Reaction of o-phenylenediamine with 2,3-dichloromaleic anhydride: Synthesis of N-substituted maleimide derivatives and 2,3-dichloropyrrolo[1,2-a] benzimidazol-1-one. X-ray structures of 2,3-dichloro-N-o-C6H 4(NH2)maleimide

Article abstract of DOI:10.1007/s10870-004-7651-2

Refluxing equimolar amounts of 2,3-dichloromaleic anhydride and o-phenylenediamine in toluene affords the three compounds 2,3-dichloro-N-o- C₆H₄(NH₂)maleimide (1), N,N′-o-C ₆H₄-bis(2,3-dichloromaleimi

Full text of DOI:10.1007/s10870-004-7651-2

Journal of Chemical Crystallography, Vol. 34, No. 11, November 2004 (ꢀC 2004)
Reaction of o-phenylenediamine with 2,3-dichloromaleic
anhydride: synthesis of N-substituted maleimide derivatives
and 2,3-dichloropyrrolo[1,2-a]benzimidazol-1-one. X-ray
structures of 2,3-dichloro-N-o-C6H4(NH2)maleimide and
N, Nꢀ-o-C6H4-bis(2,3-dichloromaleimide)
William H. Watson,(1)∗ Guanmin Wu,(2) and Michael G. Richmond(2)∗
Received June 20, 2003
Refluxing equimolar amounts of 2,3-dichloromaleic anhydride and o-phenylenediamine in
toluene affords the three compounds 2,3-dichloro-N-o-C6H4(NH2)maleimide (1), N,Nꢁ-o-
C6H4-bis(2,3-dichloromaleimide) (2), and 2,3-dichloropyrrolo[1,2-a]benzimidazol-1-one
(3). Under these conditions the former compound is observed as the major product.
Repeating the same reaction in the presence of added PTSA furnishes the heterocyclic
compound 2,3-dichloropyrrolo[1,2-a]benzimidazol-1-one, as the major product. Treatment
of compound 1 with PTSA, coupled with water removal, gives compound 3 in near quanti-
tative yield and confirms the intermediacy of 1 en route to 3. The new compounds 1–3
have been isolated by column chromatography and characterized in solution by spec-
troscopic methods. The molecular structures of the maleimide-substituted compounds 1
and 2 were determined by X-ray crystallography. 2,3-Dichloro-N-o-C6H4(NH2)maleimide
˚
˚
crystallizes in the monoclinic space group P21/c, a = 20.693(8) A, b = 5.712(2) A,
c = 8.787(4) A, β = 92.819(7) , V = 1037.3(7) A , Z = 4, and dcalc = 1.646 Mg/m3;
◦
3
˚
˚
R = 0.0604, Rw = 0.1140 for 1354 reflections with I > 2σ(I), with N,Nꢁ-o-C6H4-
˚
◦
bis(2,3-dichloromaleimide) crystallizing in the triclinic space group P-1, a = 7.9509(4) A,
◦
◦
˚
˚
˚
b = 10.2532(6) A, c = 12.1126(7) A, α = 82.637(1) , β = 87.799(1) , γ = 71.634(1) ,
V = 929.42(9) A , Z = 2, and dcalc = 1.651 Mg/m3; R = 0.0499, Rw = 0.1545 for 1977
3
reflections with I > 2σ(I).
KEY WORDS: Amine condensation reactions; maleimide heterocycles; pyrrolo[1,2-a]benzimidazol-1-one.
N-substituted maleimides.1 However, in the case
of 2,3-dichloromaleic anhydride and its reac-
tion with primary amines, both maleimide for-
mation and the direct nucleophilic substitution at
the activated vinyl carbons of 2,3-dichloromaleic
Introduction
The simple condensation reaction of maleic
anhydride with primary amines is known to give
(1) Department of Chemistry, Texas Christian University, Fort Worth,
TX 76129.
∗
(2) Department of Chemistry, University of North Texas, Denton,
TX 76203.
To whom correspondence should be addressed at: e-mails:
w.watson@tcu.edu; cobalt@unt.edu.
757
ꢀ
C
1074-1542/04/1100-0757/0 2004 Springer Science+Business Media, Inc.

758
Watson, Wu, and Richmond
anhydride by an addition–elimination sequence
represent plausible reaction pathways. The for-
mation of the corresponding N-substituted 2,3-
dichloromaleimide is universally observed as the
initial product of such reactions, followed by the
replacement of one of the chlorines.2 Only under
forcing conditions will the second chlorine group
experience a substitution with added amine. The
continued study of such reactions derives from the
use of these materials as platforms for the con-
struction of highly conjugated chromophores and
heterocyclic compounds of biological interest.3
We have recently studied the reactions of 2,3-
dichloromaleic anhydride with aniline and p-
toluidine and have presented evidence showing
that the anhydride/amine condensation reaction
occurs prior to any chloride displacement.4 Equa-
tion 1 depicts our findings for the reaction be-
tween 2,3-dichloromaleic anhydride and the latter
amine.4b
Wishing to extend our studies on the
synthesis of redox-active bidentate ligands
based on maleic anhydride, we have studied
the reaction of 2,3-dichloromaleic anhydride
with o-phenylenediamine. Herein, we report the
details associated with this reaction and the isola-
tion of 2,3-dichloro-N-o-C6H4(NH2)maleimide
(1), N,Nꢁ-o-C6H4-bis(2,3-dichloromaleimide)
(2), and 2,3-dichloropyrrolo[1,2-a]benzimidazol-
1-one (3). The structural characterization of
compounds 1 and 2 by X-ray crystallography
is presented, and the role of hydrogen bonding
in controlling the packing architecture of 2,3-
dichloro-N-o-C6H4(NH2)maleimide in the unit
cell is described.
Experimental section
General
The compounds o-phenylenediamine, 2,3-
dichloromaleic anhydride, and p-toluenesulfonic
acid (PTSA) were purchased from Aldrich Chem.
Co. and were used as received. All reaction and
spectroscopy solvents were of reagent grade and
usedasreceived. Thereportedmeltingpointswere
recorded on a Meltemp apparatus and are uncor-
rected.
The reactivity of maleic anhydride with the
difunctional amines o-phenylenediamine and 1,8-
diaminonaphthalene has also been studied over
the years.5 Here the corresponding maleimide
compound, which is expected as the initially
formed product, is often followed by a sec-
ond condensation reaction involving the pendant
amine group and one of the two maleimide car-
bonyl groups to afford heterocyclic compounds
based on pyrrolo[1,2-a]benzimidazol-1-one and
pyrrolo[1,2-a]perimidin-10-one. Equation 2 illus-
trates the net sequence for the reaction between
maleic anhydride and o-phenylenediamine.
Routine infrared spectra were recorded on
aNicolet 20 SXB FT-IR spectrometer in 0.1 mm
NaCl cells, using PC control and OMNIC soft-
1
ware, while the H and 13C NMR spectra were
recorded at 200 and 50 MHz, respectively, on
a Varian Gemini-200 spectrometer. The UV-vis
spectrum was collected on a Hewlett-Packard
8425A diode array spectrophotometer in a 1.0 cm
quartz cell.

Reaction of o-phenylenediamine with 2,3-dichloromaleic anhydride
759
Synthesis of 2,3-dichloro-N-o-C6 H4(NH2)
maleimide
values of 2 and 3 that complicated the chromato-
graphic separation over silica gel, we employed an
HCl work-up procedure that selectively extracted
compound 3 from 2 by using concentrated
HCl. The isolation of the 2 was subsequently
achieved by column chromatography over silica
gel using CH2C12 as the eluent. Yield of 2: 0.98 g
(40% yield), mp: 197–198◦C. IR (CH2C12):
ν(CO) 1803 (w, symm, maleimide), 1750 (vs,
To 0.65 g (6.00 mmol) of o-phenylene-
diamine and 1.00 g (6.00 mmol) of 2,3-
dichloromaleic anhydride in a reflux apparatus
equipped with a Dean-Stark trap was added
100 mL◦ of toluene. The reaction was heated
at 110 C for ca. 5 h, with the water that was
produced being periodically removed. After
the solution was allowed to cool to room tem-
perature, the crude solution was examined by
TLC analysis in CH2C12, which revealed the
presence of compound 1 as the major product
(Rf = 0.38), along with a small amounts of
2 (Rf = 0.70) and 3 (Rf = 0.63). The toluene
was removed under vacuum the N,Nꢁ-o-
1
asymm, maleimide) cm−1. H NMR (CDC13):
δ 7.46 (4H, aromatic). 13C NMR (CDC13): δ
127.16 (C N aromatic), 129.39 (CH aromatic),
130.18 (CH aromatic), 133.78 (C Cl), 160.89
(maleimide CO). UV-vis (CH2C12): Amax 229
(ꢀ = 13000).
C6H4-bis(2,3-dichloromaleimide)
and
2,3-
Synthesis of 2,3-dichloropyrrolo[1,2-a]
benzimidazol-1-one
dichloropyrrolo[1,2-a]benzimidazol-1-one were
isolated by column chromatography (<5%
each) over silica gel using CH2Cl2/hexane (1:1
ratio) as the eluent. Changing the eluent to
CH2C12 subsequently afforded 2,3-dichloro-N-
o-C6H4(NH2)maleimide. Compound 1: 0.83 g
To 1.00 g (6.00 mmol) of 2,3-dichloromaleic
anhydride and 0.65 g (6.00 mmol) of o-pheny-
lenediamine in a reflux apparatus equipped with
a Dean-Stark trap was added 100 mL of toluene
and 100 mg of PTSA. The reaction was heated
◦
(yield: 53%). mp: 157–158 C. IR (CH2C12):
◦
v(CO) 1798 (w, symm, maleimide), 1739 (vs,
asymm, maleimide) cm−1. 1H NMR (DMSO-d6):
δ 5.45 (b, NH2), 6.50 (t, JH–H = 7.9 Hz), 6.84
(d, JH–H = 7.9 Hz), 7.04 (d, JH–H = 7.9 Hz),
7.18 (t, JH–H = 7.9 Hz). 13C NMR (DMSO-d6):
δ 114.48 (C N aromatic), 115.31 (CH aromatic),
129.91 (CH aromatic), 130.26 (CH aromatic),
132.77 (C Cl), 146.62 (C NH2 aromatic),
162.49 (maleimide CO). UV-vis (CH2C12): Amax
288 (ꢀ = 5200), 237 (ꢀ = 29000).
at 110 C for 2 h, with water removal. After the
reaction solution was allowed to cool to room
temperature, TLC examination revealed the
presence of compound 3 as the major product, in
addition to a small amount (<5%) of compound
2. The toluene was removed under vacuum
and 2,3-dichloropyrrolo[1,2-a]benzimidazol-1-
one was subsequently isolated by column chro-
matography over silica gel using CH2C12 as
the eluent. Compound 3: yield 1.22 g (86%).
mp: 170–172◦C. IR (CH2C12): ν(CO) 1787 (m),
1
1769 (s) cm−1. H NMR (DMSO-d6): δ 7.29 (t,
Synthesis N,Nꢁ-o-C6H4-bis(2,3-dichloro-
maleimide).
JH–H = 7.9 Hz), 7.41 (t, JH–H = 7.9 Hz), 7.56
(d, JH–H = 7.9 Hz), 7.72 (d, JH–H = 7.9 Hz). 13
C
NMR (DMSO-d6): δ 111.64 (C H aromatic),
121.85 (C H aromatic), 124.85 (C H aromatic),
127.74 (C H aromatic), 130.16 (C Cl), 130.67
(C Cl), 133.29 (C N amine, aromatic), 147.05
(C N imine, aromatic), 153.76 (C N imine),
155.18 (carbonyl). UV-vis (CH2C12): λmax 350
(ꢀ = 3200), 260 (ꢀ = 12000), 229 (ꢀ = 15000).
The bis-maleimide compound 2 and the
heterocyclic compound 3 were synthesized
in good yield utilizing the same procedure
described above, except that the amount of
2,3-dichloromaleic anhydride employed was in-
creased two-fold. Given the extremely close Rf

760
Watson, Wu, and Richmond
condensation of the free amine moiety with
one of the two maleimide carbonyl groups to
furnish the heterocycle 2,3-dichloropyrrolo[1,2-
a]benzimidazol-1-one (3).9 Alternatively, the
synthesis of 3 may also be achieved directly from
the treatment of isolated 1 with added PTSA.
Under such conditions, compound 3 is obtained
in essentially quantitative yield. Compounds
1–3, whose structures are shown below, were all
isolated in their pure state by column chromatog-
raphy over silica gel and characterized in solution
by IR, NMR, and UV-vis spectroscopies.
X-ray diffraction structures of 2,3-dichloro-
N-o-C6 H4(NH2)maleimide and N,Nꢁ-o-C6 H4-
bis(2,3-dichloromaleimide)
Single crystals of 1 and 2 suitable for X-ray
crystallography were obtained from a CH2C12 so-
lution containing each compound that had been
layered with hexane. X-ray data were collected
on a Bruker SMART1000 CCD-based diffrac-
tometer at 213 K. The frames were integrated
with the available SAINT software package us-
ing a narrow-frame algorithm,6 and the structure
of each compound was solved and refined using
the SHELXTL program package.7 The molecu-
lar structures were checked by using PLATON.8
All non-hydrogen atoms were refined anisotropi-
cally. Refinement for 1 converged at R = 0.0604
and Rw = 0.1140 for 1354 independent reflec-
tions with I > 2σ(I), with 2 giving convergence
values of R = 0.0499 and Rw = 0.1545 for 1977
independent reflections with I > 2σ(I).
The IR spectrum of 1 in CH2C12 displays
two, kinematically coupled ν(CO) stretches at
1798(vw) and 1739(s) cm−1, which are readily
assignable to symmetric and antisymmetric
carbonyl stretches belonging the maleimide
moiety.10 In comparison, the IR spectrum of 2 is
virtually identical to that of 1, except for the fact
that the maleimides carbonyl groups are found
at slightly higher energy (1803 and 1750 cm−1).
The lower frequencies found in the ν(CO)
bands of 1 relative to 2 are due to the electron
donating properties of the NH2 group in 1, which
causes a low-energy shift in the two maleimide
Discussion
Synthesis and spectroscopic data
Refluxing a toluene solution containing
equimolar amounts of o-phenylenediamine and
2,3-dichloromaleic anhydride gives the com-
pounds 2,3-dichloro-N-o-C6H4(NH2)maleimide
(1), N,Nꢁ-o-C6H4-bis(2,3-dichloromaleimide)
(2), and 2,3-dichloropyrrolo[1,2-a]benzimidazol-
1-one (3). Here, the former compound is observed
as the major product. The double condensation
product 2 is produced in near quantative yield
when a 1:2 mole ratio of o-phenylenediamine
and 2,3-dichloromaleic anhydride is employed.
The effect of added PTSA on the product
distribution was also explored. The PTSA-
catalyzed reaction between equimolar amounts
of o-phenylenediamine and 2,3-dichloromaleic
anhydride in refluxing toluene proceeds to
initially give the simple condensation product 1,
as verified by TLC monitoring of the reaction
solution, followed by a relatively rapid second
1
carbonyl stretches. The H NMR spectrum of 1
in DMSO-d6 reveals a simple first-order ABCD
spectral pattern11 for the aromatic protons that
is comprised of two doublet and two triplet
resonances, in addition to a broad NH2 moiety
that was recorded at δ 5.50. Treatment of the
sample with D2O confirmed the identity of this
1
latter resonance. The H NMR spectrum of 1 in
CDC13 exhibits a 10-line spectral pattern for the
aromatic hydrogens that is centered at δ 7.46 and
that is best described by an AAꢁBBꢁ spin system.
The 13C NMR spectrum of 1 reveals seven of

Reaction of o-phenylenediamine with 2,3-dichloromaleic anhydride
761
the eight expected 13C resonances. The four
non-protonated carbon resonances at δ 114.48
(C N, aromatic), 132.77 (C Cl), 146.62
(C NH2, aromatic), and 162.49 (maleimide
CO) have been confidently assigned by chemical
shift considerations in conjunction with the 13C
NMR data obtained from an APT experiment.12
Compound 1 displays three of the four expected
protonated aryl carbons at δ 115.31, 129.91, and
130.26, whose relative intensities indicate that
the former resonance results from the accidental
degeneracy of two of the aryl carbon atoms. The
13C NMR spectrum of 2 is straightforward in
terms of revealing all six of the expected 13C
resonances, with the assignments presented in
the experimental section.
The IR spectrum of 2,3-dichloropyrrolo[1,2-
a]benzimidazol-1-one is interesting in that the
stretches at 1787 and 1769 cm−1 are the result
of the carbonyl and imine groups; however, no
definitive assignment can be may concerning the
frequency of these two moieties given their con-
jugation with the extended π system in 3.13 The
ABCD spin system associated with the 1H NMR
spectrum of 3 in DMSO-d6 exhibits two high-
field triplets at δ 7.29 and 7.41, with the low-
field doublets at 7.56 and 7.72. The 10 symmetry
unique carbons are all observed in the 13C NMR
spectrum of 3. While the unequivocal identity for
each of the 13C resonances cannot be made at this
time with certainty, the carbon atoms that can be
assuredly assigned are depicted below. These
chemical shift assignments are based on struc-
turally similar maleimide compounds prepared by
us,5 consideration of substituent effects in related
benzimidazole systems,14 and NMR data from
1H-13C HETCOR experiments.15
Table 1. X-ray Crystallographic Data and Processing Parameters
for 2,3-dichloro-N-o-C6H4(NH2)maleimide (1) and N,Nꢁ-o-C6H4-
bis(2,3-dichloromaleimide) (2)
Compound 1
Compound 2
CCDC entry no.
Space group
212899
Monoclinic,
P21/C
212898
Triclinic, P-1
˚
a (A)
20.693(8)
5.712(2)
8.787(4)
7.9509(4)
10.2532(6)
12.1126(7)
82.637(1)
87.799(1)
71.634(1)
929.42(9)
˚
b (A)
˚
c (A)
α (◦)
β (◦)
92.819(7)
1037.3(7)
γ (◦)
3
˚
V (A )
Molecular formula
fw
Formula units per
cell (Z)
Dcalcd (Mg/m3)
C10H6Cl2N2O2 C14H4C14N2O4
257.07
4
462.10
2
1.646
1.651
˚
λ (MoKcc, A)
0.71073
0.609
0.71073
0.666
Absorption coeff
(mm−1
)
Rmerge
0.133
0.042
Abs corr factor
Total reflections
0.1948/0.1241
4111
0.4068/0.3125
4681
Independent reflections
1354
1977
Data/res/parameters
R
1354/0/146
0.0604
1977/0/242
0.0499
Rw
0.1140
0.1545
GOF
Weights
0.958
1.078
[0.04F2+
[0.04F2+
(σF)2]−1
(σF)2]−1
X-ray diffraction structures
The molecular structures of 2,3-dichloro-N-
o-C6H4(NH2)maleimide (1) and N,Nꢁ-o-C6H4-
bis(2,3-dichloromaleimide) (2) were established
by X-ray diffraction analysis. Single crystals of 1
and 2 were found to exist as discrete molecules in
the unit cell with no unusually short inter- or in-
tramolecular contacts. The X-ray data collection
and processing parameters are listed in Table 1,
with Table 2 containing selected bond distances
and angles.
The thermal ellipsoid drawing of 2,3-
dichloro-N-o-C6H4(NH2)maleimide (1) is shown
in top portion of Fig. 1 and confirms the sin-
gle condensation step that has taken place be-
tween the 2,3-dichloromaleic anhydride and o-
˚
phenylenediamine. The C(l) C(2) [1.518(9) A]

762
Watson, Wu, and Richmond
Table 2. Selected Bond Distances (A) and Angles (deg) in 2,3-Dichloro-N-o-C6H4(NH2)maleimide
and N,Nꢁ-o-C6H4-bis(2,3-Dichloromaleimide)a
2,3-Dichloro-N-o-C6H4(NH2)maleimide
Bond distances
Cl(l) C(2)
N(l) C(l)
N(l) C(5)
C(l) C(2)
C(3) C(4)
1.697(7)
1.382(9)
1.468(8)
1.518(9)
1.540(9)
Cl(2) C(3)
N(l) C(4)
N(2) C(10)
C(2) C(3)
1.683(7)
1.389(9)
1.309(9)
1.318(9)
Bond angles
C(l) N(l) C(4)
C(4) N(l) C(5)
C(3) C(2) C(l)
C(1) C(2) C1(1)
C(2) C(3) C1(2)
N(l) C(4) C(3)
112.9(6)
122.4(6)
109.2(6)
120.8(5)
129.8(6)
104.2(6)
C(l) N(l) C(5)
N(l) C(l) C(2)
C(3) C(2) C1(1)
C(2) C(3) C(4)
C(4) C(3) C1(2)
124.1(6)
105.1(6)
130.0(6)
108.7(6)
121.6(5)
N,Nꢁ-o-C6H4-bis(2,3-Dichloromaleimide)
Bond distances
Cl(l) C(2)
Cl(3) C(12)
N(l) C(l)
N(l) C(5)
N(2) C(ll)
C(l) C(2)
C(3) C(4)
C(12) C(13)
1.687(5)
1.698(5)
1.391(6)
1.436(6)
1.400(6)
1.501(6)
1.504(7)
1.330(7)
Cl(2) C(3)
Cl(4) C(13)
N(l) C(4)
N(2) C(14)
N(2) C(6)
C(2) C(3)
C(ll) C(12)
C(13) C(14)
1.683(5)
1.697(5)
1.395(6)
1.396(6)
1.429(6)
1.328(7)
1.485(7)
1.486(7)
Bond angles
C(l) N(l) C(4)
C(4) N(l) C(5)
C(14) N(2) C(6)
N(l) C(l) C(2)
C(3) C(2) C1(1)
C(2) C(3) C(4)
C(4) C(3) C1(2)
N(2) C(ll) C(12)
C(13) C(12) C1(3)
C(12) C(13) C(14)
C(14) C(13) C1(4)
110.9(4)
123.6(4)
125.3(4)
105.7(4)
129.4(4)
108.5(4)
121.0(4)
105.6(4)
129.6(4)
109.1(4)
122.3(3)
C(l) N(l) C(5)
125.1(4)
110.6(4)
123.9(3)
109.1(4)
121.5(3)
130.5(4)
105.7(4)
109.0(4)
121.4(4)
128.6(4)
105.7(4)
C(14) N(2) C(ll)
C(ll) N(2) C(6)
C(3) C(2) C(l)
C(1) C(2) C1(1)
C(2) C(3) C1(2)
N(l) C(4) C(3)
C(13) C(12) C(ll)
C(11) C(12) C1(3)
C(12) C(13) C1(4)
N(2) C(14) C(13)
aNumbers in parentheses are estimated standard deviations in the least significant digits.
˚
and C(3) C(4) [1.540(9) A] C C single-bond
(1) depicted in Fig. 2 shows the structural motif
adopted by compound 1 as a result of the pen-
dant amine group and its intermolecular hydro-
gen bonding with the atoms of O(1) and O(2) of
different molecules of 1. Here the N(2) H(2)· · ·
O(1) interaction exhibits N H, H· · ·O, and
˚
distances and the C(2) C(3) [1.318(9) A] bond
length for the C C π bond exhibit acceptable
values for C C and C C bond lengths.4,5d,16 The
four different C N distances range from 1.309(9)
˚
˚
[N(2) C(10)] to 1.468(8) A [N(l) C(5)], with an
˚
average length of 1.387 A, which is consistent
N· · ·O distances of 0.87, 2.50, and 3.142(8) A,
with the nature of these linkages.4,16 The planar
five-membered ring forms an interplanar angle of
68.8(4)◦ with the phenyl ring. The packing dia-
gram of 2,3-dichloro-N-o-C6H4(NH2)maleimide
respectively, with an accompanying bond an-
gle of 130◦. The other significant intermolec-
ular hydrogen-bonding interaction involves the
N(2) H(2)· · ·O(2) atoms, with N H, H· · ·O,

Reaction of o-phenylenediamine with 2,3-dichloromaleic anhydride
763
Fig. 2. Packing diagram for 2,3-dichloro-N-o-C6H4(NH2)
maleimide (1).
Fig. 1. Thermal ellipsoid plots of 2,3-dichloro-N-
o-C6H4(NH2)maleimide (top) and N,Nꢁ-o-C6H4-bis(2,3-
dichloromaleimide) (bottom). Both plots display the thermal
ellipsoids at the 30% probability level.
angles of 59.9(3)◦ and 63.1(3)◦ with the phenyl
ring and are canted 60.8(3)◦ relative to each
other. There are three intermolecular interac-
tions involving Cl atoms that are significantly
shorter than the sum of the Van der Waals dis-
˚
˚
N· · ·O distances of 0.87, 2.41, and 3.131(8) A,
tances: C1(2)· · ·O(3) [3.073(3) A], Cl(3)· · ·O(l)
respectively, with a bond angle of 140◦ observed.
The remaining bond distances and angles in 1 are
unexceptional and do not require comment.
˚
˚
[3.052(3) A], and Cl(4)· · ·O(3) [2.972(4) A]. The
remaining bond distances and angles in 2 are
unremarkable, requiring no further comments.
The double condensation reaction between
one molecule of o-phenylenediamine and two
molecules of dichloromaleic anhydride is con-
firmed by the X-ray structure of N,Nꢁ-o-C6H4-
bis(2,3-dichloromaleimide) (2), which is shown
in the bottom portion of Fig. 1. The C C single-
bond lengths in the maleimide moieties of 2
Conclusions
The condensation reaction between equimo-
lar amounts of o-phenylenediamine and 2,3-
dichloromaleic anhydride in the absence of
added PTSA proceeds to give 2,3-dichloro-N-o-
C6H4(NH2)maleimide (1) as the major product.
The minor products in this reaction were found
to be the double condensation speices N,Nꢁ-
o-C6H4-bis(2,3-dichloromaleimide) (2) and the
heterocyclic compound 2,3-dichloropyrrolo[1,2-
a]benzimidazol-1-one (3). Carrying out the same
˚
range from 1.485(7) [C(11) C(12)] to 1.504(7) A
˚
[C(3) C(4)], with an average distance of 1.494 A.
The two maleimide π bonds of 1.328(7)
˚
[C(2) C(3)] and 1.330(7) A [C(12) C(13)] fall
within acceptable values for simple C C bond
lengths for this genre of compound.4,16 The
planar five-membered rings form interplanar

764
Watson, Wu, and Richmond
1027. (c) Katritzky, A. R.; Fan, W.-Q.; Li, Q.-L.; Bayyuk, S. J.
Heterocyclic Chem. 1989, 26, 885.
4. (a) Bodige, S.G.; Mendez-Rojas, M.A.; Watson, W.H. J. Chem.
Crystallogr. 1999, 29, 57. (b) Watson, W.H.; Wu, G.; Richmond,
M.G. J. Chem. Crystallogr. 2003, 33, 983.
5. For some representative examples of the described hete-
rocyclic condensation reactions, see: (a) Pozharskii, A.F.;
Dal’nikovskaya, V.V. Russ. Chem. Rev. 1981, 50, 816. (b)
Manukian, B.K. Helv. Chim. Ada. 1966, 49, 534. (c) Ried,
W.; Isenbruck, G. Chem. Ber. 1972, 105, 337. (d) Watson,
W.H.; Chen, T.; Richmond, M.G. J. Chem. Crystallogr. 2004,
34, 693.
reaction in the presence of PTSA affords 1
quickly, followed by the production of 2,3-
dichloropyrrolo[1,2-a]benzimidazol-1-one. Un-
der no conditions did we observe any evidence
for the substitution of the chlorine groups in 1–
3 by the o-phenylenediamine or any other amine
moiety. All new compounds were characterized in
solution by standard methods, and the molecular
structures of compounds 1 and 2 were established
by X-ray crystallography.
6. Saint Version 6.02, Bruker Analytical X-ray Systems, Inc.
Copyright 1997–1999.
7. SHELXTL Version 5.1, Bruker Analytical X-ray Systems, Inc.
Copyright 1998.
8. PLATON—A Multipurpose Crystallographic Tool, Utrecht
University, Utrecht: The Netherlands, Speck, A.L. (2001).
9. The identity of the heterocyclic compound 3 is further ascer-
tained by the substitution of the two chlorine groups by ben-
zylthio and methylthio gropups (WHW and MGR: unpublished
results). The X-ray structures of these compounds will be pub-
lished in due course.
10. Dolphin, D.; Wick, A. Tabulation of Infrared Spectral Data;
Wiley-Interscience: New York, 1977.
11. Bovey, F.A. Nuclear Magnetic Resonance; Academic Press:
New York, 1969.
Acknowledgment
We thank Dr. Alan McNaught, Strategy
Royal Society of Chemistry, for assistance
in the naming of 2,3-dichloropyrrolo[1,2-
a]benzimidazol-1-one. Financial support from
the Robert A. Welch Foundation (Grants
P-0074-WHW and B-1093-MGR) is appreciated.
12. Brown, D.W.; Nakashima, T.T.; Rabenstein, D.L. J. Mag. Res.
1981, 45, 302.
13. Rao, C.N.R. Chemical Applications of Infrared Spectroscopy;
Academic Press: New York, 1963.
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