Solid-state photodecarboxylation induced by exciting the CT bands of the complexes of arylacetic acids and 1,2,4,5-tetracyanobenzene

Article abstract of DOI:10.1021/jo951642l

Crystalline charge transfer complexes (3a, 3b, and 3c) of 1- and 2-naphthylacetic and 3-indoleacetic acid (1a, 1b, and 1c) with 1,2,4,5-tetracyanobenzene (2) were prepared by crystallization from the acetonitrile solutions. Irradiation of 3a and 3b gave methylnaphthalenes by decarboxylation and naphthyl(2,4,5-tricyanophenyl)methanes by subsequent dehydrocyanating condensation in the solid state. On the other hand, the photoreactivity of the crystal 3c was low; similar photoreaction occurred only at high temperature. These solid-state reactions are induced by exciting the CT bands of 3a and 3b. The product selectivities were different from those of the solution photoreaction. The relationships between the photoreactivities and the crystal structures of 3a and 3c are discussed.

Full text of DOI:10.1021/jo951642l

2352
J . Org. Chem. 1996, 61, 2352-2357
Solid -Sta te P h otod eca r boxyla tion In d u ced by Excitin g th e CT
Ba n d s of th e Com p lexes of Ar yla cetic Acid s a n d
1,2,4,5-Tetr a cya n oben zen e
Hideko Koshima,*,†,‡ Kuiling Ding,† Yosuke Chisaka,† Teruo Matsuura,† Yuji Ohashi,§ and
Manabu Mukasa§
Department of Materials Chemistry, Faculty of Science and Technology, Ryukoku University, Seta, Otsu
520, J apan, PRESTO, Research Development Corporation of J apan, Faculty of Science and Technology,
Ryukoku University, Seta, Otsu 520, J apan, and Department of Chemistry, Faculty of Science, Tokyo
Institute of Technology, Meguro, Tokyo 152, J apan
Received September 7, 1995X
Crystalline charge transfer complexes (3a , 3b, and 3c) of 1- and 2-naphthylacetic and 3-indoleacetic
acid (1a , 1b, and 1c) with 1,2,4,5-tetracyanobenzene (2) were prepared by crystallization from the
acetonitrile solutions. Irradiation of 3a and 3b gave methylnaphthalenes by decarboxylation and
naphthyl(2,4,5-tricyanophenyl)methanes by subsequent dehydrocyanating condensation in the solid
state. On the other hand, the photoreactivity of the crystal 3c was low; similar photoreaction
occurred only at high temperature. These solid-state reactions are induced by exciting the CT
bands of 3a and 3b. The product selectivities were different from those of the solution photoreaction.
The relationships between the photoreactivities and the crystal structures of 3a and 3c are
discussed.
In tr od u ction
back-electron transfer. However, Suzuki et al. reported
that the CT crystals of arylolefins and bis[1,2,5]thiadiazolo-
tetracyanoquinodimethane caused [2 + 2] photoaddi-
tion.13 We describe here that the preparation and
characterization of the crystalline CT complexes (3a , 3b,
and 3c) of 1- and 2-naphthylacetic and 3-indoleacetic acid
(1a , 1b, and 1c) with 2 and the occurrence of decarboxy-
lation and dehydrocyanating condensation induced by
exciting the CT bands. The correlations of the reactivi-
ties with the crystal structures are discussed.
Photoinduced electron transfer (PET) reactions in
solutions are very important, and large numbers of
examples are known.1 Photodecarboxylations of carboxy-
lic acids in solutions are known to occur via PET, when
acceptors such as acridine and 1,2,4,5-tetracyanobenzene
(2) are present.2-8 In the course of our study of the
photochemistry of the mixed crystals between different
organic molecules,9 we found several photodecarboxyla-
tion reactions which occurred accompanying the reac-
tivities and the product selectivities different from those
of solution reactions. For instance, they are the high
selective decarboxylation of the molecular crystal com-
posed of 3-indoleacetic acid and phenanthridine,10 the
decarboxylating condensation retaining the initial chiral-
ity of the charge transfer (CT) crystal of (S)-(+)-2-(6-
methoxy-2-naphthyl)propanoic acid and 211 and the
decarboxylation of the simple polycrystalline mixtures of
phenylacetic acids and 2.12 It has been thought that CT
complexes give commonly no photoproduct because of the
Resu lts a n d Discu ssion
P r ep a r a t ion a n d Ch a r a ct er iza t ion of t h e CT
Cr ysta ls. The CT crystals 3a -1c were obtained by
crystallizing from the equimolar solution of acids 1a -1c
and tetracyanobenzene 2 in acetonitrile at room temper-
ature. The results of full characterization by powder
X-ray diffractometry (PXD), differential scanning calo-
rimetry (DSC), solid-state 13C CP-MAS NMR, IR, UV, and
elemental analysis are summarized in the Experimental
Section. In the case of 3a and 3c, the crystal structures
were determined by X-ray crystallographic analysis
(Figures 2 and 3).
The compositions of 3a -3c are 1:1 of 1a -1c and 2.
Every melting curve of 3a -3c by DSC was sharp, and
further heating resulted in thermal decomposition. The
CT bands (λwidth) in the solid state measured by a
reflection method are 370-460 nm (3a ), 370-450 nm
(3b), and 370-550 nm (3c). On the other hand, the CT
bands (λmax) in the acetonitrile solutions containing 0.05
M 1a -1c and 0.05 M 2 were observed at 378 nm (1a /2,
ꢀ 20), 382 nm (1b/2, 30), and 350 and 440 nm (1c/2, 40
and 25).
† Ryukoku University.
‡ PRESTO, Research Development Corporation of J apan.
§ Tokyo Institute of Technology.
X Abstract published in Advance ACS Abstracts, March 1, 1996.
(1) Photoinduced Electron Transfer, Part C, Photoinduced Electron
Transfer Reactions: Organic Substrates; Fox, M. A., Chanon, M., Eds.;
Elsevier: Amsterdam, 1988.
(2) Noyori, R.; Kato, M.; Kawanishi, M.; Nozaki, H. Tetrahedron
1965, 25, 1125.
(3) Brimage, D. R. G.; Davidson, R. S.; Steiner, P. R. J . Chem. Soc.,
Perkin Trans. 1 1973, 526.
(4) Libman, J . J . Am. Chem. Soc. 1975, 97, 4139.
(5) Okada, K.; Okubo, K.; Oda, M. J . Photochem. Photobiol. A:
Chem. 1991, 57, 265.
(6) Tsujimoto, K.; Nakao, N.; Ohashi, M. J . Chem. Soc., Chem.
Commun. 1992, 366.
(7) Budac, D.; Wan, P. J . Photochem. Photobiol. A: Chem. 1992, 67,
135.
(8) Albini, A.; Mella, M.; Freccero, M. Tetrahedron 1994, 50, 575.
(9) Koshima, H.; Matsuura, T. Kokagaku 1995, 19, 10.
(10) Koshima, H.; Ding, K.; Matsuura, T. J . Chem. Soc., Chem.
Commun. 1994, 2053.
Acids generally form the dimers with OH‚‚‚O hydrogen
bonds in the crystals.14,15 The CdO bands in the IR
spectra of 3a and 3b shifted to 1700 and 1700 cm-1 from
(11) Koshima, H.; Ding, K.; Chisaka, Y.; Matsuura, T. Tetrahe-
dron: Asymmetry 1995, 6, 101.
(12) Koshima, H.; Ding, K.; Miyahara, I.; Hirotsu, K.; Kanzaki, M.;
Matsuura, T. J . Photochem. Photobiol. A: Chem. 1995, 87, 219.
(13) Suzuki, T.; Fukushima, T.; Yamashita, Y.; Miyashi, T. J . Am.
Chem. Soc. 1994, 116, 2793.
(14) Rajan, S. S. Acta Crystallogr. 1978, B34, 998.
(15) Karle, I. L.; Britts, K.; Gum, P. Acta Crystallogr. 1964, 17, 496.
0022-3263/96/1961-2352$12.00/0 © 1996 American Chemical Society

Solid-State Photodecarboxylation
J . Org. Chem., Vol. 61, No. 7, 1996 2353
F igu r e 1. Solid state 13C CP-MAS NMR spectra of a CT crystal 3a and its components 1-naphthylacetic acid (1a ) and 1,2,4,5-
tetracyanobenzene (2).
1690 and 1695 cm-1 of the component acids 1a and 1b,
respectively, in spite of no change of the OH‚‚‚O bands.
The crystal 3c had the CdO band at 1695 cm-1 and the
NH bands at 3390 cm-1 which are the same as those of
1c, and some other peaks of 3c changed to 1490, 1425,
920, and 765 cm-1 from 1480, 1405, 910, and 760 cm-1
of 1c, respectively.
Figure 1 shows the solid-state 13C CP-MAS NMR
spectra of 3a and its components. The chemical shifts
of the CH2COOH carbons in 3a are almost the same as
those of 1a , while the carbons of the naphthalene ring
and molecule 2 in 3a were considerably shifted to lower
magnetic field by the π-π interaction. Thus, it re-
flects16,17 that 3a has an alternate stacking structure
(Figure 2) different from those of the components 1a 14
and 2.18 The small peaks of the spinning side bands were
observed at 40-60 ppm and 190-220 ppm for 3a , 200-
220 ppm and 40-55 ppm for 1a , and 175-185 ppm and
20-30 ppm for 2.
The fluorescence spectral data of 3a -3c and their
components in the solid state by a front face arrangement
are listed in Table 1. All the fluorescence spectra of the
CT crystals were quite different from those of their
components. Namely, the fluorescence of the components
disappeared and the broad fluorescence peaks at 487 and
481 nm of 3a and 3b, respectively, which were emitted
from their CT excited states, were detected. It may be
due to the smooth energy migration from the higher
excited states to form the CT excited state. The crystal
3c had no fluorescence. We also measured the emission
spectrum of a solution of 1a (0.05 M) and 2 (0.05 M) in
acetonitrile, which had no fluorescence despite that those
of the components in acetonitrile were similar to those
in the solid state, due to the low concentration of the CT
complex equilibrated in the solution.
(16) Byrn, S. T.; Sutton, P. A.; Tobias, B.; Frye, J .; Main, P. J . Am.
Chem. Soc. 1988, 110, 1609.
(17) Koshima, H.; Chisaka, Y.; Wang, Y.; Yao, X.; Wang, H.; Wang,
R.; Maeda, A.; Matsuura, T. Tetrahedron 1994, 50, 13617.
(18) Prout, C. K.; Tickle, I. J . J . Chem. Soc., Perkin Trans. 2 1973,
520.
P h otor ea ction of th e CT Cr ysta ls. The results of
the solid-state photoreaction of the CT crystals 3a -3c

2354 J . Org. Chem., Vol. 61, No. 7, 1996
Koshima et al.
Ta ble 2. Solid -Sta te P h otor ea ction of th e CT Cr ysta ls 3
of Acid s 1 a n d 1,2,4,5-Tetr a cya n oben zen e (2)
conversion yield based on
(%)
consumed 1 (%)
CT
crystal
irrad wavelength irrad temp
(nm)
(°C)
1
2
4
5
3a
3a
3a
3a
3b
3b
3c
3c
3c
3c
>390
>390
>390
>290
>390
>290
>390
>290
>390
>390
-70
-30
15
15
15
15
15
15
60
0
0
0
0
4
30
53
11
25
0
0
0
11
3
20
33
9
15
0
0
0
6
1
65
49
76
58
0
0
0
3
4
34
37
22
28
0
0
0
1
90
Sch em e 2
F igu r e 2. Molecular packing in the crystal 3a .
Ta ble 1. F lu or escen ce Sp ectr a l Da ta of th e CT Cr ysta ls
3 a n d Th eir Com p on en ts in th e Solid Sta te
component and
CT crystal
excitation
(nm)
fluorescence
max (nm)
1-naphthylacetic acid
2-naphthylacetic acid
3-indoleacetic acid
1,2,4,5-tetracyanobenzene
CT crystal
1a
1b
1c
2
3a
3b
3c
275
275
260
275
325
325
275
341, 355
340, 352
317, 328
337, 346, 362, 378
487
CT crystal
CT crystal
481
Sch em e 1
state photoreaction of 3a and 3b initiated by the excita-
tion of the CT complex is shown in Scheme 2, which is
essentially the same as that proposed by Tsujimoto et
al.6 The condensation products 4a and 4b are produced
by the formation of coupled intermediate 8 of a radical
•CH2Ar and an anion radical 7 followed by the elimina-
tion of a cyanide anion. The formation of 5a and 5b is
attributed to the hydrogen transfer between a radical
•CH2Ar and a radical intermediate 9. The irradiation
at -70 °C of the CT crystal 3a did not cause any reaction.
This is understandable if we consider the existence of a
step requiring an activation energy, most probably the
decarboxylating step.
are summarized in Scheme 1 and Table 2. Irradiations
of 3a and 3b with a xenon lamp through a UV cut filter
(>390 nm irradiation) or with a high-pressure mercury
lamp (>290 nm irradiation) at 15 °C gave methylnaph-
thalenes (5a and 5b) by decarboxylation and naphthyl-
(2,4,5-tricyanophenyl)methanes (4a and 4b) by subse-
quent dehydrocyanating condensation. The product
selectivities and the yields with >390 nm irradiation
were comparable to those with >290 nm irradiation.
These results indicate that the reaction is induced by the
excitation of the CT bands and that the light energy of
290-390 nm wavelength region was effectively used for
the CT excitation (Table 1). The pathway of the solid-
Figure 2 illustrates the molecular packing in the
crystal 3a . The parallel and alternate stacking of the
molecules 1a and 2 with a plane to plane distance of 3.4

Solid-State Photodecarboxylation
J . Org. Chem., Vol. 61, No. 7, 1996 2355
Å implies that the π-π interaction has the CT character.
The stacking of the 1a and 2 planes in some orientation
is similar to the CT crystal of naphthalene and 2.19 The
dimeric structure of 1a in 3a is formed through OH---O
hydrogen bonding with the H---O distance of 1.83 Å. The
molecule 1a is weakly connected to the molecule 2 in the
next stacking column through OH---N with the H1---N1
distance of 3.42 Å.
It is understandable from Figure 2 that the CT
excitation occurs the electron transfer from 1a to 2 along
the stacking column to give the radical cation of 1a and
the radical anion 7 (Scheme 2). The shortest •C-C
distance between the decarboxylated radical •CH2Ar and
the phenyl ring of 2 is estimated as 3.75 Å (C1-C2) from
the crystal data. The distance is short enough for the
radical coupling to give the intermediate 8 and subse-
quently to produce 4a . Since the other •C-C distances
are 4.61 Å (C1-C3), 4.62 Å (C1-C4), and 4.68 Å (C1-
C5), the possibilities of the radical coupling are lower.
On the other hand, the production of 5a can be explained
as follows. In spite of the slightly longer H1-C2 distance
of 4.31 Å than that of C1-C2, the active radical cation 7
can abstract H+ to give the intermediate 9, from which
the radical •CH2Ar abstracts the hydrogen atom subse-
quently to produce 5a . Accordingly, these reactions to
give 4a and 5a are competitive.
On the other hand the CT crystal 3c showed less
photoreactivity. Irradiation at lower temperature than
60 °C did not cause any photoreaction and scarcely
caused photoreaction even at 90 °C. The reason for the
low reactivity of the crystal 3c is most probably due to
the back-electron transfer from the intermediate radical-
ion pair. The very slight occurrence of the photoreaction
of 3c at 90 °C may be due to the increase of the electron
transfer and the increase of the thermal motion of the
radicals and the molecules in the crystal 3c.
F igu r e 3. Molecular packing in the crystal 3c.
It should be noted that the crystal structure of 3c
(Figure 3) is somewhat different from that of 3a . The
molecular packing in the crystal of 3c also has parallel
and alternate stacking structures of 1c and 2 molecules
with a plane-to-plane distance of 3.4 Å. The stacking of
the phenyl rings of 1c and 2 generates the π-π interac-
tion and the CT character. The molecules of 1c stack
head to tail in the same column, different from the case
of the crystal 3a having head-to-head arrangement of 1a
(Figure 2). Two molecules of 1c in the adjacent columns
form the dimer structure through OH---O hydrogen
bonding with the H---O distance of 1.70 Å. The molecule
1c has two other weak interactions to the molecule 2.
One is the very weak hydrogen bonding in the same
stacking column through NH---N with the H2---N2
distance of 3.82 Å. Another one is the weak hydrogen
bonding to the the molecule 2 in the next column through
OH---N with the H1---N1 distance of 3.07 Å. The C•-C
distances between the decarboxylated radical •CH2Ar, if
it is formed, and the phenyl ring of 2 (Figure 3) are
estimated to be 4.50 Å (C1-C2), 5.09 Å (C1-C3), 5.34 Å
(C1-C4), 5.39 Å (C1-C5), and 5.61 Å (C1-C6), which
are considerably longer than those in the crystal 3a
(Figure 2) .
Ta ble 3. P h otor ea ction of Acid s 1 w ith
1,2,4,5-Tetr a cya n oben zen e (2) in Aceton itr ile
conversion yield based on
(%) consumed 1
mixture of irrad wavelength irrad time
1 and 2
(nm)
(h)
1
2
4
6
1a /2
>390
>290
>290
>290
>290
24
4
5
24
30
40
90
100
100
74
4
2
37
6
4
10
0
1a /2
79
91
90
76
81
84
62
47
1a /2a
1b/2a
1c/2a
a
Photoreaction in preparative scale.
Similar photocondensation to the solid state occurred to
give 4a -4c as the main products, and in this case, the
aldehydes 6a -6c were produced in low yields (Scheme
1 and Table 3). The reactivity of 1c with 2 was lower
than those of 1a and 1b with 2. It should be emphasized
that no formation of the decarboxylated products 5a -5c
was observed in the solution photoreaction. A similar
observation has been found in the photoreaction of a 1:1
molecular crystal composed of 1c and phenanthridine,10
in which the solid-state photoreaction gave 5c as the sole
product, while the photoreaction in acetonitrile gave
several products including a small amount of 5c. The
excitation by the irradiation at >390 nm of the solution
of 1a and 2 hardly caused the condensation reaction,
giving 4a in only 2% yield. The reason for the inef-
fectiveness is probably the low concentration of the CT
complex 3a equilibrated in the solution.
For a comparison, photoreactions of the solutions of
1a -1c (0.05 M for 1a and 1b and 0.1 M for 1c) and 2
(0.05 M) in acetonitrile were carried out by irradiating
the wavelength region of >290 nm or >390 nm at 15 °C.
The quantum yields (Φ) for the photoreaction of the
CT crystals 3a and 3b at 300-330 nm irradiation were
(19) Kumakura, S.; Iwasaki, F.; Saito, Y. Bull. Chem. Soc. J pn 1967,
40, 1826.

2356 J . Org. Chem., Vol. 61, No. 7, 1996
Koshima et al.
3c: red yellow crystal; mp 212 °C dec 228 °C; 13C CP-MAS
NMR 182, 111-135, 107, 30 ppm; IR (KBr) 3390, 3300-2400,
1695 cm-1; UV 370-450, 370-550 nm (CT bands). Anal.
Calcd for C20H11N5O2 (1:1): C, 67.98; H, 3.14; N, 19.82.
Found: C, 67.66, H, 3.31; N, 20.08.
Ta ble 4. Qu a n tu m Yield s of Solid -Sta te P h otor ea ction of
th e CT Cr ysta ls 3 a n d Solu tion P h otor ea ction of Th eir
Com p on en ts Acid s 1 a n d 1,2,4,5-Tetr a cya n oben zen e (2)a
Φ in CT crystal
Φ in acetonitrilea
CT crystal of 1 and 2
4
5
4
6
Solid -Sta te P h otor ea ction . Twenty mg of the CT crystal
pulverized in a mortar was placed between two Pyrex glass
plates and irradiated with a 400 W high-pressure mercury
lamp (>290 nm irradiation) or a 500 W xenon short arc lamp
with a UV cut filter (>390 nm irradiation) under argon at 15
°C for 24 h. The irradiated sample was methylated with
CH2N2 followed by HPLC analysis (C18 column, methanol-
water). The results are shown in Scheme 1 and Table 2.
P h otor ea ction in Solu tion s. Ten mL of the acetonitrile
solution containing 0.05 M 1a and 0.05 M 2 in a Pyrex test
tube was irradiated under argon with a 400 W high-pressure
mercury lamp for 4 h at 15 °C or with a 500 W xenon short
arc lamp through a UV cut filter for 24 h at 15 °C. The
irradiated solutions were analyzed by HPLC.
For a commom procedure in preparative scale, a solution of
1a -1c (5 mmol or 10 mmol for 1c) and 2 (5 mmol) in 100 mL
of acetonitrile was internally irradiated with a 100 W high-
pressure mercury lamp under argon at room temperature. The
mixture was submitted to filtration and preparative TLC
(silica gel plate) separations. The results are shown in Scheme
1 and Table 3 together with the HPLC analysis.
3a
3b
0.10
0.06
0.043
0.034
0.05
0.23
0.17
0.10
a
Irradiation wavelengths were 300-330 nm and >450 nm.
0.005 M 1 and 0.005 M 2.
b
measured by the thin-layer technique reported by Ito et
al.20 (Table 4). The Φ values for 4a and 5a were
comparable to those of 4b and 5b, respectively. We also
measured the Φ values for 4 and 6 in the acetonitrile
solution of 1 (0.005 M) and 2 (0.005 M) with the usual
merry-go-round technique as shown in Table 4. The Φ
values for 4a and 4b in the solid state are comparable
for those in the solution. Relatively high Φ values for
6a and 6b formation in acetonitrile compared to the final
preparative yields of 6a and 6b (Table 3) are attributable
to their facile production at the early stage of the
photoreaction. The formations of 6a and 6b are ascribed
to result from the participation to the cation-radical
species of water present in the solvent acetonitrile.
In conclusion, the CT excitation of the CT crystals
between 1- and 2-naphthylacetic acid and 1,2,4,5-tetra-
cyanobenzene causes decarboxylation and subsequent
dehydrocyanating condensation to give the methylnaph-
thalenes and the naphthyl(2,4,5-tricyanophenyl)methanes.
1a w ith 2. After irradiation of a solution containing 1a (931
mg) and 2 (891 mg) for 5 h, evaporation of the solvent followed
by filtration gave 1144 mg of a condensation product 4a , which
was recrystallized from acetonitrile to yield white crystals: mp
197-198.5 °C; 1H-NMR (CD3CN) δ 8.28 (s, 1H), 7.16-8.00 (m,
8H), 4.73 (s, 2H); IR (KBr), 3100, 3050, 2230, 1580, 1560, 1490,
915, 796, 776 cm-1; UV λmax (MeCN) 222.8 (log ꢀ 5.14), 259.4
nm (4.53). Anal. Calcd for C20H11N3: C, 81.89; H, 3.78; N,
14.33. Found: C, 82.07; H, 4.01; N, 14.39. The filtrate was
submitted to preparative TLC (benzene as an eluent) to give
an additional 83 mg of 4a and 28 mg of 1-naphthaldehyde 6a
Exp er im en ta l Section
Gen er a l P r oced u r e. 1H NMR spectra were measured on
a 60 MHz J EOL PMX-60 spectrometer with tetramethylsilane
as an internal standard. Solid-state 13C CP/MAS NMR spectra
were taken on a Bruker MSL-200 spectrometer by using
glycine as an external standard. IR spectra were recorded on
a Shimadzu IR-470 spectrophotometer and a J ASCO FT/IR-
8300 spectrophotometer. UV and fluorescence spectra were
measured on a Shimadzu UV-3100 spectrophotometer and RF-
5000 spectrofluorophotometer, respectively. Powder X-ray
diffractograms (PXD) were taken on a Rigaku Geigerflex by
using Cu-target X-ray tube equipped with RAD-C system.
X-ray crystallographic data were obtained using a Rigaku
AFC7R diffractometer with graphite-monochromated Mo KR
radiation and analyzed by teXsan. Differential scanning
calorimetry (DSC) was done on a Rigaku Thermoflex TAS-200
DSC8230D, and melting points (mp) were not corrected.
Elemental analysis was carried out with a Yanaco CHN Corder
MT-5. HPLC with a photodiode array detector were used for
determining the products on a Waters HPLC system. All the
reagents were commercially available.
P r ep a r a tion of CT Cr ysta ls. CT crystals 3a -3c were
prepared by dissolving 1:1 molar mixtures of 1a -1c and 2 in
acetonitrile by gentle heating followed by crystallizing at room
temperature and filtering. The CT crystals were characterized
by PXD, DSC, solid-state 13C CP-MAS NMR, IR, UV, fluorim-
etry, and elemental analysis. The PXD patterns of 3a -3c
were different from those of the components, indicating the
formation of new compounds. Some of the results are shown
in the text, Figure 1, and Table 1.
1
as an oil, and the H-NMR and IR spectra are consistent with
those of an authentic sample. The recovery of 2 was 9%.
1b w ith 2. After irradiation of a solution of 1b (931 mg)
and 2 (891 mg) for 24 h and evaporation of the solvent, 640
mg of 4b was obtained by filtration and recrystallization from
acetone to give white crystals: mp 210.5-211 °C; 1H-NMR
(acetone-d6) δ 8.50 (s, 1H), 8.20 (s, 1H), 7.67-7.93 (m, 4H),
7.30-7.60 (m, 3H), 4.53 (s, 2H); IR (KBr) 3100, 3040, 2950,
2230, 1595, 1540, 1505, 1488, 1380, 1360, 920, 900, 865, 830,
798, 754 cm-1; UV λmax (MeCN) 214.0 (log ꢀ 4.93), 225.8 nm
(5.08). Anal. Calcd for C20H11N3: C, 81.89; H, 3.78; N, 14.33.
Found: C, 81.80; H, 3.96; N, 14.24. The filtrate was submitted
to preparative TLC (benzene as an eluent) to give further 274
mg of 4b and 78 mg of 2-naphthaldehyde 6b, the melting point,
1H-NMR, and IR spectral data of which were identical to those
of an authentic sample. The recovery of 2 was 10%.
1c w ith 2. After irradiation of a solution containing 1c
(1755 mg) and 2 (891 mg) for 30 h, concentration of the solution
to ∼20 mL gave 569 mg of 4c as yellow needles: mp 251-254
°C (with decomposition, from MeCN); 1H-NMR (CD3CN) δ 8.23
(s, 1H), 7.87 (s, 1H), 6.90-7.57 (m, 6H), 4.37 (s, 2H); IR (KBr)
3370, 3100, 3050, 2920, 2240, 1594, 1540, 1488, 1450, 1424,
1335, 1100, 920, 748, 600 cm-1; UV λmax (MeCN) 221.6 (log ꢀ
4.96), 250.8 (4.29), 281.0 nm (3.92). Anal. Calcd for
C18H10N4: C, 76.58; H, 3.57; N, 19.85. Found: C, 76.53; H,
3.73; N, 19.83. The filtrate was submitted to preparative TLC
(hexane-ethyl acetate, 1:1, as an eluent) to give an additional
407 mg of 4c. A trace of 3-indolealdehyde 6c was also
produced. The recoveries of 1c and 2 were 26% and 24%,
respectively.
3a : yellow needle crystal; mp 219 °C dec 242 °C; 13C CP-
MAS NMR 180, 124-136, 116, 37 ppm; IR (KBr) 3400-2400,
1700 cm-1; UV 370-460 nm (CT band). Anal. Calcd for
C22H12N4O2 (1:1): C, 72.51; H, 3.33; N, 15.38. Found: C, 72.62;
H, 3.42, N, 15.28.
3b: yellow needle crystal; mp 212 °C dec 239 °C; 13C CP-
MAS NMR 180, 127-135, 116, 38 ppm; IR (KBr) 3400-2400,
1700 cm-1; UV 370-450 nm (CT band). Anal. Calcd for
C22H12N4O2 (1:1): C, 72.51; H, 3.33; N, 15.38. Found: C, 72.83;
H, 3.45; N, 15.35.
Deter m in a tion of Qu a n tu m Yield . Quantum yield was
determined in a thin-film state basically by the procedure
reported by Ito et al.20 The crystalline thin film was prepared
by addition of a small amount of acetone (0.5 mL) containing
0.05 mmol of the CT crystals in a Pyrex tube (180 × 17 i.d.
mm) and by evaporation of the solvent with a vacuum rotary
(20) Ito, Y.; Matsuura, T.; Fukuyama, K. Tetrahedron Lett. 1988,
29, 3087.

Solid-State Photodecarboxylation
J . Org. Chem., Vol. 61, No. 7, 1996 2357
evaporator. The film was irradiated on a merry-go-round
apparatus with a 400 W high-pressure mercury lamp through
a potassium chromate filter (light transmission, 300-330 nm
and >450 nm) under argon at 15 °C. The irradiation was
stopped at a small conversion (<10%) and the products formed
were analyzed by HPLC. Photocyclization of 2,4,6-triisopro-
pylbenzophenone in benzene (ΦCB ) 0.52) was used as an
actinometer. Quantum yields for the reactions in acetonitrile
were also measured simultaneously with the usual merry-go-
round technique. The results are listed in Table 4.
(MULTAN88) and refined by the full-matrix least-squares
procedure to R ) 0.072 and Rw ) 0.053 for 1566 independent
observed reflections [I > 3.00σ(I)] of total 3504 reflections with
2θ e 50.0°. 3c: monoclinic; P21/n; a ) 9.145(4) Å, b )
16.425(4) Å, c ) 11.903(3) Å, â ) 102.31(2)°; V ) 1747.0(9) Å3;
Z ) 4. The structure was solved by direct methods (SHELXS-
86) and refined by the full-matrix least-squares procedure to
R ) 0.053 and Rw ) 0.071 for 2758 independent observed
reflections [I > 1.50σ(I)] of total 4423 reflections with 2θ e
55.0°.
X-r a y Cr ysta llogr a p h ic An a lysis of th e CT Cr ysta ls.21
3a : triclinic; P1h; a ) 7.890(7) Å, b ) 16.786(8) Å, c ) 7.007(3)
Å, R ) 93.91(4)°, â ) 96.43(5)°, γ ) 90.39(6)°; V ) 919.9(10)
Å3; Z ) 2. The structure was solved by direct method
Ack n ow led gm en t. This work was partly supported
by a Grant-in-Aid for scientific research from the
Ministry of Education, Science and Culture, J apan. One
of the authors (K.D.) is a guest researcher from Zheng-
zhou University, China.
(21) The authors have deposited atomic coordinates for 3a and 3c
with the Cambridge Crystallographic Data Centre. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK.
J O951642L