Thermal rearrangement of 2,5-bis(dicyanomethylene)bicyclo[4.2.0]oct-7-ene and 2,5-bis(dicyanomethylene)bicyclo[4.2.0]octa-3,7-diene. Unexpected formation of 2,6-bis(dicyanomethylene)bicyclo[3.3.0]octa-1(5)-ene and -octa-3,7-diene, new electron acceptors

Article abstract of DOI:10.1246/bcsj.76.1793

Upon heating at 200 °C in o-dichlorobenzene, 2,5-bis(dicyanomethylene)bicyclo[4.2.0]octa-3,7-diene gave rise to 2,6-bis(dicyanomethylene)bicyclo[3.3.0]octa-3,7-diene by a rearrangement as a sole isolable product in modest yield, and no trace of 5,8-bis(dicyanomethylene)cycloocta-1,3,6-triene, the expected product, was detected. On the other hand, 2,5-bis(dicyanomethylene)bicyclo[4.2.0]octa-7-ene underwent a thermal reaction at lower temperature (110 °C in toluene) to give 5,8-bis(dicyanomethylene)-1,3-cyclooctadiene, the normal ring-opened product, and 2,6-bis(dicyanomethylene)bicyclo[3.3.0]octa-1(5)-ene, a rearranged product, in about 1:1 ratio. The rearranged product has a planar 1,1,6,6-tetracyanohexatriene structure (X-ray analysis), and shows a considerably lower electron affinity than that of tetracyano-ethylene and 7,7,8,8-tetracyano-p-quinodimethane. The electron acceptor also formed a crystalline 1:1 charge transfer complex with tetrathiafulvalene, of which electronic conductivity was near insulating (1.1 × 10^-7 S cm^-1). We have proposed a possible mechanism for the rearangements involving the zwitterionic intermediates.

Full text of DOI:10.1246/bcsj.76.1793

Ó 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 1793–1799 (2003) 1793
Thermal Rearrangement of 2,5-Bis(dicyanomethylene)bicyclo[4.2.0]oct-
-ene and 2,5-Bis(dicyanomethylene)bicyclo[4.2.0]octa-3,7-diene.
Unexpected Formation of 2,6-Bis(dicyanomethylene)bicyclo[3.3.0]octa-
7
1
(5)-ene and -octa-3,7-diene, New Electron Acceptors
ꢀ
Yoji Miyake, and Masaji Oda
Takeshi Kawase, Tomoaki Okada, Tetsuya Enomoto, Takayuki Kikuchi,
ꢀ
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043
Received February 28, 2003; E-mail: tkawase@chem.sci.osaka-u.ac.jp
ꢁ
Upon heating at 200 C in o-dichlorobenzene, 2,5-bis(dicyanomethylene)bicyclo[4.2.0]octa-3,7-diene gave rise to
,6-bis(dicyanomethylene)bicyclo[3.3.0]octa-3,7-diene by a rearrangement as a sole isolable product in modest yield,
2
and no trace of 5,8-bis(dicyanomethylene)cycloocta-1,3,6-triene, the expected product, was detected. On the other hand,
ꢁ
2
,5-bis(dicyanomethylene)bicyclo[4.2.0]octa-7-ene underwent a thermal reaction at lower temperature (110 C in tolu-
ene) to give 5,8-bis(dicyanomethylene)-1,3-cyclooctadiene, the normal ring-opened product, and 2,6-bis(dicyanometh-
ylene)bicyclo[3.3.0]octa-1(5)-ene, a rearranged product, in about 1:1 ratio. The rearranged product has a planar 1,1,6,6-
tetracyanohexatriene structure (X-ray analysis), and shows a considerably lower electron affinity than that of tetracyano-
ethylene and 7,7,8,8-tetracyano-p-quinodimethane. The electron acceptor also formed a crystalline 1:1 charge transfer
complex with tetrathiafulvalene, of which electronic conductivity was near insulating (1:1 ꢂ 10ꢃ7 S cm ). We have
proposed a possible mechanism for the rearangements involving the zwitterionic intermediates.
ꢃ1
Polycyanosubstituted ꢀ-electron systems have attracted
much attention because of their unique properties as excellent
electron acceptors. Particularly, tetracyanoethylene (TCNE)
and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) have been
widely modified to acquire insight into the relationship be-
1–4
tween the structure and the electronic properties.
,8-dicyanomethylene-1,3,6-cyclooctatriene (1),
However,
a simple
5
eight-membered ring vinylog of TCNQ, has remained un-
known to date. Although most are probably inferior to TCNQ
as an electron acceptor, 1 would still be worth studying from
structural and physicochemical points of view.
It is well known that a thermal ring opening of bicy-
clo[4.2.0]oct-7-ene produces cycloocta-1,3-diene, and that cy-
clooctatetraene is in equilibrium with a valence isomer, bicy-
Chart 1.
5
clo[4.2.0]octa-2,4,7-triene, at around room temperature. Tak-
ing advantage of these transformations, we synthesized a num-
ber of novel eight-membered-ring conjugated compounds by
thermal ring openings of the corresponding bicyclic valence
6–10
isomers (Chart 1). Among them, 5,8-dimethylene-1,3,6-
cyclooctatriene (2) and its derivatives 3–4 were prepared by
a thermal reaction of 2,5-dimethylenebicyclo[4.2.0]octa-3,7-
8
–10
dienes 5–7 in good yields.
synthesis, a thermal reaction of bicyclo[4.2.0]octa-3,7-diene-
,5-dione (9) failed to yield cycloocta-2,5,7-triene-1,4-dione
In contrast to the successful
Scheme 1.
2
11
12
(
8), giving tropone instead, involving decarbonylation.
drobromination of 11 (Scheme 1).
Based on this back
However, a slight structural modification changed the course
of the thermal reaction, and thus bicyclo[4.2.0]octa-7-ene-
ground information, we attempted the synthesis of 1 through
a thermal reaction of either 2,5-bis(dicyanomethylene)bicy-
clo[4.2.0]octa-3,7-diene (12) or its 3,4-dihydro derivative 13.
However, the attempts failed and instead we found novel rear-
rangements of 12 and 13, and studied the physicochemical
2
,5-dione (10), the 7,8-dihydro compound of 9, underwent a
clean ring opening to cycloocta-5,7-diene-1,4-dione (11).
The synthesis of 8 was attained by the bromination and dehy-
Published on the web September 15, 2003; DOI 10.1246/bcsj.76.1793

1
794 Bull. Chem. Soc. Jpn., 76, No. 9 (2003)
Rearrangement to New Electron Acceptors
1
2 in 66% yield (Scheme 2). Dideuterated compounds 12-
d2 and 13-d2 were prepared similarly from 10-d2, obtained
by the photochemical cycloaddition of 2-cyclohexene-1,4-di-
16
one with dideuterioacetylene.
Thermal Reactions. Because the pyrolytic reaction of 12
ꢁ
17
at 500 C by a flow method resulted in extensive decompo-
sition, thermal reactions were examined in solution. The heat-
ꢁ
ing of 12 in o-dichlorobenzene at 180 C for 5 h afforded a
Chart 2.
pale-yellow compound 14 in 22% yield as a sole isolated
product. The structure of 14 was assigned to 2,6-bis(dicyano-
methylene)bicyclo[3.3.0]octa-3,7-diene, based on an elemental
properties of the resulting rearranged products as electron ac-
ceptors (Chart 2).
1
analysis and spectral data (Table 1). The H NMR spectrum of
1
4 is composed of three signals with the same intensity for two
Results and Discussion
sets of olefinic protons and a set of aliphatic protons. The
spectral data indicate C2 or Ci symmetry of the molecule
and the presence of two sets of conjugated dicyanometh-
ylenecyclopentenes. When the reaction was monitored by
Synthesis of Precursors. Compound 13 was prepared by
the Knoevenagel condensation of the dione 10 with malono-
nitrile in 89% yield. The bromination and dehydrobromination
13
14,15
1
of 13 in a similar fashion to the synthesis of TCNQ
gave
H NMR in deuterated bromobenzene, the decrease of 12 es-
Scheme 2.
Table 1. Spectral Properties of New Compounds
aÞ
1H NMR
bÞ
13C NMR
cÞ
IR
UV–vis
(ꢂmax/nm (log "))
ꢃ1
(
ꢁ
CN/cm
)
(ꢃ/ppm)
(ꢃ/ppm)
1
2
3
2230
253
(3.26)
(3.18)
(4.46)
(4.56)
(4.44)
4.45 (s, 2H)
6.34 (s, 2H)
7.25 (s, 2H)
43.33
87.98
110.37
111.14
132.46
139.55
163.51
2
3
3
3
62
32sh
48
66
1
2230
254
(4.40)
(3.01)
(3.23)
(3.29)
(3.12)
3.06 (m, 4H)
4.48 (s, 2H)
6.32 (s, 2H)
29.20
48.16
86.54
110.57
139.43
176.41
3
3
3
3
33
54
72
95
110.57
14
15
16
2230
2226
2224
265sh
(4.28)
(4.50)
(4.30)
(3.20)
4.66 (ddd, J ¼ 1:2, 1.7, 2.2 Hz, 2H)
6.81 (dd, J ¼ 1:7, 5.4 Hz, 2H)
56.09
79.85
110.83
111.87
139.58
150.85
177.95
3
3
3
02
20sh
70sh
7.15 (ddd, J ¼ 1:2, 2.2, 5.4 Hz, 2H)
228
(4.03)
(4.00)
(4.07)
3.07 (s, 4H)
6.49 (AA BB , 2H)
33.07
87.68
110.82
111.28
128.51
135.56
170.34
0 0
2
3
74
43
0
0
6.68 (AA BB , 2H)
taling to 430 nm
337
(4.15)
(4.44)
(4.60)
(4.51)
3.09 (m, 4H)
3.50 (m, 4H)
26.55
37.63
80.54
112.05
166.67
172.62
3
3
3
55
73
95
111.63
a) In dichloromethane. b) In CDCl3, 270 MHz. c) In CDCl3, 67.5 MHz.

T. Kawase et al.
Bull. Chem. Soc. Jpn., 76, No. 9 (2003) 1795
Scheme 3.
sentially obeyed first-order kinetics, although the unidentifia-
bility of the majority of products (>70%) makes the kinetics
questionable. Assuming validity of the first-order kinetics,
be 2,6-bis(dicyanomethylene)bicyclo[3.3.0]octa-1(5)-ene from
analytical and spectral data and confirmed by X-ray crystallo-
graphic analysis. These results are markedly different from the
thermal reactions of other dimethylenebicyclo[4.2.0]octa-
(3),7-(di)enes 5–7 (Scheme 3).
ꢁ
ꢃ5
the rate constant at 150 C was calculated to be 1:9 ꢂ 10
ꢃ1
z
s
kJ mol . The energy value is slightly smaller than that for
and the free energy of activation ꢀG ¼ 143:1 ꢄ 0:8
ꢃ1
The deuterated compounds 14-d2, 15-d2 and 16-d2 were al-
so obtained by the thermal reaction of 12-d2 and 13-d2, whose
the ring opening of the tetraphenyl derivative 6 to 3
8
z
ꢃ1
1
(
ꢀG ¼ 153 kJ mol ). The thermal reaction was completed
H NMR spectra are informative for elucidating the mecha-
ꢁ
in 3 h at 180 C in benzonitrile, giving 14 in a similar yield,
thus suggesting that some acceleration had occurred in this
more dipolar solvent.
nism of these rearrangements to some extent. The integral
of the peaks for both olefinic protons of 14-d2 are reduced
to almost half of those of the aliphatic peaks, and both of
the signals for aliphatic protons of 16-d2 are equal in
intensity. These results indicated that two deuteriums in these
compounds are located adjacently. Moreover, the signals at
6.49 ppm for inner olefinic protons of 15 are absent in the
spectrum of 15-d2, suggesting that the formation proceeds
through a thermal ring opening of the cyclobutene ring of 13.
Similar to the reaction mechanisms of the known 2,4-di-
methylenebicyclo[4.2.0]octenes, we assumed as a probable
mechanism that the rearrangements start with the thermal ring
opening to form the strained cyclooctadienes 17, which con-
verted competitively to dimethylenecyclooctadiene 15 via E–
Z bond isomerization and to bicyclo[3.3.0]octane skeletons
via zwitterionic intermediates, as shown in Scheme 4. The
strong electron-withdrawing property of dicyanomethylene
groups seems to play an important role in determining the re-
action pathway to bicyclic compounds 14 and 16. The desired
product 1 might form from 12 as a transient species in the
mechanism because of the modest yield. However, little deci-
sive evidence has been obtained to date.
On the other hand, compound 13 underwent thermal reac-
tions more easily and cleanly than 12; upon heating 13 in deu-
ꢁ
1
terated toluene at 110 C, the H NMR signal of the aliphatic
protons of 13 at 3.06 ppm completely disappeared in only 1
hour. The disappearance of 13 also obeyed first-order kinetics
with the following kinetic and thermodynamic parameters: k
ꢁ
ꢃ4 ꢃ1
z
ꢃ1
(
80 C) = 1:40 ꢂ 10
s
; ꢀG ¼ 118:4 ꢄ 0:4 kJ mol
.
The NMR spectrum of the resulting reaction mixture indicated
a clean formation of two new products with a 56:44 ratio. One
of the products tended to decompose upon chromatographic
separation both on alumina and silica gel, but these products
can be separated by fractional crystallization. Thus, upon
standing the reaction mixture in toluene at room temperature,
a fine yellow solid 15 precipitated first of all in 44% yield, and
then yellow needles of 16 crystallized out in 22% yield from
the concentrated filtrate. The reaction was about 1.9-times
ꢁ
ꢃ4
faster in more dipolar acetonitrile [k (80 C) = 2:65 ꢂ 10
ꢃ1
s
]. In acetonitrile, however, while the yield of 16 remained
almost the same as in toluene, the yield of 15 became very
poor (4%). The poor yield of 15 in acetonitrile seems to cor-
relate with its instability on alumina, and in fact 15 decom-
posed in hot acetonitrile, giving a complex mixture. Both
Properties of New Acceptors. New compounds 12, 15
and 16, having tetracyanohexatriene or -octatetraene moieties,
are regarded as vinylogs of TCNE, and are therefore of interest
from the viewpoint of new electron acceptors. Therefore, the
electrochemical properties were examined by cyclic voltam-
metry (Table 2). While 12 and 16 show two sets of well-re-
versible one-electron reduction waves, 15 showed poorly re-
versible reduction waves, probably owing to the nonplanar
1
5 and 16 have the same molecular formula with 13, but no
interchange between the products was observed when they
were each heated in toluene.
Compound 15 was determined to be 5,8-bis(dicyanometh-
ylene)-1,3-cyclooctadiene from the spectral data, and 16 to

1
796 Bull. Chem. Soc. Jpn., 76, No. 9 (2003)
Rearrangement to New Electron Acceptors
Scheme 4. A possible mechanism of the rearrangements via thermal ring opening.
conformation and chemical liability of the unsaturated
1
=2
eight-membered ring.
ꢃ0:34 to ꢃ0:52 V) are considerably weaker than TCNE
0.22 V), TCNQ (0.18 V), thiophene derivative 18 (0.07
V) and dibenzopentalene derivative 19 (0.10 V), probably
due to the electron-donating properties of the alkyl groups.
Good single crystals of a molecular complex of the acceptor
Their electron affinities (E1
¼
aÞ
Table 2. Reduction Potentials of 12, 15, 16, Together with
TCNE, TCNQ, 18 and 19
(
18
19
1
2
Compounds
E
E
1=2
1=2
1
1
1
2
5
6
ꢃ0:34
ꢃ0:47
ꢃ0:52
0.22
ꢃ0:73
16 with toluene (1:1) suitable for X-ray analysis were obtained
as yellow plates by mixing 16 with toluene in chloroform. Al-
ꢀ
ꢃ1:47
ꢃ0:90
ꢃ0:76
ꢃ0:37
ꢃ0:54
ꢃ0:3
most no change in the infrared absorption of the cyano groups
ꢃ1
TCNE
TCNQ
(
ORTEP drawing of 16 in Fig. 1a shows a planar structure of
ꢁ ¼ 2224 cm ) suggests that the complex is nonionic. The
0.18
0.07
0.10
bÞ
cÞ
1
1
8
9
the molecule. The length of the dicyanomethylene double
ꢁ
bonds (1.35 A = 135 pm) is slightly shorter than those of neu-
þ
ꢃ3
a) V vs Ag/Ag , in 0.1 mol dm Et4NClO4/CH3CN, sweep
rate 100 mV sꢃ1. b) Ref. 18. c) Ref. 19. ꢀPeak potential.
20 21
tral TCNQ (1.362 A) or BenzoTCNQ (1.384 A), but quite
similar to those of the molecular complex of 2-chlorotetracya-
ꢁ
ꢁ
22
ꢁ
noanthraquinodimethane with benzene (1.344 A). The pack-
ing diagram of the complex in Figs. 1b and 1c shows that the
disordered toluene molecule is interposed by acceptors in the
upper and lower layers, and are captured by Y-shaped dicyano-
methylene groups of the adjacent acceptors, which lie on an al-
23
most coplane with toluene. No short contacts within van der
Waals distance were observed. The shortest intermolecular
ꢀ
ꢁ
contact between acceptors is 3.37 A (C7–C7 ), and acceptor

T. Kawase et al.
Bull. Chem. Soc. Jpn., 76, No. 9 (2003) 1797
Fig. 1. a) ORTEP view of 16 in the complex showing the atom numbering scheme. b) Molecular overlap in 16 C7H8 showing the
ꢅ
disordered atomic position for the methyl groups. c) Molecular arrangement in the 16 C7H8 crystal.
ꢅ
Table 3. Crystal Data for C-T Complex of 16 and Toluene
Table 4. Fractional Coordination and Equivalent Isotropic
Thermal Parameters for Non-Hydrogen Atoms with Esd’s
in Parentheses
1
6 C7H8
ꢅ
324.37
Formula
C14H8N4 C7H8
ꢅ
aÞ
Beq
Atom
x
y
z
Formula weight
Crystal system
Space group
Z
Triclinic
ꢂ
P1(#2)
N(1)
N(2)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
ꢃ0:3761ð5Þ
ꢃ0:0583ð5Þ
ꢃ0:0559ð5Þ
ꢃ0:0344ð5Þ
0.1156(7)
0.1696(7)
ꢃ0:1277ð5Þ
ꢃ0:2675ð6Þ
ꢃ0:0883ð6Þ
0.368(1)
0.5599(5)
0.8747(5)
0.5063(4)
0.6207(5)
0.6805(6)
0.6033(6)
0.6700(5)
0.6081(5)
0.7851(5)
0.991(1)
0.3220(5)
0.6231(5)
0.0480(5)
0.2119(5)
0.2203(6)
0.0417(6)
0.3378(5)
0.3247(5)
0.4946(6)
1.082(2)
6.2(1)
6.2(1)
3.45(9)
3.77(9)
4.4(1)
2
ꢁ
a/A
8.252(3)
8.442(3)
7.762(1)
102.23(3)
112.40(2)
62.17(2)
441.7(3)
1.746
ꢁ
b/A
ꢁ
c/A
ꢄ/
4.3(1)
ꢁ
3.83(9)
4.3(1)
4.4(1)
12.2(3)
10.4(3)
10.6(2)
16.3(4)
ꢁ
ꢁ
ꢅ/
ꢆ/
Volume/A
3
ꢁ
ꢃ3
ꢇcalcd/g cm
0.391(1)
0.507(1)
0.536(1)
0.905(1)
0.9094(9)
0.839(1)
0.932(1)
0.850(1)
0.706(1)
F000
240.00
1.11
965
ꢃ1
ꢈ(Mo Kꢄ)/cm
No. of observation
a) Beq ¼ 4=3ꢃꢃꢅ ai aj.
ij
ꢅ
R
0.064
0.065
2.63
Rw
G.F.I.
ꢁ
Table 5. Selected Bond Lengths (A), and Bond Angles
(
deg) of 16 for 16 C7H8
ꢅ
ꢁ
and toluene is 3.50 A (C6–C9). Thus, the toluene molecule
can be regarded as an inclusion of a network of acceptors
(Table 3–5).
ꢀ
ꢀ
C(1)–C(1) –C(4)
ꢀ
C(1)–C(1)
C(1)–C(2)
C(1)–C(4)
C(2)–C(3)
C(2)–C(5)
C(3)–C(4)
C(5)–C(6)
C(5)–C(7)
1.348(6)
1.432(4)
1.504(4)
1.516(5)
1.350(5)
1.537(5)
1.437(5)
1.423(5)
1.137(4)
1.138(4)
C(1)–C(1) –C(2)
ꢀ
C(2)–C(1)–C(4)
111.1(4)
112.7(4)
136.1(3)
107.0(3)
128.0(3)
124.9(3)
106.5(3)
102.4(3)
122.8(3)
120.9(3)
116.3(3)
177.3(4)
177.9(4)
ꢀ
ꢀ
The planar acceptor 16 also formed an 1:1 charge-transfer
0
C(1)–C(2)–C(3)
C(1)–C(2)–C(5)
C(3)–C(2)–C(5)
C(2)–C(3)–C(4)
0
(
C-T) complex with 2,2 ,5,5 -tetrathiafulvalene (TTF) as fine
and black needles by a diffusion method. The complex was,
however, slight ionic based on the infrared absorption of nitrile
ꢃ1
ꢃ1
ꢀ
groups (2222 cm ; ꢀꢁ ¼ 2 cm ), and the conductivity,
C(1) –C(4)–C(3)
measured on a compressed pellet with a two-probe method
ꢃ7
N(1)–C(6)
N(2)–C(7)
C(2)–C(5)–C(6)
C(2)–C(5)–C(7)
C(6)–C(5)–C(7)
N(1)–C(6)–C(5)
N(2)–C(7)–C(5)
at room temperature, was near insulating (1:1 ꢂ 10
ꢃ1
S cm ). The weak C-T interaction may be due to the consid-
erably poorer electron affinity compared with TCNQ.
Although the other tetracyanohexatriene, 12 and -octa-
tetraene 15, have a similar electron affinity to 16, no C-T com-
plex has been obtained so far.
derwent a thermal reaction at a relatively lower temperature to
give a normal ring-opened product 15 together with a rear-
ranged product 16. An interruption of conjugation on the
six-membered ring would decrease the activation energy of
the ring opening to allow the formation of 15 competitively.
The rearranged product 16, having a planar 1,1,6,6-tetracyano-
hexatriene structure, shows moderate electron affinity com-
pared with TCNE and TCNQ. The results expand the variety
of the chemistry of the polycyanosubstituted ꢀ-electron sys-
tems.
Conclusion
Whereas 2,5-dimethylenebicyclo[4.2.0]octa-3,7-dienes gave
rise to normal ring-opened products, the dicyanomethylidene
derivative 12 afforded a rearranged product 14 as a sole isol-
able product in moderate yield. The normal ring-opened prod-
uct 1 might form as a transient species, judging from the mod-
est yield; however, no evidence for the formation has been ob-
tained so far. On the other hand, the dihydro compound 13 un-

1
798 Bull. Chem. Soc. Jpn., 76, No. 9 (2003)
Rearrangement to New Electron Acceptors
3
3
CH2Cl2 (10 cm ) and acetonitrile (2 cm ). The solution was
Experimental
ꢁ
cooled below ꢃ50 C in an ethanol–dry ice bath under a N2 at-
General. The melting points were recorded on a Yanaco MP
00D apparatus and uncorrected. FAB- and EI-High resolution
mosphere and added dropwise was a solution of pyridine (289
3
5
mass spectra were measured on
mg, 3.65 mmol) and CH2Cl2 (2 cm ) over 2 min with stirring. Af-
ter the addition, the mixture was allowed to warm up to room tem-
a
JEOL JMS-SX 102
instrument. H NMR spectra (tetramethylsilane; 0 ppm as an in-
1
3
perature, stirred overnight and then water (20 cm ) and CH2Cl2
1
3
3
ternal standard) and C NMR spectra (CDCl3; 77.0 ppm as an in-
ternal standard) were recorded on JEOL EX-270 and JEOL GSX-
(10 cm ) were added. The organic layer was separated, and the
3
aqueous layer was extracted with CH2Cl2 (2 ꢂ 10 cm ). The ex-
4
00 instruments. The chemical shifts are given in ppm. IR spec-
tracts were combined, washed with water and brine, dried
(MgSO4) and concentrated under reduced pressure. The residue
was chromatographed on silica gel with CH2Cl2 to give 12 (460
mg, 66%). Recrystallization from CH2Cl2–hexane gave pale yel-
tra were obtained by a Perkin-Elmer 1650 spectrometer. Micro-
analyses were performed at the Elemental Analysis Center, Facul-
ty of Science, Osaka University. Electronic spectra (UV–vis)
were obtained on a Hitachi U-3400 instrument. Column chroma-
tography was performed with a Merck Kiesel-gel 60.
ꢁ
þ
low prisms; mp 168–169 C; MS (EI) m=z (%) 230 (M ; 38), 229
(18), 203 (69), 165 (62), 18 (100); Found: C, 73.15; H, 2.58; N,
24.24%. Calcd for C14H6N4: C, 73.04; H, 2.63; N, 24.34%.
7,8-Dideuterio-2,5-bis(dicyanomethylene)bicyclo[4.2.0]octa-
3,7-diene (12-d2): MS (EI) m=z (%) 232 (M ; 74), 231 (31), 205
(100), 167 (95).
Cyclic voltammograms were recorded on a BAS 100B/W (CV-
0W) Voltammetric Analyzer and Electrochemical Workstation.
5
All electrochemical measurements were carried out in acetonitrile
þ
ꢃ3
solutions containing 0.1 mol dm tetraethylammonium perchlo-
rate (nakarai Tesque Inc.) at 25 C under an argon atmosphere.
ꢁ
Thermal Rearrangement of 12: A solution of 12 (100 mg, 1
3
ꢁ
All of the reactions were carried out under a nitrogen or argon
atmosphere unless otherwise noted. Diethyl ether and THF were
distilled from sodium diphenylketyl prior to use. DMF was dis-
tilled from CaH2 and stored over MS 4A under a nitrogen
atmosphere. Dichloromethane and acetonittrile were distilled
from P4O10. Malononitrile, ꢅ-alanine and N-bromosuccinimide
were commercially available and used without further purifica-
tion.
mmol) in o-dichlorobenzene (20 cm ) was heated at 180 C in an
oil bath for 3 h. The solvent was removed in vacuo. Chromatog-
ꢁ
raphy of the residue on silica gel with CH2Cl2 at 0 C gave 14 (22
mg, 22%). Recrystallization from CH2Cl2 gave a pale-yellow
ꢁ
þ
powder; mp 168–169 C; MS (EI) m=z (%) 230 (M , 100), 203
(87), 165 (50); Found: C, 73.00; H, 2.88; N, 24.27%. Calcd for
C14H6N4: C, 73.04; H, 2.63; N, 24.34%.
Thermal Rearrangement of 13: A solution of 13 (1.0 g, 4.3
3
7,8-Dideuteriobicyclo[4.2.0]oct-7-ene-2,5-dione (10-d2): Di-
deuterioacetylene, generated by the slow addition of deuterium
mmol) in toluene (40 cm ) was heated at reflux for 2 h under a N2
atmosphere, and then allowed to cool and stand at room temper-
ature overnight. The yellow needles which precipitated were col-
lected by filtration to give nearly pure 15 (435 mg, 44%). The fil-
trate was concentrated under reduced pressure until an orange sol-
id appeared. The yellow suspension was heated until a homoge-
neous solution was obtained, and the resulting solution was
allowed to stand at room temperature overnight to give 16 (220
mg, 22%). Recrystallization of 16 from benzene gave yellow-or-
3
oxide (40 cm ) into a suspension of calcium carbide (64 g, 1
3
mol) with DMF (100 cm ), was bubbled into a solution of 2-cyclo-
3
hexene-1,4-dione (3.3 g, 30 mmol) in dichloromethane (250 cm )
ꢁ
under cooling at ꢃ60 C. After half of the D2O was consumed, the
solution, saturated with dideuterioacetylene, was irradiated (Pyrex
ꢁ
photoreactor and 400 W-Hg lamp was used) at ꢃ60 C with bub-
bling for 3 hours, and then allowed to warm to rt. After stirring
for 12 hours, the reaction mixture was concentrated under reduced
pressure. The residue was chromatographed on silica gel with
CH2Cl2 to give a dideuterated compound 10-d2 (3.40 g, 82%).
ꢁ
ange prisms; 15: mp 210–211 C (decomp.); MS (EI) m=z (%) 232
þ
(M , 100), 206 (46); Found: C, 72.17; H, 3.33; N, 24.06%. Calcd
ꢁ
for C14H8N4: C, 72.40; H, 3.47, N, 24.12%. 16: mp 145–146 C;
þ
þ
þ
MS (EI) m=z (%) 138 (M ; 43), 138 (6), 84 (100).
2,5-Bis(dicyanomethylene)bicyclo[4.2.0]oct-7-ene (13): To
a preheated mixture of 10 (1.36 g, 10 mmol) and malononitrile
MS (FAB) m=z (%) 232 (M , 43), 231 (M ꢃ 1, 100); Found C,
72.40; H, 3.52; N, 24.07%. Calcd for C14H8N4: C, 72.40; H, 3.47,
N, 24.12%.
ꢁ
ꢃ3
3
(
1.52 g, 23 mmol) at 80 C in an oil bath was added a 20 cm
Kinetics of the Thermal Reaction of 12 and 13: The reaction
rates of the reactions were measured by monitoring the decrease in
of a 0.1 M (0.1 mol dm ) aqueous solution of ꢅ-alanine with
stirring. After 30 min, the mixture was diluted with water (100
1
ꢁ
the appropriate peaks of the H-NMR spectra at 150 C in C6D5Br
3
ꢁ
cm ), and cooled to room temperature. The precipitated crude
product was collected by filtration, and dissolved in CH2Cl2 (50
cm ). The filtrate was extracted with CH2Cl2 (2 ꢂ 20 cm ).
The CH2Cl2 solutions were combined, washed with water, dried
for 12, and at 80 C in C7D8 or CD3CN for 13.
Complexation of 16 and TTF: A complex of 16 and TTF
3
3
(1:1) was obtained as black needles from a chloroform solution
ꢁ
ꢃ1
by slow evaporation; mp 210–212 C; IR (KBr) 2222 cm
(CN); Found C, 54.69; H, 2.82; N, 12.76; S, 29.20%. Calcd for
(
Na2SO4), and concentrated under reduced pressure. The residue
was chromatographed on silica gel with CH2Cl2 to give bis(dicya-
nomethylene) compound 13 (2.40 g, 89%). Recrystallization from
C14H8N4 C6H4S4: C, 55.02; H, 2.77, N, 12.83, S 29.38%.
ꢅ
Crystal and Experimental Data for Complex of 16 and
Toluene: A single crystal was grown by the slow evaporation
of a saturated solution of 16 in chloroform and small portion of
ꢁ
CH2Cl2–hexane gave pale-yellow prisms; mp 124–125 C; MS
þ
(
EI) m=z (%) 232 (M ; 59), 231 (33), 204 (100); Found: C,
3
ꢁ
72.40; H, 3.43; N, 24.07%. Calcd for C14H8N4: C, 72.40; H,
3.47, N, 24.12%.
toluene and its size was ca. 0:2 ꢂ 0:3 ꢂ 0:4 mm (mp 150 C,
ꢁ
decomp). The intensity data (2ꢉ < 60 ) were collected on a Ri-
gaku AFC5R diffractometer with graphite monochromated Mo
7
,8-Dideuterio-2,5-bis(dicyanomethylene)bicyclo[4.2.0]oct-
þ
ꢁ
7
-ene (13-d2): MS (EI) m=z (%) 234 (M ; 65), 233 (32), 206
Kꢄ radiation (ꢂ ¼ 0:71069 A), and the structure was solved by
(
92), 18 (100).
,5-Bis(dicyanomethylene)bicyclo[4.2.0]octa-3,7-diene (12).
Bis(dicyanomethylene) 13 (707 mg, 3.0 mmol) and N-bromosuc-
direct methods. All calculations were performed using the teXsan
crystallographic software package of Molecular Structure
Corporation. Anisotropic thermal parameters were employed
for non-hydrogen atoms and isotropic for hydrogens. All of the
2
cinimide (600 mg, 3.4 mmol) were dissolved in a mixture of

T. Kawase et al.
Bull. Chem. Soc. Jpn., 76, No. 9 (2003) 1799
hydrogens were located by calculations. The larger temperature
factor for carbons of toluene should be due to disorder. The final
cycle of the full-matrix least-squares refinement was based on 965
observed reflections (I > 3ꢊ) and 134 variable parameters.
Crystallographic data have been deposited at the CCDC, 12
Union Road, Cambridge CB2 1EZ, UK and copies can be ob-
tained on request, free of charge, by quoting the publication cita-
tion and the deposition numbers CCDC-211186.
10 M. Oda, N. Fukazawa, and Y. Kitahara, Tetrahedron Lett.,
1977, 3277.
11 Y. Kayama, M. Oda, and Y. Kitahara, Tetrahedron Lett.,
1974, 3293.
12 M. Oda, Y. Kayama, H. Miyakoshi, and Y. Kitahara, An-
gew. Chem., Int. Ed. Engl., 14, 418 (1975).
13 M. Oda, H. Oikawa, Y. Kanao, and A. Yamamuro, Tetra-
hedron Lett., 1978, 4905.
1
Misumi, J. Chem. Soc., Chem. Commun., 1982, 1065.
15 D. S. Acker and W. R. Hertler, J. Am. Chem. Soc., 84, 3370
4
S. Yamaguchi, H. Tatemitsu, Y. Sakata, T. Enoki, and S.
We thank Prof. Y. Yamashita (Tokyo Institute of Technol-
ogy) for helpful discussions and the Ministry of Education,
Culture, Sports, Science and Technology for financial support.
(
1962).
M. Oda, T. Kawase, T. Okada, and T. Enomoto, Org.
Synth., 73, 253 (1996).
The thermal reaction was carried out by passing a benzene
1
6
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