Expanded Radialenes with Bicyclo[4.3.1]decatriene Units: New Precursors to Cyclo[n]carbons

Article abstract of DOI:10.1002/chem.200305051

A new method for the formation of conjugated polyynes has been developed based on both the rearrangement of vinylidenes to alkynes and the [2+1] cheletropic fragmentation of dialkynylmethylenebicyclo-[4.3.1]deca-1,3,5-triene derivatives. A model study of the photolysis of simple dialkynylmethylenebicyclo[4.3.1]deca-1,3,5-trienes resulted in cheletropic fragmentation followed by 1,2-migration to give the corresponding linear polyynes, although undesired isomerization to methylenebicyclo[5.3.0]triene derivatives took place concurrently. Expanded [3]-, [4]-, [5]-, and [6] radialene derivatives with exocyclic bicyclo[4.3.1]decatriene units were prepared by oxidative coupling of the monomeric units as precursors to the corresponding cyclo[n]carbons, monocyclic forms of carbon clusters. The spectroscopic properties of the expanded radialenes were investigated in connection with cross conjugation of the core π system and with its perturbation by the extraannular bicyclic π system. In negative-mode laser-desorption time-of-flight (LD-TOF) mass spectra, the expanded radialenes exhibited peaks due to the corresponding cyclo[n]carbon anions (n = 18, 24, 30, and 36) formed by the stepwise loss of the aromatic indane fragments.

Full text of DOI:10.1002/chem.200305051

FULL PAPER
Expanded Radialenes with Bicyclo[4.3.1]decatriene Units:
New Precursors to Cyclo[n]carbons
[
a]
Yoshito Tobe,* Rui Umeda, Naruhito Iwasa, and Motohiro Sonoda
Abstract: ± new method for the for-
mation of conjugated polyynes has
been developed based on both the re-
arrangement of vinylidenes to alkynes
and the [2+1] cheletropic fragmenta-
tion of dialkynylmethylenebicyclo-
zation to methylenebicyclo[5.3.0]triene
derivatives took place concurrently.
Expanded [3]-, [4]-, [5]-, and [6]radia-
lene derivatives with exocyclic bicy-
clo[4.3.1]decatriene units were pre-
pared by oxidative coupling of the
monomeric units as precursors to the
corresponding cyclo[n]carbons, mono-
cyclic forms of carbon clusters. The
spectroscopic properties of the expand-
ed radialenes were investigated in con-
nection with cross conjugation of the
core p system and with its perturbation
by the extraannular bicyclic p system.
In negative-mode laser-desorption
time-of-flight (LD-TOF) mass spectra,
the expanded radialenes exhibited
peaks due to the corresponding cyclo-
[n]carbon anions (n = 18, 24, 30, and
36) formed by the stepwise loss of the
aromatic indane fragments.
[4.3.1]deca-1,3,5-triene derivatives. ±
model study of the photolysis of sim-
ple dialkynylmethylenebicyclo[4.3.1]de-
ca-1,3,5-trienes resulted in cheletropic
fragmentation followed by 1,2-migra-
tion to give the corresponding linear
polyynes, although undesired isomeri-
Keywords: alkynes
¥
carbenes
¥
cyclo[n]carbons ¥ cycloreversion ¥
radialenes
Introduction
cursors that have monocyclic frameworks of the desired
carbon numbers. In this context, a number of precursors of
cyclo[n]carbons have been prepared by utilizing a retro-
Cyclo[n]carbons, defined as n-membered monocyclic rings
of all-carbon molecules, have been attracting considerable
interest from several points of view. First, although their
unique cyclic structure among the various forms of carbon
[4]
[5]
Diels±±lder reaction, decarbonylation, and decomposi-
[6]
tion of aminotriazoles. We have developed our own
method based on the retro [2+2] fragmentation of
[4.3.2]propellatrienes to form a C(sp)ÀC(sp) bond by ex-
truding an aromatic fragment, indane, and applied it to the
[1]
allotropes has been indicated by spectroscopic methods,
detailed geometrical, electronic, and vibrational informa-
tion, which is also important with regard to aromaticity/anti-
aromaticity of dehydroannulenes, has not yet been elucidat-
ed. Next, it is thought likely that cyclo[n]carbons play a key
[7]
formation of cyclo[n]carbons. Despite the advantages of
this retro [2+2] approach, such as the ease of fragmentation
and the kinetic stability of the precursors, a few disadvantag-
es exist. For example, the preparation of the propellane unit
requires lengthy sequences and is laborious. Moreover,
owing to the relatively small angle (ca. 908) between the
triple bonds of the diethynyl[4.3.2]propellatriene unit, only
the cyclic dehydrotrimer and dehydrotetramer were ob-
tained; larger cyclic dehydrooligomers such as the dehydro-
pentamer and dehydrohexamer, with 30- and 36-membered
rings, respectively, were not obtained. In addition to these
methods, the [2+1] cheletropic fragmentation of cyclopro-
pane-containing oligodiacetylenes, such as cyclic dehydro-
[2]
role during the early stages of fullerene formation. More-
over, it has been proposed that cyclo[12]carbon and cy-
clo[18]carbon serve as precursors of the hitherto unknown,
two-dimensional carbon networks called graphyne and
[3]
graphdiyne, respectively.
Cyclo[n]carbons can be produced by laser vaporization
of graphite, but with little selectivity in cluster-size distribu-
tion. It would be advantageous for size- and shape-selectivi-
ty to generate cyclo[n]carbons from the corresponding pre-
[8]
oligomers of diethynyl[4.4.1]propellatetraenes incorporat-
ed in a fullerene structure, and 1,1-diethynyltetramethylcy-
[
a] Prof. Dr. Y. Tobe, R. Umeda, N. Iwasa, Dr. M. Sonoda
Department of Chemistry, Faculty of Engineering Science
Osaka University
and CREST, Japan Science and Technology Corporation (JST)
Toyonaka, Osaka 560-8531 (Japan)
[9]
clopropane, have been investigated by mass spectrometry,
aiming at the generation of cyclo[5n]carbons.
It has been well documented that vinylidenes equilibrate
[10]
with acetylenes at high temperature. Similarly, alkylidene
carbenes generated by the photolysis of alkylidenecyclopro-
Fax : (+81)6-6850-6229
E-mail: tobe@chem.es.osaka-u.ac.jp
Chem. Eur. J. 2003, 9, 5549 ± 5559
DOI: 10.1002/chem.200305051
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGa±, Weinheim
5549

FULL PAPER
[
11]
pane derivatives rearranged to alkynes.
Moreover, Tyk-
ments in V are not linearly conjugated (i.e., cross-conjugat-
ed), V must possess considerable kinetic stability. In addi-
tion, in the oligomers V, the radialene p system would suffer
from perturbation of the bridged cycloheptatriene system
connected to the periphery of the radialene framework.
Herein we report the synthesis of dialkynylmethylenebi-
cyclo[4.3.1]decatriene derivatives 1a, 1b, 2, and 3, the X-ray
structural characterization of 1b, and the photolysis of 1a, 2,
and 3 as a model study of the photochemical [2+1] fragmen-
tation to form corresponding linear polyynes. We also report
the synthesis and spectral properties of cyclic dehydroo-
ligomers 4±7, which have expanded radialene structures, and
their cheletropic fragmentation in negative-mode laser-de-
sorption mass spectra to provide the corresponding cyclo-
[n]carbon anions (n = 18, 24, 30, and 36).
winski developed an ingenious method for the preparation
of polyynes by use of the rearrangement of dialkynylvinyli-
denoids generated from the corresponding dibromoal-
kenes. On the basis of these previous results, we planned
to develop a new method for generating cyclo[n]carbons uti-
lizing the vinylidene-to-acetylene rearrangement. To this
end, we designed the dialkynylmethylenebicyclo[4.3.1]deca-
,3,5-triene unit I as the key unit of the precursor. That is,
we envisioned that extrusion of an aromatic fragment
indane) from I would produce dialkynylvinylidene III, pre-
sumably via the corresponding propelladiene-type valence
isomer II, and would then isomerize to form a hexatriyne
unit IV (Scheme 1). The observations underlying our design
of the carbene precursor I are the following: i) Thermally in-
[12]
[13]
1
(
Results and Discussion
Synthesis and structure of mon-
omer unit: Dibromo[4.3.1]pro-
pelladiene 8 was prepared by
treatment of dibromopropel-
lane 9, which had been pre-
pared by dibromocarbene addi-
Scheme 1. Proposed pathway for the formation of a polyyne unit.
[17]
tion to dihydroindane,
with
pyridinium hydrobromide per-
bromide followed by dehydrobromination with 1,8-diazabi-
cyclo[5.4.0]undec-7-ene (DBU). Halogen±lithium exchange
of 8 with nBuLi at À1008C followed by treatment with 1,5-
duced fragmentation of dihalomethano[10]annulenes has
been reported to form dihalocarbenes by elimination of
[14]
naphthalene, although the mechanism, that is, whether or
not the corresponding [4.4.1]propellatetraene is involved, is
[18]
bis(trimethylsilyl)penta-1,4-diyn-3-one (10) and then with
[
14b]
[19]
not clear.
pellanes has been recognized as a method for forming free
ii) Photolysis of cyclopropane-containing pro-
TMSCl afforded adduct 11 (Scheme 2).
±lthough the
[
15]
carbenes, including such peculiar species as homocubyli-
[15c]
dene.
The cyclic dehydrooligomers V of I would then
serve as precursors of cyclo[n]carbons. Since the bicyclic
unit I would be more readily prepared than the previously
employed precursor [4.3.2]propellatriene units, we expected
that this method would provided ready access to cyclo[n]car-
2
bons. In addition, since the C(sp)-C(sp )-C(sp) bond angle
of the exo methylene carbon of I must be nearly 1208, large
cyclic dehydrooligomers such as pentamers and hexamers
(
V: m = 5, 6) would be obtained, providing a route to large
cyclo[n]carbons. The corresponding large cyclic dehydro-
oligomers were not obtained from the diethynyl[4.3.2]pro-
pellatriene unit.
5 5 3 5 5 2 2
Scheme 2. a) i) C H N¥HBr , C H N , CHCl , RT; ii) DBU, toluene, 428C,
[7b,e]
35%. b) nBuLi, À1008C, then (TMS-CꢀC) C=O (10), À708C, then
2
TMSCl, THF, 46%. c) tBuLi, pentane, À1108C, then TMSCl, 80%.
The cyclic dehydrooligomers V possess expanded radia-
d) LiOH¥H
NH
PdCl
2
O, THF, RT, 100%. e) TIPS-CꢀC-Br (14), CuCl,
lene structures that have attracted a great deal of interest
2
OH¥HCl, aq. EtNH
2
,
THF-MeOH (1:2), RT, 63%. f) PhI,
[16]
with regard to their cross conjugation.
Since the p seg-
2
(PPh , CuI, Et N, RT, 91%.
3
)
2
3
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Expanded Radialenes
5549 ± 5559
1
13
spectral data ( H NMR and C NMR) of the product indi-
cated that it was a single isomer, its configuration was not
determined. ± second halogen±lithium exchange of 11 with
tBuLi effected the elimination to give 1a in 80% yield.
13
The C NMR spectrum of the product was consistent
with the open form 1a, not the closed isomer 12 with a pro-
3
pelladiene form, since it does not exhibit the quaternary sp
carbon signal present in propelladienes 8 and 11. Instead,
the bridgehead carbon signal appears at d = 138.6 ppm. In
13
addition, the C NMR spectrum of 1a indicates that the
exocyclic double bond is considerably polarized, since one
of the protons resonates at substantially lower field (C(10)
d = 167.0 ppm) than the other (C(11) d = 93.1 ppm). Neu-
enschwander et al. reported that the electron-withdrawing
groups caused polarization of the exocyclic double bond of
heptafulvene derivatives, thereby leading to large chemical-
Figure 1. ORTEP drawing of 1b with arbitrary numbering. Selected bond
lengths [ä] and bond angles [8]: C(1)ÀC(2) 1.186(2), C(2)ÀC(3) 1.441(1),
C(3)ÀC(4) 1.342(2), C(4)ÀC(5) 1.464(1), C(5)ÀC(6) 1.509(1), C(5)ÀC(9)
1
3
shift differences in the C NMR spectra of the double
[20]
bond. ±ccordingly, the polarization of the double bond of
a can be ascribed to the weak electron-withdrawing effect
1
.350(1), C(6)ÀC(7) 1.551(1), C(8)ÀC(8a) 1.356(3), C(8)ÀC(9) 1.441(2),
1
C(1)-C(2)-C(3) 177.8(1), C(2)-C(3)-C(2a) 117.6(1), C(2)-C(3)-C(4)
21.19(6), C(3)-C(4)-C(5) 130.05(5), C(5)-C(4)-C(5a) 99.8(1), C(4)-C(5)-
of the ethynyl groups. ±lternatively, the bond-angle strain
caused by the relatively short methylene bridge may also
contribute to the polarization in 1a, since ItÙ et al. demon-
1
C(6) 110.85(8), C(4)-C(5)-C(9) 116.53(10), C(5)-C(6)-C(7) 106.78(9),
C(5)-C(9)-C(8) 122.2(1), C(6)-C(5)-C(9) 128.14(10), C(6)-C(7)-C(6a)
113.8(1), C(8a)-C(8)-C(9) 124.16(7).
13
strated that the C NMR signals of the carbonyl carbon of
2
,7-methylene-brigded tropones exhibited downfield shifts
[21]
with decreasing length of the methylene bridge.
In analogy to the previously reported [2+2+2] cycload-
dition of the 1,6-methano[10]annulenes with dienophiles,
1b suitable for X-ray crystallographic analysis was obtained
by recrystallization from n-hexane.
[22]
the reaction of 1a with N-phenylmaleimide in refluxing tolu-
ene afforded adduct 13 as a sole product in 81% yield
The bond lengths and angles of the bicyclic framework
[21]
in 1b are similar to those of [4]troponophane 15. Similar-
ly, both cycloheptatriene moieties of 1b and 15 possess a
tub form. ±s shown in Figure 2, the seven-membered ring of
(
Scheme 3). Nevertheless, this result is consistent with the
Scheme 3. a) N-phenylmaleimide, toluene, reflux, 81%
Figure 2. ±ngles between the least-squares planes of 1b and 15.
bridged-triene structure of 1a, since, just as for cyclohepta-
triene itself, the valence tautomer, which is in equilibrium
with 1a, is the more reactive diene in the Diels±±lder reac-
tion.
1b is bent more severely than that of 15. Since the exocyclic
double bond of 1b is nearly perpendicular to the plane
C(5)-C(9)-C(9a)-C(5a), its conjugation with the cyclohepta-
triene p-system is not efficient. This is in accordance with
the fact that 1a, 1b, 2, and 3 do not exhibit absorption
bands in the visible region, while unbridged methylenecyclo-
heptatriene derivatives, including 18 and 20 described later,
Desilylation of 1a with LiOH¥H O afforded 1b and a
2
[23]
subsequent Cadiot±Chodkiewicz reaction
with bromo-
alkyne 14 gave the bisbutadiynyl derivative 2 as a pale
yellow solid in 63% yield. The diphenyl derivative 3 was
[25]
exhibit characteristic absorptions around 400 nm.
These
[24]
prepared by Sonogashira cross coupling of 1b with iodo-
benzene (Scheme 2).
results suggest that the large polarization of the exocyclic
double bond is mainly due to the strain around the bridge
top (C(5)-C(4)-C(5a) = 99.88), which is caused by the rela-
tively short methylene bridge rather than the conjugation of
the cycloheptatriene moiety with the electron-withdrawing
ethynyl groups. The torsional angles of the bridgehead
double bond of 1b are depicted in Figure 3. The twisting or
torsion parameter (f) represents the deviation from copla-
Bicyclo[4.3.1]decatrienes 1a, 1b, 2, and 3 are bridgehead
dienes, compounds possessing two distorted bridgehead
double bonds. In order to elucidate the deformation of the
bridgehead double bond and clarify the effect of strain on
the structure of the bicyclic framework, an X-ray structure
analysis of 1b was carried out (Figure 1). ± single crystal of
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5551

Y. Tobe et al.
FULL PAPER
of 18 indicate its polarization as in the case of 1a, the signal
for C(2) is not as much downfield shifted as that of 1a; this
implies the presence of a steric effect in the latter. The UV/
Vis spectrum of 18 (n-hexane) exhibits a strong absorption
at 385 nm (e = 3300), which is consistent with the heptaful-
[25]
vene chromophore. The formation of 18 can be explained
in terms of a 1,5-sigmatropic shift of a cyclopropane bond of
the propelladiene intermediate 12, the valence isomer of 1a,
followed by electrocyclic ring opening of the norcaradiene
moiety (Scheme 5).
Figure 3. Torsional angles of the bridgehead double bonds in 1b.
narity of the two p-type orbitals, and the out-of-plane bend-
ing parameter (c) is regarded as a measure of the extent of
[26]
rehybridization. The angle of twisting parameter t, repre-
sented by (f + f )/2, of 1b is 20.18, which is larger than
1
2
that reported for the bridgehead diene 16 (t = 11.68),
[27]
which has an oxabicyclo[4.3.1]decatriene framework. The
difference is probably due to the wider angle of the oxygen
bridge of 16 (101.98) than that of 1b (99.88), which reduces
the distortion of the double bond. On the other hand, the
angle of the vinylidene carbon (C(2)-C(3)-C(2a)) of 1b
Scheme 5. Mechanism of the fragmentation and isomerization reactions
of 1a.
(
117.68) is slightly larger than those reported for other ethy-
[28a±e]
nylethenes, which typically show angles of around 1158.
Irradiation of the extended system 2 in n-hexane yielded
[
7a,29]
Photolysis of model compounds: ±s model studies to test
the photochemical cheletropic fragmentation of the dialkyl-
methylenebicyclo[4.3.1]decatrienes, acyclic compounds 1a,
decapentayne derivative 19
in 59% isolated yield to-
gether with the isomerization product 20 in 24% yield as a
brown oil. The structure of 20 was also confirmed on the
basis of the NMR and UV/Vis spectroscopic data as in the
case of 18. In the electronic absorption spectrum, 20 exhibits
a maximum at 428 nm (e = 19400). In contrast, irradiation
of a solution of diphenyl derivative 3 in diethyl ether afford-
2
, and 3 were irradiated with a low pressure mercury lamp
in an ice bath (Scheme 4). Photolysis of 1a in n-hexane af-
[7a,29,30]
forded bis(trimethylsilyl)hexatriyne (17)
in 43% iso-
lated yield together with indane (45% yield detected by
GC). In addition, the isomerization product 18 of the start-
ing material was obtained in 30% isolated yield as a brown
oil. The structure of 18 was elucidated on the basis of its
NMR and UV/Vis spectra. The salient features of the NMR
spectrum include four vinyl proton signals at d = 6.90 (d,
[
31]
ed diphenylhexatriyne (21) in slightly lower yield (37%).
We were not able to isolate the isomerization product 22,
because it polymerized rapidly when a solution containing
22 was concentrated. Therefore, a solution of 3 in [D ]THF
was irradiated under similar conditions, and the photolysate
was analyzed by H NMR and liquid-chromatography mass
spectroscopy (LCMS). The H NMR spectrum exhibited
four vinyl proton signals corresponding to 22 at d = 7.02±
7.09 (m, 1H), 6.38±6.42 (m, 1H), and 6.19±6.27 (m, 2H)
ppm and three methylene sig-
8
1
1
H), 6.37 (dd, 1H), and 6.12±6.21 (m, 2H) ppm and eight
vinyl carbon signals at 151.3, 145.1, 144.9, 134.4, 132.0, 130.5,
28.7, and 93.5 ppm. It should be pointed out that, although
1
1
13
the C NMR chemical shifts of the exocyclic double bond
nals from the five-membered
ring of 22 at d = 3.28 (t, 2H),
2
2
.62 (t, 2H), and 1.91 (quintet,
H) ppm in addition to the sig-
nals of the methylene and aro-
matic protons of indane and 21.
In the LCMS, an LC peak cor-
responding to the molecular ion
was observed at m/z = 335
+
[
M +H]; this indicated that
Scheme 4. Cheletropic fragmentation and isomerization by photolysis of 1a, 2, and 3.
the product was an isomer of
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Expanded Radialenes
5549 ± 5559
the starting material 3. These results are consistent with the
structure formulated for 22.
To obtain even-number cyclic dehydrooligomers, oxida-
tive coupling of dehydrodimer 23b was examined
(Scheme 7). First, one of the terminal alkynyl groups of 1b
was selectively protected by a 2-hydroxypropyl group by
treatment with nBuLi (1.2 equiv) followed by acetone to
afford 24 in 81% yield. Oxidative coupling of 24 under Hay
Thus the model study showed that photochemical frag-
mentation took place, as we had expected, to yield linear
polyynes. However, because of the formation of the rear-
rangement products, it was not as efficient as the [2+2] frag-
[7a,e]
[32]
mentation of the [4.3.2]propellatrienes.
The photochemi-
conditions gave bis-protected dehydrodimer 23a, and re-
cal fragmentation, therefore, was not investigated for cyclic
dehydrooligomers of diethynylmethylenebicyclo[4.3.1]deca-
triene with expanded radialene frameworks.
Synthesis of cyclic dehydrooligomers: Macrocyclic dehy-
drooligomers of 1b with expanded radialene structures were
prepared by its copper(ii)-mediated oxidative coupling
under dilution conditions. We obtained cyclic dehydrotet-
ramer 5 as the major product (33%) together with cyclic de-
hydrotrimer 4, dehydropentamer 6, and dehydrohexamer 7
in 3%, 15%, and 7% yield, respectively (Scheme 6).
Scheme 7. a) nBuLi, THF, À788C, then acetone, 81%. b) CuCl,
TMED±,
2
O , acetone, RT, 93%. c) KOH, benzene, reflux, 93%,
d) Cu(O±c)
2
, pyridine, RT, 91%. Only one of the isomers is shown for
reasons of clarity.
moval of the protective group gave 23b as a stable yellow
solid. Oxidative coupling of 23b under dilution conditions
formed cyclic dehydrotetramer 5 exclusively in 91% yield.
The expanded radialenes 4±7 exhibit poor solubility in
organic solvents, which is minimal to allow spectral charac-
1
13
terizations by H N MR, C NMR, and UV/Vis spectroscopy.
1
3
13
C NMR spectra of cyclic dehydrooligomers: The C N MR
spectra of 4±7 indicate clearly that these are mixtures of dia-
stereomers. In particular, several signals are observed for
2
the tertiary sp carbons of the bicyclic triene framework and
2
13
the bridgehead sp carbons. The C NMR chemical shifts of
the radialene double bonds suggest that the polarization of
the double bonds increases with increasing ring size of the
expanded radialene framework (from 4 to 7). Namely, the
chemical shifts of the endocyclic carbons move up field
slightly (93.2 to 91.9 ppm), while those of the exocyclic car-
bons exhibit noticeable downfield shift (160.5 to 170.5 ppm).
The same trend was also observed for alkynyl-substituted ra-
2
Scheme 6. a) Cu(O±c) , pyridine, RT, 4 3%, 5 33%, 6 15%, 7 7%. Only
one of the diastereomers is shown for reasons of clarity.
[16a,e]
13
The expanded [3]radialene 4, which should be considera-
dialenes by Diederich et al.
Selected C NMR chemical
[16c, e]
bly strained,
is one of the relatively rare members of
shift data for expanded radialenes 4±7 are shown in Table 1.
Tykwinski et al. studied the effect of strain imposed by
the different lengths of the methylene linkage of the cross-
this class of compounds. It is also worth noting that large
macrocycles 6 and 7 were obtained from 1b, whereas only
dehydrotrimer and dehydrotetramer were isolated from the
oxidative coupling of the cyclobutene-containing diethy-
1
3
conjugated macrocycles 25 by C NMR spectroscopy and
[7b,e]
nyl[4.3.2]propellatrienes under similar conditions.
Solu-
tions of radialenes 4±7 could be stored in a cold and dark
place for a few months, but after removal of the solvent the
solid materials, in particular [3]radialene 4, tend to decom-
pose more rapidly, in contrast to our initial expectation re-
garding their kinetic stability.
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Y. Tobe et al.
FULL PAPER
1
3
Table 1. Selected C NMR (CDCl
3
) chemical shifts data (in ppm) of alkene and alkyne carbon atoms in expanded radialenes.
Compound
4
5
6
7
C(alkyne) d
C(alkene) d
77.8
93.2
90.3
160.5
76.0
92.3
79.1
166.3
75.3
92.1
76.4
169.3
75.1
91.9
76.3
170.5
[
28b]
X-ray analysis.
With decreasing number of methylene
enyne macrocycles. Expanded radialenes and dendralenes
are composed of two distinct p-electron systems that are
perpendicular to each other. One system represents in-plane
p orbitals in the macrocycle, the absorptions of which due to
homoconjugation are assigned to the bands at around
260 nm. The other system includes out-of-plane p orbitals in
the macrocycle, the absorption bands of which due to the
linearly conjugated ene-yne-yne-ene chromophore are ex-
pected to occur in a lower energy region than those of the
former system. However, it is difficult to discuss the elec-
tronic absorptions of 4±7 due to homoconjugation of the in-
plane p orbitals around 260 nm, since they possess bicyclic
triene chromophores, which also absorb in the same region.
The out-of-plane absorptions (300±350 nm) do not shift to
longer wavelengths with increasing ring size. Conversely,
they exhibit small blue shifts on going from 4 to 7 (4 344,
318 nm; 5 340 (sh), 318 nm; 6 337 (sh), 317 nm; 7 334 (sh),
313 nm). This is probably due to the decreasing planarity of
the macrocycles, which would reduce the overlap of p orbi-
tals in the ene-yne-yne-ene system, since it has been report-
ed that an expanded [6]radialene adopts a chair conforma-
13
2
linkages, the C NMR signals of the endocyclic sp carbons
of 25 exhibited slight upfield shifts, while those of the sp car-
bons moved downfield as a result of increased ring strain.
These observations were attributed to the increasing p-char-
2
acter of the s bonds of the endocyclic sp carbons, which im-
parts more s-character to the double bonds, with decreasing
ring size. The bicyclic triene framework of 4±7 exerts similar
strain effects because of the small bond angle at the bridge
top carbon. Perhaps, the effect of both ring systems counter-
acts the polarization of the exocyclic double bond, thereby
reducing the difference between the chemical shifts of the
double bond of 4 (Dd = 67.3 ppm) compared with those of
less-strained macrocycles (e.g., 7 Dd = 78.6 ppm). On the
other hand, the C NMR chemical shifts of the sp carbons
in expanded radialenes 4±7 exhibit steady downfield shifts
with decreasing ring size. Particularly, one of the sp carbons
of the most-strained 4 appeared at considerably lower field
13
(
90.3 ppm) than other (5±7) signals (76±79 ppm).
Electronic-absorption spectra of cyclic dehydrooligomers:
The UV/Vis spectra of 4±7 in CHCl are shown in Figure 4.
[16e]
tion of the macrocycle.
±lthough the spectral shapes of
3
±
lthough the preparations and purifications were carried
5±7 are similar, the spectrum of [3]radialene 4 is apparently
different. That is, the relative intensity of the longest-wave-
length absorption maximum of 4 is strong, while its molar
absorption coefficient is smaller [lmax (e) = 344 (34500) nm]
than those of 5±7. Diederich et al. also reported similar be-
out with great care to protect the products from light, the
[16c,e]
havior of expanded [3]radialenes.
This unusual trend of
expanded [3]radialenes might be explained in terms of the
effect of strain in the macrocycle on the geometries of the
ground and excited states of the molecules. Namely, the ex-
cited state geometry of 4 might be reminiscent of that of the
ground state due to the geometrical constraint, thereby facil-
itating the 0±0 transition from S0.
Laser-desorption time-of-flight mass spectra of cyclic dehy-
drooligomers: With the expanded radialenes 4±7 in hand,
we investigated the extrusion of indane fragments to pro-
duce the vinylidenes that would isomerize to the corre-
3
Figure 4. UV/Vis spectra of cyclic dehydrooligomers 4±7 in CHCl .
sponding cyclo[n]carbons (n
Scheme 8).
To this end, laser-desorption time-of-flight mass spectra
of 4±7 were measured. ±s shown in Figure 5a±d, the nega-
tive-mode laser-desorption mass spectra of 4±7 exhibited
peaks due to the cyclo[n]carbon anions (n = 18, 24, 30, and
=
18, 24, 30, and 36)
(
prepared radialenes 4±7 exhibited very week absorptions
around 460 nm due to the corresponding isomer having the
methylenecycloheptatriene moiety produced by photoisome-
rization like those of 18, 20, and 22. However, taking the
large absorption coefficient of
the chromophore in 18 and 20
into account, the proportion of
the isomerized moiety must be
negligible.
Recently, Tykwinski et al.
reported the electronic effect of
[28]
cross conjugative interactions in Scheme 8. Generation of cyclo[n]carbons from V via of vinylidenes.
5554
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGa±, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 5549 ± 5559

Expanded Radialenes
5549 ± 5559
3 4 5
Figure 5. Laser-desorption time-of-flight mass spectra of cyclic dehydrooligomers a) 4 [C18(indane) ], b) 5 [C24(indane) ], c) 6 [C30(indane) ], and d) 7
[C36(indane) ]. Insets: Expansion of the carbon anion peaks.
6
3
6) formed by the stepwise loss of the aromatic indane frag-
triene derivatives 1a, 2, and 3. The model study of the pho-
tolysis for acyclic compounds 1a, 2, and 3 by UV irradiation
revealed that cheletropic fragmentation followed by 1,2-mi-
gration gave the corresponding linear polyynes, although un-
desired isomerization took place concurrently. We prepared
the expanded radialenes 4±7 by copper(ii)-mediated oxida-
tive coupling of 1b under dilute conditions. In the electronic
spectra of 4±7, the absorptions did not exhibit large batho-
chromic shifts with increasing ring size of the macrocycles
4±7; this indicated the presence of cross-conjugative interac-
tions of the ene-yne-yne-ene chromophores. Laser-desorp-
tion mass spectra of the radialenes 4±7 exhibited, in the neg-
ative mode, peaks due to the corresponding cyclo[n]carbon
anions (n = 18, 24, 30, and 36) formed by the loss of the ar-
omatic indane fragments. It is worth noting that the forma-
[33]
ments.
±
t present, we do not have spectroscopic evidence re-
garding the structures of the carbon cluster anions thus pro-
duced. But it is reasonable to assume that these possess cy-
clocarbon structures given their stability relative to the vi-
nylidenes and the results of the photolysis of acyclic model
compounds 1a, 2, and 3. If this is the case, the formation of
À
C36 represents the first example of a cyclo[36]carbon gener-
ated from an organic precursor. ±lthough the intensities of
the parent peak relative to those of the fragments depend
on the conditions of ionization, relatively strong peaks of
C18 , C24 , and C30 were observed. By contrast, C36 , which
was produced by the loss of six indane fragments from 7 ,
was only weakly observed (Figure 5d). This may be an indi-
cation of the formation of carbon cluster anions of different
structures, since the monocyclic form of carbon clusters are
most stable within the C ±C range. Proof would be given
by photoelectron spectroscopy of the carbon anions,
which we are planning to carry out in due course.
À
À
À
À
À
À
tion of C36 from the expanded [6]radialene 7 represents the
first example of cyclo[36]carbon generated from an organic
precursor.
1
0
30
[7d]
Experimental Section
Conclusion
1
General: H NMR spectra were recorded at 308C and at 270 or 300 MHz
1
3
and C NMR spectra at 67.8, 75, or 125 MHz on a Varian Unity
Inova500, a Varian Mercury300, or a JEOL JNM-GSX-270 in CDCl
and with Me Si or residual solvent as an internal standard, unless other-
±
s an approach to all-carbon molecules from stable precur-
sors, we prepared diethynylmethylenebicyclo[4.3.1]deca-
3
4
Chem. Eur. J. 2003, 9, 5549 ± 5559
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGa±, Weinheim
5555

Y. Tobe et al.
FULL PAPER
1
wise stated. IR spectra were recorded by using KBr disks with a J±SCO
FTIR-410. Electronic spectra were recorded on a HIT±CHI U-3310
spectrometer. Mass-spectral analyses were performed on a JEOL JMS-
DX303HF or a JMS-700 spectrometer for EI and F±B ionization. LCMS
analyses were undertaken with a Shimadzu LCMS2010 with an ±PCI
ionizer. For most of the M±LDI-TOF mass measurements, a Shimadzu/
Kratos ±XIM±-CFR spectrometer was employed. Elemental analyses
were performed on a Perkin±Elmer 2400II analyzer. Melting points were
measured with a hot-stage apparatus and are uncorrected. Column chro-
matography and TLC were performed with Merck silica gel 60 (70±230
mesh ±STM) and Merck silica gel 60 F254, respectively. Flash chromatog-
raphy was performed with Fuji Silysia silica gel (BW-300). ±nalytical GC
was carried out on a Shimadzu GC-8± gas chromatograph equipped with
a flame-ionization detector. Preparative HPLC separation was undertak-
en with a J±I LC-908 chromatograph by using 600î20 mm J±IGEL-1H
colorless solid. 1a: m.p. 85±868C; H NMR (300 MHz, CDCl
3
): d =
6.47±6.45 (m, 2H), 5.97±5.95 (m, 2H), 2.59 (dt, J = 11.5, 5.2 Hz, 2H),
2.33±2.27 (m, 2H), 2.13±1.88 (m, 2H), 0.17 (s, 18H); C NMR (75 MHz,
CDCl ): d = 167.0 (s), 138.6 (s), 127.0 (d), 114.6 (d), 99.7 (s), 95.0 (s),
93.1 (s), 50.5 (t), 36.6 (t), 0.0 (q); IR (KBr): ~n = 3037, 2954, 2854, 2153,
1655, 1561, 1457, 1334, 1245, 1048, 983, 843, 757, 727, 699 cm ; UV/Vis
1
3
3
À1
+
(n-hexane): lmax (e) = 258 nm (16500); MS (EI) m/z: 336 [M ]; elemen-
tal analysis calcd (%) for C21
8.46.
2
H28Si : C 74.93, H 8.46; found: C 74.83, H.
1
0-(Diethynylmethylene)bicyclo[4.3.1]deca-1,3,5-triene (1b): ± solution
of LiOH¥H O (43.6 mg, 1.04 mmol) in H O (4 mL) was added over
2 2
1
(
±
0 min with stirring to a solution of 1a (350 mg, 1.04 mmol) in THF
11 mL) at room temperature, followed by addition of THF (11 mL).
fter 3 h, the mixture was diluted with water and extracted with diethyl
ether. The organic layer was washed with saturated NaHCO solution
and brine, and dried over MgSO . Removal of the solvent afforded 1b
3
and 2H GPC columns with CHCl
from commercial suppliers and used as received. Solvents were dried
drying agent in parentheses) and distilled prior to use: THF (Li±lH
followed by sodium benzophenone ketyl), benzene (CaH ), pyridine
3
as eluent. ±ll reagents were obtained
4
1
(
205 mg, 100%) as
300 MHz, CDCl ): d = 6.52±6.49 (m, 2H), 6.04±6.01 (m, 2H), 2.92 (s,
H), 2.62 (dt, J = 11.6, 5.0 Hz, 2H), 2.38±2.32 (m, 2H), 2.17±1.91 (m,
a
colorless solid. 1b: m.p. 59±618C;
H N MR
(
4
(
3
2
2
2
(
KOH), acetone (K
2
CO
3
), pentane (CaH
2
).
13
3
H); C NMR (75 MHz, CDCl ): d = 168.0 (s), 139.0 (s), 127.3 (d),
1
0,10-Dibromo[4.3.1]propella-2,4-diene (8): Pyridinium hydrobromide
114.9 (d), 90.8 (s), 78.5 (s), 78.0 (d), 50.9 (t), 36.7 (t); IR (KBr): ~n =
perbromide (85.3 g, 0.267 mol) was added to a mechanically stirred solu-
tion of 9 (51.9 g, 0.178 mol) in CH Cl (645 mL) and pyridine (27 mL).
fter the mixture had been stirred at room temperature for 2.5 h, an
3272, 3036, 3002, 2953, 2921, 2853, 2100, 1657, 1561, 1440, 1357, 1331,
À1
2
2
1265, 1047, 951, 876, 831, 796, 743, 683 cm ; UV/Vis (n-hexane): lmax (e)
+
±
= 246 nm (17600); MS (EI) m/z: 192 [M ]; elemental analysis calcd
aqueous solution of sodium thiosulfate (0.2m, ca. 1000 mL) was added,
and the reaction mixture was extracted with ether. The organic layer was
separated and washed with aqueous sodium thiosulfate (0.2m) and dried
over MgSO . Removal of the solvent in vacuo afforded 85.9 g of the tet-
4
rabromide as a colorless solid, which was employed in the following reac-
tion without further purification.
(%) for C15
0-{Bis[(triisoproylylsilyl)butadiynyl]methylene}bicyclo[4.3.1]deca-1,3,5-
triene (2): ± solution of 1b (39 mg, 0.20 mmol) in methanol/THF (3 mL,
:1, v/v) was added dropwise over 6 min to a mixture of NH OH¥HCl
73 mg, 1.02 mmol), 70% aqueous solution of ethylamine (256 mg,
.98 mmol), and CuCl (20 mg, 0.20 mmol) dissolved in methanol/THF
H12: C 93.71, H 6.29; found: C 93.36, H 6.29.
1
2
(
3
2
±
solution of 1,8-diazabicyclo[5.4.0]undec-7-ene (144.6 g, 0.950 mol) in
(6 mL, 2:1, v/v) at 08C under a nitrogen atmosphere. ±fter being stirred
toluene (75 mL) was added dropwise over 1.5 h to a mechanically stirred
solution of the tetrabromide in toluene (550 mL) under a nitrogen atmos-
phere. The mixture was stirred at 408C for 7 days, then diluted with
water (500 mL) and extracted with ether. The organic layer was washed
at room temperature for 30 min, a solution of 1-bromo-2-(triisopropylsi-
[
30]
lyl)ethyne (14) (175 mg, 0.66 mmol) in methanol/THF (5 mL, 2:1, v/v)
was added. The reaction mixture was stirred for 2.5 h at room tempera-
ture. During the reaction, the flask was covered with aluminum foils to
protect the products from light. ±fter HCl (50mL, 0.5n) had been
added, the mixture was extracted with ether. The organic layer was
with brine and dried over MgSO
4
. Evaporation of the solvent gave a
brown solid, which was purified by chromatography (n-hexane) followed
[
15b,e,f]
by recrystallization from methanol to afford propelladiene 8
5%) as a colorless solid.
(19.3 g,
washed with saturated NaHCO
3
solution and brine, and dried over
3
MgSO . ±fter removal of the solvent under reduced pressure, purifica-
4
tion by flash chromatography (n-hexane) afforded 2 (71 mg, 63%) and
Ketone adduct 11: ± solution of nBuLi in n-hexane (25.2 mL, 1.50m) was
added dropwise over 3 h to a solution of dibromide 8 (10.1 g, 34.7 mmol)
dissolved in THF (70 mL) at À1008C under a nitrogen atmosphere. ±fter
the mixture had been stirred for 2 h at À1008C, a solution of 1,5-bis(tri-
the monosubstitution product (8 mg, 10%) as pale yellow solids. 2: m.p.
1
1
46±1478C; H NMR (300 MHz, CDCl
3
): d = 6.50±6.47 (m, 2H), 6.02±
5
.99 (m, 2H), 2.60 (dt, J = 11.5, 4.9 Hz, 2H), 2.39±2.33 (m, 2H), 2.17±
1
3
[
18]
2.09 (m, 1H), 2.02±1.94 (m, 1H), 1.09 (brs, 42H); C NMR (75 MHz,
CDCl ): d = 171.9 (s), 138.4 (s), 127.5 (d), 115.2 (d), 91.2 (s), 89.5 (s),
8.1 (s), 75.6 (s), 69.9 (s), 50.8 (t), 37.2 (t), 18.5 (q), 11.3 (d); IR (KBr): ~n
methylsilyl)penta-1,4-dien-3-one (10)
(14.1 g, 62.6 mmol) in THF
(
50 mL) was added dropwise over 1 h. ±fter being stirred for 2 h, the
3
8
mixture was slowly warmed to room temperature, then chlorotrimethylsi-
lane (TMSCl; 7.5 g, 69.3 mmol) was added dropwise over 15 min. ±fter
being stirred for 1.5 h at room temperature, the mixture was poured into
=
3039, 2944, 2866, 2200, 2095, 1634, 1462, 1385, 1335, 1070, 1016, 997,
À1
9
18, 882, 793, 737, 680 cm ; UV/Vis (n-hexane): lmax (e) = 306 (19600),
+
2
88 (19200), 269 (15400), 256 nm (13300); MS (F±B) m/z: 552 [M ]; el-
saturated NaHCO
was washed with brine and dried over MgSO
3
solution and extracted with ether. The organic layer
. ±fter removal of the sol-
emental analysis calcd (%) for C37
0.20, H 9.64.
Monosubstitution product: m.p. 67±698C; H NMR (300 MHz, CDCl
2
H52Si : C 80.36, H 9.48; found: C
4
8
vent under reduced pressure, purification by chromatography (n-hexane)
gave 11 (7.2 g, 42%) as a pale yellow solid. The NMR spectra of the
1
3
): d
product revealed that it consisted of a single diastereomer. 11: m.p. 87±
= 6.51±6.48 (m, 2H), 6.03±5.97 (m, 2H), 2.92 (s, 1H), 2.67±2.56 (m, 2H),
1
8
5
0
1
1
1
88C; H NMR (300 MHz, CDCl
3
): d = 6.04 (dd, J = 7.1, 2.5 Hz, 2H),
2.39±2.32 (m, 2H), 2.17±2.06 (m, 1H), 2.02±1.94 (m, 1H), 1.08 (brs,
1
3
.87 (dd, J = 7.1, 2.5 Hz, 2H), 2.99±2.92 (m, 2H), 1.87±1.67 (m, 4H),
3
21H); C NMR (75 MHz, CDCl ): d = 170.0 (s), 138.8 (s), 138.6 (s),
1
3
.30 (s, 9H), 0.20 (s, 18H); C NMR (75 MHz, CDCl
3
): d = 128.3 (d),
127.5 (d), 127.3 (d), 115.3 (d), 114.8 (d), 91.0 (s), 89.6 (s), 87.9 (s), 78.3
(d), 77.9 (s), 75.4 (s), 70.5 (s), 50.9 (t), 37.1 (t), 36.8 (t), 18.6 (q), 11.3 (d);
IR (KBr): ~n = 3299, 3033, 2944, 2866, 2203, 2094, 1651, 1561, 1461, 1335,
22.3 (d), 106.0 (s), 89.3 (s), 70.8 (s), 48.2 (s), 47.8 (s), 35.8 (t), 29.6 (t),
.5 (q), À0.4 (q); IR (KBr): ~n = 3033, 2960, 2901, 2875, 2163, 1451, 1377,
À1
À1
250, 1105, 1076, 1036, 925, 763, 751, 730, 704 cm ; MS (F±B) m/z: 426
1074, 1018, 995, 915, 883, 856, 838, 795, 735, 681 cm ; MS (F±B) m/z:
+
+
[
M
+HÀBr]; elemental analysis calcd (%) for C24
H
37OSi
3
Br: C 57.00, H
372 [M ].
7
.38; found: C 56.89, H 7.41.
1
0-[Bis(phenylethynyl)methylene]bicyclo[4.3.1]deca-1,3,5-triene
PdCl (PPh (73 mg, 0.104 mmol) and CuI (40 mg, 0.21 mmol) were
added under an argon atmosphere to a solution of iodobenzene (835 mg,
4.09 mmol) in Et N(100 mL), which had been degassed thoroughly by
(3):
1
0-{Bis[(trimethylsilyl)ethynyl]methylene}bicyclo[4.3.1]deca-1,3,5-triene
2
3 2
)
(
1a): ± solution of tBuLi in pentane (2.41 mL, 1.47m) was added drop-
wise over 20 min to solution of the ketone adduct 11 (1.59 g,
a
3
3
.14 mmol) in THF (38 mL) and pentane (38 mL) at À1108C. ±fter
bubbling argon for 2 h. ±fter the mixture had been stirred at room tem-
perature for 5 min, a solution of 1b (198 mg, 1.03 mmol) in degassed
Et N(50 mL) was added dropwise over 20 min. ±fter 20 h, the solvent
3
being stirred for 2 h at À1108C, the reaction mixture was warmed up
slowly to room temperature, followed by addition of TMSCl (630 mg,
0
.63 mmol). ±fter 1 h, water was added, and the reaction mixture was ex-
tracted with ether. The organic layer was washed with brine and dried
over MgSO . ±fter removal of the solvent under reduced pressure, purifi-
cation by chromatography (n-hexane) afforded 1a (842 mg, 80%) as a
was removed under reduced pressure. The residue was subjected to chro-
matography (n-hexane/diethyl ether 10:0 to 9:1) to afford 3 (323 mg,
4
91%) as a pale yellow solid, together with iodobenzene (401 mg). 3: m.p.
1
110±1118C; H NMR (300 MHz, CDCl
3
): d = 7.50±7.46 (m, 4H), 7.32±
5556
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGa±, Weinheim
www.chemeurj.org Chem. Eur. J. 2003, 9, 5549 ± 5559

Expanded Radialenes
5549 ± 5559
7
5
2
1
.28 (m, 6H), 6.53±6.52 (m, 2H), 6.06±6.04 (m, 2H), 2.71 (dt, J = 11.5,
under a nitrogen atmosphere. The reaction mixture was stirred at room
temperature for 2 h, with all apparatus covered with aluminum foil to
shield the mixture from light. The solvent was concentrated to ca.
200 mL, and the mixture was passed through a column of silica gel
.1 Hz, 2H), 2.38 (ddd, J = 11.5, 5.1, 1.2 Hz, 2H), 2.20±2.12 (m, 1H),
1
3
.09±1.94 (m, 1H); C NMR (75 MHz, CDCl
3
): d = 165.0 (s), 139.2 (s),
31.8 (d), 128.1 (d), 127.2 (d), 123.3 (s), 115.1 (d), 92.9 (s), 89.7 (s), 84.7
(
s), 50.9 (t), 36.9 (t); IR (KBr): ~n = 3040, 2918, 2850, 1654, 1490, 1441,
(CHCl
leave ca. 20 mL. The poorly soluble dehydrotetramer 5 was filtered off
and washed with ether and CHCl . The solid was purified by flash chro-
matography (CHCl ) to afford 5 (89 mg) as an orange solid. The filtrate
was concentrated under reduced pressure, diluted with HCl (100mL,
.5n), and extracted with CHCl . The organic layer was washed with sa-
turated NaHCO solution and brine, and dried over MgSO . ±fter most
of the solvent had been removed under reduced pressure, the mixture
was again passed through a column of silica gel (CHCl ). The solvent was
removed by evaporation, and the products were separated by preparative
HPLC. Further purification by flash chromatography (CHCl ) afforded
3
). Most of the solvent was removed under reduced pressure to
À1
1
340, 1317, 1100, 1069, 960, 916, 885, 839, 800, 755, 736, 690 cm ; UV/
+
Vis (n-hexane): lmax (e) = 275 nm (37700); MS (EI) m/z: 344 [M ]; ele-
mental analysis calcd (%) for C27 20: C 94.15, H 5.85; found: C 93.75, H
.67.
2+2+2] Cycloadduct 13: ± solution of 1a (43 mg, 0.13 mmol) and N-
3
H
3
5
0
3
[
3
4
phenylmaleimide (24 mg, 0.14 mmol) in toluene (2.0 mL) was heated at
reflux with stirring under a nitrogen atmosphere. ±fter 7 h, the solvent
was removed under reduced pressure. The residue was purified by flash
chromatography (n-hexane/ether 9:1) followed by preparative HPLC to
3
3
afford the adduct 13 (53 mg, 81%) as a colorless solid. 13: m.p. 213±
1
dehydrotrimer 4 (8 mg, 3%) as a red solid, dehydrotetramer 5 (3 mg,
combined yield 33%) as an orange solid, dehydropentamer 6 (42 mg,
2
158C; H NMR (300 MHz, CDCl
3
): d = 7.46±7.33 (m, 3H), 7.18±7.13
(
m, 2H), 6.09±6.03 (m, 2H), 3.61 (brs, 2H), 3.31 (brs, 2H), 2.03±1.96 (m,
1
3
15%) as a reddish orange solid, and dehydrohexamer 7 (20 mg, 7%) as a
2
H), 1.91±1.69 (m, 3H), 1.60±1.44 (m, 1H), 0.19 (s, 18H); C N MR
): d = 177.8 (s), 154.2 (s), 131.8 (s), 131.3 (d), 129.1 (d),
28.6 (d), 126.4 (d), 103.2 (s), 100.0 (s), 94.5 (s), 40.7 (d), 35.1 (d), 34.9
1
yellow solid. 4: decomposed gradually from ca. 1508C;
H N MR
(
75 MHz, CDCl
3
1
(
(
300 MHz, CDCl
m, 6H), 2.32±2.24 (m, 6H), 2.14±1.85 (m, 6H); C NMR (75 MHz,
): d = 160.59 (s), 160.52 (s), 160.47 (s), 138.76 (s), 138.69 (s),
3
): d = 6.47±6.41 (m, 6H), 5.96±5.91 (m, 6H), 2.58±2.47
1
3
(
s), 27.8 (t), 27.7 (t), 0.1 (q); IR (KBr): ~n = 3057, 2958, 2899, 2863, 2154,
CDCl
3
1
7
776, 1714, 1597, 1499, 1387, 1249, 1221, 1183, 1036, 978, 957, 842, 750,
37, 699 cm ; LD-TOF MS (negative ion mode) m/z: 509.2 [M ]; ele-
À1
À
138.66 (s), 138.60 (s), 127.65 (d), 127.63 (d), 115.32 (d), 93.20 (s) and two
small peaks at 93.23 (s) and 93.18 (s), 90.25 (s), 90.20 (s), 77.80 (s) and a
2 2
mental analysis calcd (%) C31H35NO Si : C 73.04, H 6.92; found: C 72.74,
small peak at 77.82 (s), 51.05 (t), 36.88 (t); IR (KBr): ~n = 3037, 2939,
H 6.99.
À1
2
848, 2187, 1660, 1455, 1349, 1071, 1046, 963, 955, 843, 814, 736 cm
UV/Vis (CHCl ): lmax (e)
75 nm (22600); LD-TOF MS (negative ion mode) m/z: 569.9 [M ].
;
Photolysis of 1a: Nitrogen was bubbled into a solution of 1a (40.0 mg,
.12 mmol) in n-hexane (3 mL) in a quartz tube. The solution was irradi-
3
= 344 (34500), 321 (29100), 312 (28300),
0
À
2
ated in an ice bath with a 60 W low-pressure mercury lamp for 6 h. The
solvent and indane were removed by evaporation, and the products were
separated by preparative HPLC to afford 17 (14.0 mg, 46%) as a color-
less solid and 18 (14.6 mg, 30%) as a reddish brown oil. The quantity of
1
5
=
: decomposed gradually from ca. 1408C; H NMR (300 MHz, CDCl
3
): d
6.49±6.42 (m, 8H), 5.99±5.94 (m, 8H), 2.64±2.48 (m, 8H), 2.36±2.26
m, 8H), 2.16±1.86 (m, 8H); C NMR (125 MHz, CDCl
s), 138.79 (s), 138.77 (s), 138.66 (s), 138.62 (s) and two small peaks
38.72 and 138.70, 127.64 (d), 127.61 (d), 115.29 (d), 92.30 (s), 79.11 (s),
6.01 (s), 51.00 (t), 37.02 (t); IR (KBr): ~n = 3036, 2939, 2914, 2849, 2208,
650, 1436, 1351, 1074, 1048, 965, 955, 838, 733 cm ; UV/Vis (CHCl
max (e) = 340 (sh, 51700), 318 nm (67600); LD-TOF MS (negative ion
13
(
(
1
7
1
l
3
): d = 166.30
indane formed was determined by calibrated GC with undecane as an in-
1
ternal standard. 18: H NMR (270 MHz, CDCl
3
): d = 6.90 (dd, J = 9.7,
2
7
.1 Hz, 1H), 6.37 (d, J = 9.7 Hz, 1H), 6.21±6.12 (m, 2H), 3.14 (t, J =
.4 Hz, 2H), 2.63 (t, J = 7.4 Hz, 2H), 1.86 (quin, J = 7.4 Hz, 2H), 0.21
À1
3
):
1
3
(
s, 9H), 0.19 (s, 9H); C NMR (67.8 MHz, CDCl
3
): d = 151.3 (s), 145.1
À
mode) m/z: 760.1 [M ].
(
s), 144.9 (s), 134.4 (d), 132.0 (d), 130.5 (d), 128.7 (d), 104.8 (s), 103.7 (s),
1
6
=
: decomposed gradually from ca. 1608C; H NMR (300 MHz, CDCl
3
): d
1
00.4 (s), 99.8 (s), 93.5 (s), 38.7 (t), 38.3 (t), 24.0 (t), 0.1 (q), À0.2 (q); IR
6.51±6.45 (m, 10H), 6.03±5.98 (m, 10H), 2.69±2.52 (m, 10H), 2.40±2.28
(m, 10H), 2.17±1.90 (m, 10H); C NMR (75 MHz, CDCl
(s), 138.78 (s), 138.72 (s), 138.64 (s), 138.56 (s), 127.59 (d), 127.52 (d),
15.34 (d), 115.29 (d), 92.06 (s), 76.42 (s), 76.41 (s), 75.31 (s), 75.28 (s),
0.91 (t), 37.22 (t); IR (KBr): ~n = 3035, 2936, 2914, 2849, 2210, 1644,
436, 1347, 1080, 954, 906, 879, 838, 733 cm ; UV/Vis (CHCl
337 (sh, 59700), 317 nm (78600); LD-TOF MS (negative ion mode) m/
(
KBr): ~n = 3025, 2957, 2925, 2852, 2136, 1542, 1249, 1041, 945, 842,
1
3
À1
3
): d = 169.30
7
3
58 cm ; UV/Vis (n-hexane): lmax (e) = 385 nm (3300); MS (EI) m/z:
36 [M ]; HRMS (EI) calcd for C21H28Si : 336.1730; found: 336.1750.
2
+
1
5
1
Photolysis of 2: Irradiation of 2 (40.0 mg, 0.072 mmol) in n-hexane
3 mL) was conducted as described above for 6 h. The products were sep-
(
À1
3
): lmax (e)
arated by flash chromatography (n-hexane) to afford 19 (18.3 mg, 59%)
as a pale yellow solid and a mixture of the starting material 2 and its
=
À
z: 950.2 [M ].
1
isomer 20 (11.7 mg). The amount of 20 (24%) was estimated by H N MR
1
7
=
: decomposed gradually from ca. 1408C; H NMR (300 MHz, CDCl
3
): d
integration of the vinyl proton of 20 relative to that of 2 for the mixture.
The mixture was further irradiated as described above to consume 2 com-
pletely. Pure sample 20 was thus isolated in 12% yield after chromatog-
raphy followed by preparative HPLC. Indane was detected in the crude
6.51±6.44 (m, 12H), 6.02±5.96 (m, 12H), 2.67±2.52 (m, 12H), 2.39±2.28
m, 12H), 2.16±1.89 (m, 10H); C NMR (75 MHz, CDCl ): d = 170.53
3
s), 138.73 (s), 138.70 (s), 138.57 (s), 127.55 (d) and a small peak at 127.47
d), 115.24 (d), 91.92 (s), 76.28 (s), 76.15 (s), 75.13 (s), 50.84 (t), 37.20 (t);
IR (KBr): ~n = 3034, 2932, 2914, 2850, 2212, 1638, 1436, 1345, 1087, 953,
13
(
(
(
1
1
products by H NMR (irradiation in [D
300 MHz, CDCl ): d = 7.13±7.07 (m, 1H), 6.48±6.44 (m, 1H), 6.30 (dt,
J = 5.4, 4.5 Hz, 2H), 3.14 (t, J = 7.2 Hz, 2H), 2.65 (t, J = 7.2 Hz, 2H),
8
]THF) and by GC. 20: H N MR
(
3
À1
9
(
07, 837, 793, 734 cm ; UV/Vis (CHCl
3
): lmax (e) = 334 (sh, 60800), 313
88500), 294 nm (78800); LD-TOF MS (negative ion mode) m/z: 1140.3
1
3
1
.90 (quin, J
CDCl ): d = 155.9 (s), 147.7 (s), 146.5 (s), 135.2 (d), 133.1 (d), 131.8 (d),
30.6 (d), 91.3 (s), 90.4 (s), 90.2 (s), 90.0 (s), 81.6 (s), 80.9 (s), 74.9 (s),
4.1 (s), 39.3 (t), 38.7 (t), 24.0 (t), 18.6 (q), 11.40 (d), 11.39 (d); IR (KBr):
=
7.2 Hz, 2H), 1.01 (brs, 42H); C NMR (75 MHz,
À
[
M ].
3
Singly protected bicyclic triene 24: ± solution of nBuLi in n-hexane
1
7
(
(
5.3 mL, 1.59m) was added dropwise over 40 min to a solution of 1b
1.47 g, 7.65 mmol) in THF (140 mL) cooled to À788C under an argon at-
~
n = 3028, 2942, 2865, 2174, 2089, 1529, 1458, 1289, 1242, 1072, 996, 882,
À1
mosphere. ±fter 2 h, acetone (0.63 g, 10.3 mmol) was added dropwise
over 5 min. The reaction mixture was stirred at À788C for 1 h and then
slowly warmed up to room temperature. The mixture was poured into sat-
7
63, 678, 661 cm ; UV/Vis (n-hexane): lmax (e)
=
428 (19400), 304
+
(
12700), 285 (13700), 270 nm (11100); MS (EI) m/z: 552 [M ].
Photolysis of 3: Irradiation of 3 (38.0 mg, 0.109 mmol) in diethyl ether
3 mL) was conducted as described above for 10 h. The products were
separated by flash chromatography (n-hexane) to afford 21 (9.0 mg,
7%) as a pale yellow solid. Indane was detected in the crude products
urated NaHCO
washed with brine and dried over MgSO
3
solution and extracted with ether. The organic layer was
. ±fter removal of the solvent
(
4
under reduced pressure, purification by flash chromatography (n-hexane/
EtO±c 9:1 to 5:5) yielded 24 (1.54 g, 81%) as a yellow oil, the doubly
protected product (0.26 g, 10%) as a pale yellow solid, and unreacted 1b
): d = 6.51±6.50 (m, 2H), 6.04±
.00 (m, 2H), 2.91 (s, 1H), 2.68±2.54 (m, 2H), 2.34±2.31 (m, 2H), 2.18±
3
1
by H NMR (irradiation in [D
crude products by H NMR (irradiation in [D ]THF) and by LCMS (m/z:
3
8
]THF) and by GC. 21 was detected in the
1
1
8
(
90 mg). 24: H NMR (300 MHz, CDCl
3
+
35 [M +H]).
6
1
3
Cyclic dehydrooligomers 4±7: Compound 1b (280 mg, 1.46 mmol) in pyri-
1.91 (m, 3H), 1.55 (s, 6H); C NMR (75 MHz, CDCl ): d = 166.49 (s),
3
dine (150 mL) was added through a Hershberg dropping funnel over 21 h
139.02 (s), 138.98 (s), 127.30 (d), 127.08 (d), 114.94 (d), 114.82 (d), 94.57
to a suspension of Cu(O±c)
2
(3.98 g, 22.0 mmol) in pyridine (300 mL)
(s), 91.15 (s), 78.92 (s), 77.47 (d), 65.48 (s), 50.83 (t), 36.79 (t), 36.60 (t),
Chem. Eur. J. 2003, 9, 5549 ± 5559
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGa±, Weinheim
5557

Y. Tobe et al.
FULL PAPER
3
1.32 (q); IR (KBr): ~n = 3392, 3287, 3034, 2981, 2933, 2852, 2101, 1441,
CCDC-208630 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge via www.ccdc.cam.
ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
À1
1
M
363, 1338, 1270, 1165, 950, 896, 838, 752, 730 cm ; MS (EI) m/z: 250
+
[
]; HRMS (EI) calcd for C18
H
18O: 250.1358; found: 250.1364.
1
Doubly protected product: m.p. 126±1278C; H NMR (300 MHz, CDCl
3
):
(
+44)1223-336033; or deposit@ccdc.cam.ac.uk).
d = 6.47±6.45 (m, 2H), 5.98±5.96 (m, 2H), 2.57 (dt, J = 11.4, 5.1 Hz,
1
3
2
1
6
3
1
3
H), 2.19±1.85 (m, 4H), 1.52 (s, 12H); C NMR (75 MHz, CDCl ): d =
64.97 (s), 138.99 (s), 127.05 (d), 114.80 (d), 94.12 (s), 91.54 (s), 77.34 (s),
5.44 (s), 50.72 (t), 36.62 (t), 31.34 (q), 31.33 (q); IR (KBr): ~n = 3341,
033, 2979, 2936, 2852, 1655, 1561, 1455, 1375, 1361, 1288, 1231, 1167,
140, 952, 904, 838, 731 cm ; MS (EI) m/z: 308 [M ]; HRMS (EI) calcd
: 308.1776; found: 308.1760.
Doubly protected bicyclic triene dehydrodimer 23a: ± mixture of CuCl
1.01 g, 9.74 mmol) and tetramethylethylenediamine (385 mg, 3.31 mmol)
[
1] a) S. H. Yang, C. L. Pettiette, J. Conceicao, O. Cheshnovsky, R. E.
Smalley, Chem. Phys. Lett. 1987, 139, 233±238; b) S. H. Yang, K.
Taylor, M. J. Craycraft, J. Conceicao, C. L. Pettiette, O. Cheshnov-
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J. Phys. Chem. 1993, 97, 3460±3462.
À1
+
for C21
24 2
H O
(
in acetone (20 mL) was stirred at room temperature for 1 h, and the blue
skim of this mixture was used as a catalyst. The catalyst solution (7.5 mL)
was added dropwise over 10 min to an air-saturated solution of 24
[
[
2] For reviews see, a) H. Schwarz, Angew. Chem. 1993, 105, 1475±
1
478; Angew. Chem. Int. Ed. Engl. 1993, 32, 1412±1415; b) N. S.
(
1.54 g, 6.16 mmol) in acetone (120 mL), and the reaction mixture was
Goroff, Acc. Chem. Res. 1996, 29, 77±83.
stirred at room temperature for 17 h while air was bubbled through a
needle immersed in the solution. ±fter HCl (200mL, 0.5n) had been
added, the acetone was evaporated in vacuo, and the residue was extract-
3] a) F. Diederich, Y. Rubin, Angew. Chem. 1992, 104, 1123±1146;
Angew. Chem. Int. Ed. Engl. 1992, 31, 1101±1123; b) F. Diederich,
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Chem. Soc. Rev. 1999, 28, 107±119.
ed with ether. The organic layer was washed with saturated NaHCO
3
sol-
ution and brine, and dried over MgSO . ±fter removal of the solvent
4
[
[
4] a) F. Diederich, Y. Rubin, C. B. Knobler, R. L. Whetten, K. Schriver,
K. N. Houk, Y. Li, Science 1989, 245, 1088±1090; b) F. Diederich, Y.
Rubin, O. L. Chapman, N. S. Goroff, Helv. Chim. Acta 1994, 77,
under reduced pressure, purification by flash chromatography (n-hexane/
EtO±c 9:1 to 7:3) afforded 23a (1.43 g, 93%) and recovered 24 (40 mg).
1
2
6
6
3a: m.p. 89±908C; H NMR (300 MHz, CDCl
3
): d = 6.47±6.45 (m, 4H),
1
441±1457.
5] a) Y. Rubin, C. B. Knobler, F. Diederich, J. Am. Chem. Soc. 1990,
12, 1607±1617; b) Y. Rubin, M. Kahr, C. B. Knobler, F. Diederich,
.01±5.96 (m, 4H), 2.63±2.52 (m, 4H), 2.36±2.28 (m, 4H), 2.17±1.88 (m,
1
3
3
H), 1.52 (s, 12H); C NMR (75 MHz, CDCl ): d = 168.23 (s), 138.81
1
(
s), 138.71 (s), 127.27 (d), 127.23 (d), 115.26 (d), 114.71 (d), 94.91 (s),
C. L. Wilkins, J. Am. Chem. Soc. 1991, 113, 495±500; c) S. W. McEl-
vany, M. M. Ross, N. S. Goroff, F. Diederich, Science 1993, 259,
9
3
2
4
1.59 (s), 76.80 (s), 76.26 (s), 74.37 (s), 65.45 (s), 50.78 (t), 37.10 (t),
6.68 (t), 31.31 (q), 31.29 (q); IR (KBr): ~n = 3386, 3034, 2980, 2934, 2850,
1
594±1596.
À1
215, 1654, 1439, 1363, 1335, 1266, 1166, 951, 838, 729 cm ; MS (EI) m/z:
[
6] G. ±. ±damson, C. W. Rees, J. Chem. Soc. Perkin Trans. 1 1996,
+
98 [M ]; HRMS (EI) calcd for C36
H O
34 2
: 498.2559; found: 498.2557.
1535±1543.
Bicyclic triene dehydrodimer 23b: Powdered KOH (12 mg, 0.21 mmol)
was added with stirring to a solution of 23a (90 mg, 0.18 mmol) in ben-
zene (25 mL). The mixture was heated at 958C so that the solvent slowly
distilled out. ±fter completion of the reaction (monitored by HPLC), the
mixture was cooled to room temperature and HCl (100mL, 0.5n) was
added. The mixture was extracted with ether, and the organic layer was
[7] a) Y. Tobe, T. Fujii, K. Naemura, J. Org. Chem. 1994, 59, 1236±
1237; b) Y. Tobe, T. Fujii, H. Matsumoto, K. Naemura, Y. ±chiba, T.
Wakabayashi, J. Am. Chem. Soc. 1996, 118, 2758±2759; c) Y. Tobe,
H. Matsumoto, K. Naemura, Y. ±chiba, T. Wakabayashi, Angew.
Chem. 1996, 108, 1924±1926; Angew. Chem. Int. Ed. Engl. 1996, 35,
1800±1802; d) T. Wakabayashi, M. Kohno, Y. ±chiba, H. Shiro-
maru, T. Momose, T. Shida, K. Naemura, Y. Tobe, J. Chem. Phys.
washed with saturated NaHCO
over MgSO . Removal of the solvent gave 23b (64 mg, 93%) as a pale
yellow solid. 23b: decomposed gradually from ca. 1608C; H N MR
300 MHz, CDCl ): d = 6.49±6.47 (m, 4H), 6.02±5.99 (m, 4H), 2.91 (s,
H), 2.60 (dt, J = 11.6, 5.1 Hz, 4H), 2.37±2.32 (m, 4H), 2.15±2.08 (m,
3
solution followed by brine and dried
1
997, 107, 4783±4787; e) Y. Tobe, T. Fujii, H. Matsumoto, K. Tsu-
muraya, D. Noguchi, N. Nakagawa, M. Sonoda, K. Naemura, Y.
chiba, T. Wakabayashi, J. Am. Chem. Soc. 2000, 122, 1762±1775.
4
1
±
(
3
[
8] a) L. Isaacs, P. Seiler, F. Diederich, Angew. Chem. 1995, 107, 1636±
1639; Angew. Chem. Int. Ed. Engl. 1995, 34, 1466±1469; b) L. Isascs,
F. Diederich, R. F. Haldiman, Helv. Chim. Acta 1997, 80, 317±342.
9] a) ±. de Meijere, S. I. Kozhushkov, Top. Curr. Chem. 1999, 201, 1±
2
2
1
1
3
H), 2.05±1.89 (m, 2H); C NMR (75 MHz, CDCl
3
): d = 169.9 (s),
38.9 (s), 138.7 (s), 127.5 (d), 127.3 (d), 115.3 (d), 114.9 (d), 91.2 (s), 78.3
[
(
d), 77.8 (s), 74.7 (s), 50.9 (t), 37.1 (t), 36.8 (t); IR (KBr): ~n = 3275, 3036,
4
2; b) ±. de Meijere, S. I. Kozhushkov, Chem. Eur. J. 2002, 8, 3195±
2
6
939, 2914, 2848, 1640, 1433, 1330, 1222, 1046, 951, 903, 839, 795, 741,
À1
3202.
84 cm ; UV/Vis (CHCl
3
): lmax (e) = 323 (15200), 305 (19000), 285 nm
+
[10] For a review on the generation of vinylidenes by FVP from alkynes,
see: R. F. C. Brown, Eur. J. Org. Chem. 1999, 3211±3222, and refer-
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11] a) R. K. Brinton, J. Phys. Chem. 1968, 72, 321±327; b) J. C. Gillbert,
J. R. Butler, J. Am. Chem. Soc. 1970, 92, 7493±7494; c) ±. S. Kende,
Z. Goldschmidt, R. F. Smith, J. Am. Chem. Soc. 1970, 92, 7606±
(
17300); MS (EI) m/z: 382 [M ]; elemental analysis calcd (%) for
22: C 94.20, H 5.80; found: C 93.95, H 5.77.
32
C H
Oxidative coupling of 23b: Compound 23b (101 mg, 0.26 mmol) in pyri-
dine (250 mL) was added through a Hershberg dropping funnel over 20 h
to a suspension of Cu(O±c) (3.84 g, 21.1 mmol) in pyridine (200 mL)
2
under a nitrogen atmosphere. The reaction mixture was stirred at room
temperature for 6 h, with all apparatus covered with aluminum foil to
shield it from light. The solvent was concentrated to ca. 200 mL, and the
[
[
[
7
607.
12] a) S. Eisler, R. R. Tykwinski, J. Am. Chem. Soc. 2000, 122, 10736±
0737; b) E. T. Chernick, S. Eisler, R. R. Tykwinski, Tetrahedron
1
mixture was passed through a column of silica gel (CHCl
al of the solvent, the crude product was purified by flash chromatography
CHCl ) followed by preparative HPLC to afford 5 (91 mg, 91%) as an
3
). ±fter remov-
Lett. 2001, 42, 8575±8578; c) ±. L. K. Shi Shun, E. T. Chernick, S.
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(
3
13] Part of this work was reported preliminarily: Y. Tobe, N. Iwasa, R.
Umeda, M. Sonoda, Tetrahedron Lett. 2001, 42, 5485±5488.
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orange solid.
Crystal data for 1b: Crystal dimensions 0.42î0.42î0.34 mm, orthorhom-
À3
bic, space group Pnma (#62), 1calcd
1
=
1.150 gcm , Z
=
3
4, a
=
3.0782(2), b = 12.3136(2), c = 6.8979(1) ä, V = 1110.84 ä , 2qmax
=
5
58, MoKa radiation (l = 0.71069 ä), T = À1008C. Of the 20913 reflec-
tions that were collected, 1329 were unique. The structure was solved by
direct methods (SIR92) and expanded by using Fourier techniques
(
DIRDIF94). The non-hydrogen atoms were refined anisotropically. Hy-
drogen atoms were refined isotropically. The final cycle of full-matrix
least-squares refinement was based on 1329 of all reflections (2q<54.96)
and 99 variable parameters, and converged with R = 0.079, R = 0.090.
w
5558
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGa±, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 5549 ± 5559

Expanded Radialenes
5549 ± 5559
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3
119; d) K. Komatsu, M. Fujimori, K. Okamoto, Tetrahedron 1977,
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26] For a definition of deformation angles in bridgehead olefins, see:
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18] H. Hauptmann, Tetrahedron 1976, 32, 1293±1297.
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Received: January 17, 2003
Revised: ±ugust 7, 2003 [F5051]
Chem. Eur. J. 2003, 9, 5549 ± 5559
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¹ 2003 Wiley-VCH Verlag GmbH & Co. KGa±, Weinheim
5559