Synthesis and photoinitiated isomerizations of 3-(4-nitrophenyl)- and 3-(4-aminophenyl)bicyclo[2.2.1]hepta-2,5-diene-2-carbaldehyde and -2-carboxylic acid derivatives

Article abstract of DOI:10.1023/A:1012325417400

3-(4-Nitrophenyl)bicyclo[2.2.1]hepta-2,5-diene-2-carbaldehyde and its derivatives at the formyl group were synthesized. By reduction of the nitro group the corresponding 3-(4-aminophenyl)-substituted compounds were obtained, as well as 4,4′-bis(bicyclo[2.2.]]hepta-2,5-dien-2-yl)azobenzenes. Irradiation of the resulting norbornadiene derivatives in the region of their absorption maxima resulted in valence isomerization with formation of the corresponding quadricyclanes. The reverse transformations are promoted by molybdenum(VI) oxide as heterogeneous catalyst. 4,4′-Bis(bicyclo[2.2.1]hepta-2,5-dien-2-yl)azobenzenes undergo reversible (on heating) photochemical E/Z isomerization at the N=N bond.

Full text of DOI:10.1023/A:1012325417400

Russian Journal of Organic Chemistry, Vol. 37, No. 1, 2001, pp. 67 71. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 1, 2001,
pp. 77 81.
Original Russian Text Copyright
2001 by Dubonosov, Galichev, Chernoivanov, Bren’, Minkin.
Synthesis and Photoinitiated Isomerizations
of 3-(4-Nitrophenyl)- and 3-(4-Aminophenyl)bicyclo[2.2.1]hepta-
2,5-diene-2-carbaldehyde and -2-carboxylic acid Derivatives*
A. D. Dubonosov, S. V. Galichev, V. A. Chernoivanov, V. A. Bren’, and V. I. Minkin
Research Institute of Physical and Organic Chemistry, Rostov State University,
pr. Stachki 194/2, Rostov-on-Don, 344090 Russia
Received June 2, 2000
Abstract 3-(4-Nitrophenyl)bicyclo[2.2.1]hepta-2,5-diene-2-carbaldehyde and its derivatives at the formyl
group were synthesized. By reduction of the nitro group the corresponding 3-(4-aminophenyl)-substituted
compounds were obtained, as well as 4,4 -bis(bicyclo[2.2.1]hepta-2,5-dien-2-yl)azobenzenes. Irradiation of
the resulting norbornadiene derivatives in the region of their absorption maxima resulted in valence isomeriza-
tion with formation of the corresponding quadricyclanes. The reverse transformations are promoted by
molybdenum(VI) oxide as heterogeneous catalyst. 4,4 -Bis(bicyclo[2.2.1]hepta-2,5-dien-2-yl)azobenzenes
undergo reversible (on heating) photochemical E/Z isomerization at the N N bond.
Photochemical valence isomerization of substituted
norbornadienes into corresponding quadricyclanes
(Scheme 1) attracts interests from the viewpoints of
both its possible application for accumulation of solar
energy [1 4] and study of energy transfer mechanisms
in organic molecules [5, 6].
photoisomerization quantum yield
we synthesized
3-(4-nitrophenyl)bicyclo[2.2.1]hepta-2,5-diene-2-carb-
aldehyde and its derivatives Ia Id, methyl 3-(4-nitro-
phenyl)bicyclo[2.2.1]hepta-2,5-diene-2-carboxylate
(Ie), 3-(4-aminophenyl)-2-dicyanovinylbicyclo[2.2.1]-
hepta-2,5-diene (IIa), and methyl 3-(4-aminophenyl)-
bicyclo[2.2.1]hepta-2,5-diene-2-carboxylate (IIb)
(Table 1). The Z/E photoisomerization shown in
Scheme 2 was studied with 4,4 -bis(3-formylbicyclo-
[2.2.1]hepta-2,5-dien-2-yl)azobenzene (Va) and
4,4 -bis[3-(2-cyano-2-ethoxycarbonylvinyl)bicyclo-
[2.2.1]hepta-2,5-dien-2-yl)azobenzene (Vb).
Scheme 1.
Compounds Ia and Ie were synthesized by the
Diels Alder reaction of cyclopentadiene with the
corresponding substituted acetylenes [1, 3]. Norborna-
diene derivatives Ib Id were prepared from aldehyde
Ia and ethylene glycol, acetophenone, and malono-
nitrile, respectively. The reduction of nitrophenyl-
substituted compounds Id and Ie with iron(II) sulfate
in aqueous ammonia gave 4-aminophenyl derivatives
IIa and IIb. Bis-norbornadiene Va was obtained
by reduction of aldehyde Ia with zinc in alkaline
medium; treatment of Va with ethyl cyanoacetate
afforded bis-norbornadiene derivative Vb. The struc-
ture of products I, II, and V was confirmed by the
I, III, R1 = NO2; R2 = CHO (a), 1,3-dioxolan-2-yl (b),
CH CHCOPh (c), CH C(CN)2 (d), COOCH3 (e); II, IV,
R1 = NH2; R2 = CH C(CN)2 (a), COOCH3 (b).
The efficiency of this process increases when the
long-wave boundary ( ) of absorption of initial
norbornadienes shifts to bthe red region. In continua-
tion of studies on the effect of substituent at the
double bond of norbornadiene on the
value and
b
1
electron absorption, IR, and H NMR spectra. The
electron absorption spectrum of methyl ester IIb is
____________
*
This study was financially supported by the Russian Founda-
tion for Basic Research (projects nos. 98-03-33076 and
00-15-97320).
well consistent with the data reported in [1, 3]. The
presence of an electron-donor substituent (R1 = NH2)
1070-4280/01/3701-0067$25.00 2001 MAIK Nauka/Interperiodica

68
DUBONOSOV et al.
Scheme 2.
V, VI, R = CHO (a), CH C(CN)COOC2H5 (b).
in the phenyl ring leads to a red shift of the long-wave
2-dicyanovinyl-3-(4-nitrophenil)bicyclo[2.2.1]hepta-
2,5-diene (Id) are characterized by anomalously high
quantum yields ( = 0.6 and 0.75, respectively) for
compounds containing an electron-acceptor group
in the phenyl ring at the double bond. Moreover,
despite the presence of electron-donor amino group
(R1 = NH2), the quantum yield for photoisomerization
of 2-(4-aminophenyl)-3-dicyanovinylbicyclo[2.2.1]-
absorption boundary ( = 445 nm) and increases the
b
quantum yield of quadricyclane formation ( = 0.2).
Electron-acceptor substituent (R1 = NO2) affects the
long-wave absorption boundary to a lesser extent
(
= 415 nm), while the quantum yield decreases
tob0.01. The spectral and photochemical parameters
of 3-(4-nitrophenyl)bicyclo[2.2.1]hepta-2,5-diene-2-
carbaldehyde and its derivatives (Table 2) conform to
the above relations only partially.
hepta-2,5-diene (IIa), is as low as 0.1 ( = 620 nm).
b
By analogy with [2], these data may be explained by
the through-space interaction between
orbitals of
Aldehyde Ia and its derivatives Ib Id absorb in
the unsubstituted double bond in Ic and Id and the
other C C bond bearing two electron-acceptor sub-
stituents. In the ground state this interaction is weak,
but it becomes significant in the excited state. As
a result, the quantum yield of the reaction increases.
the region 310 390 nm, and
successively increases
b
from 420 nm for initial aldehyde Ia to 480 nm for
dicyanomethylene derivative Id. As with bicyclo-
[2.2.1]hepta-2,5-diene-2-carboxylic acid derivatives
Ie and IIb, the presence of electron-donor amino
group in the phenyl substituent of IIa gives rise to
Azobenzene derivatives Va and Vb are charac-
a considerable red shift of
of compounds I and II in the region of their long-
wave absorption maxima using a DRSh-250 mercury
(to 620 nm). Irradiation
terized by
values of 500 and 560 nm, respectively
b
b
(Table 2). These compounds give rise to two types of
photochemical processes: E/Z-isomerization at the
N N bond and valence isomerization into the corre-
sponding quadricyclanes. Irradiation of compounds
Va and Vb in weakly polar solvents (e.g., in toluene)
lamp (filtered light;
= 365 nm for Ia, Ib, Ie, and
irr
III; = 436 nm for Ic, Id, and V) changes their
irr
electron absorption spectra which become typical of
quadricyclane structures [1, 3, 4] (see figure). How-
for 3 5 min (
= 365 nm) induces fast E/Z iso-
irr
ever, the quantum yields
in parallel to (Table 2). 2-(2-Benzoylvinyl)-3-
(4-nitrophenyl)bicyclo[2.2.1]hepta-2,5-diene (Ic) and
did not always change
merization which is accompanied by reduction of
the molar absorption coefficient at the long-wave
maximum and by a small blue shift (5 nm) which is
b
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 1 2001

SYNTHESIS AND PHOTOINITIATED ISOMERIZATIONS
69
Table 1. Yields, melting points, and elemental analyses of norbornadiene derivatives I, II, and V
Found, %
H
Calculated, %
Comp.
no.
Yield,
%
mp,
C
Formula
C
N
C
H
N
Ia
Ib
Ic
Id
60
51
30
70
42
25
30
91
57
78
69.82
67.41
76.88
70.70
66.56
78.81
74.87
80.26
75.35
4.55
5.28
4.94
3.93
4.76
5.01
6.17
5.19
5.17
5.93
5.02
4.15
14.47
5.20
16.18
5.92
6.77
9.30
C14H11NO3
C16H15NO4
C22H17NO3
C17H11N3O2
C15H13NO4
C17H13N3
C15H15NO2
C28H22N2O2
C38H32N4O4
69.70
67.36
76.95
70.58
66.41
78.74
74.67
80.36
75.31
4.60
5.30
4.99
3.83
4.83
5.05
6.27
5.30
5.30
5.81
4.91
4.08
14.53
5.16
16.21
5.81
6.70
9.21
130
145
127
Ie
52 53
145 146
105
IIa
IIb
Va
Vb
175
215
typical of such processes [7]. This transformation is
reversible, and the initial E isomers are formed on
heating. Irradiation of compound Va at = 405 nm
or of Vb at = 436 nm leads to formation of quadri-
cyclanes VIa and VIb, respectively; however, the
quantum yields of these transformations are low:
0.025. The electron absorption spectrum of VIb
toluene as eluent and was then recrystallized from
octane. Yield 6 g (60%). Light-yellow crystals. IR
1
spectrum, , cm : 1647, 1594, 1580, 1500, 1340.
1H NMR spectrum, , ppm: 2.10 2.20 m (2H, C7H2),
3.96 m (1H, 4-H), 4.24 m (1H, 1-H), 6.94 m (2H, 5-6,
6-H), 7.56 8.27 m (4H, C6H4), 9.85 m (1H, CHO).
2-[3-(4-Nitrophenyl)bicyclo[2.2.1]hepta-2,5-dien-
2-yl]-1,3-dioxolane (Ib). Aldehyde Ia, 1 g, was dis-
solved in 10 ml of benzene, and 0.26 ml of ethylene
glycol and a few crystals of p-toluenesulfonic acid
(
= 340 nm) is well simulated by the spectrum
ofma4x,4 -dimethylazobenzene (
= 335 nm) [7].
Quadricyclanes VIa and VIb unmdeaxrgo E/Z isomeriza-
tion at the N N bond on irradiation at = 313 nm.
All photochemically generated quadricyclanes (III,
IV, and VI) are stable at room temperature; their
reverse transformation into initial bicyclo[2.2.1]hepta-
2,5-dienes was effected by the procedure described in
[3, 8] using molybdenum(VI) oxide as heterogeneous
catalyst. The rate constant of the reverse reaction was
2
3
1
10 to 10
s
at 21 C.
EXPERIMENTAL
The electron absorption spectra were measured on
a Specord M-40 spectrophotometer. Solutions of nor-
bornadiene derivatives in 2-propanol were irradiated
with a DRSh-250 mercury lamp using a set of light
filters. The IR spectra were recorded from mulls in
1
mineral oil on a Specord 75IR instrument, and the H
NMR spectra were obtained on a Varian Unity 300
spectrometer (300 MHz) in CDCl3.
3-(4-Nitrophenyl)bicyclo[2.2.1]hepta-2,5-diene-
2-carbaldehyde (Ia). 3-(4-Nitrophenyl)-2-propynal,
7.3 g, was dissolved in 50 ml of toluene, and 8 g of
cyclopentadiene was added to the solution. The mix-
ture was refluxed for 4 h, and the solvent was distilled
off under reduced pressure. The residue was purified
by column chromatography on aluminum oxide using
Electron absorption spectra of 2-(2-benzoylvinyl)-3-(4-
nitrophenyl)bicyclo[2.2.1]hepta-2,5-diene (Ic) in 2-propanol
(1) before irradiation, (2) after 0.5-min irradiation, (3) after
2-min irradiation, (4), after 5-min irradiation, and (5) after
15-min irradiation;
= 436 nm.
irr
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 1 2001

70
DUBONOSOV et al.
Table 2. Spectral parameters of norbornadiene derivatives
I, II, and V and quadricyclanes III, IV, and VI
4.24 m (1H, 4-H), 4.77 m (1H, 1-H), 7.09 m (2H,
5-H, 6-H), 7.80 8.37 m (4H, C6H4).
Methyl 3-(4-nitrophenyl)bicyclo[2.2.1]hepta-2,5-
diene-2-carboxylate (Ie). Methyl 3-(4-nitrophenyl)-2-
propynoate, 1.8 g, was dissolved in 40 ml of toluene,
and 1.7 g of cyclopentadiene was added. The mixture
was refluxed for 4 h, and the solvent was removed
under reduced pressure. The residue was purified by
chromatography on aluminum oxide using toluene
hexane (3:1) as eluent. The eluate was evaporated
to obtain 1 g (42%) of product Ie which was recrys-
tallized from heavy petroleum ether. Pale yellow
a
Comp.
no.
,
nm
b, nm Quantum
(I, II, V) yield
b, nm
(III, IV, VI)
max
(
3
10 )
Ia
Ib
Ic
Id
310 (4.5)
420
435
470
480
415
620
445
500
560
0.12
0.05
0.60
0.75
0.01
0.1
0.20
0.025
0.023
390
410
400
340
380
380
330
490
500
328 (13.1)
387 (22.6)
386 (29.8)
322 (15.3)
505 (36.2)
353 (20.7)
381 (16.4)
417 (21.0)
Ie
IIa
IIb
Va
Vb
1
crystals. IR spectrum, , cm : 1713, 1593, 1513,
1
1340. H NMR spectrum, , ppm: 2.13 2.29 m (2H,
C7H2), 3.68 m (3H, OCH3), 3.85 m (1H, 4-H), 4.09 m
(1H, 1-H), 6.95 7.01 m (2H, 5-H, 6-H), 7.63 8.20 m
(4H, C6H4).
a
In 2-propanol.
Methyl 3-(4-aminophenyl)bicyclo[2.2.1]hepta-
2,5-diene-2-carboxylate (IIb). A mixture of 0.87 g
of ether Ie and 6.9 g of iron(II) sulfate in 87 ml of
concentrated aqueous ammonia was heated for 2 h on
a water bath. The product was extracted into toluene,
the extract was dried over anhydrous calcium chloride
and evaporated, and the residue was purified by
chromatography on aluminum oxide using chloroform
as eluent. The product was recrystallized from
methanol. Yield 0.2 g (30%). Yellow powder. IR
were added. The mixture was refluxed for 2.5 h in
a flask equipped with a Dean Stark trap. The solution
was cooled, treated with an aqueous solution of
sodium carbonate, and dried over anhydrous sodium
sulfate. The solvent was removed under reduced pres-
sure, and the residue was purified by chromatography
on aluminum oxide using toluene as eluent. The prod-
uct was recrystallized from methanol. Yield 0.6 g
1
(51%). Pale yellow crystals. IR spectrum, , cm :
1
1
1633, 1585, 1513, 1340. H NMR spectrum, , ppm:
spectrum, , cm : 3440, 3353, 1688, 1633, 1607,
2.06 2.16 m (2H, C7H2), 3.86 4.18 m [6H, 4-H, 1-H,
O(CH2)2O], 5.54 m (1H, OCHO), 6.90 7.00 m (2H,
5-H, 6-H), 7.60 8.25 m (4H, C6H4).
1
1580, 1505. H NMR spectrum, , ppm: 2.00 2.16 m
(2H, C7H2), 3.69 m (3H, OCH3), 3.85 4.02 m (4H,
4-H, 1-H, NH2), 6.65 m (2H, 5-H, 6-H), 7.63 8.20 m
(4H, C6H4).
2-(2-Benzoylvinyl)-3-(4-nitrophenyl)bicyclo-
[2.2.1]hepta-2,5-diene (Ic) was synthesized by the
procedure reported in [9] from aldehyde Ia and
acetophenone. The product was purified by chromato-
graphy on aluminum oxide using toluene as eluent.
3-(4-Aminophenyl)-2-dicyanovinylbicyclo[2.2.1]-
hepta-2,5-diene (IIa) was synthesized as described
above for ester IIb. Violet crystals. IR spectrum, ,
1
1
cm : 3451, 3347, 2193, 1623, 1593, 1511. H NMR
spectrum, , ppm: 2.20 m (2H, C7H2), 3.95 m (1H,
4-H), 4.10 m (2H, NH2), 4.68 m (1H, 1-H), 6.69
7.51 m (7H, C6H4, 5-H, 6-H, CH ).
1
Yellow powder. IR spectrum, , cm : 1647, 1593,
1
1567, 1513, 1340. H NMR spectrum, , ppm: 2.18
2.28 m (2H, C7H2), 4.09 m (1H, 4-H), 4.38 m (1H,
1-H), 7.03 7.08 m (2H, 5-H, 6-H), 7.53 8.32 m (11H,
C6H5, C6H4, 2CH ).
4,4 -Bis(3-formylbicyclo[2.2.1]hepta-2,5-dien-2-
yl)azobenzene (Va). Aldehyde Ia, 0.5 g, was dis-
solved in 20 ml of 2-propanol on heating, and 0.5 ml
of a 30% solution of sodium hydroxide was added.
Zinc powder, 2 g, was slowly added in portions with
stirring, and the mixture was heated for 0.5 h while
stirring. The unreacted zinc was filtered off, and the
filtrate was cooled. The precipitate ( 0.4 g) was
purified by chromatography on aluminum oxide with
toluene as eluent and was recrystallized from 2-pro-
2-Dicyanovinyl-3-(4-nitrophenyl)bicyclo[2.2.1]-
hepta-2,5-diene (Id). Aldehyde Ia, 2 g, was dissolved
in 20 ml of methanol on heating, 0.6 g of malono-
nitrile was added, and the mixture was made slightly
alkaline (pH 8 9) by adding 10 ml of aqueous sodium
carbonate. The mixture was stirred for 0.5 h on
heating and for 0.5 h without heating. The product
was isolated as an orange powder (1.7 g) which was
recrystallized from methanol. Orange needles. IR
panol. Yield 91%. Orange crystals. IR spectrum,
,
1
1
1
spectrum, , cm : 2220, 1600, 1560, 1520, 1340.
cm : 1651, 1593, 1560. H NMR spectrum, , ppm:
1H NMR spectrum, , ppm: 2.32 2.46 m (2H, C7H2),
2.19 2.28 m (4H, C7H2, C7 H2), 4.00 4.22 m (4H,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 1 2001

SYNTHESIS AND PHOTOINITIATED ISOMERIZATIONS
71
1-H, 4-H, 1 -H, 4 -H), 6.95 m (4H, 5-H, 6-H, 5 -H,
6 -H), 7.55 8.42 m (8H, 2C6H4), 9.91 m (2H, 2CHO).
2. Yoshida, Z.I., J. Photochem., 1985, vol. 29, nos. 1 2,
pp. 27 40.
3. Chernoivanov, V.A., Dubonosov, A.D., Popova, L.L.,
Galichev, S.V., Borodkin, G.S., Bren’, V.A., and
Minkin, V.I., Zh. Org. Khim., 1993, vol. 29, no. 11,
pp. 2148 2152.
4,4 -Bis[3-(2-cyano-2-ethoxycarbonylvinyl)bi-
cyclo[2.2.1]hepta-2,5-dien-2-yl]azobenzene (Vb).
Compound Va, 0.3 g, was dissolved in 40 ml of
2-propanol, 0.2 ml of ethyl cyanoacetate and a few
drops of aqueous sodium carbonate were added, and
the mixture was stirred for 2 h under slight heating.
It was then left to stand for 5 h at room temperature,
and 0.25 g of the product was isolated, which was
recrystallized from 2-propanol. Dark red needles. IR
spectrum, , cm : 2220, 1724, 1580. H NMR spec-
trum, , ppm: 1.33 m (6H, 2CH3), 2.26 3.31 m (4H,
2C7H2), 4.00 4.87 m (4H, 1-H, 4-H, 1 -H, 4 -H),
4.30 m (4H, 2CH2), 6.88 7.02 m (4H, 5-H, 6-H, 5 -H,
6 -H), 7.40 8.40 m (10H, 2C6H4, 2CH ).
4. Chernoivanov, V.A., Dubonosov, A.D., Bren, V.A.,
Minkin, V.I., Suslov, A.N., and Borodkin, G.S., Mol.
Cryst. Liquid Cryst., 1997, vol. 297, pp. 239 245.
5. Bonfantini, E.E. and Officer, D.L., J. Chem. Soc.,
Chem. Commun., 1994, pp. 1445 1446.
1
1
6. Tung, C., Zhang, L., Cao, H., and Tanimoto, Y.,
J. Am. Chem. Soc., 1997, vol. 119, no. 23, pp. 5348
5354.
7. Organicheskie fotokhromy (Organic Photochromes),
El’tsov, A.V., Ed., Leningrad: Khimiya, 1982, ch. 3,
p. 131.
8. Hirao, K., Yamashita, A., and Yonemitsu, O., Tetra-
hedron Lett., 1988, vol. 29, pp. 4109 4112.
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Chernoivanov, V.A., Usp. Khim., 1991, vol. 60, no. 5,
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 1 2001