Thermal and photochemical rearrangements of 3-arylamino-2-phenyl-1H-inden- 1-ones to n-arylphthal-imides

Article abstract of DOI:10.3987/COM-13-12721

Upon heating to above their melting temperatures, 3-arylamino-2-phenyl-1H- inden-1-ones and 2,2′-diphenyl-3,3′-bis(arylimino)-[2,2′- biindan]-1,1′-dione undergo a skeletal rearrangement to afford N-arylphthalimides along with benzoic acid in the presence of atmospheric oxygen. The photoreaction of these compounds in acetonitrile also results in the formation of these products. The mechanism of the reactions, including the formation of a peroxyl radical followed by its conversion to a nitrogen-centered radical, is proposed.

Full text of DOI:10.3987/COM-13-12721

HETEROCYCLES, Vol. 87, No. 6, 2013
1289
HETEROCYCLES, Vol. 87, No. 6, 2013, pp. 1289 - 1299. © 2013 The Japan Institute of Heterocyclic Chemistry
Received, 1st April, 2013, Accepted, 26th April, 2013, Published online, 2nd May, 2013
DOI: 10.3987/COM-13-12721
THERMAL AND PHOTOCHEMICAL REARRANGEMENTS OF
3
-ARYLAMINO-2-PHENYL-1H-INDEN-1-ONES TO N-ARYLPHTHAL-
IMIDES
Masayuki Kawai, Eriko Sakanoshita, Motoko Akita, and Keiji Kobayashi*
Department of Chemistry, Graduate School of Material Science, Josai University,
Keyakidai, Sakado, Saitama 350-0295, Japan; E-mail: kobayak@josai.ac.jp
Abstract
-arylamino-2-phenyl-1H-inden-1-ones and 2,2’-diphenyl-3,3’-bis(arylimino)-
2,2’-biindan]-1,1’-dione undergo skeletal rearrangement to afford
–
Upon heating to above their melting temperatures,
3
[
a
N-arylphthalimides along with benzoic acid in the presence of atmospheric
oxygen. The photoreaction of these compounds in acetonitrile also results in the
formation of these products. The mechanism of the reactions, including the
formation of a peroxyl radical followed by its conversion to a nitrogen-centered
radical, is proposed.
INTRODUCTION
3
3
The homolytic cleavage of carbon(sp )-carbon(sp ) bonds is a fundamental reaction to generate carbon
radicals. The ease of their dissociation is attributed both to steric repulsion around these C-C bonds and
to the resonance stabilization of the dissociated carbon radicals, which may exist in thermal equilibrium
1
with their precursors in solution. In the solid state, the resulting radical pairs usually undergo
recombination because of restricted molecular and atomic displacements in crystalline lattices. Thus, a
2
reversible change in color is induced in the solid state. Such homolytic dissociation of a C-C single
3
4
bond in the solid state is realized thermally as well as by mechanical energy. To develop novel
solid-state thermochromic compounds due to the generation of radical pairs and their recombination, we
designed 2,2’-diphenyl-3,3’-bis(arylimino)-[2,2’-biindan]-1,1’-dione (2) as a potential candidate of such
compounds by the structural modification of 2,2’-diphenyl-[2,2’-biindan]-1,1’,3,3’-tetrone (4) (Scheme 1),
5
which shows mechanochemical dissociation of its central bond with the application of external pressure.
In the course of the preparation of 2, its precursor compounds 3-arylimino-2-phenyl-1H-inden-1-ones
(1a-d) have been found to show a novel thermal reaction in a melt with the participation of atmospheric

1290
HETEROCYCLES, Vol. 87, No. 6, 2013
oxygen. Furthermore, not only thermal but also photochemical reactions of these compounds were
observed. In this paper, we describe novel thermal and photochemical rearrangement reactions of 1, 2
and 3 to afford N-arylphthalimides, which proceed via a stable carbon radical as an intermediate.
Ar
H
Ar
O
O
N
O
N
O
O
O
Ph
Ph
Ph
Ph
Ph
N
O
Ar
a: Ar = C H -
Ar = p-Cl-C H -
1
6
5
2
3
6
4
4
b:
c:
p-Me-C H -
p-MeO-C H -
6 4
Ar = p-MeO-C6H4-
6
4
d:
p-Cl-C H -
6
4
Scheme 1
RESULTS AND DISCUSSION
a-1d were readily obtained by the condensation of 2-phenyl-1,3-indandione with corresponding anilines
1
in the presence of TiCl . On the basis of the results of X-ray crystallographic analyses of 1b and 1c, the
4
resulting condensation products were revealed to take an enamine form rather than an imino form, as
represented by the structural forms of 1b and 1c (Figure 1). The NH hydrogen is hydrogen-bonded
with the neighboring molecule at the carbonyl oxygen to form an infinite chain. The enamine structure
is also retained in solution as proven by the occurrence of the NH proton at 7.2 ppm and by the absence of
the proton attached to the tertiary carbon in its NMR spectra. Such isomeric structures were also
revealed for the other derivatives 1a and 1d, judging from their NMR spectra.
Figure 1. X-Ray structure of 1b: Selected distances [Å] and angles [ ]: N1-C1 1.335(2), C1-C2
1
.394(2), C2-C3 1.446(2), O1-C3 1.234(1), C1-N1-C10 125.5(1), C1-C2-C3 107.6(1), O1-C3-C2 17.8(1).

HETEROCYCLES, Vol. 87, No. 6, 2013
1291
Upon heating the solid samples of 1a-1d up to 250 C, they melted gradually over a wide range,
indicating decomposition. The products of this thermal decomposition were easily identified on the
1
basis of the H NMR spectra of the resulting mixture, which involve signals identical to those of authentic
1
samples of N-arylphthalimide and benzoic acid (Scheme 2). Figure 2 shows the H NMR spectrum of
the reaction mixture from 1b as an example. The product distribution was estimated from the signal
intensities to be approximately 84% N-tolylphthalimide and 75% benzoic acid. Similar reactions were
also observed for the other derivatives to afford the oxidative rearrangement product and benzoic acid in
an approximately 1:1 ratio and with 70-80% yields.
〇
〇
〇
*
*
*
ppm
1
Figure 2. H NMR spectrum of reaction mixture after thermal decomposition of 1b.
N-tolylphthalimide. ＊: Signals of benzoic acid.
○
: Signals of
H
Ar
N
O
O
or h
N Ar
+
Ph
2
CO H
Ph
[
O ]
O
a: Ar = C H -
1
6 5
b:
c:
d:
p-Me-C H -
p-MeO-C H -
p-Cl-C H -
6 4
6
4
6
4
Scheme 2
To gain further insight into the thermal reactions of 1b, thermal analysis by differential scanning
calorimetry (DSC) was carried out within the temperature range from 180 to 330 C in atmospheric and
nitrogen environments. In nitrogen, 1b showed a sharp melting point at 250.8 C with an endothermic
energy of 137.2 J/g. However, in air, the DSC profile changed to a broad endothermic curve with a
maximum heat flow at 248 C. From this DSC profile, it can be seen that the reaction of 1b with

1292
HETEROCYCLES, Vol. 87, No. 6, 2013
oxygen takes place at approximately 245 C and is completed before reaching its intrinsic melting point,
observable in nitrogen. Thus, we assume that a plausible mechanism of these oxidative rearrangements
includes successive ring opening and closure, as shown in Scheme 3. The peroxy radical, formed via the
6
initial hydrogen abstraction by molecular oxygen, could be intramolecularly added to the C=N double
7
bond to yield a new radical with a free valence on the N atom. The conversion of the resulting
8
dioxetane intermediate to diketo compounds has been mentioned in the literature, and the intramolecular
9
addition of a N-centered radical to the carbonyl group to afford a lactam ring has also been reported.
The C2 carbon of the indenone framework is considered to be released as a benzoyl carbon, which can
enter the chain reaction by hydrogen abstraction from the starting compound 1.
Ar
Ar
Ar
Ar
NH
O
N
O
N
O
N
O
O2
O2
O2
O
O
O
Ph
Ph
Ph
Ph
O
1
1
Ph CO
Ph CHO
Ph CO H
2
Ar
N
O
O
O
O
N
Ar
Ph
N
Ar
O
O
Ph
O
O
Scheme 3
With the intention of detecting a possible reaction intermediate, we monitored the reaction using
temperature-dependent IR spectra (Figure 3). The change in the IR spectral profile with the temperature
is in good agreement with that observed in DSC. As noted earlier, the NH hydrogen of 1b in the
crystalline state is hydrogen-bonded with the neighboring molecule at the carbonyl oxygen. Therefore,
-1
the absorption bands at 3250 and 1657 cm are attributed to absorption of the hydrogen-bonded N-H and
C=O, respectively. At the completion of the reaction above 280 C, the N-H absorption band disappears
-1
and the C=O band shifts to a higher wavelength of 1725 cm .
Closer examination of Figure 3 indicates the appearance of new absorption bands at 3470 cm in the NH
-1
-1
region and at 1670 cm in the carbonyl region, both being at wavenumbers higher than those at the outset.
These bands occur transiently in a narrow temperature range at approximately 240 C and are therefore
attributed to molecules of 1 having no intermolecular hydrogen bonds. We can conclude that the
relaxation of the crystalline lattice accompanying the cleavage of intermolecular hydrogen bonds occurs
prior to hydrogen abstraction by oxygen, which is accelerated with increasing temperature and with the
progress of the reaction.

HETEROCYCLES, Vol. 87, No. 6, 2013
1293
(a)
(b)
1
80 o
C
C
180 oC
Abs.
Ab As .b s.
3
30 o
3
30 oC
1850
1800
1700
Wave 1n 8u 5m0 ber /cm-1
1650
３
０００
２８００
３
５００
Wav ３e n０ u０m０ b３e ０r /cm-1
-1
Figure 3. Temperature-dependent FT-IR spectra of 1b in (a) 2800-3500 cm region and (b) 1620-1850
-1
cm region recorded with raising the temperature from 180 to 330 C (2 C/min).
Next, the thermal reactions of 2 and 3 were investigated with the aim of realizing the solid-state cleavage
of the central C-C bond and the recombination of the resulting radicals. The dimeric compounds 2 and 3
were prepared by the oxidative dimerization of 1d and 1c, respectively, using iodine. The diastereomeric
separation of the meso- and dl-forms of 2 was accomplished by column chromatography on silica gel
using benzene as the eluent. The dl isomer was eluted fast, followed by the meso isomer. The isomeric
1
0
structure of dl-2 was determined unambiguously by X-ray crystallographic analysis (Figure 4).
Figure 4. ORTEP drawing of X-ray molecular structures of dl-2. Selected distances [Å], angles [ ],
and torsions [ ]: for dl-2: C1-C16 1.581(3), C1-C10 1.546(3), C16-C25 1.538(3), C1-C16-C25 113.8(2),
1
0
C10-C1-C16 114.8(2), C10-C1-C16-C25 65.0(2), C1-C9-N1-C31 178.0(2), C16-C24-N2-C37 175.9(2).

1294
HETEROCYCLES, Vol. 87, No. 6, 2013
The central C-C bond length of dl-2 (1.581(3) Å) is considerably larger than the lengths of common
3
3
C(sp )-C(sp ) bonds, indicating steric congestion around the central C-C bond. In accord with this
1
observation, H NMR signals assignable to protons at the 2 and 6 positions of the 4-chlorophenyl ring
showed remarkably broad signals at 6.3 ppm to show restricted rotation about the aryl-C bond at room
temperature. The X-ray crystal structural analysis of the isolated 3 showed that it is the dl form.
Contrary to our expectation at the outset, dl-2, meso-2, and dl-3 did not undergo reactions in the solid
state up to 200 C. Upon further heating these compounds displayed a color change from pale yellow to
orange in the solid state and at around 240 C they melted to become dark brown.
The major products were readily identified as N-arylphthalimide from the NMR and mass spectra of the
reaction mixture. Chromatography on silica gel indeed afforded N-arylphthalimide in 43% yield.
There was no appreciable difference in the results between the dl and meso forms. The fate of the C2
carbon atom, which was incorporated in benzoic acid in the thermal reaction of 1, could not be identified
despite considerable effort. Thus, we assume that the benzoyl radical formed according to Scheme 3
could not enter a chain reaction because of the absence of hydrogen in 2 and 3, therefore, more complex
reactions are involved in the fate of the benzoyl radical intermediate.
We also carried out the photoreaction of 2 and 3 to determine whether the C-C bond cleavage could be
induced by photoirradiation. The expected photoreactions did not take place in 2 or 3. On the other
hand, their monomeric precursors 1a-1d exhibited a photoreaction. An acetonitrile solution of 1a was
irradiated for 20 min in an atmospheric environment using a high-pressure mercury lamp through a Pyrex
filter. The NMR and mass spectral analyses of the reaction mixture revealed the formation of
N-arylphthalimide and benzoic acid in 87% and 81% yields, respectively. Similarly, the photoreaction
of 1b-1d under aerobic conditions afforded the corresponding N-(p-substituted-phenyl)phthalimide and
benzoic acid, each with approximately 80% yield, the products being identical to those obtained in the
thermal reactions. When 1a was irradiated in nitrogen atmosphere for 40 min, no reaction was induced,
indicating the intervention of atmospheric oxygen in the photochemical oxidative rearrangement. Thus,
for the photoreaction, the same reaction mechanism as that considered for the thermal reaction could also
be applicable (Scheme 3). Alternatively, taking into consideration the fact that 2-phenyl-1,3-indandione
1
1
affords phthalic anhydride upon photolysis (Scheme 4), a mechanism including Norrish type 1 bond
cleavage followed by ring closure would be possible if the tautomerization from the enamine to imino
form via 1,3-hydrogen migration was photochemically induced (Scheme 4). However, this was not the
case judging from the lack of photoreactivity of 1a in nitrogen atmosphere, as noted above.

HETEROCYCLES, Vol. 87, No. 6, 2013
1295
H
O
O
O
Ph
Ph
H
Ph
h
O
H
O
O
Ar
Ar
Ar
H
NH
O
N
N
O
Ph
Ph
H
Ph
H
Ph
N Ar
O
O
Scheme 4
EXPERIMENTAL
All the decomposition points were determined using a Yanaco MS-500V apparatus and are uncorrected.
12
1
13
The H NMR (400 MHz) and C NMR (100 MHz) spectra were recorded using a Varian spectrometer.
Chemical shifts are given in  values (ppm) using TMS as the internal standard. IR spectra were
recorded on a Shimadzu FTIR-8200PC spectrometer. Mass spectra were taken on a Shimadzu
GCMS-QP5050A mass spectrometer. Elementary combustion analysis was performed using a Yanaco
CHN CORDER MT-6 analyzer. All reactions were monitored by TCL employing a 0.25 mm silica gel
plate (Merck 60F 254). Column chromatography was carried out on silica gel (Merck 60N spherical).
Typical Procedure for the Preparation of 1a. To a stirred solution of 2-phenyl-1,3-indandione (2.00 g,
8
.99 mmol) in chlorobenzene (150 mL), aniline (0.84 g, 8.99 mmol) and small amounts of titanium
tetrachloride (ca. 2 mL) were added at room temperature. The mixture was heated at reflux for 3 h.
Aqueous workup, three times of extraction with CHCl , and drying over anhydrous MgSO afforded a
3
4
reddish solution. After the solvent was removed under reduced pressure, the remaining solids were
chromatographed on silica gel using CH Cl as the eluent to give 1a with 66% yield. The other
2
2
derivatives 1b-1d were prepared in a similar procedure using the corresponding p-substituted anilines
instead of aniline. Further purification was achieved by recrystallization from MeCN.
1
2
3
-Anilino-2-phenyl-1H-inden-1-one (1a): yield 66%. orange needles. decom. temp. 208 C; MS m/z
+
-1 1
2
97 (M ); IR (Nujol) 3232, 1662 cm ; H NMR (CDCl )  6.70 (1H, d, J = 7.2 Hz), 7.07 (2H, d, J = 7.9
3
1
3
Hz), 7.16 (2H, m), 7.21 (1H, s), 7.30-7.22 (6H, m), 7.33 (2H, d, J = 8.2 Hz), 7.51 (1H, d, J = 7.3 Hz); C
NMR (CDCl )  111.05, 120.05, 121.12, 124.51, 125.83, 126.53, 128.44, 128.99, 129.92, 131.21, 131.61,
3
1
34.34, 138.38, 156.77,192.08. Anal. Calcd for C H NO: C, 84.82; H, 5.08; N, 4.71. Found: C, 84.57;
21 15
H, 4.89; N, 4.35.

1296
HETEROCYCLES, Vol. 87, No. 6, 2013
1
2
2
-Phenyl-3-(p-toluidino)-1H-inden-1-one (1b): yield 54%. red needles. decom. temp. 243 C; MS
+
-1 1
m/z 311 (M ); IR 3250, 1657 cm ; H NMR (CDCl )  2.39 (3H, s), 6.63 (1H, d, J = 7.5 Hz), 7.03 (2H, d,
3
J = 8.1 Hz), 7.10 (2H, d, J = 8.1 Hz), 7.16 (1H, t, J = 7.5 Hz), 7.21 (1H, t, J = 7.4 Hz), 7.24 (1H, s, -NH),
13
7
.27 (1H, t, J = 7.0 Hz), 7.34 (2H, t, J = 7.8 Hz), 7.39 (2H, d, J = 8.2 Hz), 7.52 (1H, d, J = 7.0 Hz): C
NMR (CDCl )  21.01, 110.55, 120.50,120.98, 124.93, 126.45, 128.55, 1128.96, 129.57, 131.05, 131.75,
3
1
34.68, 135.59, 136.19, 138.10, 157.67, 191.76. Anal. Calcd for C H NO: C, 84.86; H, 5.50; N, 4.50.
22 17
Found: C, 84.39; H, 5.43; N, 4.21.
1
2
3
-(p-Anisidino)-2-phenyl-1H-inden-1-one (1c): yield 65%. red crystals. decom. temp. 206 C; MS m/z
+
-1 1
3
27 (M ). IR (Nujol) 3228, 1662 cm ; H NMR (CDCl )  3.82 (3H, s), 6.53 (1H, d, J = 7.5 Hz), 6.83
3
(2H, m), 7.10 (2H, m), 7.15 (1H, t, J = 7.5 Hz), 7.20 (1H, s, -NH), 7.21 (1H, t, J = 8.0 Hz), 7.28 (1H, t, J
1
3
=
6.8 Hz), 7.33 (2H, t, J=8.0 Hz), 7.40 (2H, d, J = 7.9 Hz), 7.52 (1H, d, J = 6.8 Hz); C NMR (CDCl ) 
3
5
5.57, 109.79, 114.19, 120.45, 120.98, 126.39, 126.96, 128.58, 128.95, 129.94, 130.94, 130.99, 131.82,
34.89, 137.91, 158.18, 158.28, 191.57. Anal. Calcd for C H NO : C, 80.71; H, 5.23; N, 4.28. Found:
1
2
2
17
2
C, 80.94; H, 5.30; N, 4.02.
1
2
3
-(4-Chlorophenyl)amino-2-phenyl-1H-inden-1-one (1d): yield 54%. red needles. decom. temp. 235
+
-1 1

C; MS m/z 331 (M ); IR (Nujol) 3238, 1662 cm ; H NMR (CDCl )  6.80 (1H, d, J = 7.3 Hz), 6.99 (2H,
3
1
3
d, J = 8 Hz), 7.07 (1H, s, -NH), 7.18-7.35 (9H, m), 7.55 (1H, d, J = 7.0 Hz); C NMR (CDCl ) 119.64,
3
1
1
4
21.37, 125.29, 126.79, 128.47, 128.97, 129.04, 129.30, 129.36, 130.04, 131.13, 131.34, 131.40, 136.83,
38.41, 155.94, 192.20. Anal. Calcd for C H ClNO: C, 76.02; H, 4.25; N, 4.22. Found: C, 75.78; H,
2
1
14
.25; N, 4.15.
Typical Procedure for the Preparation of 2,2’-diphenyl-3,3’-bis(4-chlorophenylimino)-
2,2’-biindan]-1,1’-dione.
To a stirred solution of potassium t-butoxide (0.57 g, 5.08 mmol) in EtOH (120 mL),
-(4-chlorophenyl)amino-2-phenyl-1H-inden-1-one (1d) (1.66 g, 5.02 mmol) was added at 50 C and the
[
3
mixture was stirred for 15-20 min. Iodine (0.69 g, 2.71 mmol) was added to the resulting orange
solution and the mixture was stirred for 1 h at reflux. After quenching with aqueous NH Cl, the organic
4
layer was extracted with CHCl , dried over anhydrous MgSO , and concentrated by evaporation. The
3
4
residual solids were chromatographed on silica gel with CHCl as the eluent. The fraction that eluted
3
fast was recrystallized from MeCN to give the crystalline sample of dl-2 as the 1:1 solvate with MeCN.
The solvent molecules were removed by heating the powdered solids under vacuum to give analytical
pure solvent-free samples. The fraction that eluted more slowly was recrystallized from benzene to give
meso-2.

HETEROCYCLES, Vol. 87, No. 6, 2013
1297
dl-2,2’-Diphenyl-3,3’-bis(4-chlorophenylimino)-[2,2’-biindan]-1,1’-dione (dl-2): yield 24%. yellow
+
-1 1
blocks. mp 226 C; MS m/z 660 (M ); IR (Nujol) 1662, 1728 cm ; H NMR (CDCl )  6.26 (4H, broad
3
doublet), 6.95 (2H, d, J = 7.4 Hz), 7.20 (4H, d, J = 7.9 Hz), 7.31 (2H, t, J = 7.4 Hz), 7.33 (4H, t, J = 7.0
Hz), 7.36 (2H, t, J = 7.0 Hz), 7.49 (2H, t, J = 7.6 Hz), 7.58 (4H, d, J = 7.9 Hz), 7.79 (2H, d, J = 7.6 Hz);
1
3
C NMR (CDCl )  116.92, 122.34, 123.85, 125.15, 126.49, 127.49, 127.59, 127.71, 129.03, 129.92,
3
1
3
31.36, 131.70, 135.36, 140.19, 146.05, 165.57, 193.86. Anal. Calcd for C H Cl N O : C, 76.25; H,
42
26
2
2
2
.96; N, 4.24. Found (for solids desolvated in vacuo): C, 75.98; H, 4.31; N, 4.39.
meso-2,2’-Diphenyl-3,3’-bis(4-chlorophenylimino)-[2,2’-biindan]-1,1’-dione (meso-2): yield 16%.
1
2
+
-1 1
yellow blocks. decom. temp. 223 C; MS m/z 660 (M ); IR (Nujol) 1660, 1733, 1718 cm ; H NMR
(
CDCl )  6.65 (4H, broad d), 6.66 (2H, d, J = 7.6 Hz), 7.2–7.3 (12H, m), 7.46 (2H, t, J = 7.5 Hz), 7.52
3
1
3
(
4H, d, J = 7.4 Hz), 7.88 (2H, d, J = 7.5 Hz); C NMR (CDCl )  118.70, 124.08, 126.61, 126.83, 128.07,
3
1
28.22, 128.30, 128.86, 129.69, 130.94, 132.30, 132.50, 134.25, 149.20. Anal. Calcd for C H Cl N O :
42 26 2 2 2
C, 76.25; H, 3.96; N, 4.24. Found: C, 75.67; H, 4.23; N, 4.40.
dl-2,2’-Diphenyl-3,3’-bis(4-methoxyphenylimino)-[2,2’-biindan]-1,1’-dione (dl-3): yield 35%. yellow
1
2
+
-1 1
blocks. decom. temp. 224 C: MS m/z 652 (M ); IR (Nujol) 1651, 1724 cm ; H NMR (CDCl )  3.80
3
(6H, s), 6.27 (4H, d, J = 8.0 Hz), 6.77 (4H, A B ), 6.99 (2H, d, J = 7.4 Hz), 7.26 (2H, t, J = 7.4 Hz), 7.28
2 2
(
4H, t, J = 7.9 Hz), 7.36 (2H, t, J = 8.0 Hz), 7.44 (2H, t, J = 7.5 Hz), 7.61 (4H, A B ), 7.77 (2H, d, J = 7.5
2
2
1
3
Hz); C NMR (CDCl )  114.60, 118.76, 123.99, 125.79, 126.93, 128.16, 128.32, 131.08, 132.40, 132.67,
3
1
33.28, 137.54, 142.09, 142.90, 156.40, 167.18, 196.29. Anal. Calcd for C H N O : C, 80.96; H, 4.94;
44 32 2 4
N, 4.29. Found (for solids desolvated in vacuo): C, 80.65; H, 4.81; N, 4.32.
The X-ray crystallographic data were collected at on a Rigaku AFC 5S diffractometer, using graphite
monochromated Mo-K radiation (= 0.71075 Å). Crystal data for 1b: C H NO, P2 /n (#14), a =
22
17
1
o
3
3
1
2.895(4), b = 10.479(4), c = 13.222(4) Å, = 114.279(13) , V = 1628.7(9) Å , Z = 4, D = 1.270 g/cm ,
calc
R = 0.0328, wR = 0.0609, GOF = 1.106. Crystal data for 1c: C H NO , Pbcn (#60), a = 9.528(4), b =
1
2
22 17
2
3
3
1
4.187(5), c = 24.920(9) Å, V = 3368.7(21) Å , Z = 8, D = 1.291 g/cm , R = 0.0988, wR = 0.2107,
calc 1 2
GOF = 1.056. Crystal data for dl-2(MeCN): C H Cl N O , P2 /n (#14), a = 13.049(3), b = 13.255(2),
4
4
29
2
3
2
1
o
3
3
c = 20.671(5) Å, = 105.610(9) , V = 3443.3(13) Å , Z = 4, D = 1.355 g/cm , R = 0.0408, wR =
calc
1
2
0
1
0
.0889, GOF = 1.016. Crystal data for dl-3(MeCN): C H N O , P2 /n (#14), a = 12.9391(3), b =
46 35 3 4 1
o
3
3
3.2480(3), c = 20.5249(4) Å,= 103.043(7) , V = 3427.57(11) Å , Z = 4, D = 1.344 g/cm , R =
calc
1
.0607, wR = 0.1540, GOF = 1.040. Crystallographic data have been deposited with the Cambridge
2
Crystallographic Data Centre as the following supplementary publication nos. 1b; CCDC 928984. 1c;
CCDC 928985. dl-2(MeCN); CCDC 928980. dl-3 (MeCN); CCDC 928981. Copies of the data can be

1298
HETEROCYCLES, Vol. 87, No. 6, 2013
obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ UK, (faz:
44-(0)1223-356033 or e-mail: deposit@ccdc.cam.ac.uk).
+
Thermal and Photoreactions
A thermal reaction was carried out on a heating stage (Imoto IMC-0203) by increasing the temperature by
5
C per minute. The resulting mixture was chromatographed on a silica gel columun or directly
subjected to NMR measurement.
A photoreaction was performed for an acetonitrile solution of the sample (0.5 mM) by iradiation with a
high-pressure Hg lamp (Riko UVL-400HA) through a Pyrex filter in an atmospheric environment at 0 C.
After irradiation for 20 min, the solvent was removed under reduced pressure at room temperature. The
resulting mixture was chromatographed on a silica gel columun or directly subjected to NMR
measurement.
The products were identified by referring to the spectra of authentic samples of N-arylphthalimides, all of
which are already known or commercially available. Percent conversion was determined by NMR
analysis of the reaction mixture.
Differential scannibg calorimetry (DSC) was performed on a Rigaku DSC 8230 thermoanalyzer at a
heating rate of 2 C/min using aluminum sample pans. Sample weights were ca 0.6 mg.
Temperature-dependent FT-IR spectra were recorded on a JASCO FT/IR-6100 FTIR spectrometer
equipped with an IR microscope, IRT-5000. The temperature was raised 2 C per minute from 180 C
to 330 C.
REFERENCES AND NOTES
1
. For example: (a) E. Font-Sanchis, C. Aliaga, K. -S. Focsaneanu, and J. C. Scaiano, Chem. Commun.,
2
002, 1576; (b) M. Frenette, C. Aliaga, E. Font-Sanchis, and J. C. Scaiano, Org. Lett., 2004, 6,
579; (c) M. Gomberg, J. Am. Chem. Soc., 1900, 22, 757. This is the classical example of
2
recombination of the carbon-radical pair, but was later disproved by the establishment of its correct
quinonoid structure. See, (d) H. Lankamp, W. Th. Nauta, and C. MacLean, Tetrahedron Lett., 1968,
9
, 249; (e) J. M. McBride, Tetrahedron, 1974, 30, 2009; (f) H. Voltz, W. Lotsch, and H.-W. Schnell,
Tetrahedron, 1970, 26, 5343.
2
. (a) P. Kiri and G. Hyett, Adv. Mater. Lett., 2010, 1, 86; (b) K. Amimoto and T. Kawato, J.
Photochem. Photobiol., 2005, 6, 207; (c) G. Kaupp, CrystEngComm, 2009, 11, 388; (d) E. Hadjoudis
and I. M. Mavridis, Chem. Soc. Rev., 2004, 33, 579.

HETEROCYCLES, Vol. 87, No. 6, 2013
1299
3
. R. W. Baldock, P. Hudson, A. R. Katritzky, and F. Soti, J. Chem. Soc., Perkin Trans. 1, 1974, 1422.
. (a) Y. Mori, N. Yamada, M. Kanazawa, Y. Horikoshi, Y. Watanabe, and K. Maeda, Bull. Chem. Soc.
Jpn., 1996, 69, 2355; (b) K. Maeda and T. Hayashi, Bull. Chem. Soc. Jpn., 1970, 43, 429; (c) J.
Ohkanda, Y. Mori, K. Maeda, and E. Osawa, J. Chem. Soc., Perkin Trans. 2, 1992, 59.
. (a) A. L. Buchachenko, M. V. Motyakin, and I. I. Aliev, in Reactivity of Molecular Solids, ed by. E.
Boldyreva and V. Boldyrev, John Wiley & Sons, Chichester, 1999, pp. 222-239; (b) M. V. Motyakin,
L. M. Pisarenko, P. Schuler, and H. B. Stegmann, Magn. Reson. Chem., 1995, 33, 471.
. K. U. Ingold, Acc. Chem. Res., 1969, 2, 1.
4
5
6
7
. L. M. Postnikov, N. G. Zarubin, E. V. Vichutinskaya, V. Y. Shlyapintokh, N. V. Martynov, and Y. E.
Bryuske, Izv. Akad.. Nauk SSSR, Ser. Khim., 1968, 2, 260.
8
. (a) J. D. Boyd, C. S. Foote, and D. K. Imagawa, J. Am. Chem. Soc., 1980, 102, 3641; (b) H. O. House,
R. J. Outcalt, J. L. Haack, and D. VanDerveer, J. Org. Chem., 1983, 48, 1654; (c) A. Krebs, H.
Schmalstieg, O. Jarchow, and K.-H. Klaska, Tetrahedron Lett., 1980, 21, 3171; (d) Y.-Z. Chen, L.-Z.
Wu, M.-L. Peng, D. Zhang, L.-P. Zhang, and C.-H. Tung, Tetrahedron, 2006, 62, 10688; (e) A. P.
Schaap, R. S. Handley, and B. P. Giri, Tetrahedron Lett., 1987, 28, 935; (f) M. Balcl, Y.
Taskesenliqil, and M. Harnandar, Tetrahedron Lett., 1989, 30, 3339.
9
. S. Kim, G. H. Joe, and J. Y. Do, J. Am. Chem. Soc., 1993, 115, 3328.
1
0. The crystals of dl-2 and dl-3 were isolated as the 1:1 solvates with acetonitrile. The solvent
molecules were readily released thermally or under reduced pressure. The thermal reaction was
conducted using the solvent-free solids.
1
1. J. Rigaudy and P. Derible, Bull. Soc. Chim. Fr., 1965, 3047, 3055, and 3061.
2. This refers to the temperature at which the crystals start to melt with decomposition.
1