Topochemical reaction of 7-bromoethoxycarbonyl-7-cyano-1,4-benzoquinone methide in the solid state

Article abstract of DOI:10.1246/cl.2006.918

Topochemically controlled [2 + 2] photocycloaddition took place at the quinoid double bond of the 7-bromoethoxycarbonyl-7-cyano-1,4-benzoquinone methide (1) to afford its cyclobutane dimer. Copyright

Full text of DOI:10.1246/cl.2006.918

918
Chemistry Letters Vol.35, No.8 (2006)
Topochemical Reaction of 7-Bromoethoxycarbonyl-7-cyano-1,4-benzoquinone
Methide in the Solid State
Takahito Itoh,ꢀ1 Kyoko Tachino,1 Takahiro Uno,1 Masataka Kubo,1 Norimitsu Tohnai,2 and Mikiji Miyata2
1Division of Chemistry for Materials, Graduate School of Engineering, Mie University,
1577 Kurimamachiya-cho, Tsu, Mie 514-8507
2Department of Material and Life Science, Graduate School of Engineering, Osaka University and Handai FRC,
2-1 Yamadaoka, Suita, Osaka 565-0871
(Received May 16, 2006; CL-060579; E-mail: itoh@chem.mie-u.ac.jp)
Topochemically controlled [2 þ 2] photocycloaddition
(1) was prepared by the method reported previously.7 Knoevena-
gel condensation of 1,4-cyclohexanedione monoethylene ketal
with bromoethyl cyanoacetate followed by deprotection of
the ketal afforded 4-[cyano(bromoethoxycarbonyl)methylene]-
cyclohexanone (2) (55% yield) as white needles. Oxidation of
2 with activated manganese dioxide in the refluxing benzene
gave 1 (41% yield), which was recrystallized from a mixture
of dichloromethane and hexane to afford orange needles.
The crystals of 1 were heated at 60 ꢁC, lower than its melting
point (81.4 ꢁC), in the dark in vacuo, or irradiated using a 400 W
high-pressure Hg lamp at 30 ꢁC (Table 1).
took place at the quinoid double bond of the 7-bromoethoxycar-
bonyl-7-cyano-1,4-benzoquinone methide (1) to afford its
cyclobutane dimer.
Solid-state organic reactions have attracted much attention
as an environment-friendly synthetic method because of sol-
vent-free processes, and also solid-state reactions under topo-
chemical control are more attractive in the points of providing
products with specific structures in a high conversion and selec-
tivity. Until now, enormous solid-state organic reactions have
been reported.1 There are a large number of the organic reactions
under topochemical control for the low molecular product for-
mation, but monomers that can be polymerized topochemically
are limited to derivatives of diacetylene,2 2,5-distyrylpyrazine,3
triene and triacetylene,4 and muconic acid and sorbic acid.5
Recently, we found that polymerization reactions of 7,7,8,8-
tetrakis(alkoxycarbonyl)quinodimethanes proceed topochemi-
cally and we explained the relationship between topochemical
polymerization reactivity and the monomer packing in the crys-
tals.6 To find a general rule to predict this relationship for
the quinoid compounds, we expanded the investigation of the
solid-state polymerizations to quinine methides as a member
of the quinoid family.7a In the course of the research, we found
that a cyclobutane dimer of 7-bromoethoxycarbonyl-7-cyano-
1,4-benzoquinone methide (1) might be formed by the topo-
chemically controlled [2 þ 2] photocycloaddition reaction
(Scheme 1). Here, we report the synthesis of 1 and its solid-state
reaction.
On the thermally induced reaction, 1 retained the crystal
shape except for the color change from orange to pale yellow,
and the white solids with Mn of 85,000 (GPC, polystyrene stand-
ard, THF eluent) were isolated in 84% yield by the dissolution–
reprecipitation treatment. The isolated product was character-
1
ized by H and 13C NMR and IR spectroscopies and elemental
analysis, and it was found to be a homopolymer of 1 with chemi-
cal structures similar to the polymers obtained by the solution
polymerizations of substituted quinone methides.7b The change
in crystallinity during the reaction was investigated by the pow-
der XRD measurement. The powder XRD pattern for the 1 crys-
tals showed very sharp peaks: at 41% conversion it showed the
coexistence of monomer crystal phase and the polymer amor-
phous phase, and at 84% conversion it became broad and there
were no significant peaks, indicating that the monomer crystals
collapsed with a progress of polymerization and amorphous
polymers might be formed. On the other hand, on the photoin-
duced reaction at 30 ꢁC, 1 retained the crystal shape during the
irradiation, but it turned orange to pale orange after a few hours.
GPC measurement of the reaction mixture showed two compo-
nents, corresponding to unreacted 1 and the reaction product
with the molecular weight of 540, and the conversions to the re-
7-Bromoethoxycarbonyl-7-cyano-1,4-benzoquinone methide
O
O
O
O
NCCH2CO2R
AcONH4 / AcOH
1
action product determined by H NMR were to be 90% for 4
days and 94% for 59 days, respectively. The reaction products
were isolated in 77 and 84% yields as pale yellow powders by
1)
2)
MnO2
+
H
O
NC
CO2R
NC
CO2R
Table 1. Thermally induced and photoinduced reactions of 1 in
the solid state in vacuo
R = CH2CH2Br
2
1
Light
source
Temp
/ꢁC
Time
/days
Conv.a
/%
solid state
h
ν
∆
Mn
O
O
H
solid state
dark
Hg
lump
Hg
lump
aIsolated yield.
60
30
28
4
84
77
85,000
540
H
CO2R
H
H
O
n
CN
30
59
84
540
NC
CO2R NC
CO2R
Scheme 1.
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.8 (2006)
919
Table 2. Crystallographic data for crystals of 1 and dimer
Dimer
(1:1 complex)
Compound
formula
fw
crystal system
space group
1
90°
C11H8BrNO3
282.09
triclinic
C28H22Br2N2O6
642.30
triclinic
ꢀ
ꢀ
b
P1(#2)
P1(#2)
˚
a/A
4.108(1)
11.388(2)
11.496(2)
90.96(2)
94.58(2)
90.96(2)
535.0(2)
2
7.821(1)
11.178(2)
17.083(3)
72.91(2)
89.72(2)
76.71(2)
1386.0(5)
2
˚
b/A
a
view from a-axis
Figure 1. Crystal structure of 1.
˚
c/A
ꢁ/deg
ꢂ/deg
ꢃ/deg
considered, therefore, that in the photoinduced reaction the
cyclobutane dimer was formed by topochemically controlled
[2 þ 2] cycloaddition and in the thermally induced reaction
amorphous polymer was obtained. Further studies on the rela-
tionship of the reactions in the solid state and crystal structures
for the quinoid family are now in progress.
3
˚
V/A
Z
Dcalcd/g cmꢂ3
unique reflecns
no. obsd reflens
R1
1.751
1803
5727
0.067
1.539
4654
13615
0.078
This work was supported by Grant-in-Aid for Scientific
Research (No. 18350062) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
R, Rw
GOF
2ꢄmax/deg
temp/ꢁC
0.101, 0.213
1.9
136.5
ꢂ180
0.108, 0.228
1.91
136.5
ꢂ60
References and Notes
1
G. M. Schmidt, Pure Appl. Chem. 1971, 27, 647; V.
Ramamurthy, K. Venkatesan, Chem. Rev. 1987, 87, 433;
G. R. Desiraju, Crystal Engineering: The Design of Organic
Solids, Elsevier, Amsterdam, Oxford, New York, Tokyo,
1989; Y. Ito, Synthesis 1998, 1; K. Tanaka, F. Toda, Chem.
Rev. 2000, 100, 1025.
the dissolution–reprecipitation treatment (repeated three times)
using dichloromethane as a solvent and hexane as a precipitant.
The isolated reaction product was characterized by 1H and
13C NMR, IR spectroscopies and elemental analysis, and deter-
mined to be the cyclobutane dimer.8 And also, single-crystal
structure analysis of the reaction product crystals, obtained by
recrystallization from benzene, supported the cyclobutane dimer
structure, though it was a 1:1 complex of the dimer with benzene
(Table 2). This indicates that the photoinduced [2 þ 2] cycload-
dition took place at the double bond of the quinoid ring of 1 in
the solid state.
On contrast, when 1 was irradiated in toluene solution at
30 ꢁC for 4 days, no cyclobutane dimer was obtained and instead
its homopolymer with Mn of 5,100 was obtained in 82% yield.
Therefore, the dimer formation is regarded as the specific reac-
tion in the solid state.
To clarify the relationship of the reaction product with the
molecular packing mode of 1 in the crystals, we investigated
the crystal structures of 1 by X-ray crystallography. The single
crystals were prepared successfully by slow solvent evaporation
from a mixture solution of hexane with dichloromethane. The
crystallographic data of 1 are summarized in Table 2 together
with the data of the cyclobutane dimer, and the crystal structure
of 1 is shown in Figure 1. The 1 molecules stack along a-axis to
form a columnar structure, which is similar to the molecular
packing of 7-cyano-7-propoxycarbonyl-1,4-benzoquinone me-
thide, where an amorphous polymer was formed in the solid-
state polymerization.7a However, as in Figure 1 two nearest-
neighboring molecules lie in parallel with the double bonds
oriented in the same direction with a maximal distance between
2
3
4
G. Wegner, Pure Appl. Chem. 1997, 49, 443; T. Ogawa,
Prog. Polym. Sci. 1995, 20, 943.
M. Hasegawa, Chem. Rev. 1983, 83, 507; M. Hasegawa, Adv.
Phys. Org. Chem. 1995, 30, 117.
J. Xiao, M. Yang, J. W. Lauher, F. W. Fowler, Angew.
Chem., Int. Ed. 2000, 39, 2132; T. Hoang, J. W. Lauher, F.
W. Fowler, J. Am. Chem. Soc. 2002, 124, 10656.
A. Matsumoto, T. Odani, Macromol. Rapid Commun. 2001,
22, 1195; A. Matsumoto, Polym. J. 2003, 35, 95.
T. Itoh, S. Nomura, T. Uno, M. Kubo, K. Sada, M. Miyata,
Angew. Chem., Int. Ed. 2002, 41, 4306; S. Nomura, T.
Itoh, H. Nakasho, T. Uno, M. Kubo, K. Sada, K. Inoue, M.
Miyata, J. Am. Chem. Soc. 2004, 126, 2035.
5
6
7
8
a) T. Itoh, S. Nomura, N. Saitoh, T. Uno, M. Kubo, K. Sada,
M. Miyata, Macromolecules 2004, 37, 7938. b) S. Iwatsuki,
T. Itoh, X. S. Meng, Macromolecules 1993, 26, 1213.
Mp 45–46 ꢁC; IR (KBr): 2966, 2222, 1728, 1678, 1247,
1146, 664 cmꢂ1
;
1H NMR (CDCl3): ꢀ 8.59 (d, J ¼ 10:88
Hz, 1H), 7.78 (d, J ¼ 10:56 Hz, 1H), 6.69 (d, J ¼ 10:56
Hz, 1H), 6.57 (d, J ¼ 10:56 Hz, 1H), 5.28 (dd, J ¼ 8:57,
8.57 Hz, 1H), 4.52–4.61 (m, 4H), 4.39–4.50 (m, 1H), 3.58
(t, J ¼ 5:28 Hz, 4H), 3.35 (d, J ¼ 8:25 Hz, 1H), 3.27 (d,
J ¼ 8:90 Hz, 1H); 13C NMR (CDCl3): ꢀ 195.2, 160.8,
158.2, 158.1, 140.2, 137.2, 136.6, 135.0, 114.9, 113.1,
109.0, 106.5, 65.6, 47.6, 45.7, 45.4, 43.2, 27.7, 27.3; Anal.
Calcd for C22H16Br2N2O6: C, 46.84; H, 2.86; N, 4.97%.
Found: C, 47.03; H, 2.95; N, 4.84%.
˚
the reacting quinoid double bonds of 3.5 A, conditions of which
allowed to form a cyclobutane dimer by photodimerization. It is
Published on the web (Advance View) July 15, 2006; doi:10.1246/cl.2006.918