 75.9 ,d), 56.2 ,s), 55.5 ,s),
32.7 ,t), 32.6 ,t), 18.7 ,t), 18.6 ,q), 11.2 ,d); IR ,KBr) 3263,
2132, 1244, 1020, 994, 882, 849, 671 cm21; EI MS m/z 348
,M1). HRMS calcd for C24H32Si 348.2273, found 348.2237.
2097, 1609, 1204, 1110, 1094, 938, 837, 757, 680 cm21
.
To a solution of 2.76 g ,13.6 mmol) of the above compound
in 56 mL of THF was added 9.04 mL ,15.0 mmol) of
1.66 M BuLi in hexane at 08C. The mixture was stirred at
08C for 3 h, then 4.81 g ,15.6 mmol) of triisopropylsilyl
tri¯uoromethanesulfonate was added dropwise. The mixture
was stirred at room temperature for 30 min. Water was
added and the mixture was extracted with ether. The extract
was washed with saturated NaCl solution ,brine) and dried
over MgSO4. Removal of the solvent followed by ¯ash
chromatography gave 4.87 g ,99%) of 6b as pale yellow
1.1.4. 1,3,5-Tris{[11-ꢀtriisopropylsilyl)ethynyl[4.3.2]pro-
pella-2,4,10-trien-10-yl]butadiynyl}benzene ꢀ9a). To a
¯ask ®lled with nitrogen containing 0.61 mg ,3.2 mmol) of
CuI and 3.30 mg ,3.2 mmol) of Pd2,dba)3´CHCl3 was added
a solution of 179 mg ,0.514 mmol) of 7b and 41 mg
,0.106 mmol) of 1,3,5-tris,bromoethynyl)benzene ,8a)16a
in 4 mL of benzene followed by 46 mg ,0.30 mmol) of
1,2,2,6,6-pentamethylpiperidine. The mixture was stirred
at room temperature for 8 h, then poured into 100 mL of
1M HCl and extracted with ether. The extract was washed
with brine and dried over MgSO4. A crude product obtained
on the same scale was combined and puri®ed by ¯ash chro-
matography to afford 168 mg ,67%) of 9a as a yellow solid.
1
oil. H NMR ,CDCl3) d 5.76±5.94 ,m, 4H), 1.91±2.01
,m, 2H), 1.14±1.66 ,m, 4H), 1.09 ,brs, 21H); 13C NMR
,CDCl3) d 129.9 ,s), 128.9 ,d), 127.5 ,d), 126.6 ,s), 122.6
,d), 121.5 ,d), 97.4 ,s), 95.8 ,s), 59.1 ,s), 56.0 ,s), 32.2 ,t),
31.7 ,t), 18.6 ,q), 18.5 ,t), 11.2 ,d); IR ,neat) 2143, 1612,
1203, 1125, 1007, 882, 839, 756, 666 cm21; EI MS m/z 359
,M1). HRMS calcd for C22H31ClSi 359.0263, found
359.0261.
1
Mp 74±758C; H NMR ,CDCl3) d 7.56 and 7.53 ,s, ratio
1:9, total 3H), 5.79±5.90 ,m, 12H), 1.93±2.01 ,m, 6H),
1.46±1.64 ,m, 6H), 1.04±1.38 ,brs, 63H); 13C NMR
,CDCl3) d 137.4 ,s), 136.1 ,s), 129.7 ,s), 128.1 ,d), 122.9
,s), 121.9 ,d), 100.5 ,s), 98.4 ,s), 80.9 ,s), 78.0 ,s), 75.9 ,s),
75.1 ,s), 56.7 ,s), 56.3 ,s), 33.1 ,t), 33.0 ,t), 18.8 ,q), 11.4
,d). Small signals with ca. one-tenth intensities are observed
at 137.5 ,s), 136.6 ,d), 129.6 ,s), 128.7 ,d), 123.1 ,s), 121.5
,d), 100.5 ,s), 80.6 ,s), 77.8 ,s), 76.2 ,s), 75.3 ,s), 18.7 ,q),
11.5 ,d); IR ,KBr) 2200, 2137, 2123, 1576, 1070, 1011, 881,
675 cm21; FAB MS m/z 1189 ,M1).
1.1.2. 10-[ꢀTriisopropylsilyl)ethynyl]-11-[ꢀtrimethylsilyl)-
ethynyl][4.3.2]propella-2,4,10-triene ꢀ7a). A solution of
115 mg ,300 mmol) of Pd,PhCN)2, 38.1 mg ,200 mmol) of
CuI, and 3.59 g ,10.0 mmol) of 6b in 13 mL of THF was
degassed by three freeze±thaw cycles and the ¯ask was
®lled with argon. 162 mg ,800 mmol) of P,t-Bu)3, 1.21 g
,12.0 mmol) of diisopropylamine, and 1.18 g ,12.0 mmol)
of ,trimethylsilyl)acetylene were added in this order. The
mixture was heated at re¯ux temperature for 8 h and at 508C
overnight. During the reaction, additional ,trimethylsilyl)-
acetylene ,1.28 g, 13.0 mmol) was added. The mixture was
diluted with water and ether and the aqueous phase was
acidi®ed with 1N HCl. The aqueous layer was separated
and extracted with ether. The combined extract was washed
with saturated NaHCO3 solution and brine, and then dried
,MgSO4). The product was puri®ed by ¯ash chromato-
1.1.5. [4.3.2]Propellatriene-fused [16.16.16]ꢀ1,3,5)cyclo-
phaneoctadecaynehexaene ꢀ5a). To a solution of 186 mg
,0.156 mmol) of 9a in 8 mL of THF was added 134 mL
,141 mg, 2.35 mmol) of acetic acid followed by 1.56 mL
of 1.0 M solution of Bu4NF in THF, and the solution was
stirred at room temperature for 1 h. The mixture was diluted
with water and extracted with ether. The extract was washed
with brine and dried over MgSO4. In another run, to obtain
an NMR sample of 9b, the solvent was evaporated to
dryness to give an oil which turned dark immediately
owing to polymerization [1H NMR ,CDCl3) d 7.53 ,s,
3H), 5.82±5.92 ,m, 12H), 3.75 ,s, 3H), 0.84±2.05 ,m,
18H)].
1
graphy, yielding 3.56 g ,85%) of 7a as a brown oil. H
NMR ,CDCl3) d 5.81±5.86 ,m, 4H), 1.88±2.00 ,m, 2H),
1.39±1.63 ,m, 2H), 1.07±1.34 ,m, 2H), 1.08 ,brs, 21H),
0.17 ,s, 9H); 13C NMR ,CDCl3) d 134.1 ,s), 132.5 ,s),
128.70 ,d), 128.68 ,d), 121.7 ,d), 121.6 ,d), 100.6 ,s),
98.7 ,s), 97.9 ,s), 96.7 ,s), 55.9 ,s), 55.6 ,s), 32.8 ,t), 32.7
,t), 18.7 ,t), 18.6 ,q), 11.2 ,d), 0.1 ,q); IR ,neat) 2143, 1250,
1029, 844, 670 cm21; EI MS m/z 421 ,M1). HRMS calcd for
C27H40Si2 420.7856, found 420.7848.
Accordingly, the above extract was concentrated to ca.
5 mL and diluted with 5 mL of pyridine. The solvent was
removed under reduced pressure again to ca. 5 mL and
diluted with 80 mL of pyridine. This solution was added
dropwise to a mixture of 2.83 g ,15.6 mmol) of Cu,OAc)2
in 210 mL of pyridine during a 5.5-h period. During the
reaction and subsequent isolation procedures, the ¯asks
and chromatography columns were covered with an
aluminum foil to protect the product 5a from room light,
otherwise it readily changed into yet unidenti®ed materials.
After being stirred at room temperature for 19 h, the mixture
was ®ltered through a short column of silica gel and the
solvent was removed under reduced pressure. The product
was puri®ed by ¯ash chromatography to give 78 mg ,70%)
1.1.3. 10-Ethynyl-11-[ꢀtriisopropylsilyl)ethynyl][4.3.2]-
propella-2,4,10-triene ꢀ7b). To a suspension of 692 mg
,5.00 mmol) of K2CO3 in 50 mL of MeOH was added a
solution of 1.05 g ,2.50 mmol) 7a in 20 mL of THF. The
mixture was stirred at room temperature for 1 h, then
concentrated in vacuo to remove most of the MeOH. The
mixture was diluted with ether and the extract was washed
with water and brine, and dried ,MgSO4). Removal of the
solvent followed by ¯ash chromatography gave 834 mg
,96%) of 7b as a dark orange oil, which solidi®ed in a
1
of 5a as a bright yellow solid. Dec. .1408C; H NMR
1
refrigerator. Mp 39±408C; H NMR ,CDCl3) d 5.78±5.89
,CDCl3) d 7.49 ,brm, 6H), 5.90 ,brd, Jˆ10.2 Hz, 12H),
5.81 ,brd, Jˆ7.8 Hz, 12H), 1.97±2.17 ,m, 12H), 1.58±
1.67 ,m, 6H), 1.40±1.53 ,m, 6H), 1.19±1.30 ,m, 12H);
13C NMR ,CDCl3) d 136.2 ,d, smaller signals observed at
,m, 4H), 3.16 ,s, 1H), 1.90±2.00 ,m, 2H), 1.40±1.63 ,m,
2H), 1.11±1.28 ,m, 2H), 1.08 ,brs, 21H); 13C NMR ,CDCl3)
d 134.8 ,s), 130.9 ,s), 128.5 ,d), 128.4 ,d), 121.9 ,d), 121.8

Y. Tobe et al. / Tetrahedron 57 32001) 3629±3636
3635
136.3 and 136.1), 135.2 ,s, a small signal observed at 135.1),
127.6 ,d, a signal with similar intensity observed at 127.7),
122.69 ,s, smaller signals observed at 122.74, 122.71,
122.66, and 122.64), 122.2 ,d, broad), 82.06 ,s, smaller
signals observed at 82.10, 82.03, 82.01), 80.4 ,s), 80.0 ,s),
77.1 ,s), 75.47 ,s, signals with similar intensities observed at
75.48 and 75.44, and smaller signals observed at 75.52 and
75.41), 74.6 ,s), 56.8 ,s, a smaller signal observed at 56.9),
33.1 ,t), 18.8 ,t); IR ,KBr) 2200, 2163, 2127, 1572, 1375,
1244, 1078, 877, 738, 677 cm21; UV±Vis ,CHCl3) lmax
,log e) 426 ,4.65), 391 ,4.78), 363 ,4.71), 281 ,5.24) nm;
FAB MS m/z 1435 ,M1).
¯ash chromatography to afford 200 mg ,39%) of 9c as a
dark yellow solid. Mp 96±978C; 1H NMR ,CDCl3) d
5.78±5.92 ,m, 12H), 1.93±2.05 ,m, 6H), 1.40±1.68 ,m,
6H), 1.21±1.33 ,m, 6H), 1.09 ,brs, 63H); 13C NMR
,CDCl3) d 140.9 ,s), 138.6 ,s), 129.5 ,s), 128.11 ,d),
128.06 ,d), 122.2 ,s), 122.01 ,d), 121.99 ,d), 101.3 ,s),
98.5 ,s), 85.2 ,s), 78.3 ,s), 75.4 ,s), 56.9 ,s), 56.3 ,s), 33.1
,t), 32.9 ,t), 18.9 ,t), 18.7 ,q), 11.3 ,d); IR ,KBr) 2197, 2137,
1290, 1072, 882, 841, 774, 672 cm21
.
1.1.9. [4.3.2]Propellatriene-fused hexachloro[16.16.16]-
ꢀ1,3,5)cyclophaneoctadecaynehexaene ꢀ5b). Deprotection
of 259 mg ,200 mmol) of 9c was undertaken as described for
the case of 9a using 180 mg ,3.00 mmol) of acetic acid and
2.00 mL ,2.00 mmol) of 1.0 M THF solution of Bu4NF in
10 mL of THF. The mixture was extracted with benzene, the
organic phase was washed with saturated NaHCO3 solution
and brine, and dried over MgSO4. The solution was concen-
trated to 100 mL by evaporation and was used in the subse-
quent reaction.
1.1.6. 1,3,5-Trichloro-2,4,6-tris[ꢀtrimethylsilyl)ethynyl]-
benzene ꢀ8b). To
a degassed solution of 11.2 g
,20.0 mmol) of 1,3,5-trichloro-2,4,6-triiodobenzene,25
2.08 mg ,1.80 mmol) of Pd,PPh3)4, and 686 mg
,3.60 mmol) of CuI in 80 mL of THF was added under
argon atmosphere 7.29 g ,72.0 mmol) of diisopropylamine
followed by 8.84 g ,90.0 mmol) of ,trimethylsilyl)acetyl-
ene, and the mixture was heated under re¯ux for 30 h.
During the reaction additional ,trimethylsilyl)acetylene
,total 295 mg, 3.00 mmol) was added occasionally. Then
the mixture was diluted with 1N HCl and ether, and the
organic layer was separated. The aqueous layer was
extracted with ether and the combined extract was washed
with saturated NaHCO3 solution and brine, and dried over
MgSO4. After removal of the solvent, the product was
isolated by ¯ash chromatography followed by recrystalliza-
tion from hexane ,and preparative HPLC for the mother
liquor after several recrystallizations) to give 5.79 g ,62%)
of 8b as a white solid. Mp 155±1568C; 1H NMR ,CDCl3) d
0.29 ,s); 13C NMR ,CDCl3) d 138.9 ,s), 122.6 ,s), 107.9 ,s),
97.2 ,s), 20.23 ,q); IR ,KBr) 2168, 1251, 1069, 1035, 857,
758 cm21; EI MS m/z 472, 470, 468 ,rel. intensity ca. 1:2:2,
M1).
To a solution of 3.63 g ,20.0 mmol) of Cu,OAc)2 in 300 mL
of pyridine was added dropwise the above solution during a
21-h period. The mixture was worked up as in the case of 5a,
except for the fact that ®nal puri®cation was carried out by
preparative HPLC, to give 100 mg ,61%) of 5b as a bright
yellow solid. Caution! A sample of this compound decom-
posed violently, catching ®re when it was scratched with a
1
spatula. Mp 96±978C; H NMR ,CDCl3) d 5.89±5.92 ,m,
12H), 5.81±5.83 ,m, 12H), 1.97±2.17 ,m, 12H), 1.58±1.67
,m, 6H), 1.40±4.53 ,m, 6H), 1.19±1.30 ,m, 12H); 13C NMR
,CDCl3) d 141.5 ,s), 135.9 ,s), 134.8 ,s), 127.8 ,d), 122.8
,d), 122.5 ,s), 122.2 ,s), 84.9 ,s), 80.9 ,s), 79.6 ,s), 77.9 ,s),
77.3 ,s), 57.2 ,s), 57.1 ,s), 33.2 ,t), 29.4 ,t), 18.8 ,t); FAB
MS m/z 1650±1638 ,the most abundant peak at 1642, M1).
1.1.7. 1,3,5-Trichloro-2,4,6-trisꢀbromoethynyl)benzene
ꢀ8c). To a solution of 266 mg ,0.570 mmol) of 8b in
11 mL of acetone was added 354 mg ,1.99 mmol) of NBS
followed by 29 mg ,0.17 mmol) of silver ,I) nitrate and the
mixture was stirred at room temperature for 10 h. During
the reaction, the reaction ¯ask was protected from light
by wrapping with an aluminum foil. The same reaction was
undertaken in another run, and the reaction mixture was
combined and worked up as follows. The mixture was diluted
with water and benzene, and the organic layer was washed
with water and brine, and then dried ,MgSO4). Removal of
the solvent in vacuo left a yellow solid which was recrystal-
lized from benzene to give 430 mg ,67%) of 8c as a colorless
Acknowledgements
This work was supported by Grants-in-Aid from the
Ministry of Education, Science, Sports and Culture of
Japan and Nagase Science Foundation. Y. T. thanks Shin-
Etsu Chemicals Co. for a generous gift of organosilicon
reagents.
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