Nickel-catalyzed dimerization of [5]cumulenes (Hexapentaenes)

Article abstract of DOI:10.1246/bcsj.78.2188

Tetraaryl[5]cumulenes react with low-valent nickel complexes at the second double bond to produce novel [4]radialene derivatives that are head-to-head dimers of [5]cumulenes. The head-to-head dimers are also synthesized by a stepwise route. On the other hand, the nickel-catalyzed dimerization of [5]cumulenes with bulky substituents produces other types of extended [4]radialenes and [5]radialenones depending on the bulkiness of the terminal alkyl substituents. Thus, tetrakis-t-butyl[5]cumulene and 1,4-bis(2,2,6,6- tetramethylcyclohexylidene)[3]cumulene react at the central double bond to give the corresponding [4]radialene and [5]radialenone, whereas 1,4-bis(2,2,5,5- tetramethylcyclopentylidene)[3]cumulene and its benzo-annelated derivative react at the second double bond in a head-to-tail manner to afford the corresponding extended [4]radialenes. Tetrakis-t-butyl[5]radialenone was converted into [5]radialene by using a methylation-dehydration procedure. The extended [4]- and [5]radialenes and [5]radialenones have been fully characterized by spectroscopic analyses, X-ray crystallography, and/or independent chemical synthesis. The properties of these novel exocyclic π-electron systems have been investigated in detail. The aryl-substituted [4]radialenes exhibit facile bond rotation with low energy barriers. The [5]radialene and [5]radialenone form the corresponding cations easily by the addition of an acidic proton. The selectivity of the nickel-catalyzed dimerization of [5]cumulenes is discussed on the basis of theoretical calculations.

Full text of DOI:10.1246/bcsj.78.2188

2188 Bull. Chem. Soc. Jpn., 78, 2188–2208 (2005)
ꢀ 2005 The Chemical Society of Japan
Nickel-Catalyzed Dimerization of [5]Cumulenes (Hexapentaenes)
ꢀ
Yoshiyuki Kuwatani, Gaku Yamamoto,1 Masaji Oda,2 and Masahiko Iyoda
Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397
1Department of Chemistry, School of Science, Kitasato University, Sagamihara 228-8555
2Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043
Received June 15, 2005; E-mail: iyoda-masahiko@c.metro-u.ac.jp
Tetraaryl[5]cumulenes react with low-valent nickel complexes at the second double bond to produce novel
[4]radialene derivatives that are head-to-head dimers of [5]cumulenes. The head-to-head dimers are also synthesized
by a stepwise route. On the other hand, the nickel-catalyzed dimerization of [5]cumulenes with bulky substituents pro-
duces other types of extended [4]radialenes and [5]radialenones depending on the bulkiness of the terminal alkyl sub-
stituents. Thus, tetrakis-t-butyl[5]cumulene and 1,4-bis(2,2,6,6-tetramethylcyclohexylidene)[3]cumulene react at the
central double bond to give the corresponding [4]radialene and [5]radialenone, whereas 1,4-bis(2,2,5,5-tetramethylcyclo-
pentylidene)[3]cumulene and its benzo-annelated derivative react at the second double bond in a head-to-tail manner to
afford the corresponding extended [4]radialenes. Tetrakis-t-butyl[5]radialenone was converted into [5]radialene by using
a methylation–dehydration procedure. The extended [4]- and [5]radialenes and [5]radialenones have been fully charac-
terized by spectroscopic analyses, X-ray crystallography, and/or independent chemical synthesis. The properties of these
novel exocyclic ꢀ-electron systems have been investigated in detail. The aryl-substituted [4]radialenes exhibit facile
bond rotation with low energy barriers. The [5]radialene and [5]radialenone form the corresponding cations easily by
the addition of an acidic proton. The selectivity of the nickel-catalyzed dimerization of [5]cumulenes is discussed on
the basis of theoretical calculations.
Long cumulated sp carbon chains as well as oligomeric
acetylenes are among the simplest units for molecular wires.1–5
Although oligomeric acetylenes have been investigated exten-
sively in recent years,6,7 long-chain cumulenes have remained
mostly unexamined, presumably due to the difficulty of han-
dling cumulenes.8–11 The aryl-substituted cumulenes were
mostly investigated in the 1950’s12–15 and 1960’s,16–20 and
the research interests were mainly focused on the electronic
spectral behavior of these linear monodisperse ꢀ-conjugated
systems with relation to color chemistry. Thus, aryl-substituted
butatrienes ([3]cumulenes) and hexapentaenes ([5]cumulenes)
were investigated extensively.21–26 However, the chemistry of
aryl-substituted [7]- and higher cumulenes was studied only in
limited cases.27 As for the alkyl-substituted allenes and cumu-
lenes, a number of works for the synthetic use of allenes have
recently been reported.28–31 In addition, the syntheses and
properties of alkyl-substituted [3]- and higher cumulenes have
been reported by several groups,32–41 but the instability of
these compounds in atmospheric oxygen prevents the develop-
ment of their use.42–44
Although cumulenic double bonds have a wide variety of
potential reactive sites, which may lead to novel cyclic dimers,
trimers, and oligomers, difficulty in controlling the reactivity
has prevented the utilization of cumulenes in organic synthesis.
One of the most accessible reactions is the formation of radia-
lenes (polymethylenecycloalkanes).45–47 In our previous stud-
ies, we reported the synthesis of [4]- and [6]radialenes using
nickel-catalyzed cyclooligomerization of [3]cumulenes.48,49
Based on our continuing interest in the synthetic use of cumu-
lenes as building blocks for constructing cyclic ꢀ-electron sys-
tems, we also investigated the reactions of [5]cumulenes with
transition-metal complexes and have reported some results in a
preliminary form.50–55 As summarized in Scheme 1, hexapen-
taene may formally dimerize to yield the symmetrical [2 þ 2],
[4 þ 4], and [6 þ 6] dimers. Since the transition-metal-cata-
lyzed dimerization of hexapentaene proceeds via metallacyclic
intermediates, head-to-head (H–H) or head-to-tail (H–T) di-
mers at C1–C2, C2–C3, or a C4-symmetric C3–C4 dimer are ex-
pected to form selectively depending on the regioselectivity of
the complexation of hexapentaene with transition metals. The
main purpose of this report is to explore the regioselectivity of
the transition-metal-catalyzed dimerization of [5]cumulenes.
As has been reported previously, tetra-t-butyl[5]cumulene
(1) dimerizes thermally at 200 ꢁC to afford a C3–C4 dimer,
tetrakis(di-t-butylvinylidene)cyclobutane (2),56–59 whereas the
thermal dimerization of tetramethyl[5]cumulene (3) at a lower
temperature produces a C1–C6 dimer, octamethylcyclododeca-
1,3,7,9-tetrayne (4) (Scheme 2).60–63 Since the complexation of
[5]cumulenes with [RhCl(PPh3)2] has recently been shown to
take place at the C2–C3 double bond to form 1:1 complexes,64
a new type of dimerization products (C2–C3 dimers) can be ex-
pected by the reactions of [5]cumulenes with transition-metal
complexes, and this strategy could provide a new methodology
for preparing novel extended radialenes.
Radialenes and their derivatives have received growing at-
tention from synthetic chemists, spectroscopists, and material
scientists.65–67 Thus, a variety of radialenes with novel elec-
tronic properties have been synthesized and their properties
have been investigated.45–47,68–71 Recently, expanded radi-
alenes constructed by the insertion of ethynediyl or buta-1,3-
Published on the web December 9, 2005; DOI 10.1246/bcsj.78.2188

Y. Kuwatani et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2189
Hexapentaene
[2 + 2]
[2 + 2]
[6 + 6]
1
2 3 4 5 6
[4 + 4]
H-H C2-C3
H-T C2-C3
C3-C4
H-H C1-C2
H-T C1-C2
H-H C1-C4
H-T C1-C4
C2-C5
C1-C6
Scheme 1.
R
R
R
Ar
Ar
R
R
R
R
Ar
Ar
Ar
Ar
R
1
Ar
Ar
2
8: R2 =
9: R2 =
5: Ar = Ph
6: Ar = 4-MeC6H4
7: Ar = 4-t-BuC6H4
R
R
R
R
3
4
R
R
R
R
R
R
Scheme 2.
diynediyl moiety into the cyclic radialene framework have
been reported.72,73 These expanded radialenes can be regarded
as new carbon allotropes with all carbon networks, new pre-
cursors to cyclo[n]carbons, and functionalized cross-conjugat-
ed ꢀ-cavities.74–76 In contrast, upon insertion of cumulenic sp-
carbons into the exocyclic double bond of radialenes, a new se-
ries of extended radialenes can be formed. Such ꢀ-extended
radialenes are expected to constitute novel oligocumulene sys-
tems with interesting structures.50–55
R
R
O
R
R
R
R
10: R2 =
11: R2 =
13: R2
=
14: R = t-Bu
12: R2 =
In this paper, we describe the reactions of [5]cumulenes
with nickel(0) complexes to produce a variety of extended
[4]radialenes and [5]radialenones 2, 5–9, and 12–14, together
with the thermal dimerization of [5]cumulenes to afford ex-
tended [4]radialenes 10 and 11. Furthermore, unique structures
and novel electronic properties of radialenes 5–12 and radiale-
nones 13 and 14 as well as the characterization of exotic prop-
erties of extended [4]radialenes and [5]radialenones are de-
scribed (Scheme 3).
Scheme 3.
droxylation of 20c with SnCl2 2H2O in dry THF–ether at 0 ꢁC
ꢂ
for 1 h produced 17 in 88% yield. All of the [5]cumulenes
15–17 were obtained as stable orange or red crystals.
Although the reductive dehydroxylation of the diols 26a–d
with SnCl2 gave no [5]cumulenes, the syntheses of 1 and
21–23 were achieved by the dehalogenation of the bis-allenic
dihalides 27a–d (Scheme 4). The diol 26a was converted into
the corresponding dibromide 27a with concd hydrobromic acid
in acetic acid (90%), whereas 27b was prepared by the reaction
of 26b with concd hydrochloric acid in dioxane–acetic acid
(78%). The conversions of 26c and 26d into 27c (73%) and
27d (91%), respectively, were carried out using PBr3 in ben-
zene at 55 ꢁC.59 The dehalogenation of the dihalides 27a,
27b, 27c, and 27d with zinc or butyllithium produced cumu-
lenes 21, 22, 23, and 1 in 95, 96, 90, and 85% yields, respec-
tively. All of the cumulenes were stable yellow compounds
that could be stored for a long time at room temperature.
Nickel-Catalyzed Syntheses of Tetraaryl[5]cumulene
Dimers. Nickel-catalyzed cyclooligomerization of [3]cumu-
lenes is a simple and efficient method for the synthesis of
Results and Discussion
Synthesis of [5]Cumulenes.
Tetraphenylhexapentaene
(15) and tetrakis(4-methylphenyl)hexapentaene (16) were pre-
pared according to a literature method (Scheme 4).8 The final
reductive dehydroxylation of 20a and b was carried out using
SnCl2 2H2O77 (1.1 equiv) in dry ether at 0 ꢁC for 1 h to pro-
ꢂ
duce 15 and 16 in 87 and 94% yields, respectively. Tetrakis-
(4-t-butylphenyl)hexapentaene (17) was prepared starting from
4,40-di-t-butylbenzophenone (18c).78 Thus, the reaction of 18c
with lithium acetylide in THF at room temperature for 4 h led
to the acetylenic alcohol 19c in 95% yield. The oxidative
coupling of 19c with Cu(OAc)2 H2O in methanol–pyridine
at 60 ꢁC for 10 h gave 20c in 85% yield.79 The reductive dehy-
ꢂ

2190 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Nickel-Catalyzed Dimerization of [5]Cumulenes
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
SnCl
Cu(OAc)2
LiC≡CH
THF
2
O
HCl
Pyridine, MeOH
Ar
OH
OH
HO
20
15: Ar = Ph
18
19
16: Ar = 4-MeC6H4
17: Ar = 4-t-BuC6H4
(a: Ar = Ph; b: Ar = 4-MeC6H4; c: Ar = 4-t-BuC6H4)
R
R
R
R
R
R
R
R
HBr, HCl, or PBr3
Cu(OAc)2
LiC≡CH
THF
O
27a ∼ 27d
Pyridine, MeOH
OH
OH
HO
26
24
25
a: R2
=
b: R2
=
c: R2
=
d: R = t-Bu
But
But
Br
Cl
Br
Br
But
But
Br
27a
Zn
Cl
27b
BunLi
Br
27c
Zn
Br
27d
Zn
But
But
But
But
21
22
23
1
Scheme 4.
Table 1. Nickel-Catalyzed Dimerization of 15–17
Entry
Compd.
mol %
Solv.
Temp/ꢁC
YieldsaÞ
Ni(0)
complex
5–7
28
1
2
3
4
5
6
15
15
15
15
16
17
[Ni(PPh3)4]bÞ
50
20
50
10
25
100
THF
DMF
benzene
benzene
benzene
benzene
25
25
25
80
80
80
53
64
40
61
57
34
0
0
10
0
0
0
[Ni(PPh3)4]bÞ
[Ni(PPh3)4]bÞ
[Ni(CO)2(PPh3)2]
[Ni(CO)2(PPh3)2]
[Ni(CO)2(PPh3)2]
a) Isolated yield. b) Prepared in situ from [NiBr2(PPh3)2], PPh3, and zinc in a 1:2:4 molar ratio.
[4]- and [6]radialenes.45–49 However, tetraarylbutatrienes were
Ar
Ar
stable under the oligomerization conditions, and the starting
[3]cumulenes were recovered unchanged after the reaction
with low-valent nickel complexes, presumably due to the steri-
cally crowded coordination site around the nickel center. Tet-
raarylhexapentaenes having less crowded ligand positions
were expected to react with low-valent nickel complexes to
yield oligomers. The reaction of tetraphenylhexapentaene
(15) with [Ni(PPh3)4] proceeded smoothly at ambient temper-
ature to afford the head-to-head (C2–C3) dimer 5 as the main
product with no formation of a trimer, the [6]radialene deriv-
ative48,49 (Table 1). The reaction of 15 in benzene gave a small
amount of the reduction product 28 along with 5. The reaction
of 15 with [Ni(CO)2(PPh3)2] produced solely 5 in 61% yield.
Under similar conditions, tetrakis(4-methyphenyl)hexapen-
taene (16) and tetrakis(4-t-butylphenyl)hexapentaene (17) gave
the corresponding dimers 6 and 7 in 57 and 34% yields, re-
spectively (Table 1). The relatively low yield in the dimeriza-
tion of 17 can be attributed to the existence of bulky substitu-
ents, which may have disturbed the C–C bond formation at
the C2-position by a concomitant repulsive interaction. The
Ar
Ar
Ar
Ar
Ar
Ar Ni(0) cat.
Ar
Ar
Ar
15: Ar = Ph
16: Ar = 4-MeC6H4
17: Ar = 4-t-BuC6H4
Ar
5: Ar = Ph
6: Ar = 4-MeC6H4
7: Ar = 4-t-BuC6H4
Ar
Ar
Ar
Ar
28
Scheme 5.
extended radialenes 5–7 have a deep blue color, and the color
in solution gradually disappears upon standing at room temper-
ature (Scheme 5).
Since the spectroscopic characterization of the extended
[4]radialene 5 left some uncertainty, we synthesized 5 by an in-
dependent stepwise pathway (Scheme 6). Palladium-catalyzed
cross-coupling of 1,2-dibromo-3,4-bis(diphenylmethylidene)-

Y. Kuwatani et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2191
Ph
R
R
[PdCl2(PPh3)2]
CuI, Et3N
R
R
R
Br
Ph
Ph
OH
Ph
R
R
R
R
+
2
∆
85 °C, 2 h
Ph
Br
Ph
29
19a
R
=
R
R
Ph
Ph
Ph Ph
OH
Ph
Ph
Ph
Ph
Ph
11: R2
21: R2
=
22: R2 =
10: R2
=
SnCl2·2H2O
HCl, ether
Ph
Ph
−50 °C, 30 min
Ph
Ph
OH
Ph
12: R2
=
23: R2
=
Ph Ph
30
5
R
R
Scheme 6.
R
R
R
R
[RhCl(PPh3)3]
Benzene
Ph3P
Cl Rh
Ph3P
cyclobutene (29)80,81 with 1,1-diphenyl-2-propyn-1-ol (19a)
produced the corresponding enediyne derivative 30 in 73%
yield using the Sonogashira reaction. Reductive dehydroxyla-
R
R
=
1: R = t-Bu 21: R2
31: R = t-Bu 32: R2 =
tion of 30 with SnCl2 2H2O in ether gave 5 in 68% yield.
ꢂ
The compound 5 thus obtained exhibited identical spectral
data to those of the product from the nickel-catalyzed reaction.
Thermal and Nickel-Catalyzed Dimerization of Tetra-
alkyl[5]cumulenes with Bulky Substituents. Tetraalkylhexa-
pentaenes with bulky substituents showed high stability
against light and atmospheric oxygen, presumably due to the
Scheme 7.
crystals of 22 gradually dimerized without melting at 250–
260 ꢁC for 2 h to afford 11 in 21% yield, together with uniden-
tified products. The yield of 11 increased by heating 22 at 270–
275 ꢁC for 5 min (51%). The formations of 10–12 show that
hexapentaenes 21–23 reacted only at the central, perpendicular
double bond (C3–C4) in the thermal dimerization, presumably
due to the crisscross structure of the intermediate for the ther-
mal [2 þ 2] reaction.
2
protection of the terminal Csp -carbon with bulky substituents
from approaching molecules. However, the central cumulenic
ꢀ-system is still reactive towards transition metals to form a
dimer. Odd-numbered cumulenes bear two types of double
bonds, i.e., double bonds with lateral and perpendicular ꢀ-
orbitals to substituents. Thermal dimerization of tetra-t-butyl-
hexapentaene 1 takes place at the central C3–C4 (perpendicu-
lar) double bond to form the corresponding dimer 2,56–59 and
the coordination of 1 to [Fe2(CO)9] leads to a very stable 1:1
complex at the central perpendicular bond.82 However, tetra-
arylhexapentaenes 15–17 dimerize with low-valent nickel
complexes to form the C2–C3 (lateral) head-to-head dimers
5–7, and the complex formation of 15 with late transition met-
als reported in literature also occurs at the lateral bonds,64,83–85
suggesting the favorable reactivity of the C2–C3 (lateral) dou-
ble bond of [5]cumulenes for transition metals. The unique re-
activity of 1 can be considered as a result of the steric effect of
the bulky substituent, and the reactivities of bulky-substituted
[5]cumulenes may be modified by changing the size of termi-
nal substituents.
By considering the bulkiness and synthetic facility, tetra-t-
butylhexapentaene (1) and its counterparts 21–23 were chosen
as candidates. These four [5]cumulenes have almost similar
structures except for the bond angles at the terminal carbon,
which affect the steric requirement in the reaction at the C2–C3
double bond. The reported X-ray structure of 23 indicates the
angle of 122ꢁ for the inside of the 6-membered ring at the sp2
carbon.86 The corresponding angle can be expected to be larger
in 1 and to be smaller in 21 and 22.
In contrast, the reaction of 21 with [RhCl(PPh3)3] in ben-
zene at room temperature for 3 h afforded the rhodium com-
plex 32 at the C2–C3 double bond in 80% yield (Scheme 7).
Surprisingly, the reaction of 1 under similar conditions also
produced the corresponding lateral rhodium complex 31, re-
flecting the less bulkiness of the [RhCl(PPh3)2] group than
[Fe(CO)4] which coordinates at the central C3–C4 double bond
of 1.82 The results imply that the C2–C3 lateral double bond of
the [5]cumulenes 1 and 21 endows them with better coordina-
tion ability.
Secondly, dimerization of the [5]cumulenes 1 and 21–23 us-
ing [Ni(CO)2(PPh3)2] was investigated (Scheme 8). The reac-
tion of 21 with 0.5 equiv of [Ni(CO)2(PPh3)2] in refluxing ben-
zene for 24 h afforded the lateral (C2–C3) head-to-tail dimer 8
exclusively in 82% yield. In a similar manner, the reaction of
22 with [Ni(CO)2(PPh3)2] (0.5 equiv) in the presence of PPh3
(1 equiv) in refluxing benzene for 24 h gave the head-to-tail
(C2–C3) dimer 9 in 64% yield. Interestingly, the reaction of
23 carrying the even bulkier substituents with 1 equiv of [Ni-
(CO)2(PPh3)2] in refluxing benzene for 2 days produced the
C3–C4 [4]radialene 12 (32%) and the corresponding C3–C4
[5]radialenone 13 (36%), reflecting the favorable reactivity
of the central double bond. In the case of 1 bearing the bulkiest
substituents, the reaction of 1 with 1.0 equiv of [Ni(CO)2-
(PPh3)2] and 3.0 equiv of PPh3 in refluxing benzene proceeded
slowly for 8 days to afford predominantly the [5]radialenone
14 in 74% yield, together with a small amount of the [4]radi-
alene 2 (6%). All [4]radialenes 2, 8, 9, and 12 and [5]radi-
alenones 13 and 14 are stable colorless or yellow crystals at
The thermal dimerization of 21–23 was attempted according
to the reported procedure56–59 for 1 (Scheme 7). Thus, 23 was
heated at 220 ꢁC for 2 min to produce 12 in 91% yield, whereas
the heating of 21 at 240 ꢁC for 5 min formed 10 in 69% yield,
together with the unchanged 21 (24%). In the case of 22, the

2192 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Nickel-Catalyzed Dimerization of [5]Cumulenes
[Ni(CO)2(PPh3)2]
benzene, reflux
21
8
[Ni(CO)2(PPh3)2]
benzene, reflux
22
9
[Ni(CO)2(PPh3)2]
+
benzene, reflux
23
O
13
12
[Ni(CO)2(PPh3)2]
benzene, reflux
+
1
O
14
2
Scheme 8.
room temperature. The different selectivity observed in the
reactions of 21–23 and 1 with [Ni(CO)2(PPh3)2] clearly sug-
gests that the bulkiness of the terminal substituents in the
[5]cumulenes controls the course of the coordination and the
following oligomerization reactions.
Ph
Br
Br
Ph
Ph
[PdCl2(PPh3)2], CuI
+
X
HO
Et3N, 85 °C, 2 h
Ph
29
33: X = none
34: X = CMe2
35: X = S
Novel Structures and Electronic Properties of Tetra-
aryl[5]cumulene Dimers. The head-to-head dimers 5–7 pre-
pared from tetraarylhexapentaenes 15–17 show a deep blue
color, presumably due to the unusual bis-butatriene structure.
Since the stepwise synthesis of the extended [4]radialene 5
allows us to access novel extended [4]radialenes conjugated
with cumulative double bonds, syntheses of the [4]radialenes
39–41 with end-cap groups have been planned. The ring sys-
tems at the bis-butatriene termini can be expected to provide
the [4]radialenes new characteristics of near-IR absorptions,
low HOMO–LUMO separations, and redox properties. Thus,
a series of [4]radialenes containing terminal fluorene, dimeth-
yldihydroanthracene, and thioxanthene groups have been syn-
thesized by the stepwise route as shown in Scheme 9. The
cross-coupling reaction of the dibromide 29 with the acety-
lenic alcohol 33 under the Sonogashira conditions afforded
the corresponding diol 36 in 68% yield. The reductive dehy-
droxylation of 36 with SnCl2 in dry ether containing gaseous
HCl at ꢃ50 ꢁC for 30 min produced the extended radialene
39 in 49% yield. In a similar manner, the Sonogashira reaction
of 29 with 34 and 35 yielded the diol 37 (62%) and 38 (37%),
respectively. The reductive dehydroxylation of 37 and 38 with
X
X
Ph
Ph
Ph
Ph
OH
OH
Ph
Ph
Ph
SnCl2·2H2O
HCl, ether
Ph
X
X
36: X = none
37: X = CMe2
38: X = S
39: X = none
40: X = CMe2
41: X = S
Scheme 9.
39–41 possess a crowded molecular structure, they are stable
deep-colored crystals at room temperature.
The extended [4]radialenes 5–7 and 39–41 can be expected
to possess a twisted C2-symmetric structure with a puckered
conformation to reduce the congestion among the terminal
aromatic substituents. The inside aromatic rings (ring A, see
Fig. 2) at the C1-position should be stacked on each other as
has been found in aryl-substituted [4]radialenes.87,88 In the
SnCl2 2H2O in ether afforded the desired 40 (61%) and
41 (93%), respectively. Although the extended [4]radialenes
ꢂ

Y. Kuwatani et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2193
log
ε
5.0
4.0
A2
A3
CHCl3
B3
5
3.0
2.0
39
40
41
A4
B4
300
400
500
600
700
800
λ / nm
Fig. 3. The electronic spectra of [4]radialenes 5 and 39–41
in THF.
7.4
7.0
6.6
δ / ppm
Fig. 1. 1H NMR spectrum of [4]radialene 5.
C
B
B
B
B
D
A
A
A
A
5
39
40
41
Fig. 2. Optimized molecular structures of the extended radialenes 5 and 39–41 by density functional calculations (B3LYP/
6-31G(d)). Four phenyl rings in 5 and two phenyl rings in 39, 40, and 41 are marked as rings A–D and A and B, respectively,
as indicated in the structures.
1
1H NMR spectrum of 5 (Fig. 1), the signals for these stacked
phenyl groups were observed separately from the other signals
of aromatic protons in a high field at ꢁ 6.88, 6.83, and 6.73 (p-,
o-, and m-positions in the ring A). Two triplet signals at ꢁ 6.98
(2H) and 6.68 (4H) were also observed separately to be as-
signed for p- and m-positions of the outer phenyl ring at the
C1-position (ring B). The signals of rings C and D protons
overlapped in the range of ꢁ 7.34–7.29 (10H) and 7.11–7.06
the rings B in these [4]radialenes. In the H NMR spectra of
39–41, the signals for the stacked phenyl groups (ring A) ap-
peared at a high field similar to that observed for 5 (ꢁ 6.94–
6.86, 6.84–6.87, and 6.76–6.74 for p-, o-, and m-positions, re-
spectively). The spectrum of 39 shows a doublet (2H) at a high
field of ꢁ 6.21, which can be assigned to the 1-position of the
fluorene ring shielded by the ring B. The spectra of 40 and 41
also show a high-field doublet (2H) at ꢁ 6.29 and 6.26, respec-
tively, assigned to the protons of the 1-position of dihydro-
anthracene and thioxanthene rings. Furthermore, an additional
triplet (2H) appeared at a high field of ꢁ 6.03 for 40 and ꢁ
6.06 for 41. These high-field shifts of aromatic protons suggest
terminal–terminal overlapping between the two aromatic moi-
1
(14H). In the H NMR spectrum of the p-tolyl substituted 6,
the aromatic protons gave four sets of AA0XX0-pattern signals
at higher fields in the range of ꢁ 7.23–6.52 owing to the elec-
tron-donating methyl groups. The corresponding signals for 7,
however, appeared at a lower field in the range of ꢁ 7.46–6.82
ppm. Presumably, repulsive interaction between bulky t-butyl
groups significantly alter the conformation of the [4]radialene
skeleton. This unusual substituent effect was also observed in
the electronic spectrum of 7. The absorption maximum of 5 at
the longest wavelength was observed at 623 nm and the corre-
sponding absorption of 6 was shifted to 694 nm. However, the
absorption maximum of 7 appeared at 623 nm. This also sug-
gests a conformational change in 7 due to the repulsion be-
tween bulky t-butyl substituents.
1
eties of the end-capped bis-butatriene structure. The H NMR
signals of some dihydroanthracene and thioxanthene protons
in 40 and 41 exhibited broadening at room temperature pre-
sumably due to rotation of the butatriene moieties, as described
later.
The electronic spectra of 5 and 39–41 show very intense
broad absorption at the near-IR region (Fig. 3). The longest ab-
sorption maxima of 40 and 41 appear at 688 (log " ¼ 4:44)
and 754 (4.47) nm, respectively. Thus, appreciable bathochro-
mic shifts are observed relative to the absorption of 5, whereas
the longest absorption maximum of 39 is observed at the short-
er wavelength of 583 nm (log " ¼ 3:93) as compared with
those of 40 and 41. This hypsochromic shift is also unusual be-
cause the absorption maxima of the fluorene-substituted buta-
triene and hexapentaene exhibit a large bathochromic shift (ca.
60 nm) as compared to those of tetraphenyl counterparts.8,89
The extended [4]radialenes 39–41 are also assumed to have
a C2-symmetric structure, although the increased planarity of
the terminal substituents may change the conformation of
these molecules. As shown in Fig. 2, the optimized structures
of 5 and 39–41 calculated by the density functional method
(B3LYP/6-31G(d)) suggest that increasing planarity of the ter-
minal substituents causes on increase in the torsional angle of

2194 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Nickel-Catalyzed Dimerization of [5]Cumulenes
(a)
(b)
C(37)
C(31)
C(9)
C(8)
C(7)
C(25)
C(6)
C(2)
C(1)
C(5)
C(43)
C(3)
C(4)
C(49)
C(11)
C(55)
C(10)
C(19)
C(13)
C(12)
ꢁ
ꢀ
Fig. 4. ORTEP drawing of extended [4]radialene 41. Selected bond lengths (A) and angles ( ) are as follows: C(1)–C(2) 1.525(3),
C(2)–C(3) 1.485(3), C(3)–C(4) 1.459(3), C(4)–C(1) 1.490(3), C(1)–C(5) 1.353(3), C(4)–C(10) 1.357(3), C(10)–C(11) 1.216(3),
C(11)–C(12) 1.361(3); C(4)–C(1)–C(2) 88.6(2), C(1)–C(2)–C(3) 88.8(2), C(3)–C(4)–C(1) 91.2(3), C(2)–C(1)–C(5) 140.8(2),
C(4)–C(1)–C(5) 130.1(2), C(1)–C(2)–C(6) 140.1(2), C(1)–C(4)–C(10) 138.7(2), C(3)–C(4)–C(10) 129.4(2), C(3)–C(7)–C(8)
169.0(3).
C
The longest absorption maxima of 1,2-bis(9-fluorenylidene)-
ethene (480 nm) and 1,2-bis(10,10-dimethyl-9,10-dihydroan-
thracen-9-ylidene)ethene (481 nm) are observed at almost the
same wavelength but apparently in a longer region than that
of tetraphenylbutatriene (431 nm).89 In a similar manner, the
longest absorption of bis(fluorenylidene)[3]cumulene (543 nm)
is observed at much longer region than that of octaphenyl[5]-
cumulene (489 nm) in benzene.90
S
Ph2
D
Ph1
H7
H8
Ph1
CHCl3
H
H6
Ph2
H1
2
1
Ph
D
Ph
H5
S
3
6
C
/ H
2
7
H2
H
/ H
H4
4
5
H3
H
/ H
41
1
8
H
/ H
60 °C
Fortunately, single crystals of 41 were obtained by recrys-
tallization from a mixture of CS2–CH2Cl2–ether, and the mo-
lecular structure of 41 was determined by X-ray analysis. As
shown in Fig. 4, 41 has a C2-symmetric structure with a planar
4-membered ring, although the known substituted [4]radi-
alenes usually adopt a puckered conformation.87,88,91–93 The
puckering angle of the 4-membered ring in 41 is only 1.1ꢁ,
and the planar structure brings about repulsive interactions
among its substituents to cause considerable deformation in the
molecular skeleton. Thus, the bond angles of C(2)–C(1)–C(5)
and C(1)–C(2)–C(6) (averaged 140.5ꢁ) are significantly larger
than those of C(4)–C(1)–C(5) and C(3)–C(2)–C(6) (averaged
130.5ꢁ). The 4-membered ring is also transformed to a trape-
CHCl3
2
5
H
H
−50°C
4
6
3
H
H
H
8
H
7
1
H
H
δ / ppm
6.0
7.5
7.0
6.5
Fig. 5. 1H NMR of 41 in CDCl3 at 60 and ꢃ50 ꢁC.
ꢀ
corresponding bond lengths (1.260 and 1.348 A) of tetraphen-
ylbutatriene.94
1
ꢀ
zoid, which contains a long C(1)–C(2) bond of 1.525(3) A,
The H NMR spectra of 39–41 are temperature dependent.
ꢀ
short C(3)–C(4) bond of 1.459(3) A and two normal C(2)–
ꢀ
C(3) and C(1)–C(4) single bonds (averaged 1.488 A). The but-
tressed phenyl groups (ring B in Fig. 2) bend away from the
exocyclic butatriene units at ring sp2-carbons (C(3) and C(4))
and at exocyclic sp-carbons (C(7) and C(10)). The averaged
angle difference of both sides of the exocyclic double bonds
As shown in Fig. 5, the signals of the phenyl groups in 41 re-
main to be sharp throughout the temperature range examined,
indicating that the rotation of the phenyl groups is fast on the
NMR time scale, and their chemical shifts are similar to those
of the octaphenyl analogue 5. In contrast, the signals of the thi-
oxanthene moieties are very broad at ambient temperature,
split into eight separate signals upon lowering the temperature,
and coalesce into four signals at high temperatures. This be-
havior can be reasonably ascribed to the internal rotation about
the cumulene bonds. Decoupling and qualitative saturation
transfer experiments at low temperatures enabled the signal as-
signments to be determined as given in Fig. 5. Coalescence of
the H4 and H5 signals (ꢁꢂ ¼ 52 Hz) took place at 15 ꢁC, giv-
ing a rate constant of kc ¼ 116 sꢃ1. Quantitative saturation
at C(3) and C(4) is 10.2ꢁ [= C(2){C(3){C(7) ꢃ ÀC(4){C(3){
=
À
Cð7Þ ¼ 11:2ꢁ;
À= C(1){C(4){C(10) ꢃ ÀC(3){C(4){C(10) ¼
=
9:2ꢁ] and the averaged angle for out-of-plane bending at these
carbons is 6.8ꢁ. Furthermore, significant twisting of the cumu-
lative bonds is also observed, presumably due to a repulsive
interaction between two partially overlapped thioxanthene
units (ring D in Fig. 2). The torsion angles between the 4-
membered ring and the thioxanthene moieties are about 20ꢁ.
Interestingly, the butatriene units show bond alternation with
transfer experiments (H2 was irradiated and H7 was observed)
the shorter C(sp)–C(sp) bond (averaged 1.217 A) and longer
2
at ꢃ20 ꢄ 1 ꢁC gave the rate constant of 3:6 ꢄ 0:4 sꢃ1
.
A
95,96
ꢀ
similar temperature dependence of the 1H NMR spectrum
ꢀ
C(sp)–C(sp ) length (averaged 1.364 A) as compared with the

Y. Kuwatani et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2195
was also observed in 40 at a higher temperature range than that
in 41. The exchange rate was estimated to be k ¼ 3:5 ꢄ 0:4 sꢃ1
at 0 ꢁC by the saturation transfer method. The free energies of
activation for the cumulenic bond rotation were deduced to be
ꢁGz ¼ 13:7 and 14.9 kcal molꢃ1 for 41 (in CDCl3 at ꢃ20 ꢁC)
and 40 (in CDCl3 at 0 ꢁC), respectively.
X
X
C
C
X
D
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
D
D
D
X
X
X
C
C
1
In contrast to the H NMR spectra of 40 and 41, the spec-
trum of 39 at room temperature showed sharp and well-
resolved signals, suggesting that the energy barrier for bond
rotation in 39 is fairly high as compared to those in 40 and 41.
In fact, the free energy of activation for the rotation was found
to be ꢁGz ¼ 17:8 kcal molꢃ1 in C2D2Cl4 at 27 ꢁC by satura-
tion transfer studies. In any case, the extended [4]radialenes
39–41 exhibit low rotational barriers of the end-cap groups
and can be regarded as the first twin-rotor system created on
a radialene frame.
In order to discuss the observed energy barriers, the stability
of both the ground states and the transition states for rotation
should be considered. As shown in Figs. 2 and 4, the inner
wings of the thioxanthene and dihydroanthracene rings in 41
and 40 significantly twist and overlap each other with the
39: X = none
40: X = CMe2
41: X = S
42
TS for single rotation
X
D
C
X
C
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
D
X
X
43
TS for simultaneous rotation
39': X = none
40': X = CMe2
41': X = S
Scheme 10.
shortest C C distance being the sum of the van der Waals ra-
ꢂꢂꢂ
ꢀ
dii (3.4 A). In the case of 39, however, the fluorene rings do
not overlap, even though the twisting is to some extent because
log ε
8
5.0
of the H H repulsion. In accordance with these structural fea-
ꢂꢂꢂ
9
tures, the H7 proton signal shows a large upfield shift in 41 (ꢁ
6.06 at ꢃ50 ꢁC) and 40 (ꢁ 6.03 at ꢃ30 ꢁC) in the 1H NMR
spectra (CDCl3) due to the shielding effect of the confronting
aromatic ring, while the upfield shift is moderate in 39 (ꢁ 7.10
at 22 ꢁC in C2D2Cl4). These molecular deformations cause the
destabilization of the ground state, which is larger in 40 and 41
than in 39. Thus, the molecular deformations in 39–41 at the
ground state allow us to estimate the order of the destabiliza-
tion as 41 ꢅ 40 > 39.
10
4.0
3.0
A characteristic feature of the overcrowding in 39–41 is the
unsymmetrical steric interactions of the end-capped aromatic
rings on both terminals of the bis-cumulenic linkage, although
the known barriers for the thermal-bond rotation of double
bonds have been mainly investigated on the motion of funda-
mentally symmetrical olefinic and cumulenic bonds.97 A plau-
sible bond rotation process of 39–41 is depicted in Scheme 10.
The butatriene bonds rotate one at a time by way of the tran-
sition state 42, rather than simultaneously by way of 43 be-
cause 43 is considered to be far less stable than 42. This diradi-
caloid transition state 42 is stabilized by the conjugation of
these radicals among both the tricyclic aromatic system and
the extended [4]radialene framework. The contribution of the
latter conjugation is similar in 39–41, while the conjugation
in the terminal moieties significantly depends on the X part
in the tricyclic aromatic group. In 41, the sulfur atom partici-
pates in the conjugation and the transition state for 41 is stabi-
lized more effectively than those for 39 and 40.
300
400
500
λ / nm
Fig. 6. The electronic spectra of [4]radialenes 8, 9, and 10
in THF.
tochemical rotation of double bonds has been employed for the
bottom-up construction of molecular motors.108–111 We believe
that our bis-butatriene system can contribute to the develop-
ment of the studies on molecular motors, molecular switches,
and chemosensors. To our knowledge, the ꢁGz value of
13.7 kcal molꢃ1 for 41 is the lowest reported so far for the en-
ergy barriers to rotation around an olefinic or cumulenic bond
by way of a diradicaloid transition state.
Characteristic Structures of [4]Radialenes Derived from
Alkyl-Substituted [5]Cumulenes. The [4]radialenes 2 and
8–12 are very stable toward light and air. Based on the molec-
ular models and MM2 calculations, the polyallenic [4]radi-
alenes 2 and 10–12 have a planer structure with D4h symmetry,
whereas the [4]radialenes 8 and 9 are planar D2h-symmetric
molecules. The 1H and 13C NMR spectra of 2 and 10–12
reflect their highly symmetric structures. As shown in Fig. 6,
the electronic spectra of 8 and 9 exhibit an end absorption
up to 450 nm, indicating elongation of ꢀ-conjugation, whereas
The rotational barriers of the cumulenic double bonds in
39–41 are much lower than the reported barriers for the known
butatrienes and bis-butatrienes (20–30 kcal molꢃ1).98–101 There
has been considerable recent interest in the restricted rotation
of single and double bonds because of their potential use in
molecular-scale motors, thermochromic devices, molecular
switches, and chemosensors.102–107 Thus, the thermal and pho-

2196 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Nickel-Catalyzed Dimerization of [5]Cumulenes
C(25)
C(28)
C(12)
C(13)
C(7)
C(4)
C(3)
C(24)
C(11)
C(1)
C(5)
C(1')
C(9) C(10)
C(6)
C(16)
C(21')
C(2)
C(8)
C(21)
C(1)
C(22)
C(21)
C(17)
C(23)
C(2)
C(20)
C(3)
Fig. 8. ORTEP drawing ꢁof [4]radialene 8. Selected bond
ꢀ
lengths (A) and angles ( ) as follows: C(1)–C(2) 1.510(6),
Fig. 7. ORTEP drawing of [4]radialene 11. Selected bond
C(2)–C(3) 1.502(6), C(3)–C(4) 1.492(6), C(4)–C(1)
1.512(6), C(1)–C(5) 1.333(6), C(5)–C(6) 1.263(6), C(6)–
C(7) 1.322(6), C(2)–C(8) 1.340(6), C(3)–C(9) 1.333(6),
C(9)–C(10) 1.252(6), C(10)–C(11) 1.330(6), C(4)–C(12)
1.333(6); C(4)–C(1)–C(2) 90.2(4), C(1)–C(2)–C(3)
88.5(4), C(2)–C(3)–C(4) 91.3(4), C(3)–C(4)–C(1)
88.8(3), C(13)–C(7)–C(16) 110.2(4), C(17)–C(8)–C(20)
109.9(4), C(21)–C(11)–C(24) 110.4(4), C(25)–C(12)–
C(28) 109.0(4).
ꢁ
ꢀ
lengths (A) and angles ( ) as follows: C(1)–C(2) 1.309(4),
C(2)–C(3) 1.300(4), C(1)–C(21) 1.499(4), C(1)–C(210)
1.510(4), C(21)–C(22) 1.304(4), C(22)–C(23) 1.298(4);
C(2)–C(1)–C(21) 135.8(3), C(2)–C(1)–C(210) 133.9(3),
C(21)–C(1)–C(210) 90.2(3), C(1)–C(2)–C(3) 173.9(3),
C(1)–C(21)–C(22) 134.8(3), C(22)–C(21)–C(10) 135.3(3),
C(1)–C(21)–C(10) 89.8(3), C(21)–C(22)–C(23) 177.8(3).
the spectrum of 10 shows an end absorption only up to 350 nm,
corresponding to the existence of an orthogonal allenic ꢀ-
bond.
rings are in the range of 109.0–110.4ꢁ. The slight deformation
from D2h-symmetry of 8 observed in the crystal can be dis-
solved in solution because of the lack of serious intramolecular
constraints.
Structures and Properties of Extended [5]Radialene and
[5]Radialenones. The structures and properties of extended
[5]radialenones 13 and 14 have attracted considerable atten-
tion because the carbonyl groups in 13 and 14 can be expected
to possess high polarities. The structure of 14 was determined
by X-ray crystallography (Fig. 9).52 The central 5-membered
ring of 14 clearly shows a highly planar structure: The maxi-
To elucidate the exact molecular structure of the [4]radi-
alene with exocyclic allenic bonds, the crystal structure of
11 was determined by X-ray analysis.51 The crystallographic
data revealed that the molecule 11 is located on a crystallo-
graphic center of symmetry. The central 4-membered ring of
the molecule is perfectly planar. Figure 7 shows the molecular
projection of 11 onto the 4-membered ring plane together with
the important structural parameters, indicating a very charac-
teristic feature of 11 with a widely spread planar structure in
its center. The four benzocyclopentene substituents are ap-
proximately perpendicular with the puckered angles of ca. 10ꢁ
in the cyclopentene rings. Consequently, the molecule has a
very beautiful shape like a pinwheel or cogwheel.
ꢀ
mum atomic deviation from the least-squares plane is 0.03 A.
The planar structure extends to the exocyclic allenic bonds
ꢀ
with a maximum atomic deviation of 0.24 A. The bond dis-
tances in the carbonyl and allenic moieties of the molecule are
normal, while the bond angles C(2)–C(1)–C(10) [129.2(6)ꢁ]
and C(3)–C(4)–C(40) [129.9(7)ꢁ] are significantly larger than
the expected value of 126ꢁ, although the long distance between
the neighboring t-butyl substituents causes no short contact. A
similar angular deformation was found in tetrakis(1,3-dithia-
indanylidene)cyclopentanone due to significant non-bonded
repulsion between the substituents of exocyclic bonds.71 Al-
though the [5]radialenes prefer the half-chair conformation,112
the planar structure of 14 may be due to the absence of steric
strain between the t-butyl substituents as the result of the
extension of the exocyclic bonds by a cumulenic structure.
Bulky tetramethylcyclohexylidene rings and t-butyl groups
covering the outside of the [5]radialenones 13 and 14 seem
to protect the reactive ꢀ-electronic system. An interesting be-
havior of 13 and 14 is solvatochromism. As shown in Fig. 10, a
solution of 14 exhibits a pale yellow color in benzene or THF,
but bright yellow in methanol or acetic acid. Similarly, solu-
tions of 13 in benzene and methanol are pale yellow and bright
yellow, respectively. The UV–vis spectra of 13 and 14 show
strong (215–250 nm, log " ¼ ca. 4.5) and weak (300–430 nm,
log " ¼ ca. 3.5) absorptions. Although the strong absorptions
The X-ray structures of [4]radialenes previously deter-
mined have a puckered 4-membered ring due to the steric re-
pulsion between the neighboring substituents on the exocyclic
bonds.87–89 An extension of the double bonds of [4]radialenes
to the allenic bonds in 11 releases the severe steric repulsion
between the neighboring substituents. No significant contact
ꢀ
shorter than 4 A was found between the methyl groups in tetra-
methylindane parts.
The radialene framework of 8 and 9 can be expected to
adopt a planar structure with D2h symmetry instead of a puck-
ered structure with C2v symmetry: The Raman spectrum of 9
exhibits very strong cumulenic absorption at 1995 cmꢃ1, while
the IR spectrum shows a very weak peak at 1955 cmꢃ1. The
molecular structure of 8 was determined by X-ray crystallo-
graphic analysis, as shown in Fig. 8. The molecule adopts a
slightly puckered conformation with the angle of 11.9ꢁ with
partial bending of the exocyclic double bonds, presumably due
to the packing force in the crystal lattice. The terminal tetra-
methylcyclopentane rings adopt a half-chair conformation in
order to release torsional strain between methyl groups. The
bond angles at the inside sp2-carbon atom of the cyclopentane

Y. Kuwatani et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2197
O
CF3COOH
C(10)
C(40)
C(4)
C(3)
C(30)
C(41)
C(11)
C(5)
C(1)
C(2)
C(20)
+
O
H
44a
O
14
C(21)
C(31)
Fig. 9. ORTEP drawing ofꢁ[5]radialenone 14. Selected bond
+
+
ꢀ
lengths (A) and angles ( ) as follows: C(1)–C(2) 1.492,
O
O
C(2)–C(3) 1.483, C(3)–C(4) 1.490, C(4)–C(5) 1.488, C(5)–
C(1) 1.476, C(5)–O 1.206, C(1)–C(10) 1.322, C(10)–C(11)
1.302, C(2)–C(20) 1.318, C(20)–C(21) 1.312, C(3)–C(30)
1.320, C(30)–C(31) 1.310, C(4)–C(40) 1.325, C(40)–C(41)
1.286; C(1)–C(2)–C(3) 107.8, C(2)–C(3)–C(4) 107.8,
C(3)–C(4)–C(5) 108.1, C(4)–C(5)–C(1) 107.7, C(5)–C(1)–
C(2) 108.4, C(1)–C(2)–C(20) 123.9, C(20)–C(2)–C(3)
128.4, C(2)–C(3)–C(30) 126.4, C(30)–C(3)–C(4) 125.7,
C(40)–C(4)–C(5) 122.0, C(4)–C(5)–O 126.2, C(2)–C(1)–
C(10) 129.2, C(3)–C(4)–C(40) 129.9, O–C(5)–C(1) 126.0,
C(5)–C(1)–C(10) 122.4, C(1)–C(10)–C(11) 175.4, C(2)–
C(20)–C(21) 177.7, C(3)–C(30)–C(31) 179.2, C(4)–
C(40)–C(41) 175.4. The estimated standard deviations
H
44b
H
44c
Scheme 11.
PhLi
Ph OH
THF
98%
45
MeLi
ꢁ
THF
90%
ꢀ
are 0.009–0.011 A and 0.7–0.8 for bond distances and
angles.
O
14
log ε
5.0
4.0
3.0
TFA
46
O
OH
Scheme 12.
cies 44, the nucleophilic addition of organolithium reagents
was examined (Scheme 12). The reaction of 14 with PhLi in
THF gave the corresponding alcohol 45 in 98% yield, whereas
a similar reaction of 14 with MeLi directly afforded the [5]-
radialene 46 in 90% yield. The facile formation of 46 may
be due to either the overcrowded structure of the adduct or
the stability of the cationic intermediate.
2.0
300
400
500
600
700
800
λ / nm
Solutions of both compounds 45 and 46 in TFA exhibit an
intense deep blue color, and the electronic spectra show the
absorption maxima at ca. 800 nm (log " ꢆ 3:8) tailing up to
1100 nm (Fig. 11). These spectra suggest the formation of
the corresponding carbocations, which have a small HOMO–
LUMO gap. The cationic species in solution were found to
be stable, and we took the 1H and 13C NMR spectra of the cat-
ion derived from 46. The 1H NMR spectrum of 46 measured in
a CDCl3–CF3COOD (1:1) solution showed that the original
signal for the olefinic proton observed at ꢁ 5.02 in CDCl3 dis-
appeared, and that the signals for the protons of the t-butyl
substituent shifted to a lower field. Disappearance of the ole-
finic proton signals can be explained by the formation of the
carbocation 47. The equilibrium between carbocation and the
original olefin caused H–D exchange at the methyl group in
47 (Scheme 13), and the methyl group in 47-d and 47-d2
was observed at ꢁ 2.87 as very weak signals with a complicat-
ed coupling pattern due to geminal deuterons. The cationic
carbon signal in the 13C NMR appeared at a very low field
Fig. 10. The electronic spectra of [5]radialenone 14 in THF
(solid line), MeOH (dotted line), and TFA (broken line).
The bathochromic shift in TFA represents the contribution
of the cationic structure of the protonated 14 as shown in
Scheme 11.
of 13 and 14 show a small dependence on the solvent, the
wavelengths of the weak absorptions vary with the solvent
used. Thus, the absorption maxima of 14 appeared at 378
(log " ¼ 3:36) and 408 (log " ¼ 3:27) nm in THF, and the ab-
sorption bands bathochromically shift with an increase in the
polarity of the solvent. Although the X-ray analysis of 14 re-
veals a normal bond length for the carbonyl part, protonation
of the C=O group easily exhibits a remarkable solvatochrom-
ism. The color of 14 in trifluoroacetic acid (TFA) changes to a
deep violet [621 nm (log " ¼ 3:51)]. The interesting contribu-
tion of the resonance structures 44b and 44c for the protonated
ketone 44a is considered to be as shown in Scheme 11.
In order to confirm the unusual stability of the cationic spe-

2198 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Nickel-Catalyzed Dimerization of [5]Cumulenes
log ε
C2 carbon atoms.
5.0
A plausible reaction mechanism for the nickel-catalyzed
dimerization of [5]cumulenes is depicted in Scheme 14. The
reaction of a Ni(0) complex with [5]cumulenes affords a bis-
cumulene complex, which leads to the corresponding 5-mem-
bered nickelacycle in the case of [5]cumulenes possessing less-
hindered substituents. Tetraaryl[5]cumulenes 5–7 can be con-
sidered to produce the nickelacycle (A) by the formation of
a C–C bond at the C2-position, and lead to a head-to-head
(C2–C3) dimer after reductive elimination. In the case of
[5]cumulenes with bulky substituents, formation of the similar
metallacycle (A) is considered to be difficult because of the
concomitant repulsive interaction, which deviates the reaction
course. Thus, the cumulenes 1 and 21–23 form the metallacy-
cle (C) by changing the bond-forming manner to afford head-
to-tail (C2–C3) dimers 8 and 9. The cumulenes with more
bulky substituents (1 and 23) can not form this metallacycle
and lead to the formation of the metallacycle (D) with the
shifts of the coordination site. A simple reductive elimination
from D affords the symmetric [4]radialenes 2 and 12, whereas
the CO insertion followed by reductive elimination from E
results in the formation of the [5]radialenones 13 and 14.
The nickelacycle intermediates play a critical role in the for-
mation of the dimeric products of [5]cumulenes. Therefore, the
theoretical calculations of the intermediates were examined.
According to the theoretical calculations (B3LYP/BS-I and
BS-II114) of the nickelacycle intermediates A–D (R ¼ H,
L ¼ PH3, and n ¼ 2), the most stable isomer is A, which forms
from the reaction at the second double bond (C2–C3) of
[5]cumulene in a head-to-head manner. The other intermediate
B, which produces the same dimer after reductive elimination,
is less stable than A by 14 kcal molꢃ1. Thus, a plausible inter-
mediate for the formation of the head-to-head dimer is consid-
ered to be A. The preferential formation of A than to B is in
good agreement with the general tendency for nickelacycle
formation by the oxidative cyclization of two ꢀ-compornents.
The head-to-tail nickelacycle C formed from the reaction at the
same double bond is the second most stable isomer, which has
a higher energy than the metallacycle A by 6 kcal molꢃ1. The
nickelacycle D is considerably more unstable than A and not
the structure with minimum energy. Therefore, the most pref-
erable intermediate of the nickel-catalyzed dimerization of
[5]cumulene is the metallacycle A, which leads to the head-
to-head dimer after reductive elimination. Large substituents
at the terminal of [5]cumulene would affect the stability of
the nickelacycle intermediate due to the steric repulsion among
the substituents and the phosphine ligands on the nickel atom.
The magnitude of the steric destabilization in the reaction at
the second double bond of [5]cumulenes is consistent with
those of the bond angles of the geminal substituents at the
[5]cumulenes (1 and 21–23). Thus, the [5]cumulenes with
5-membered ring substituents (21 and 22) afforded the head-
to-tail dimer via the nickelacycle C, whereas 1 and 23 gave
the [4]radialene and the [5]radialenone via the nickelacycle D.
4.0
3.0
2.0
400
600
800
1000
λ / nm
Fig. 11. The electronic spectra of [5]radialenone 14 (dotted
line), [5]radialene 46 (solid line), and carbinol 45 (broken
line) in TFA.
CF3COOD
CH3
46
47
CH2D
47-d
CHD2
47-d2
Scheme 13.
(ꢁ 208.4), shifted from ꢁ 142.7 in the original spectrum of 46.
Considerable low-field shifts were also observed for allenic
sp-carbon signals (ꢁ 228 ppm) and for sp2-, and for even sp3-
carbons. Thus, the NMR spectral characteristics of 47 reflect
the highly delocalized nature of the cationic charge.
Nickel-Catalyzed Dimerization of [5]Cumulenes. The
nickel-catalyzed dimerization of [5]cumulenes reported here
is a versatile strategy for the synthesis of novel radialene deriv-
atives conjugated with cumulative double bonds. It is shown
that the terminal substituents of [5]cumulenes play a major
role in determining the reaction pathway. Since the cyclodi-
merization of cumulenes proceeds via a nickelacycle inter-
mediate, the regiochemistry of the products may be determined
by the formation of the 5-membered nickelacycles from the
corresponding bis-ꢀ-complexes.47–49 The preference of the
C2–C3 double bond in the coordination to transition metals
is observed for [5]cumulenes as shown in the formation of rho-
dium complexes. However, this preference can be deviated by
a steric interference of the terminal substituents, and tetra-t-
butyl[5]cumulene (1) forms a C3–C4 complex with Fe(CO)5.
According to the theoretical investigation of Hoffmann,113
the regiochemistry of the formation of 5-membered metallacy-
cles from the corresponding bis-olefin complex is governed by
the LUMO of the coordinating olefins. The preferable forma-
tion of C–C bonds at the carbon atom with a large orbital co-
efficient in the LUMO should determine the reaction course.
When two [5]cumulenes coordinate to nickel(0) at the C2–C3
double bond, a large orbital coefficient in the LUMO is expect-
ed at the C2-position (terminal position of the conjugation in
Summary
The nickel-catalyzed reactions of [5]cumulenes provided
are an effective method for the syntheses of a variety of
[5]cumulene dimers. In the case of tetraaryl[5]cumulenes,
ꢀ
the ꢀ -molecular orbital) and the bis-ꢀ-complex should lead
to a nickelacycle with the formation of the C–C bond at the

Y. Kuwatani et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2199
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
or
R
R
R
R
NiLn
R
R
R
R
Ni
Ln
Ni
Ln
(B)
R
R
R
R
R
R
R
R
(A)
R
5-7
R
R
R
R
R
R
R
R
R
R
R
R
R
NiLn
R
R
R
R
R
R
Ni
R
Ln
R
R
R
(C)
8 and 9
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
NiLn
R
R
R
Ni
Ln
(D)
R
R
R
R
R
NiLn
2 and 12
R1
R
6R
R
2
3
4
5
L = CO
R
R
R
R
R
R
R
R
1: R = t-Bu
15: R = Ph
16: R = 4-MeC6H4 17: R = 4-t-BuC6H4
R
R
R
R
21: R2
23: R2
=
=
22: R2 =
R
R
NiLn
R
R
O
O
(E)
13 and 14
Scheme 14.
on a Varian XL-100, JEOL JNM-PMX 60Si, JNM-FX 90Q, JNM-
GSX 400, or JNM-GX 500 instrument. Spectra are reported (in ꢁ)
referenced to Me4Si. Unless otherwise noted, CDCl3 was used as
the solvent. Data are reported as follows: chemical shifts, multi-
plicity (s = singlet, d = doublet, t = triplet, dd = double dou-
blet, dt = double triplet, td = triplet doublet, m = multiplet, and
br = broad), coupling constant (Hz), and integration. In the orga-
nometallic compounds 31 and 32, the coupling constants between
the carbons and 103Rh (or 31P) are described. IR spectra were tak-
en on a Hitachi EPI-G3 or a Jasco R-800 FT-IR-3 spectrometer.
Raman spectra were measured on a Jasco R-800 spectrometer.
Electronic spectra were obtained on a Hitachi EPS-3T or a U-
3400 instrument and are reported in nanometers (log ") (sh =
shoulder). Mass spectral analyses (MS) were performed on a
JEOL JMS-OISG-2 instrument. Only the intense or structurally
diagnostic mass spectral fragment ion peaks are reported. Melting
points were determined on a Mettler FP-2 apparatus and are un-
corrected.
Preparation of Tetraarylhexapentaenes 15–17. 1,1-Bis(4-t-
butylphenyl)-2-propyn-1-ol (19c): Gaseous acetylene was in-
troduced into dry THF (200 mL) for 30 min at ꢃ78 ꢁC. A solution
of n-BuLi (1.5 M in hexane, 50 mL, 76 mmol) was added via sy-
ringe while passing acetylene through the solution below ꢃ50
ꢁC and the mixture was stirred for 1 h at the same temperature.
A solution of 18.0 g (61.1 mmol) of 4,40-di-t-butylbenzophenone
(18c) in 50 mL of dry THF was added dropwise within 10 min.
The mixture was allowed to warm to ambient temperature and
stirred for 4 h. After cooling to ꢃ50 ꢁC, a mixture of 50 mL of
saturated aqueous NH4Cl and 50 mL of water was added and
the mixture was allowed to warm to room temperature. The mix-
ture was extracted with 3 ꢇ 100 mL of benzene and the extracts
head-to-head dimers are selectively formed, reflecting the sta-
bility of the metallacyclic intermediate. The tetraaryl[5]cumu-
lene dimers have an extended [4]radialene framework with an
intense blue color in solution. Furthermore, this extended
[4]radialene system with terminal dimethyldihydroanthracene
and thioxanthene units exhibits low rotational barriers for the
cumulenic double bonds. The easy rotation of the cumulenic
double bonds at ambient temperatures will be useful in de-
veloping molecular motors, molecular switches, and chemo-
sensors. The cyclodimerization of [5]cumulenes with bulky
alkyl substituents produces head-to-tail [4]radialenes, tetrakis-
(allenylidene)[4]radialenes, and [5]radialenones. The struc-
tures of [4]radialenes and [5]radialenone have been confirmed
by X-ray analyses. The preferential formation of [4]radialenes
or [5]radialenones depends on the bulky alkyl substituents of
[5]cumulenes, the reaction pathway having been proven by
MO calculations by considering the stability of the metallacy-
clic intermediates. The [5]radialenones exhibit solvatochrom-
ism. The color of the benzene solution is a pale yellow, where-
as the color in methanol is a bright yellow. Additionally, solu-
tions of [5]radialenone in trifluoroacetic acid exhibit an
intense blue color, reflecting the formation of stable carbocat-
ions. The cationic charge is delocalized on the extended [5]-
radialene framework. Finally, we can conclude that the extend-
ed [4]radialenes and [5]radialenes have a possible multifunc-
tionality based on the unique arrangements of their cumulated
double bonds.
Experimental
General Procedures. 1H and 13C NMR spectra were recorded

2200 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Nickel-Catalyzed Dimerization of [5]Cumulenes
were dried over MgSO4. After removal of the solvent in vacuo,
the residue was purified by chromatography on alumina with di-
ethyl ether–benzene as the eluent. The resultant solid after remov-
al of the solvent was recrystallized from ether–hexane to give
18.6 g (95%) of the alcohol. 19c: colorless needles (hexane–ether),
mp 176.5–177.5 ꢁC; 1H NMR (60 MHz, CCl4) ꢁ 7.37 (d, J ¼ 8 Hz,
4H), 7.27 (d, J ¼ 8 Hz, 4H), 2.67 (s, 1H), 2.28 (s, 1H), 1.33 (s,
18H); Anal. Calcd for C23H28O: C, 86.20; H, 8.81%. Found: C,
86.10; H, 8.79%.
the cumulene 15, the cumulene 16 was obtained from the diol 20b
in 94% yield. 16: deep red crystals, mp >250 ꢁC (lit.18 318–320
1
ꢁC); H NMR (500 MHz, CD2Cl2–CS2) ꢁ 7.36 (d, J ¼ 8 Hz, 8H),
7.15 (d, J ¼ 8 Hz, 8H), 2.38 (s, 12H); 13C NMR (125 MHz, CD2-
Cl2–CS2) ꢁ 147.9, 138.4, 135.4, 129.31, 129.27, 126.3, 123.8,
21.5; IR (KBr) 3016, 2910, 2000, 1600, 1506, 1284, 1175, 1012,
821, 718, 610, 573, 469 cmꢃ1; UV ꢃmax (THF) 502 (log " 4.89),
497 (4.89), 494 (4.88), 429 (4.19), 372 (4.08), 296 (4.51), 255
nm (4.64).
1,1-Diphenylpropyn-1-ol (19a): In a similar manner to that
described above, 19a was obtained from benzophenone (18a) in
96% yield. 19a: colorless needles (hexane–ether), mp 46.5–48
ꢁC (lit.115 47–48 ꢁC); 1H NMR (60 MHz, CCl4) ꢁ 7.57–7.03 (m,
10H), 2.77 (s, 1H), 2.63 (s, 1H).
1,1,6,6-Tetrakis(4-t-butylphenyl)-1,2,3,4,5-hexapentaene
(17): To a solution of 1.07 g (1.67 mmol) of the diol 20c in 20 mL
of dry THF were added 1.38 g (6.12 mmol) of SnCl2 2H2O and
ꢂ
10.0 mL of ether saturated with gaseous HCl at 0 ꢁC. The mixture
was stirred for 1 h at 0 ꢁC. Then 100 mL of CH2Cl2 and 100 mL of
water were added. The organic layer was separated and washed
successively with water, aqueous NaHCO3, and brine, and then
dried over MgSO4. After removal of the solvent, the residue
was passed through a short column of alumina with CH2Cl2 as
the eluent. The collected crystals after removal of the solvent were
washed with ether to give the cumulene 17 (893 mg, 88%). 17: or-
1,1-Bis(4-methylphenyl)propyn-1-ol (19b):
In a similar
manner to that described above, 19b was obtained from 4,40-di-
methylbenzophenone (18b) in 86% yield. 19b: colorless needles
(hexane–ether), mp 84.5–86.0 ꢁC (lit.18 87–88 ꢁC); 1H NMR (60
MHz, CCl4) ꢁ 7.30 (d, J ¼ 8 Hz, 4H), 6.97 (d, J ¼ 8 Hz, 4H), 2.61
(s, 1H), 2.47 (s, 1H), 2.28 (s, 6H).
1
1,1,6,6-Tetrakis(4-t-butylphenyl)-2,4-hexadiyne-1,6-diol
(20c): To a stirred solution of 4.79 g (24.0 mmol) of Cu(OAc)2
ange crystals, mp >250 ꢁC; H NMR (100 MHz) ꢁ 7.55 (d, J ¼ 9
Hz, 8H), 7.43 (d, J ¼ 9 Hz, 8H), 1.34 (s, 36H); 13C NMR (125
MHz, CD2Cl2–CS2) ꢁ 151.8, 148.6, 135.8, 129.7, 126.9, 126.0,
124.1, 34.9, 31.7; MS (FD) m=z 604 (Mþ); IR (KBr) 3050,
2955, 2003, 1602, 1506, 1462, 1364, 1270, 1109, 1013, 834,
614 cmꢃ1; UV ꢃmax (THF) 503 (log " 4.90), 430 (4.18), 372
(4.09), 297 (4.55), 255 nm (4.66). Anal. Calcd for C46H52: C,
91.34; H, 8.66%. Found: C, 91.00; H, 8.65%.
ꢂ
H2O in methanol–pyridine (1:1, 100 mL) was added a solution of
3.85 g (12.0 mmol) of the alcohol 19c in 100 mL of methanol–pyr-
idine (1:1) at 60 ꢁC and the solution was stirred for 10 h at the
same temperature. After cooling to room temperature, the solvent
was evaporated in vacuo and a mixture of 100 mL of ether–CS2
(v/v ¼ 4=1) and 250 mL of 2 M HCl was added to the residue.
The aqueous phase was extracted with 2 ꢇ 100 mL of ether–CS2
(v/v ¼ 4=1) and the combined organic phase was washed succes-
sively with 2 M HCl, water, and brine, and then dried over
MgSO4. After removal of the solvent in vacuo, the residue was
purified by recrystallization from ether–hexane to give the diol
Preparation of Tetraalkylhexapentaenes 1 and 21–23. 1-
Ethynyl-2,2,5,5-tetramethylcyclopentanol (25a): Gaseous acet-
ylene was introduced into dry THF (100 mL) for 30 min at ꢃ78
ꢁC. A solution of n-BuLi (1.5 M, 33 mL, 50 mmol) in hexane
was added via syringe while passing acetylene through the solu-
tion below ꢃ50 ꢁC, and the mixture was stirred for 30 min at the
same temperature. The solution of 5.61 g (40.0 mmol) of 2,2,5,5-
tetramethylcyclopentanone (24a) in 15 mL of dry THF was added
dropwise for 10 min and the mixture was allowed to warm to am-
bient temperature and stirred for 3 h. After addition of water (20
mL) and K2CO3 (30 g), the organic layer was separated and the
aqueous phase was extracted with 2 ꢇ 20 mL of ether. The com-
bined extracts were dried over MgSO4. After removal of the sol-
vent in vacuo, the residue was distilled under reduced pressure to
give 30.1 g (96%) of the alcohol. 25a: colorless liquid, bp 95 ꢁC
(31 mmHg); MS m=z 166 (Mþ); 1H NMR (90 MHz) ꢁ 2.26 (s, 1H),
1.78 (brs, 1H), 1.72–1.47 (m, 4H), 1.18 (s, 6H), 1.08 (s, 6H);
13C NMR (22.5 MHz) ꢁ 84.7, 84.1, 75.0, 47.0, 37.9, 28.8, 25.0;
IR (neat) 3490, 2933, 2858, 2098, 1469, 1387, 1371, 1302, 1256,
20c (3.26 g, 85%). 20c: colorless crystals, mp >270 ꢁC; H NMR
1
(60 MHz, CCl4) ꢁ 6.93 (brs, 16H), 1.98 (s, 2H), 0.96 (s, 36H);
Anal. Calcd for C46H54O2: C, 86.47; H, 8.52%. Found: C, 86.18;
H, 8.66%.
1,1,6,6-Tetraphenyl-2,4-hexadiyne-1,6-diol (20a): In a sim-
ilar manner to that described above, 20a was obtained from 1,1-
diphenylpropyn-1-ol (19a) in 89% yield. 20a: colorless crystals,
mp 147–149 ꢁC (lit.18 150–151 ꢁC); 1H NMR (60 MHz, CCl4) ꢁ
7.58–7.10 (m, 20H), 2.47 (s, 2H).
1,1,6,6-Tetrakis(4-methylphenyl)-2,4-hexadiyne-1,6-diol
(20b): In a similar manner to that described above, 20b was
obtained from 1,1-bis(4-methylphenyl)propyn-1-ol (19b) in 89%
yield. 20b: colorless crystals, mp 170–171 ꢁC (lit.18 205–206
1
ꢁC); H NMR (60 MHz, CCl4) ꢁ 7.27 (d, J ¼ 8 Hz, 8H), 7.00 (d,
J ¼ 8 Hz, 8H), 2.33 (s, 2H), 2.30 (s, 12H).
1232, 1188, 1150, 1095, 1063, 1017, 975, 865, 647, 630 cmꢃ1
;
Anal. Calcd for C11H18O: C, 79.46; H, 10.91%. Found: C, 79.46;
H, 11.06%.
1,1,6,6-Tetraphenyl-1,2,3,4,5-hexapentaene (15): A solution
of 2.07 g (4.99 mmol) of the diol 20a in 25 mL of dry ether was
cooled to ꢃ50 ꢁC and then 1.24 g (5.50 mmol) of SnCl2 2H2O
2-Ethynyl-1,1,3,3-tetramethylindan-2-ol (25b): In a similar
manner to that described above, 25b was obtained from 1,1,3,3-
tetramethylindan-2-one (24b) in 81% yield. 25b: colorless liquid,
bp 83–85 ꢁC (0.1 mmHg); MS m=z 214 (Mþ); 1H NMR (100 MHz)
ꢁ 7.29–7.07 (m, AA0BB0, 4H), 2.62 (s, 1H), 1.96 (s, 1H), 1.40 (s,
6H), 1.38 (s, 6H); IR (neat) 3509, 3310, 2079 cmꢃ1; Anal. Calcd
for C15H18O: C, 84.07; H, 8.47%. Found: C, 83.74; H, 8.68%.
1-Ethynyl-2,2,6,6-tetramethylcyclohexanol (25c): In a sim-
ilar manner to that described above, 25c was obtained from
2,2,6,6-tetramethylcyclohexanone (24c) in 89% yield. 25c: color-
less liquid, bp 120–121 ꢁC (38 mmHg) (lit.116 bp 129.5 ꢁC at 50
ꢂ
and 6.0 mL of ether saturated with gaseous HCl was added. The
mixture was allowed to warm to 0 ꢁC and stirred for 1 h at 0 ꢁC.
The resulting orange solids were filtered off and were washed suc-
cessively with water, EtOH, and ether to give the cumulene 15
(1.66 g, 87%). 15: orange prisms, mp >250 ꢁC (lit.2 298 ꢁC);
1H NMR (60 MHz, CCl4) ꢁ 7.59–7.13 (m); IR (KBr) 3046, 1997,
1592, 1490, 1452, 1444, 1279, 1175, 1082, 1028, 921, 770, 755,
694, 632, 622, 608, 523 cmꢃ1; UV ꢃmax (THF) 485 (log " 4.87),
433 (sh, 4.36), 367 (4.09), 286 (4.51), 271 (4.53), 254 nm (4.70).
1,1,6,6-Tetrakis(4-methylphenyl)-1,2,3,4,5-hexapentaene
(16): In a similar manner to that described for the preparation of
1
mmHg); MS m=z 180 (Mþ); H NMR (60 MHz, CCl4) ꢁ 2.30 (s,

Y. Kuwatani et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2201
1H), 1.61 (s, 1H), 1.55–1.30 (m, 6H), 1.13 (s, 6H), 1.05 (s, 6H);
Anal. Calcd for C12H20O: C, 79.94; H, 11.18%. Found: C, 79.94;
H, 11.31%.
the residue was purified by column chromatography on alumina
with a mixture of hexane and benzene as the eluent to give 724
mg (78%) of the product. 27b: colorless plates (ether–hexane),
1
1,4-Bis(1-hydroxy-2,2,5,5-tetramethylcyclopentyl)butadiyne
(26a): To a solution of 24.0 g (120 mmol) of Cu(OAc)2 H2O in a
mp 185–186 ꢁC; MS m=z 462 (Mþ); H NMR (400 MHz) ꢁ 7.29–
7.24 (m, 4H), 7.20–7.17 (m, 4H), 1.52 (s, 12H), 1.51 (s, 12H);
ꢀ
105.4, 48.3 , 30.81, 30.75 (asterisk shows two types of signals
ꢂ
ꢀ
ꢀ
mixture of pyridine (120 mL) and methanol (100 mL) was added a
solution of 9.98 g (60.0 mmol) of the alcohol 25a in 20 mL of pyr-
idine and the solution was stirred for 12 h at 60 ꢁC. After cooling
to room temperature, the solvent was evaporated in vacuo and a
mixture of 100 mL of ether and 300 mL of 2 M HCl was added
to the residue. The aqueous layer was extracted with 2 ꢇ 100 mL
of ether and the combined extracts were washed successively with
2 M HCl, aqueous 2 M NaOH, water, and brine, and then dried
over MgSO4. After removal of the solvent in vacuo, the residual
solid was washed with hexane to afford 5.78 g of the product.
The washings were concentrated in vacuo and purified by column
chromatography on alumina with a mixture of benzene and ether
as the eluent to produce an additional 3.18 g of the diol 26a (total
8.96 g, 90%). 26a: colorless crystals, mp 178–179 ꢁC; MS m=z 330
(Mþ); 1H NMR (90 MHz) ꢁ 1.89 (s, 2H), 1.76–1.47 (m, 8H), 1.18
(s, 12H), 1.08 (s, 12H); 13C NMR (22.5 MHz) ꢁ 84.8, 80.2, 71.4,
47.9, 38.1, 28.8, 25.1; IR (KBr) 3590, 3485, 2945, 2855, 2130,
1470, 1383, 1369, 1317, 1299, 1260, 1225, 1183, 1150, 1092,
1062, 1008, 967, 919, 860 cmꢃ1; Anal. Calcd for C22H34O2: C,
79.95; H, 10.37%. Found: C, 79.83; H, 10.55%.
13C NMR (100 MHz) ꢁ 195.6, 148.2 , 136.8 , 127.5 , 122.5,
ꢀ
overlapped); Anal. Calcd for C30H32Cl2: C, 77.74; H, 6.96; Cl,
15.30%. Found: C, 77.79; H, 6.97; Cl, 15.42%.
2,3-Dibromo-1,4-bis(2,2,6,6-tetramethylcyclohexylidene)-1,3-
butadiene (27c): To a solution of the diol 26c (3.59 g, 10.0
mmol) in benzene (50 mL) was added PBr3 (1.5 mL, 15 mmol).
The mixture was heated to 55 ꢁC and stirred for 4 h. After cooling
to room temperature, the reaction mixture was poured into 200 mL
of ice-water (200 mL) and extracted with Et2O (3 ꢇ 100 mL). The
combined organic extracts were washed with water and dried over
MgSO4. After evaporation of the solvent under reduced pressure,
the collected crystals were washed with methanol to afford 27c
(3.43 g). The combined washings were concentrated in vacuo,
and the residue was purified by column chromatography on alumi-
na with hexane as the eluent to give 119 mg of the product. A
total of 3.55 g (73%) of the product was obtained. 27c: colorless
crystals (CH2Cl2–ethanol), mp 232.5–234.5 ꢁC (lit.33 233.5 ꢁC);
1H NMR (60 MHz, CCl4) ꢁ 1.66–1.40 (m, 12H), 1.23 (s, 12H),
1.16 (s, 12H).
1,4-Bis(2-hydroxy-1,1,3,3-tetramethyl-2-indanyl)butadiyne
(26b): In a similar manner to that described for the preparation of
26a, the diol 26b was obtained from the alcohol 25b in 86% yield.
26b: colorless crystals (hexane–benzene), mp 205.3–207.2 ꢁC; MS
m=z 426 (Mþ); 1H NMR (100 MHz) ꢁ 7.30–7.09 (m, AA0BB0,
8H), 2.02 (s, 2H), 1.44 (s, 12H), 1.41 (s, 12H); IR (KBr) 3558,
3449, 2146 cmꢃ1; Anal. Calcd for C30H34O2: C, 84.47; H, 8.03%.
Found: C, 84.48; H, 8.06%.
1,4-Bis(1-hydroxy-2,2,6,6-tetramethylcyclohexyl)butadiyne
(26c): In a similar manner to that described for the preparation
of 26a, the diol 26c was obtained from the alcohol 25c in 89%
yield. 26c: colorless crystals, mp 161–163 ꢁC (lit.33 mp 173 ꢁC);
1H NMR (60 MHz, CCl4) ꢁ 1.70 (s, 2H), 1.60–1.30 (m, 12H), 1.17
(s, 12H), 1.08 (s, 12H).
2,3-Dibromo-1,4-bis(2,2,5,5-tetramethylcyclopentylidene)-
1,3-butadiene (27a): To a solution of the diol 26a (2.31 g,
6.99 mmol) in acetic acid (70 mL) was added a solution of 48%
HBr and the mixture was stirred for 1 h at ambient temperature.
The reaction mixture was diluted with a mixture of water (300
mL) and 2 M NaOH (200 mL), and extracted with ether (500 mL).
The organic extracts were washed with 2 M NaOH, water, and
brine successively, and then dried over MgSO4. After removal
of the solvent under reduced pressure, the collected crude crystals
were washed with methanol to afford 2.88 g (90%) of the cumu-
lene 27a: yellow prisms, mp ca. 250 ꢁC (sublimed); MS m=z 454
(Mþ); 1H NMR (60 MHz, CCl4) ꢁ 1.67 (s, 8H), 1.25 (s, 12H), 1.18
(s, 12H); Anal. Calcd for C22H32Br2: C, 57.91; H, 7.06; Br,
35.02%. Found: C, 57.67; H, 7.07; Br, 35.56%.
3,4-Dibromo-1,1,6,6-tetra-t-butyl-1,2,4,5-hexatetraene (27d):
To a stirred solution of the diol 26d (1.34 g, 4.01 mmol) in ben-
zene (20 mL) was added PBr3 (1.0 mL, 10 mmol). The mixture
was heated to 55 ꢁC and stirred for 6 h. After cooling to room tem-
perature, the mixture was poured into a mixture of water (100 mL)
and saturated aqueous Na2CO3 (60 mL) and extracted with ether
(3 ꢇ 60 mL). The combined organic extracts were washed with
saturated aqueous Na2CO3 and dried over MgSO4. After evapora-
tion of the solvent under reduced pressure, the residual solids were
purified by column chromatography on silica gel with a mixture
of benzene and hexane as the eluent. The collected fractions of
the product were concentrated in vacuo to give crystals, which
were washed with methanol (1.68 g, 91%). 27d: colorless prisms
(CH2Cl2–ethanol), mp 229.5–230.5 ꢁC (sublimed, lit.59 mp 232–
1
233 ꢁC); H NMR (60 MHz, CCl4) ꢁ 1.27 (s).
1,4-Bis(2,2,5,5-tetramethylcyclopentylidene)-1,2,3-butatriene
(21): A mixture of the dibromide 27a (913 mg, 2.00 mmol), zinc
powder (654 mg, 10.0 mmol), and THF (20 mL) was irradiated by
ultrasonic wave for 30 min under an argon atmosphere and stirred
for 30 min. The mixture was filtered and the filtrate was evaporat-
ed under reduced pressure. The residue was purified by column
chromatography on silica gel with hexane as the eluent. The crude
crystalline product obtained by evaporation of the fractions was
purified by washing with methanol to produce 566 mg (95%) of
the cumulene 21: yellow needles (CH2Cl2–hexane), mp 225–
1
226 ꢁC (decomp.); MS m=z 296 (Mþ); H NMR (90 MHz) ꢁ 1.72
(s, 8H), 1.19 (s, 24H); 13C NMR (22.5 MHz) ꢁ 149.7, 144.7, 132.1,
47.2, 39.6, 29.3; IR (KBr) 2940, 2925, 2870, 2845, 1453, 1449,
1382, 1376, 1360, 1345, 1311, 1304, 1242, 1212, 1111, 1072,
1013, 989, 960, 834, 650, 534 cmꢃ1; Anal. Calcd for C22H32: C,
89.12; H, 10.88%. Found: C, 88.89; H, 10.89%.
2,3-Dichloro-1,4-bis(1,1,3,3-tetramethyl-2-indanylidene)-1,3-
butadiene (27b):
To a solution of the diol 26b (853 mg,
2.00 mmol) in a mixture of dioxane (20 mL) and acetic acid
(20 mL) was added a solution of 36% HCl (10 mL) and the mix-
ture was stirred for 7 days at ambient temperature. The reaction
mixture was poured into water (150 mL) and the crystals formed
were collected and washed with water. The crude crystals were
dissolved in benzene and the organic solution was dried over
MgSO4. After removal of the solvent under reduced pressure,
1,4-Bis(1,1,3,3-tetramethyl-2-indanylidene)-1,2,3-butatriene
(22): To a stirred solution of 27b (232 mg, 0.501 mmol) in THF
(10 mL) was added a solution of n-BuLi (1.5 M, 0.40 mL, 0.60
mmol) in hexane via syringe at ꢃ70 ꢁC and the mixture was stir-
red for 1 h. After the addition of 0.5 mL of water, the mixture was
allowed to warm to ambient temperature. Then the mixture was

2202 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Nickel-Catalyzed Dimerization of [5]Cumulenes
diluted with hexane (20 mL), and dried over MgSO4. After evap-
oration of the solvent under reduced pressure, the residual solid
was purified by column chromatography on alumina with a mix-
ture of benzene and hexane (1:1) as the eluent. The crude crystal-
line product obtained was further purified by washing with hexane
to give 189 mg (96%) of the cumulene 22: pale yellow crystals
(pentane), mp ca. 240 ꢁC (decomp.); MS m=z 392 (Mþ); 1H NMR
(400 MHz) ꢁ 7.28–7.19 (m, AA0BB0, 8H), 1.51 (s, 24H); 13C NMR
(100 MHz, CDCl3) ꢁ 150.7, 148.5, 144.2, 133.2, 127.4, 122.6,
50.3, 30.8; UV–vis ꢃmax (THF) 230 (4.95), 245 (5.22), 324 (4.56),
345 nm (4.57); Anal. Calcd for C30H32: C, 91.78; H, 8.22%.
Found: C, 91.53; H, 8.24%.
1,4-Bis(2,2,6,6-tetramethylcyclohexylidene)-1,2,3-butatriene
(23): In a similar manner to that described for the preparation of
21, 1,4-bis(2,2,6,6-tetramethylcyclohexylidene)-1,2,3-butatriene
(23) was obtained (586 mg, 90%) from the reaction of 27c (969
mg, 2.00 mmol) with zinc powder (654 mg, 10.0 mmol). 23: yellow
prisms, mp 203.5–204.5 ꢁC (decomp., lit.33 mp 188–189 ꢁC); MS
m=z 324 (Mþ); 1H NMR (90 MHz) ꢁ 1.60–1.43 (m, 12H), 1.20
(s, 24H); 13C NMR (22.5 MHz) ꢁ 154.3, 138.9, 132.1, 40.6, 37.8,
31.2, 18.9.
129.0, 128.3, 127.8, 127.7, 127.6, 127.43, 127.36, 127.2, 123.1;
MS m=z 760 (Mþ); IR (KBr) 3033, 2028, 1970, 1597, 1492,
1447, 1178, 1076, 1031, 770, 693, 627, 525 cmꢃ1; Raman (KBr)
2030, 1970 cmꢃ1 (C=C=C); UV ꢃmax (THF) 623 (log " 4.22),
413 (4.95), 384 (sh, 4.76), 293 (4.58), 230 nm (4.63); Anal. Calcd
for C60H40: C, 94.70; H, 5.30%. Found: C, 94.36; H, 5.30%. See
Table 1, Entry 2. When the reaction was carried out in DMF as the
solvent, an aqueous work-up was carried out as follows. The fil-
tered reaction mixture was poured into 200 mL of 2 M HCl and
extracted with 3 ꢇ 100 mL of a mixture of cyclohexane and ben-
zene (1:1). The organic phase was washed successively with 2 M
HCl, aqueous NaHCO3, water, and brine, and then dried over
MgSO4. The residue after removal of the solvent was purified
by chromatography on silica gel with a mixture of cyclohexane
and benzene as the eluent. The [4]radialene 5 (122 mg, 64%)
was obtained from 74 mg (0.10 mmol) of [NiBr2(PPh3)2], 52 mg
(0.20 mmol) of PPh3, 26 mg (0.40 mmol) of activated zinc dust
in 2 mL of dry DMF, and 190 mg (0.499 mmol) of the cumulene
15 in 25 mL of dry DMF. In this reaction, the reaction mixture
was stirred for 10 min at room temperature. See Table 1, Entry 3.
When the reaction was carried out in dry benzene similarly to that
described above, a mixture of the [4]radialene 5 (76 mg, 40%)
and the hydrogenated compound 28 (20 mg, 10%) was obtained
from a reaction of the mixture of 186 mg (0.250 mmol) of [NiBr2-
(PPh3)2], 131 mg (0.500 mmol) of PPh3, and 65 mg (1.0 mmol) of
activated zinc dust, with 190 mg (0.5 mmol) of the cumulene 15 in
25 mL of dry benzene.
1,1,6,6-Tetra-t-butyl-1,2,3,4,5-hexapentaene (1): A mixture
of the dibromide 27d (921 mg, 2.00 mmol), zinc powder (2.62 g,
40.1 mmol), and THF (20 mL) was irradiated by ultrasonic waves
for 2 h under an argon atmosphere. The reaction mixture was di-
luted with 20 mL of hexane and filtered. The filtrate was evaporat-
ed in vacuo and the residue was purified by column chromatogra-
phy on alumina with hexane as the eluent. The crystalline product
was further purified by washing with methanol to produce 509 mg
(85%) of 1: yellow prisms; mp 184.5–185.5 ꢁC (lit.57 mp 188–189
1,1,6,6-Tetraphenyl-1,5-hexadien-3-yne (28): Pale yellow
needles (from hexane–ether), mp 162–163 ꢁC (lit.16 160 ꢁC);
1H NMR (90 MHz) ꢁ 7.43–7.20 (m, 20H), 6.10 (s, 2H); 13C NMR
(22.5 MHz) ꢁ 151.9, 141.8, 139.3, 130.0, 128.3, 128.3, 128.2,
128.1, 128.0, 107.7, 93.5; MS m=z 382 (Mþ); IR (KBr) 3014,
1952, 1496, 1448, 1442, 1071, 1030, 998, 868, 772, 763, 697, 657,
644, 568, 494, 479 cmꢃ1; UV ꢃmax 365, 361, 251 nm.
1
ꢁC); H NMR (60 MHz, CCl4) ꢁ 1.28 (s).
Nickel-Catalyzed Dimerization of Tetraaryl[5]cumulenes
15–17. Reaction of 15 with [Ni(PPh3)4]: See Table 1, Entry 1.
To a 50 mL round-bottomed two-necked flask containing a mag-
netic stirring bar was added 186 mg (0.250 mmol) of [NiBr2-
(PPh3)2], 131 mg (0.500 mmol) of PPh3, and 65 mg (1.0 mmol) of
activated zinc dust. A rubber septum was placed over one neck of
the flask and a three-way stopcock adapter attached with an argon-
filled balloon in the other. 5 mL of dry THF was added through the
septum by a syringe. The flask was evacuated and filled with
argon several times (vacuum line). The flask was irradiated with
ultrasonic waves for 5 min and the mixture was stirred for 40 min
at room temperature. Another 50 mL round-bottomed two-necked
flask containing a magnetic stirring bar and a rubber septum was
placed, evacuated, and filled with argon. To the flask was added a
solution of 190 mg (0.499 mmol) of the cumulene 15 in 25 mL of
dry THF and the flask was evacuated and filled with argon. After
the red-brown catalyst formed, the solution of the catalyst was
added via syringe with stirring and the resulting mixture was stir-
red for 1 h at room temperature. After the addition of 20 mL of
benzene, the mixture was passed through a short column of alumi-
na. The residue after removal of solvent was purified by chroma-
tography on silica gel with a mixture of cyclohexane and benzene
as the eluent. The collected crystals after removal of the solvent
were washed with Et2O to give the [4]radialene 5 (101 mg, 53%).
1,2-Bis(3,3-diphenylallenylidene)-3,4-bis(diphenylmethylene)-
cyclobutane (5): Deep blue needles (from cyclohexane–ether),
mp ca. 210 ꢁC (decomp.); 1H NMR (500 MHz) ꢁ 7.34–7.29 (m,
10H), 7.11–7.06 (m, 14H), 6.98 (t, J ¼ 8 Hz, 2H), 6.88 (t, J ¼ 8
Hz, 2H), 6.83 (d, J ¼ 8 Hz, 4H), 6.73 (t, J ¼ 8 Hz, 4H), 6.68 (t,
J ¼ 8 Hz, 4H); 13C NMR (125 MHz) ꢁ 147.8, 141.1, 140.5, 139.5,
138.7, 138.4, 136.7, 136.5, 131.0, 130.7, 130.2, 129.5, 129.2,
Reaction of the Cumulene 15 with [Ni(CO)2(PPh3)2]: To a
50 mL round-bottomed two-necked flask containing a magnetic
stirring bar were added 190 mg (0.499 mmol) of the cumulene 15,
32 mg (50.1 mmol) of [Ni(CO)2(PPh3)2], and 30 mL of dry ben-
zene. The flask was evacuated and filled with argon. The mixture
was heated to reflux for 30 min. After cooling to room tempera-
ture, the mixture was passed through a short column of alumina
with benzene as the eluent. After removal of solvent, the residue
was purified by chromatography on silica gel with hexane as the
eluent. The collected crystals after removal of the solvent were
washed with ether to give the [4]radialene 5 (115 mg, 61%).
Reaction of the Cumulene 16 with [Ni(CO)2(PPh3)2]: In a
similar manner to that described for the reaction of the cumulene
15, the [4]radialene 6 (50 mg, 57%) was obtained from the reac-
tion of 87 mg (0.20 mmol) of the cumulene 16 with 32 mg (50.1
mmol) of [Ni(CO)2(PPh3)2] in dry benzene (30 mL). The collected
crystals after chromatography on silica gel were washed with pen-
tane to give the [4]radialene 6.
1,2-Bis[3,3-bis(4-methylphenyl)allenylidene]-3,4-bis[bis(4-
methylphenyl)methylene]cyclobutane (6): Dark blue needles
(from hexane–ether), mp ca. 210 ꢁC (decomp.); 1H NMR (500
MHz) ꢁ 7.23 (d, J ¼ 8:0 Hz, 4H), 7.06 (d, J ¼ 8:3 Hz, 4H), 7.05
(d, J ¼ 8:3 Hz, 4H), 6.99 (d, J ¼ 8:3 Hz, 4H), 6.88 (d, J ¼ 8:0
Hz, 4H), 6.69 (d, J ¼ 8:0 Hz, 4H), 6.54 (d, J ¼ 8:3 Hz, 4H), 6.52
(d, J ¼ 8:0 Hz, 4H), 2.42 (s, 6H), 2.17 (s, 6H), 2.14 (s, 6H), 2.12
(s, 6H); 13C NMR (125 MHz) ꢁ 146.8, 139.1, 138.7, 137.9, 137.7,
137.3, 137.0, 136.8, 136.1, 135.82, 135.78, 135.6, 131.3, 130.8,
129.8, 129.5, 128.81, 128.78, 128.5, 128.4, 127.7, 122.0, 21.5,

Y. Kuwatani et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2203
21.4, 21.08, 21.06; MS m=z 872 (Mþ); IR (KBr) 3016, 2912,
2028, 1970, 1606, 1508, 1178, 1109, 1019, 814, 718, 610, 523,
478 cmꢃ1; Raman (KBr) 2029, 1972 cmꢃ1 (C=C=C); UV ꢃmax
(THF) 694 (log " 4.21), 424 (4.97), 385 (sh, 4.66), 310 (4.62),
238 nm (4.64); Anal. Calcd for C68H56: C, 93.54; H, 6.46%.
Found: C, 93.25; H, 6.50%.
Reaction of the Cumulene 17 with [Ni(CO)2(PPh3)2]: In a
similar manner to that described for the preparation of the [4]radi-
alene 5, the [4]radialene 7 (61 mg, 34%) was obtained from
181 mg (0.299 mmol) of the cumulene 17, 192 mg (0.300 mmol)
of [Ni(CO)2(PPh3)2] and 90 mL of dry benzene. The collected
crystals after chromatography on silica gel with a mixture of hex-
ane and benzene as the eluent were washed with ether to give the
[4]radialene 7.
was passed through a short column of alumina with benzene as the
eluent. The collected crystals were washed with ether to give the
[4]radialene 5 (26 mg, 68%).
Thermal Dimerization of Cumulenes with Bulky Substitu-
ents 21–23. 1,2,3,4-Tetrakis[(2,2,5,5-tetramethylcyclopentyli-
dene)methylene]cyclobutane (10): To a Pyrex tube with 5 mm
diameter was added 59 mg (0.20 mmol) of the cumulene 21 and
the tube was sealed under reduced pressure (<0:1 mmHg). The
tube was heated for 5 min at 240 ꢁC in an oil bath preheated prior
to use. After cooling to room temperature, the mixture in the tube
was dissolved in CH2Cl2 and the solution was evaporated in va-
cuo. The residue was purified by chromatography on silica gel
to give the [4]radialene 10 (41 mg, 69%), together with the un-
changed 21 (14 mg, 24%). 10: colorless needles (from ether–etha-
nol), mp ca. 330 ꢁC (decomp.); 1H NMR (90 MHz) ꢁ 1.61 (s,
16H), 1.09 (m, 48H); 13C NMR (22.5 MHz) ꢁ 188.5, 133.4, 112.1,
45.2, 39.8, 30.3; MS m=z 592 (Mþ); UV ꢃmax (cyclohexane) 328
(log " 3.41), 309 (3.38), 275 (sh, 4.19), 265 (4.34), 257 (sh, 4.29),
218 nm (5.11); Anal. Calcd for C44H64: C, 89.12; H, 10.88%.
Found: C, 88.94; H, 10.92%.
1,2-Bis[3,3-bis(4-t-butylphenyl)allenylidene]-3,4-bis[bis(4-t-
butylphenyl)methylene]cyclobutane (7): Dark blue microcrys-
tals, mp ca. 220 ꢁC (decomp.); 1H NMR (500 MHz) ꢁ 7.46 (m,
8H), 7.30 (d, J ¼ 8:7 Hz, 4H), 7.29 (d, J ¼ 8:4 Hz, 4H), 7.16 (d,
J ¼ 8:7 Hz, 4H), 6.93 (d, J ¼ 8:4 Hz, 4H), 6.89 (d, J ¼ 8:7 Hz,
4H), 6.82 (d, J ¼ 8:7 Hz, 4H), 1.40 (brs, 18H), 1.25 (s, 18H),
1.24 (s, 18H), 1.11 (brs, 18H); 13C NMR (125 MHz) ꢁ 150.9,
150.6, 150.3, 149.3, 148.9, 139.3, 138.2, 137.8, 137.6, 136.1,
135.8, 133.8, 130.3, 130.2, 129.6, 129.2, 129.0, 125.3, 124.9,
124.6, 124.4, 122.0, 34.8, 34.7, 34.43, 34.37, 31.4, 31.4, 31.3,
31.2; MS m=z 1208 (Mþ); IR (KBr) 3025, 2986, 2958, 2864,
2030, 1606, 1506, 1464, 1396, 1365, 1272, 1200, 1108, 1015,
837, 615, 576 cmꢃ1; Raman (KBr) 2027, 1975 cmꢃ1 (C=C=C);
UV ꢃmax (THF) 623 (log " 4.19), 515 (sh, 4.09), 416 (4.83),
390 (sh, 4.67), 303 (4.67), 234 nm (4.68); HRMS (FABþ) m=z
found 1208.8094, calcd for C92H104, 1208.8138.
Stepwise Synthesis of Extended [4]Radialene 5. 1,2-Bis(3-
hydroxy-3,3-diphenylprop-1-ynyl)-3,4-bis(diphenylmethylene)-
cyclobutene (30): To a 50 mL round-bottomed two-necked flask
containing a magnetic stirring bar was added a mixture of 540 mg
(1.00 mmol) of the dibromide 29, 521 mg (2.50 mmol) of 19a,
35 mg (50 mmol) of [PdCl2(PPh3)2], and 10 mg (53 mmol) of
CuI. After 20 mL of Et3N was added, the flask was evacuated
and filled with argon. The mixture was heated for 2 h at 85 ꢁC with
stirring. Then the mixture was poured into 150 mL of dilute 2 M
HCl and extracted with 3 ꢇ 50 mL of ether. The extracts were
washed successively with aqueous dilute HCl, water, and brine,
and then dried over Na2SO4. The residue after removal of the sol-
vent was purified by chromatography on silica gel with benzene as
the eluent. The collected crystals from yellow fractions were
washed with a mixture of hexane and ether to give the diol 30
(582 mg, 73%). 30: yellow needles (from hexane–CH2Cl2), mp
192–194 ꢁC (decomp.); 1H NMR (400 MHz) ꢁ 7.39–7.34 (m,
8H), 7.29 (d, J ¼ 7:5 Hz, 4H), 7.23–7.12 (m, 18H), 6.84 (d,
J ¼ 7:5 Hz, 4H), 6.79 (t, J ¼ 7:5 Hz, 2H), 6.68 (t, J ¼ 7:5 Hz,
4H), 2.23 (s, 2H); 13C NMR (100 MHz) ꢁ 144.2, 140.8, 139.9,
139.6, 138.4, 133.4, 131.8, 130.5, 128.1, 127.6, 127.50, 127.48,
127.4, 127.0, 126.0, 107.3, 79.7, 74.7; MS m=z 794 (Mþ), 776,
671, 612, 182; IR (KBr) 3400, 3035, 3005, 1596, 1490, 1450,
1444, 998, 764, 743, 696, 642 cmꢃ1; Anal. Calcd for C60H42O2:
C, 90.65; H, 5.33%. Found: C, 90.42; H, 5.27%.
1,2,3,4-Tetrakis[(1,1,3,3-tetramethyl-2-indanylidene)methyl-
ene]cyclobutane (11): The cumulene 22 (78.5 mg, 0.200 mmol)
was heated at 270–275 ꢁC for 5 min under an argon atmosphere.
After cooling to room temperature, the mixture was purified by
column chromatography on alumina with benzene as the eluent to
give 40 mg (51%) of the [4]radialene 11: colorless prisms (ether–
1
hexane), mp 331–333 ꢁC; H NMR (400 MHz, CD2Cl2–CS2, 1:4)
ꢁ 7.11–7.06 (m, 8H), 6.99 (m, 8H), 1.35 (s, 48H); 13C NMR (100
MHz, CD2Cl2–CS2, 1:4) ꢁ 189.8, 148.5, 134.2, 127.2, 122.4,
112.5, 48.2, 31.6; MS m=z 784 (Mþ); Raman (KBr) 2030, 1978,
1948, 1900 cmꢃ1 (C=C=C); UV ꢃmax (THF) 329 (log " 3.40),
310 (3.39), 279 (sh, 4.27), 271 (4.45), 265 (4.52), 256 nm (sh,
4.43); Anal. Calcd for C60H64: C, 91.78; H, 8.22%. Found: C,
91.63; H, 8.26%.
1,2,3,4-Tetrakis[(2,2,6,6-tetramethylcyclohexylidene)methyl-
ene]cyclobutane (12): To a Pyrex tube with 10 mm diameter was
added 33 mg (0.10 mmol) of the cumulene 23. The tube was evac-
uated and filled with gaseous argon. Then the tube was heated for
2 min at 220 ꢁC in an oil bath preheated prior to use. After cooling
to room temperature, the mixture in the tube was dissolved in
CH2Cl2 and the solution was evaporated in vacuo. The residue
was purified by chromatography on silica gel with hexane as the
eluent. The collected crystals after removal of the solvent were
washed with methanol to give the [4]radialene 12 (30 mg, 91%).
12: colorless needles (from ether–ethanol), mp 315 ꢁC (sublimed);
1H NMR (90 MHz) ꢁ 1.80–1.25 (m, 24H), 1.12 (s, 48H); 13C NMR
(22.5 MHz) ꢁ 192.5, 127.6, 109.4, 40.9, 35.5, 31.7, 19.2; MS m=z
648 (Mþ); IR (KBr) 1957, 1917 cmꢃ1; UV ꢃmax (cyclohexane)
318 (log " 3.42), 300 (3.38), 268 (sh, 4.19), 259 (4.28), 252 (sh,
4.27), 215 nm (5.13); Anal. Calcd for C48H72: C, 88.82; H,
11.18%. Found: C, 88.75; H, 11.28%.
Reaction of Tetraalkylhexapentaene with [RhCl(PPh3)3].
Rh-Complex 32 of the Cumulene 21: To a 50 mL round-bot-
tomed two-necked flask with a magnetic stirring bar was added
62 mg (0.21 mmol) of the cumulene 21 and 185 mg (0.200 mmol)
of [RhCl(PPh3)3]. The flask was evacuated and filled with argon.
Then 25 mL of benzene was added and the mixture was stirred for
3 h at room temperature. The mixture was evaporated in vacuo and
the residue was purified by chromatography on silica gel with ben-
zene as the eluent. The collected crystals were recrystallized from
a mixture of hexane and CH2Cl2 to give the Rh-complex 32
(188 mg, 80%). 32: yellow prisms (hexane–CH2Cl2), mp 183–
[4]Radialene 5 from the Diol 30: To a suspension of 40 mg
(50 mmol) of the diol 30 and 23 mg (0.10 mmol) of SnCl2 2H2O in
ꢂ
5 mL of dry ether was added 2 mL of saturated solution of HCl in
ether at ꢃ50 ꢁC. The suspension was stirred for 30 min at ꢃ50 ꢁC
and a mixture of 30 mL of CH2Cl2 and 20 mL of water was added.
Then the organic phase was separated and washed with brine, and
then dried over Na2SO4. The residue after removal of the solvent

2204 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Nickel-Catalyzed Dimerization of [5]Cumulenes
1
185 ꢁC (decomp.); H NMR (270 MHz) ꢁ 7.73 (brs, 12H), 7.33–
the solvent gave the [4]radialene 12 (52 mg, 32%) and the follow-
ing fractions gave the [5]radialenone 13 (61 mg, 36%). 13: yellow
needles (ethanol), mp 226–227 ꢁC; 1H NMR (400 MHz) ꢁ 1.69–
1.58 (m, 8H), 1.47–1.34 (m, 16H), 1.19 (s, 12H), 1.17 (s, 12H),
1.14 (s, 12H), 1.12 (s, 12H); 13C NMR (100 MHz) ꢁ 202.4, 196.7,
191.1, 128.1, 126.9, 107.7, 101.4, 41.7, 40.8, 35.9, 35.7, 31.5,
31.4, 30.9, 30.8, 19.3, 19.0; MS m=z 676 (Mþ); IR (KBr) 1947,
1919, 1691 cmꢃ1; UV ꢃmax (cyclohexane) 408 (sh, log " 3.26),
378 (3.39), 313 (3.47), 298 (3.64), 263 (sh, 4.22), 246 (4.70),
215 nm (4.78); Anal. Calcd for C49H72O: C, 86.92; H, 10.72%.
Found: C, 86.50; H, 10.73%.
7.22 (m, 18H), 1.66 (m, 4H), 1.51 (s, 6H), 1.44 (t, J ¼ 7 Hz, 2H),
1.23 (t, J ¼ 7 Hz, 2H), 1.08 (s, 6H), 0.94 (s, 6H), 0.18 (s, 6H);
13C NMR (67.8 MHz) ꢁ 153.4 (d, J ¼ 1:5 Hz), 148.3 (d, J ¼ 2
Hz), 142.8 (dt, J ¼ 3:5 and 2.5 Hz), 138.7 (d, J ¼ 1:5 Hz), 135.4
(brt, J ¼ 5 Hz), 131.8 (t, J ¼ 21 Hz), 129.5, 127.6 (t, J ¼ 5 Hz),
113.3 (dt, J ¼ 18:5 and 4 Hz), 106.8 (dt, J ¼ 14:5 and 4 Hz), 48.5,
46.3, 45.1, 44.6, 40.1, 39.75, 39.69, 39.4, 30.7, 29.9, 29.7, 28.5;
MS (FAB) m=z 924 (Mþ þ H ꢃ Cl); IR (KBr) 2018 cmꢃ1; Anal.
Calcd for C58H62ClP2Rh: C, 72.61; H, 6.51%. Found: C, 72.44;
H, 6.64%.
Rh-Complex 31 of the Cumulene 1: In a similar manner to
that described for the preparation of the Rh-complex 32, the Rh-
complex 31 (137 mg, 71%) was obtained from 61 mg (0.20 mmol)
of the cumulene 1 and 185 mg (0.200 mmol) of [RhCl(PPh3)3] in
25 mL of benzene. In this reaction, the reaction mixture was stir-
red for 24 h at room temperature. 31: yellow prisms (hexane–CH2-
Cl2), mp 170–173 ꢁC (decomp.); 1H NMR (270 MHz) ꢁ 7.69 (brs,
12H), 7.36–7.23 (m, 18H), 1.64 (s, 9H), 1.09 (s, 9H), 0.99 (s, 9H),
0.68 (s, 9H); 13C NMR (67.8 MHz) ꢁ 159.9 (d, J ¼ 1:5 Hz), 144.1
(q, J ¼ 2 Hz), 142.7 (dt, J ¼ 4 and 3 Hz), 135.1 (brs), 134.0 (d,
J ¼ 1:5 Hz), 131.8 (t, J ¼ 21 Hz), 129.5, 127.6 (t, J ¼ 1:5 Hz),
120.5 (dt, J ¼ 18 and 3 Hz), 111.4 (dt, J ¼ 14 and 4 Hz), 42.2
(d, J ¼ 1:5 Hz), 39.7, 38.6, 37.7, 35.2, 32.5, 32.28, 32.26; MS
(FAB) m=z 928 (Mþ þ H ꢃ Cl); IR (KBr) 2025 cmꢃ1; Anal. Calcd
for C58H66ClP2Rh: C, 72.31; H, 6.90; Cl, 3.68%. Found: C, 71.92;
H, 7.00; Cl, 4.07%.
Reaction of the Cumulenes with 1 and 21–23 with [Ni(CO)2-
(PPh3)2]. 2,3,4,5-Tetrakis(2,2-di-t-butylvinylidene)cyclopen-
tanone (14) and 1,2,3,4-Tetrakis(2,2-di-t-butylvinylidene)-
cyclobutane (2): To a 25 mL round-bottomed two-necked flask
containing a magnetic stirring bar was added 120 mg (0.399
mmol) of the cumulene 1, 256 mg (0.400 mmol) of [Ni(CO)2-
(PPh3)2], 315 mg (1.20 mmol) of PPh3, and 10 mL of dry benzene.
The flask was evacuated and filled with argon. The mixture was
heated to reflux for 8 days with stirring. After cooling to room
temperature, the reaction mixture was passed through a short col-
umn of Al2O3 with benzene as the eluent. The residue after re-
moval of the solvent was purified by chromatography on silica
gel with a mixture of hexane and benzene as the eluent. The initial
fractions after removal of the solvent gave the [4]radialene 2 (7
mg, 6%). 2: colorless crystals (hexane–ether); 1H NMR (270 MHz)
ꢁ 1.20 (s); 13C NMR (67.8 MHz) ꢁ 194.8, 129.9, 108.2, 36.6, 32.4.
The following fractions gave the [5]radialenone 14 (93 mg, 74%).
14: yellow prisms (ether–methanol), mp 220 ꢁC (sublimed);
1H NMR (400 MHz) ꢁ 1.25 (s, 36H), 1.24 (s, 36H); 13C NMR
(100 MHz) ꢁ 205.1, 199.2, 192.2, 130.6, 129.0, 107.0, 100.7,
36.7, 36.6, 32.5, 32.2; MS m=z 628 (Mþ); IR (KBr) 1908, 1691
cmꢃ1; UV ꢃmax (THF) 408 (log " 3.27), 378 (3.36), 315 (sh,
3.36), 300 (sh, 3.75), 270 (sh, 4.15), 244 nm (4.67); Anal. Calcd
for C45H72O: C, 85.92; H, 11.54%. Found: C, 85.64; H, 11.64%.
2,3,4,5-Tetrakis[(2,2,6,6-tetramethylcyclohexylidene)methyl-
ene]cyclopentanone (13): To a 30 mL round-bottomed flask
containing a magnetic stirring bar was added 162 mg (0.499
mmol) of the cumulene 23, 320 mg (0.500 mmol) of [Ni(CO)2-
(PPh3)2], and 10 mL of dry benzene. The flask was evacuated
and filled with gaseous argon. The mixture was heated to reflux
for 2 days with stirring. After cooling to room temperature, the
mixture was passed through a short column of Al2O3 with ben-
zene as the eluent. The residue after removal of the solvent was
purified by chromatography on silica gel with a mixture of hexane
and benzene as the eluent. The initial fractions after removal of
1,3-Bis(2,2,5,5-tetramethylcyclopentylidene)-2,4-bis[2-(2,2,-
5,5-tetramethylcyclopentylidene)vinylidene]cyclobutane (8):
To a 100 mL round-bottomed flask containing a magnetic stirring
bar was added 593 mg (2.00 mmol) of the cumulene 21, 639 mg
(1.00 mmol) of [Ni(CO)2(PPh3)2], and 50 mL of dry benzene. The
flask was evacuated and filled with gaseous argon. The mixture
was heated under reflux for one day with stirring. After cooling
to room temperature, the mixture was passed through a short col-
umn of Al2O3 with benzene as the eluent. The residue after re-
moval of the solvent was purified by chromatography on silica
gel with hexane as the eluent to give the [4]radialene 8 (485 mg,
82%). 8: yellow needles (hexane–CH2Cl2), mp 281–282 ꢁC (de-
comp.); 1H NMR (400 MHz) ꢁ 1.68 (s, 8H), 1.65 (s, 8H), 1.45
(s, 24H), 1.23 (s, 24H); 13C NMR (100 MHz) ꢁ 155.9, 155.2,
148.9, 145.2, 136.7, 118.5, 48.0, 46.1, 41.6, 40.6, 30.3, 27.8; MS
m=z 592 (Mþ); Raman (KBr) 2005 (C=C=C), 1637, 1610 cmꢃ1
(C=C); UV ꢃmax (cyclohexane) 431 (sh, log " 3.82), 406 (3.93),
334 (4.98), 323 (sh, 4.73), 285 (4.22), 260 (sh, 4.42), 253 nm
(4.46); Anal. Calcd for C44H64: C, 89.12; H, 10.88%. Found: C,
88.78; H, 10.92%.
1,3-Bis(1,1,3,3-tetramethyl-2-indanylidene)-2,4-bis[2-(1,1,3,3-
tetramethyl-2-indanylidene)vinylidene]cyclobutane (9): A so-
lution of 39 mg (0.10 mmol) of the cumulene 22, 32 mg (50 mmol)
of [Ni(CO)2(PPh3)2], 26 mg (0.10 mmol) of PPh3 and 10 mL in
dry benzene was heated to reflux for one day under an argon at-
mosphere. After cooling to room temperature, the mixture was
passed through a short column of alumina with benzene as the elu-
ent. The crystals obtained after removal of the solvent were wash-
ed with a mixture of hexane and benzene to give the [4]radialene 9
(25 mg, 64%). 9: yellow needles (benzene–CH2Cl2), mp 365–367
ꢁC (decomp.); 1H NMR (400 MHz, CD2Cl2–CS2, 1:4) ꢁ 7.20–7.08
(m, 16H), 1.78 (s, 24H), 1.58 (s, 24H); 13C NMR (100 MHz,
CD2Cl2–CS2, 1:4) ꢁ 156.3, 154.6, 150.0, 149.7, 148.9, 145.9,
137.7, 127.4, 127.1, 122.4, 122.2, 119.0, 50.9, 49.1, 31.8, 29.0;
MS m=z 784 (Mþ); IR (KBr) 1955 cmꢃ1; Raman (KBr) 1995 (cu-
mulene), 1635, 1615, 1590 cmꢃ1 (C=C); UV ꢃmax (cyclohexane)
437 (log " 3.89), 408 (4.02), 384 (3.89), 363 (sh, 4.10), 338 (5.03),
318 (sh, 4.66), 285 (sh, 4.23), 282 (4.21), 263 (4.55), 236 nm
(4.36); Anal. Calcd for C60H64: C, 91.78; H, 8.22%. Found: C,
91.68; H, 8.21%.
Stepwise Synthesis of Extended [4]Radialenes 39–41. 1,2-
Bis[2-(9-hydroxyfluoren-9-yl)ethynyl]-3,4-bis(diphenylmethyl-
ene)cyclobutene (36): In a similar manner to that described for
the preparation of the diol 30, 536 mg (68%) of the diol 36 was
obtained from 540 mg (1.00 mmol) of the dibromide 29 and 516
mg (2.50 mmol) of the alcohol 33. 36: yellow needles (hexane–
CH2Cl2), mp ca. 205 ꢁC (decomp.); 1H NMR (400 MHz) ꢁ 7.57
(d, J ¼ 7:5 Hz, 4H), 7.34 (t, J ¼ 7:5 Hz, 4H), 7.29 (d, J ¼
7:5 Hz, 4H), 7.20 (t, J ¼ 7:5 Hz, 4H), 7.15 (d, J ¼ 7:7 Hz, 4H),
7.05–6.96 (m, 6H), 6.77 (d, J ¼ 7:5 Hz, 4H), 6.76 (t, J ¼
7:5 Hz, 2H), 6.65 (t, J ¼ 7:5 Hz, 4H), 2.55 (s, 2H); 13C NMR

Y. Kuwatani et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2205
(100 MHz) ꢁ 146.4, 140.6, 140.3, 139.7, 139.2, 138.2, 133.5,
131.4, 130.6, 129.5, 128.4, 127.6, 127.4, 127.2, 127.0, 124.6,
120.0, 105.1, 75.8, 74.9; MS m=z 792 (Mþ); IR (KBr) 3520,
3020, 1603, 1488, 1479, 1450, 1443, 1350, 1284, 1178, 1152,
1067, 1019, 1000, 975, 930, 906, 890, 770, 756, 741, 726, 696,
680, 640, 618, 577, 523 cmꢃ1; Anal. Calcd for C60H38O2: C,
91.11; H, 4.84%. Found: C, 90.36; H, 5.46%.
na with benzene as the eluent. The crystals obtained after removal
of the solvent were washed with ether to give the [4]radialene 39
(74 mg, 49%). 39: dark blue leaflets (ether–cyclohexane), mp ca.
210 ꢁC (decomp.); 1H NMR (400 MHz) ꢁ 7.67–7.60 (m, 6H),
7.47–7.40 (m, 10H), 7.32–7.27 (m, 4H), 7.15–7.07 (m, 4H),
6.94 (t, J ¼ 7:5 Hz, 2H), 6.85 (d, J ¼ 7:5 Hz, 4H), 6.76 (t, J ¼
7:5 Hz, 4H), 6.21 (d, J ¼ 7:5 Hz, 2H); 13C NMR (100 MHz) ꢁ
141.4, 141.0, 140.9, 139.7, 139.6, 139.3, 139.2, 139.1, 138.5,
135.7, 133.8, 132.0, 131.1, 128.6, 128.5, 128.2, 128.1, 127.5,
127.2, 126.8, 125.0, 124.8, 120.1, 119.9; MS (FAB) m=z 757.5
(Mþ þ H); Raman (KBr) 2022, 1927 cmꢃ1 (C=C=C); UV ꢃmax
(THF) 583 (log " 3.93), 532 (sh, 3.81), 379 (sh, 4.55), 355
(4.58), 319 (4.55), 278 (sh, 4.63), 259 (4.80), 227 nm (sh, 4.87);
Anal. Calcd for C60H36: C, 95.21; H, 4.79%. Found: C, 94.85;
H, 4.93%.
1,2-Bis[2-(9-hydroxy-10,10-dimethyl-9,10-dihydroanthra-
cen-9-yl)ethynyl]-3,4-bis(diphenylmethylene)cyclobutene (37):
In a similar manner to that described for the preparation of the diol
30 except the aqueous work-up, 546 mg (62%) of the diol 37 was
obtained from 540 mg (1.00 mmol) of the dibromide 29 and
621 mg (2.50 mmol) of the alcohol 34. To the reaction mixture
was added 20 mL of benzene and the mixture was passed through
a short column of alumina with benzene as the eluent. The residue
after removal of the solvent was purified by chromatography
on silica gel with a mixture of ether and benzene as the eluent.
37: yellow prisms (hexane–CH2Cl2), mp >150 ꢁC (decomp.);
1H NMR (400 MHz) ꢁ 7.78 (dd, J ¼ 8:0 and 1.5 Hz, 4H), 7.46
(dd, J ¼ 8:0 and 1.0 Hz, 4H), 7.29 (td, J ¼ 8:0 and 1.5 Hz, 4H),
7.24 (d, J ¼ 7:5 Hz, 4H), 7.19–7.12 (m, 6H), 7.09 (td, J ¼ 8:0
and 1.0 Hz, 4H), 6.82 (d, J ¼ 7:5 Hz, 4H), 6.78 (t, J ¼ 7:5 Hz,
2H), 6.68 (t, J ¼ 7:5 Hz, 4H), 2.41 (s, 2H), 1.59 (s, 6H), 1.45 (s,
6H); 13C NMR (100 MHz) ꢁ 142.8, 140.8, 139.8, 138.5, 135.9,
133.2, 131.7, 130.6, 128.5, 127.9, 127.6, 127.4, 127.4, 127.0,
126.6, 125.5, 108.7, 79.1, 67.9, 37.9, 33.1, 32.2; MS m=z 874
(Mþ); IR (KBr) 3500, 3350, 3040, 3010, 2960, 1598, 1490,
1446, 1042, 962, 910, 758, 720, 698, 647, 570, 524 cmꢃ1; Anal.
Calcd for C64H50O2: C, 90.58; H, 5.78%. Found: C, 90.24; H,
5.80%.
1,2-Bis[2-(9-hydroxythioxanthen-9-yl)ethynyl]-3,4-bis(diphen-
ylmethylene)cyclobutene (38): In a similar manner to that de-
scribed for the preparation of the diol 30 except the manner of
aqueous work-up, 315 mg (37%) of the diol 38 was obtained from
540 mg (1.00 mmol) of the dibromide 29 and 596 mg (2.50 mmol)
of the alcohol 35. The work-up was carried out as follows. To the
reaction mixture was added 20 mL of benzene and the resulting
mixture was passed through a short column of alumina with ben-
zene as the eluent. The residue after removal of the solvent was
purified by chromatography on silica gel with a mixture of ether
and benzene as the eluent. 38: yellow needles (from hexane–
CH2Cl2), mp 181–182 ꢁC (decomp.); 1H NMR (400 MHz, ace-
tone-d6) ꢁ 7.76 (d, J ¼ 7:5 Hz, 4H), 7.43 (t, J ¼ 7:5 Hz, 4H),
7.30 (t, J ¼ 7:5 Hz, 4H), 7.27 (t, J ¼ 7:5 Hz, 4H), 7.17–7.14 (m,
4H), 7.07–7.03 (m, 6H), 6.84–6.79 (m, 6H), 6.73 (t, J ¼ 7:5 Hz,
4H), 2.79 (s, 2H); 13C NMR (100 MHz, acetone-d6) ꢁ 141.4,
141.0, 140.9, 139.0, 137.8, 134.4, 132.2, 132.0, 131.6, 128.8,
128.4, 128.3, 128.2, 128.0, 127.6, 127.4, 127.3, 106.6, 79.1,
70.6; MS (FD) m=z 854 (Mþ); IR (KBr) 3513, 3038, 1580,
1562, 1490, 1458, 1442, 1342, 1262, 1170, 1152, 1135, 1060,
1032, 1013, 998, 968, 937, 900, 772, 753, 731, 713, 694, 650,
632, 517, 455 cmꢃ1; Anal. Calcd for C60H38O2S2: C, 84.28; H,
4.48; S, 7.50%. Found: C, 84.16; H, 4.51; S, 7.42%.
1,2-Bis[2-(10,10-dimethyl-9,10-dihydroanthracen-9-ylidene)-
vinylidene]-3,4-bis(diphenylmethylene)cyclobutane (40): To a
solution of 88 mg (0.10 mmol) of the diol 37 in 10 mL of dry ether
was added 45 mg (0.20 mmol) of SnCl2 2H2O and then an ethere-
ꢂ
al solution (1.0 mL) saturated with gaseous HCl was added at
ꢃ65 ꢁC. The suspension was stirred for 30 min at ꢃ65 ꢁC. Then
a mixture of 20 mL of CH2Cl2 and 1 mL of Et3N was added.
The mixture was passed through a short column of alumina with
benzene as the eluent. The crystals obtained after removal of
the solvent were washed with ether to give the [4]radialene 40
(51 mg, 61%). 40: dark blue needles (hexane–CH2Cl2), mp 228–
230 ꢁC (decomp.); 1H NMR (400 MHz, ꢃ20 ꢁC) ꢁ 7.59 (t, J ¼
7:2 Hz, 2H), 7.57–7.46 (m, 12H), 7.28 (td, J ¼ 8:0 and 1.0 Hz,
2H), 7.14 (td, J ¼ 8:0 and 1.0 Hz, 2H), 6.99 (dd, J ¼ 8:0 and
1.0 Hz, 2H), 6.97–6.91 (m, 4H), 6.87 (d, J ¼ 7:7 Hz, 4H), 6.74
(t, J ¼ 7:7 Hz, 4H), 6.29 (dd, J ¼ 8:0 and 1.0 Hz, 2H), 6.03 (td,
J ¼ 8:0 and 1.0 Hz, 2H), 1.66 (s, 12H); 13C NMR (100 MHz,
ꢃ20 ꢁC) ꢁ 143.7, 143.6, 141.2, 140.7, 139.6, 139.3, 137.1,
133.5, 131.6, 131.5, 131.1, 130.8, 130.0, 129.4, 129.0, 128.2,
128.04, 127.96, 127.57, 127.56, 126.9, 126.5, 125.9, 125.2,
124.1, 116.6, 38.8, 32.5; MS m=z 840 (Mþ); IR (KBr) 2015,
1945 cmꢃ1; Raman (KBr) 2030, 1955 cmꢃ1 (C=C=C); UV ꢃmax
(THF) 688 (log " 4.44), 630 (sh, 4.01), 442 (5.01), 380 (sh, 4.41),
319 (sh, 4.50), 300 (4.59), 239 nm (4.54); Anal. Calcd for C66H48:
C, 94.25; H, 5.75%. Found: C, 93.77; H, 5.95%.
1,2-Bis(diphenylmethylene)-3,4-bis[2-(9-thioxanthenylidene)-
vinylidene]cyclobutane (41): To a solution of 86 mg (0.10
mmol) of the diol 38 in 10 mL of dry ether was added a 45 mg
(0.20 mmol) of SnCl2 2H2O and then an ethereal solution (1.0
ꢂ
mL) saturated with gaseous HCl was added at ꢃ65 ꢁC. The sus-
pension was stirred for 30 min at ꢃ65 ꢁC and a mixture of 20 mL
of CH2Cl2 and 1 mL of Et3N was added. Then the mixture was
passed through a short column of alumina with benzene as the
eluent. The crystals obtained after removal of the solvent were
washed with ether to give the [4]radialene 41 (76 mg, 93%). 41:
dark green leaflets (CS2–CH2Cl2–ether), mp ca. 250 ꢁC (de-
1
comp.); H NMR (400 MHz, ꢃ60 ꢁC) ꢁ 7.57–7.51 (m, 10H), 7.22
(d, J ¼ 8:0 Hz, 2H), 7.19 (t, J ¼ 8:0 Hz, 2H), 7.12 (t, J ¼ 8:0 Hz,
2H), 7.11 (d, J ¼ 8:0 Hz, 2H), 7.07 (d, J ¼ 8:0 Hz, 2H), 6.97 (t,
J ¼ 7:5 Hz, 2H), 6.86 (t, J ¼ 8:0 Hz, 2H), 6.84 (d, J ¼ 7:5 Hz,
4H), 6.74 (t, J ¼ 7:5 Hz, 4H), 6.26 (d, J ¼ 8:0 Hz, 2H), 6.06 (t,
J ¼ 8:0 Hz, 2H); 13C NMR (100 MHz, 30 ꢁC) ꢁ 141.4, 140.9,
139.8, 137.8, 136.8, 132.0, 131.8, 131.3, 131.1, 131.0, 130.3,
130.2, 129.2, 128.2, 127.7, 127.5, 127.3, 126.7, 124.8, 115.4;
MS m=z 820 (Mþ); IR (KBr) 2020, 1948 cmꢃ1; Raman (KBr)
2025, 1950 cmꢃ1 (C=C=C); UV ꢃmax (THF) 754 (log " 4.47),
684 (sh, 4.05), 498 (4.72), 434 (4.76), 374 (4.34), 325 (sh,
1,2-Bis[2-(9-fluorenylidene)vinylidene]-3,4-bis(diphenylmeth-
ylene)cyclobutane (39): To a suspension of 158 mg (0.200
mmol) of the diol 36 and 90 mg (0.40 mmol) of SnCl2 2H2O in
ꢂ
20 mL of dry ether was added an ethereal solution (8.0 mL) satu-
rated with gaseous HCl at ꢃ50 ꢁC. The suspension was stirred for
30 min at ꢃ50 ꢁC and a mixture of 30 mL of CH2Cl2 and 50 mL of
water was added. Then the organic layer was separated and wash-
ed with brine, and then dried over Na2SO4. The residue after re-
moval of the solvent was passed through a short column of alumi-

2206 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Nickel-Catalyzed Dimerization of [5]Cumulenes
ꢁ
ꢀ
4.41), 303 (4.49), 273 (4.77), 247 nm (4.80); Anal. Calcd for
C60H36S2: C, 87.77; H, 4.42; S, 7.81%. Found: C, 87.20; H,
4.50; S, 8.06%.
chromated Mo Kꢄ (ꢃ ¼ 0:71069 A) radiation at 23 C. Among a
total of 9759 reflections measured, 9548 were unique and the
observed 2361 reflections that had I > 3:00ꢅðIÞ, were used for
the refinement. The crystal structure was solved by a direct meth-
od and refined by the full-matrix least-squares method. All of
the non-hydrogen atoms were refined anisotropically. Crystal data
for 8: C44H64, MW 592.99, monoclinic, space group P21=n
Reactions of [5]Radialenone 14 with Organometallic Re-
agents. 2,3,4,5-Tetrakis(3,3-di-t-butylallenylidene)-1-phenyl-
cyclopentan-1-ol (45): To a 50 mL round-bottomed two-necked
flask containing a magnetic stirring bar was added a solution of
189 mg (0.300 mmol) of [5]radialenone 14 in 5 mL of dry THF.
The flask was evacuated and filled with argon. A solution of
0.20 mL (0.36 mmol) of PhLi [1.5 M in ether–cyclohexane (3:7)]
was added via syringe with stirring at ꢃ60 ꢁC and the mixture
was stirred for 30 min at the same temperature. Then the mixture
was allowed to warm to room temperature and further stirred for
30 min at room temperature. After cooling to 0 ꢁC, 1 mL of satu-
rated aqueous NH4Cl was added and then anhydrous K2CO3 was
added. The viscous aqueous phase was extracted with 2 ꢇ 10 mL
of ether and the combined organic extracts were evaporated in va-
cuo. The residue was purified by chromatography on silica gel
with a mixture of hexane and benzene as the eluent to give the al-
cohol 45 (208 mg, 98%). 45: colorless needles (pentane), mp 197–
198 ꢁC; 1H NMR (270 MHz) ꢁ 7.56 (d, J ¼ 7 Hz, 2H), 7.20 (t, J ¼
7 Hz, 2H), 7.10 (t, J ¼ 7 Hz, 1H), 2.13 (s, 1H), 1.24 (s, 18H), 1.23
(s, 18H), 1.22 (s, 18H), 0.92 (s, 18H); 13C NMR (67.8 MHz) ꢁ
199.6, 198.1, 147.0, 129.9, 127.6, 127.1, 126.0, 125.6, 113.3,
104.0, 81.1, 36.8, 36.63, 36.60, 35.9, 32.7, 32.4, 32.3, 32.2; MS
m=z 706.5 (Mþ); IR (KBr) 3565, 2950, 2895, 2858, 1912, 1908,
1603, 1483, 1450, 1392, 1363, 1214, 1132, 1052, 1040, 1032,
1020, 980, 950, 927, 905, 872, 822, 792, 736, 702, 691, 673,
597, 578, 523, 505 cmꢃ1; UV ꢃmax (cyclohexane) 313 (sh, log "
3.35), 294 (sh, 3.58), 266 (sh, 3.98), 206 nm (4.93); Anal. Calcd
for C51H78O: C, 86.62; H, 11.12%. Found: C, 86.47; H, 11.22%.
2,3,4,5-Tetrakis(3,3-di-t-butylallenylidene)-1-methylenecy-
clopentane ([5]Radialene, 46): To a 50 mL round-bottomed
two-necked flask containing a magnetic stirring bar was added a
solution of 189 mg (0.300 mmol) of the [5]radialenone 14 in
5 mL of dry THF. The flask was evacuated and filled with argon.
A solution of 0.22 mL (0.33 mmol) of MeLi (1.5 M in ether) was
added via syringe at ꢃ60 ꢁC and the mixture was stirred for
20 min at this temperature. Then the mixture was allowed to warm
to room temperature and further stirred for 30 min at room temper-
ature. After cooling to 0 ꢁC, 1 mL of saturated aqueous NH4Cl was
added. Then anhydrous K2CO3 was added and the viscous aque-
ous phase was extracted with 2 ꢇ 10 mL of ether. The combined
organic phase was evaporated in vacuo and the residue was puri-
fied by chromatography on silica gel with a mixture of hexane and
benzene as the eluent to give the [5]radialene 46 (170 mg, 90%):
pale yellow needles (pentane), mp 228–229.5 ꢁC (decomp.);
1H NMR (270 MHz) ꢁ 5.02 (s, 2H), 1.24 (s, 36H), 1.23 (s, 36H);
13C NMR (67.8 MHz) ꢁ 199.3 (s), 199.1 (s), 142.7 (s), 129.2 (s),
127.9 (s), 107.0 (s), 104.3 (s), 100.2 (t), 37.1 (s), 36.5 (s), 32.6
(q), 32.4 (q); MS m=z 626.5 (Mþ); IR (KBr) 3068, 2950, 2895,
2855, 1957, 1929, 1912, 1717, 1618, 1604, 1482, 1470, 1448,
1392, 1363, 1235, 1214, 1110, 1039, 1026, 979, 961, 926, 896,
855, 833, 824, 718, 698, 646, 576, 503, 482 cmꢃ1; UV ꢃmax
(cyclohexane) 360 (sh, log " 2.91), 340 (sh, 3.32), 331 (3.37),
229 (sh, 4.77), 222 (4.85), 217 nm (sh, 4.83); Anal. Calcd for
C46H74: C, 88.11; H, 11.89%. Found: C, 87.95; H, 11.96%.
ꢀ
ꢀ
ꢀ
(No. 14), a ¼ 25:381ð3Þ A, b ¼ 6:387ð3Þ A, c ¼ 26:478ð2Þ A, ꢆ ¼
118:190ð8Þꢁ, V ¼ 3783ð2Þ A , Z ¼ 4, Dcalcd ¼ 1:041 g cmꢃ3
,
ꢀ 3
Fð000Þ ¼ 1312, ꢇ(Mo Kꢄ) = 0.54 cmꢃ1
,
R ¼ 0:053, Rw
¼
0:052, GOF ¼ 1:61. Crystallographic data have been deposited
with Cambridge Crystallographic Data Centre: Deposition num-
ber CCDC-280611 for compound 8. Copies of the data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge, CB2 1EZ, UK; Fax: +44
1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
We thank Prof. S. Sakaki (Kyoto University) for the theoret-
ical calculations of the nickelacycle intermediates. We are
grateful to Prof. T. Kawashima, Prof. K. Goto, and Mr. M.
Yamamura (the University of Tokyo) for the measurement
of high resolution mass spectra. This work was partly support-
ed by a Grant-in-Aid for Scientific Research from the Ministry
of Education, Culture, Sports, Science and Technology, Japan
and by CREST of JST (Japan Science and Technology Corpo-
ration).
References
1
2
J. M. Tour, Chem. Rev., 96, 537 (1996).
P. F. H. Schwab, M. D. Levin, and J. Michl, Chem. Rev.,
99, 1863 (1999).
3
1350 (1999).
R. E. Martin and F. Diederich, Angew. Chem., Int. Ed., 38,
4
J. M. Tour, Acc. Chem. Res., 33, 791 (2000).
D. K. James and J. M. Tour, Chem. Mater., 16, 4423
5
(2004).
6
‘‘Modern Acetylene Chemistry,’’ ed by P. J. Stang and
F. Diederich, Wiley-VCH, Weinheim (1995).
7
8
M. B. Nielsen and F. Diederich, Chem. Rec., 2, 189 (2002).
H. Fischer, ‘‘The Chemistry of Alkenes,’’ ed by S. Patai,
Wiley-Interscience, New York (1964), p. 1025.
H. Hopf, ‘‘The Chemistry of Ketenes, Allenes, and Related
Compounds,’’ ed by S. Patai, Wiley-Interscience, New York
(1980), p. 779.
10 H. Hopf, ‘‘Classics in Hydrocarbon Chemistry,’’ Wiley-
VCH, Weinheim (2000), p. 171.
11 L. Brandsma, ‘‘Synthesis of Acetylenes, Allenes, and Cu-
mulenes,’’ Elsevier, Amsterdam (2004).
12 P. Cadiot and A. Willemart, Bull. Soc. Chim. Fr., 1951,
100.
13 R. Kuhn and H. Krauch, Chem. Ber., 88, 309 (1955).
14 R. Kuhn and H. Fischer, Chem. Ber., 92, 1849 (1959).
15 D. Y. Curtin and W. H. Richardson, J. Am. Chem. Soc., 81,
4719 (1959).
16 R. Kuhn and H. Fischer, Chem. Ber., 94, 3060 (1961).
17 W. M. Jones and C. D. Broaddus, J. Org. Chem., 26, 2316
(1961).
9
X-ray Crystallography of the Extended [4]Radialene 8.
A
yellow crystal with the dimensions 0:20 ꢇ 0:30 ꢇ 0:40 mm3 ob-
tained by recrystallization from CH2Cl2–ethyl acetate was used
for the diffraction measurement. All measurements were per-
formed on a Rigaku AFC5R diffractometer with graphite mono-
18 W. Ried, W. Schlegelmilch, and S. Piesch, Chem. Ber., 96,
1221 (1963).
19 R. Kuhn, H. Fischer, and H. Fischer, Chem. Ber., 97, 1760

Y. Kuwatani et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2207
(1964).
55 M. Iyoda, Y. Kuwatani, and M. Oda, J. Chem. Soc., Chem.
Commun., 1992, 399.
56 H. D. Hartzler, J. Am. Chem. Soc., 88, 3155 (1966).
57 H. D. Hartzler, J. Am. Chem. Soc., 93, 4527 (1971).
58 T. Inoue, T. Kaneda, and S. Misumi, Tetrahedron Lett., 15,
2969 (1974).
59 T. Negi, T. Kaneda, H. Mizuno, T. Toyoda, Y. Sakata, and
S. Misumi, Bull. Chem. Soc. Jpn., 47, 2398 (1974).
60 L. T. Scott and G. J. DeCicco, Tetrahedron Lett., 17, 2663
(1976).
20 H. Fischer and H. Fischer, Chem. Ber., 100, 755 (1967).
21 I. M. Blake, L. H. Rees, T. D. W. Claridge, and H. L.
Anderson, Angew. Chem., Int. Ed., 39, 1818 (2000).
22 G. Dyker, S. Borowski, G. Henkel, A. Kellner, I. Dix, and
P. G. Jones, Tetrahedron Lett., 41, 8259 (2000).
23 M. Ogasawara, H. Ikeda, K. Ohtsuka, and T. Hayashi,
Chem. Lett., 2000, 776.
24 K. Mizuno, H. Maeda, H. Sugita, S. Nishioka, T. Hirai, and
A. Sugimoto, Org. Lett., 3, 581 (2001).
25 W. Skibar, H. Kopacka, K. Wurst, C. Salzmann, K.-H.
Ongania, F. F. de Biani, P. Zanello, and B. Bildstein, Organo-
metallics, 23, 1024 (2004).
61 G. Santiago, K. N. Houk, G. J. DeCicco, and L. T. Scott,
J. Am. Chem. Soc., 100, 692 (1978).
62 M. Kaftory, I. Agmon, M. Ladika, and P. J. Stang, J. Am.
Chem. Soc., 109, 782 (1987).
63 P. J. Stang, Acc. Chem. Res., 15, 348 (1982).
64 H. Werner, R. Wiedemann, N. Mahr, P. Steinert, and J.
Wolf, Chem.—Eur. J., 2, 561 (1996).
65 H. Hopf, Angew. Chem., Int. Ed. Engl., 31, 931 (1992).
66 Y. Zhao, K. Campbell, and R. R. Tykwinski, J. Org.
Chem., 67, 336 (2002).
26 T. Kawase, Y. Minami, N. Nishigaki, S. Okano, H. Kurata,
and M. Oda, Angew. Chem., Int. Ed., 44, 316 (2004).
27 R. Kuhn and H. Zahn, Chem. Ber., 84, 566 (1951).
28 ‘‘Modern Allene Chemistry,’’ ed by N. Krause and A. S. K.
Hashmi, Wiley-VCH, Weinheim (2004), Vols. 1 and 2.
29 H. F. Schuster and G. M. Coppola, ‘‘Allenes in Organic
Synthesis,’’ Wiley-Interscience, New York (1984).
30 A. S. K. Hashmi, Angew. Chem., Int. Ed., 39, 3590 (2000).
31 T. L. Gilchrist, J. Chem. Soc., Perkin Trans. 1, 2001, 2491.
32 W. M. Schubert, T. H. Liddicoet, and W. A. Lanka, J. Am.
Chem. Soc., 76, 1929 (1954).
33 F. Bohlmann and K. Kieslich, Chem. Ber., 87, 1363
(1954).
34 L. Skattebøl, Tetrahedron Lett., 6, 2175 (1965).
35 F. T. Bond and D. E. Bradway, J. Am. Chem. Soc., 87,
4799 (1965).
67 T. Hopfner, P. G. Jones, B. Ahrens, I. Dix, L. Ernst, and
¨
H. Hopf, Eur. J. Org. Chem., 2003, 2596.
68 S. K. Koster and R. West, J. Org. Chem., 40, 2300 (1975).
69 T. Sugimoto, H. Awaji, Y. Misaki, Z. Yoshida, Y. Kai, H.
Nakagawa, and N. Kasai, J. Am. Chem. Soc., 107, 5797 (1985).
70 T. Sugimoto, Y. Misaki, T. Kajita, Z. Yoshida, Y. Kai, and
N. Kasai, J. Am. Chem. Soc., 109, 4106 (1987).
71 T. Sugimoto, Y. Misaki, Y. Arai, Y. Yamamoto, Z.
Yoshida, Y. Kai, and N. Kasai, J. Am. Chem. Soc., 110, 628
(1988).
36 G. Maier, Tetrahedron Lett., 6, 3603 (1965).
37 W. R. Moore and T. M. Ozretich, Tetrahedron Lett., 8,
3205 (1967).
72 M. B. Nielsen, M. Schreiber, Y. G. Baek, P. Seiler, S.
Lecomte, C. Boudon, R. R. Tykwinski, J.-P. Gisselbrecht, V.
38 L. K. Bee, J. Beeby, J. W. Everett, and P. J. Garratt, J. Org.
Chem., 40, 2212 (1975).
39 T. Yoshida, R. M. Williams, and E. Negishi, J. Am. Chem.
Soc., 96, 3690 (1974).
Gramlich, P. J. Skinner, C. Bosshard, P. Gunter, M. Goss, and
¨
F. Diederich, Chem.—Eur. J., 7, 3263 (2001).
73 Y. Tobe, R. Umeda, N. Iwasa, and M. Sonoda, Chem.—
Eur. J., 9, 5549 (2003).
40 H. Yamazaki, J. Chem. Soc., Chem. Commun., 1976, 841.
41 M. Tigchelaar, H. Kleijn, C. J. Elsevier, J. Meijor, and P.
Vermeer, Tetrahedron Lett., 22, 2237 (1981).
42 W. L. Krestinsky, Chem. Ber., 59, 1930 (1926).
43 L. Skattebøl, Tetrahedron, 21, 1357 (1965).
44 M. Iyoda, K. Nishioka, M. Nose, S. Tanaka, and M. Oda,
Chem. Lett., 1984, 131.
74 U. H. F. Bunz, Top. Curr. Chem., 201, 131 (1999).
75 U. H. F. Bunz, Y. Rubin, and Y. Tobe, Chem. Soc. Rev.,
28, 107 (1999).
76 F. Diederich, Chem. Commun., 2001, 219.
77 H. Stephen, J. Chem. Soc., Trans., 127, 1874 (1925).
78 N. P. Buu-Hoi, R. Royer, N. D. Xuong, and K. V. Thang,
Bull. Soc. Chim. Fr., 1955, 1204.
45 L. Hagelee, R. West, J. Calabrese, and J. Norman, J. Am.
Chem. Soc., 101, 4888 (1979).
79 P. Siemsen, R. C. Livingston, and F. Diederich, Angew.
Chem., Int. Ed., 39, 2632 (2000).
46 B. Hagenbruch, K. Hesse, S. Hunig, and G. Klug, Liebigs
Ann. Chem., 1981, 256.
80 F. Toda, H. Ishihara, and K. Akagi, Tetrahedron Lett., 10,
2531 (1969).
¨
47 G. Wilke, Angew. Chem., Int. Ed. Engl., 27, 185 (1988).
48 M. Iyoda, S. Tanaka, H. Otani, M. Nose, and M. Oda,
J. Chem. Soc., Chem. Commun., 1983, 1058.
49 M. Iyoda, S. Tanaka, H. Otani, M. Nose, and M. Oda,
J. Am. Chem. Soc., 110, 8494 (1988).
50 M. Iyoda, Y. Kuwatani, and M. Oda, J. Am. Chem. Soc.,
111, 3761 (1989).
51 M. Iyoda, M. Oda, Y. Kai, N. Kanehisa, and N. Kasai,
Chem. Lett., 1990, 2149.
52 M. Iyoda, Y. Kuwatani, M. Oda, Y. Kai, N. Kanehisa, and
N. Kasai, Angew. Chem., Int. Ed. Engl., 29, 1062 (1990).
53 Y. Kuwatani, G. Yamamoto, and M. Iyoda, Org. Lett., 5,
3371 (2003).
81 F. Toda, K. Kumada, N. Ishiguro, and K. Akagi, Bull.
Chem. Soc. Jpn., 43, 3535 (1970).
82 R. B. King and C. A. Harmon, J. Organomet. Chem., 88,
93 (1975).
83 L. Song, A. M. Arif, and P. J. Stang, J. Organomet. Chem.,
395, 219 (1990).
84 I. Kovacik, M. Laubender, and H. Werner, Organo-
metallics, 16, 5607 (1997).
85 B. Bildstein, M. Schweiger, H. Angleitner, H. Kopacka,
K. Wurst, K.-H. Ongania, M. Fontani, and P. Zanello, Organo-
metallics, 18, 4286 (1999).
86 H. Irngartinger and W. Gotzmann, Angew. Chem., Int. Ed.
Engl., 25, 340 (1986).
¨
54 M. Iyoda, Y. Kuwatani, M. Oda, K. Tatsumi, and A.
Nakamura, Angew. Chem., Int. Ed. Engl., 30, 1670 (1991).
87 M. Iyoda, H. Otani, M. Oda, Y. Kai, Y. Baba, and N.
Kasai, J. Am. Chem. Soc., 108, 5371 (1986).

2208 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Nickel-Catalyzed Dimerization of [5]Cumulenes
J. Am. Chem. Soc., 119, 2069 (1997).
102 E. M. Geertsema, N. Koumura, M. K. J. ter Wiel, A.
Meetsma, and B. L. Feringa, Chem. Commun., 2002, 2962.
103 J. Raker and J. E. Glass, J. Org. Chem., 67, 6113 (2002).
104 Z. Dominguez, H. Dang, M. J. Strouse, and M. A.
Garcia-Garibay, J. Am. Chem. Soc., 124, 7719 (2002).
105 A. Levy, P. U. Biedermann, and I. Agranat, Org. Lett., 2,
1811 (2000).
88 H. Hart, L. Ward, K. Tanaka, and F. Toda, Tetrahedron
Lett., 23, 2125 (1982).
89 H. Fischer and W. D. Hell, Angew. Chem., Int. Ed. Engl., 6,
954 (1967).
90 R. Kuhn and K. Wallenfels, Ber. Dtsch. Chem. Ges., 71,
783 (1938).
91 F. D. van Remoortere and F. P. Boer, J. Am. Chem. Soc.,
92, 3355 (1970).
92 F. W. Nader and C.-D. Waker, Angew. Chem., Int. Ed.
Engl., 24, 852 (1985).
106 C.-T. Chen and Y.-C. Chou, J. Am. Chem. Soc., 122, 7662
(2000).
93 T. Matsuo, A. Sekiguchi, M. Ichinohe, K. Ebata, and H.
Sakurai, Bull. Chem. Soc. Jpn., 71, 1705 (1988).
94 Z. Berkovitch-Yellin and L. Leiserowitz, Acta Crystal-
logr., Sect. B, 33, 3657 (1997).
107 N. Koumura, E. M. Geertsema, A. Meetsma, and B. L.
Feringa, J. Am. Chem. Soc., 122, 12005 (2000).
108 R. P. Feynman, ‘‘Miniaturization,’’ ed by H. D. Gilbert,
Reinhold, New York (1961).
95 J. Sandstrom, ‘‘Dynamic NMR Spectroscopy,’’ Academic
¨
Press, London (1982), Chap. 4.
96 G. Yamamoto, Bull. Chem. Soc. Jpn., 65, 1967 (1992).
97 P. U. Biedermann, J. J. Stezowski, and I. Agranat, Eur. J.
Org. Chem., 2001, 15.
98 R. Kuhn and K. L. Scholler, Chem. Ber., 87, 598 (1954).
99 K. Bertsch, G. Karich, and J. C. Jochims, Chem. Ber., 110,
3304 (1977).
100 A. Auffrant, B. Jaun, P. D. Jarowski, K. N. Houk, and F.
Diederich, Chem.—Eur. J., 10, 2906 (2004).
109 K. E. Drexler, ‘‘Nanosystems: Molecular Machinery,
Manufacturing, and Computation,’’ Wiley, New York (1992).
110 T. R. Kelly, H. De Silva, and R. A. Silva, Nature, 401, 150
(1999).
111 N. Koumura, R. W. J. Zijlstra, R. A. van Delden, N.
Harada, and B. L. Feringa, Nature, 401, 152 (1999).
112 M. Iyoda, H. Otani, M. Oda, Y. Kai, Y. Baba, and N.
Kasai, J. Chem. Soc., Chem. Commun., 1986, 1794.
113 A. Stockis and R. Hoffmann, J. Am. Chem. Soc., 102, 2952
(1980).
101 The rotational barrier (28.9 kcal molꢃ1) of p-nitrophenyl
substituted tetraethynylethene dianion was calculated and dis-
cussed on the basis of the formation of the bis-butatriene structure:
A. Hilger, J.-P. Gisselbrecht, R. R. Tykwinski, C. Boudon, M.
114 M. Sumimoto, N. Iwane, T. Takahama, and S. Sakaki,
J. Am. Chem. Soc., 126, 10457 (2004).
115 M. Midland, J. Org. Chem., 40, 2250 (1975).
116 H. Sobotka and J. D. Chanly, J. Am. Chem. Soc., 71, 4136
(1949).
Schreiber, R. E. Martin, H. P. Luthi, M. Gross, and F. Diederich,
¨