Regioselective synthesis of 4-aryl-3,4-dihydro-1,3,5-triazino[2,1-a] isoindol-2-ones

Article abstract of DOI:10.1007/s00706-008-0860-1

The condensation of binucleophilic 3-amino-1-arylimino-1H-isoindoles with bifunctional 1-chloro-benzylisocyanates occurs regioselectively resulting in 3,4-dihydro-1,3,5-triazino[2,1-a]isoindol-2-one derivatives. The structures of the synthesized compounds were unambiguously established by NOE experiments.

Full text of DOI:10.1007/s00706-008-0860-1

Monatsh Chem 139, 939–943 (2008)
DOI 10.1007/s00706-008-0860-1
Printed in The Netherlands
Regioselective synthesis of 4-aryl-3,4-dihydro-1,3,5-triazino[2,1-a]-
isoindol-2-ones
Angelina V. Biitseva1, Olha V. Hordiyenko1, Volodymyr A. Sukach2, Myhailo V. Vovk2,
Konstantin A. Pichugin3, Irina S. Konovalova3, Oleg V. Shishkin3
1
Chemistry Department, Kyiv National Taras Shevchenko University, Kyiv, Ukraine
2
Institute of Organic Chemistry, National Academy of Sciences, Kyiv, Ukraine
3
STC ‘‘Institute for Single Crystals’’, National Academy of Sciences, Kharkiv, Ukraine
Received 31 October 2007; Accepted 24 November 2007; Published online 18 February 2008
# Springer-Verlag 2008
isoindol-6-ones are known to be prepared by reaction
of 3-imino-1H-isoindol-1-one with formaldehyde
and amines [7].
Abstract The condensation of binucleophilic 3-amino-
1-arylimino-1H-isoindoles with bifunctional 1-chloro-
benzylisocyanates occurs regioselectively resulting in
3,4-dihydro-1,3,5-triazino[2,1-a]isoindol-2-one deriva-
tives. The structures of the synthesized compounds
were unambiguously established by NOE experiments.
A simple approach to fused 1,3,5-triazines which
is based on the reaction of 2-aminoazoles and 2-ami-
noazines with 1-chloroalkylisocyanates has been
elaborated earlier [8]. Upon exploring the interaction
of 1-aryl-1-chloro-2,2,2-trifluoroethylisocyanates and
3-amino-1-arylimino-1H-isoindoles as binucleophi-
lic aminoazole system two isomeric [1,3,5]triazino-
isoindolones A and B have been isolated (Fig. 1).
It has been found that the regioselectivity of this re-
action depends on both reaction temperature and
nature of substituents in Ar and Ar0 [9]. The ap-
proach mentioned above seems to be one of the most
efficient ways to the fused [1,3,5]triazino[2,1-a]-
isoindolones.
Keywords Heterocycles; Cyclizations; NMR Spectroscopy;
3-Amino-1-arylimino-1H-isoindoles; 4-Aryl-3,4-dihydro-
1,3,5-triazino[2,1-a]isoindol-2-ones.
Introduction
In the last few years compounds possessing a broad
spectrum of biological activity have been found
among derivatives of 1H-isoindole [1] and 1,3,5-tri-
azine [2–4]. Therefore, the development of efficient
synthesis approaches to the compounds bearing iso-
indole and triazine units in the same molecule be-
came of considerable interest. A limited number of
fused 1,3,5-triazinoisoindoles, that were described to
date includes 4-amino-2,6-diimino-2,6-dihydro[1,3,5]-
triazino[2,1-a]isoindole, which was synthesized by
interaction of 3-amino-1-imino-1H-isoindole and
N-cyanoguanidine and was used in the dye synthesis
[5, 6]. A few (3R)-3,4-dihydro[1,3,5]triazino[2,1-a]-
Fig. 1 Isomeric triazinoisoindolones obtained from 1-aryl-1-
chloro-2,2,2-trifluoroethylisocyanates and 3-amino-1-aryl-
imino-1H-isoindoles
Correspondence: Olha V. Hordiyenko, Chemistry Depart-
ment, Kyiv National Taras Shevchenko University, 01033
Kyiv, Ukraine. E-mail: ov_hordiyenko@univ.kiev.ua

940
A. V. Biitseva et al.
Scheme 1
It should be noticed that bifunctional nucleophiles
the behavior of 1-aryl-1-chloro-2,2,2-trifluoroethyl-
isocyanates [9].
are reported to react with 1-aryl-1-chloro-2,2,2-tri-
fluoroethylisocyanates and 1-chlorobenzylisocyanates
in different manner due to tautomeric equilibria be-
tween isocyanate and N-arylidenecarbamoyl forms
[10–12]. Here we report on our further study of the
interaction of 3-amino-1-arylimino-1H-isoindoles
with 1-chlorobenzylisocyanates and 1-chloro-1-phe-
nylbenzylisocyanate.
To confirm the structure of the synthesized triazi-
noisoindoles 3 an NOE experiment was performed for
the 2,6-dimethylphenylimino compound 3e. This ex-
periment reveals the presence of an NOE between
pairs of signals at ꢀ ¼ 2.01, 6.60ppm and 1.30,
7.42ppm (Fig. 2). For an alternative structure B these
effects should not be observed, that unequivocally
confirms the proposed structure of compounds 3.
Notably, in the 1H NMR spectrum of 3e protons of
methyl groups are observed as two sharp singlets at
ꢀ ¼ 1.30 and 2.01 ppm due to their non-equivalence,
Results and discussion
Unexpectedly, it was found that the reaction of
3-amino-1-arylimino-1H-isoindoles 1a–1c with 1-
chlorobenzylisocyanates 2 in toluene in the presence
of Et3N did not take place, and only the starting 1H-
isoindoles were isolated from the reaction mixture. It
was reasonable to suggest that concurrent alkylation
of Et3N by 2 takes place instead of the desired carba-
¨
moylation of 1. When the less nucleophilic Hunig’s
base was used instead of Et3N the reaction resulted
in smooth formation of the desirable 3,4-dihydro-
1,3,5-triazino[2,1-a]isoindol-2-ones 3 of type A as
the sole isolated products (Scheme 1). It should be
noted that the reaction occurred regioselectively irre-
spective of substituents in Ar and Ar0, in contrast to
Fig. 2 NOE Experiment data for 3e
Scheme 2

4-Aryl-3,4-dihydro-1,3,5-triazino[2,1-a]isoindol-2-ones
941
which is caused by restricted rotation about C–N
bond of the 2,6-dimethylphenyl residue. The high
field shift of one methyl group protons (ꢀ ¼ 0.6 ppm)
is caused by influence of Ar0 ring currents.
Another similar bielectrophilic reagent, 1-chloro-
1-phenylbenzylisocyanate (2d), was explored in the
reaction with 3-amino-2,6-dimethylphenylimino-
1H-isoindole (1c). As in the previous case, it was
demonstrated that the reaction occurs regioselect-
ively on heating the reagents without any base in
CH2Cl2 and results in formation of one isomeric
triazinoisoindole 3f in high yield (86%) (Scheme 2).
The structure of 3f was also confirmed by an NOE
Scheme 3
˚
C(7) single bond (1.314(3) A) is considerably short-
˚
er than the C(7)¼N(1) double bond (1.346(3) A).
For comparison, the average values of C(sp2)–NH2
single and N¼C(sp2) double bonds are 1.34 and
1
experiment. In contrast to 3e, in the H NMR spec-
˚
1.28 A [14]. Therefore, it is possible to conclude a
trum of triazinoisoindole 3f the protons of the methyl
groups of the 2,6-dimethylphenyl moiety are observed
as only one 6-proton singlet at ꢀ ¼ 1.55ppm. The
NOE between these protons and 2,6- (ꢀ ¼ 7.59ppm)
and 3,5-protons (ꢀ ¼ 7.37 ppm) of the phenyl moie-
ties of the triazine ring (12 and 5% enhancement)
allows us to assign the structure of the synthesized
compound to 6-(2,6-dimethylphenyl)imino-4,4-di-
phenyl-3,4-dihydro-[1,3,5]triazino[2,1-a]isoindol-2-
one (3f) with type A skeleton.
considerable contribution of the bipolar zwitter ionic
resonance form C0 into the total structure of the
molecule 1b similar to the related compound [15,
16] (Scheme 3). In the crystal phase the molecules
1b form centrosymmetrical dimers due to the in-
termolecular hydrogen bond N(3)–H(3NA)ꢁ ꢁ ꢁN(1)0
0
0
ꢀ
˚
(ꢂx, 1 ꢂ y, 1 ꢂ z) Nꢁ ꢁ ꢁH 2.05 A, N–Hꢁ ꢁ ꢁN 173 .
Taking into account the equilibrium between ami-
no-imino and diimino forms of the starting arylimi-
noisoindoles 1a–1c [17] on one hand, and isocyanate
and N-arylidenecarbamoyl forms of isocyanates 2a–
2d [10] on the other hand, two alternative routes of
compounds 3a–3f formation could be suggested
(Scheme 4). According to literature data for the in-
teraction of 1-chlorobensylisocyanates with C,N–,
C,O–, and C,S– binucleophiles [11, 12, 18] the first
most probable step of the reaction seems to be al-
kylation of isoindole at endocyclic nitrogen atom
leading to intermediates D. They undergo further
intramolecular carbamoylation at the exocyclic ni-
trogen atom of the imino group giving rise com-
pounds 3a–3f.
To the contrary to starting isoindole derivatives 1
the synthesized 4-aryl-3,4-dihydro-1,3,5-triazino[2,1-
a]isoindol-2-ones 3 have the Ar moiety in an
(E)-configuration at the exocyclic C¼N bond. This
1
conclusion comes from the H NMR spectra of all
studied compounds 3a–3f where the doublet at ꢀ ¼
6.40–6.70 ppm was observed assigned to 7-H of tria-
zinoisoindole moiety. Its high field shift at ꢀ ¼ 2 ppm
in comparison with starting compounds 1a–1c can
be explained by the shielding influence of ring cur-
rents of the Ar moiety [13].
For one of the starting isoindoles 1b we examined
its structure in the solid state by X-ray diffraction. It
was demonstrated that compound 1b exists in the
tautomeric form of 3-amino-1-arylimino-1H-isoin-
dole with (Z)-configuration of 2,4-xylidine residue
at the exocyclic C¼N bond. The aryl substituent at
the N(2) atom is oriented almost orthogonally re-
latively the isoindole bicycle (the C(14)–C(9)–
N(2)–C(6) torsion angle is 87.4(3)ꢀ). This leads
to disruption of conjugation between ꢁ-systems of
these fragments manifested itself in elongation of
To conclude, the interaction of 3-amino-1-aryl-
imino-1H-isoindoles and 1-chlorobenzylisocyanates
occurs regioselectively and results in formation of 4-
˚
the C(9)–N(2) bond (1.436(4) A) which is close to
˚
the mean value for non-conjugated systems (1.43 A)
[14]. The analysis of the bond lengths within the
N(1)¼C(7)–N(3) fragment shows that the N(3)–
Fig. 3 X-Ray molecular structure of 1b with the atom num-
bering used in crystallographic analysis

942
A. V. Biitseva et al.
Scheme 4
(CH3), 65.74, 123.10, 123.75, 126.22, 127.21, 128.43,
128.62, 129.40, 130.19, 131.20, 131.56, 131.76, 136.17,
136.72, 149.82, 153.71, 156.19, 158.82 ppm; MS: m=z ¼
467.2 [MH]þ.
aryl-3,4-dihydro-1,3,5-triazino[2,1-a]isoindol-2-ones
3 with high yields. The structure of the synthesized
compounds 3 was established by NOE experiments.
rac-4-(4-Chlorophenyl)-6-[(4-methylphenyl)imino]-3,4-
dihydro[1,3,5]triazino[2,1-a]isoindol-2(6H)-one
(3b, C23H17ClN4O)
Experimental
3-Amino-1-arylimino-1H-isoindoles 1a–1c were prepared
starting from phthalonitrile and corresponding amines [17].
The amines are commercially available; they were used with-
out additional purification. Isocyanates 2 were prepared as it
has been reported [18, 19]. Toluene and CH2Cl2 were dried
over P2O5. Melting points were measured on a Boetius micro-
scope hot plate apparatus. 1H and 13C NMR spectra were
measured on Mercury (Varian) 400 spectrometer (400MHz
1H and 100 MHz 13C) in DMSO-d6 solutions with TMS as
internal standard. Elemental analyses for C, H, and N were
conducted using Perkin-Elmer C, H, and N Analyzer, their
results were found to be in good agreement (ꢃ0.2%) with the
calculated values. Mass spectra were recorded on Agilent
1100 LC=MSD instrument with chemical ionization (CI).
From 1a (0.47 g, 2 mmol) and 2b (0.40 g, 2 mmol). Yield
1
0.61g (76%); mp 246–247ꢀC; H NMR: ꢀ ¼ 2.35 (s, CH3),
6.48 (d, 1H, J ¼ 2 Hz), 6.67 (d, 2H, J ¼ 7.2 Hz), 6.74 (d, 1H,
J ¼ 7.2Hz), 7.16 (d, 2H, J ¼ 7.2 Hz), 7.34 (d, 2H, J ¼ 7.6 Hz),
7.49 (t, 1H, J ¼ 7.2 Hz), 7.55 (d, 2H, J ¼ 7.6 Hz), 7.69 (t, 1H,
J ¼ 7.2Hz), 7.99 (d, 1H, J ¼ 7.2 Hz), 8.45 (d, J ¼ 2 Hz, NH)
ppm; 13C NMR: ꢀ ¼ 20.80 (CH3), 65.21, 123.74, 124.55,
126.40, 127.51, 128.39, 128.92, 129.57, 130.01, 131.51,
131.69, 135.92, 136.21, 136.90, 150.02, 153.68, 156.39,
157.92 ppm; MS: m=z ¼ 401.1 [MH]þ.
rac-6-[(2,4-Dimethylphenyl)imino]-4-phenyl-3,4-dihydro-
[1,3,5]triazino[2,1-a]isoindol-2(6H)-one (3c, C24H20N4O)
From 1b (0.50 g, 2 mmol) and 2a (0.34 g, 2 mmol). Yield
1
0.55g (73%); mp 221–222ꢀC; H NMR: ꢀ ¼ 1.56 (s, CH3),
General procedure for the synthesis of 4-aryl-3,4-dihydro-
1,3,5-triazino[2,1-a]isoindol-2-ones (3a–3e)
2.29 (s, CH3), 6.49 (d, 1H, J ¼ 2.2 Hz), 6.57 (d, 1H, J ¼
7.6 Hz), 6.64 (d, 1H, J ¼ 7.6 Hz), 6.95 (d, 1H, J ¼ 7.6 Hz),
6.98 (s, 1H), 7.36 (br, s, Ph), 7.49 (t, 1H, J ¼ 7.6 Hz),
7.70 (t, 1H, J ¼ 7.6 Hz), 8.02 (d, 1H, J ¼ 7.6 Hz), 8.45 (d,
J ¼ 2.2Hz, NH) ppm; 13C NMR: ꢀ ¼ 17.49 (CH3), 20.24
(CH3), 65.31, 123.39, 125.97, 126.37, 127.09, 127.43, 128.41,
128.78, 129.13, 130.75, 131.31, 131.59, 132.01, 132.29,
136.53, 137.08, 152.22, 152.35, 157.17, 158.82 ppm; MS:
m=z ¼ 381.2 [MH]þ.
1-Chlorobenzylisocyanate (2a–2c) (0.2mmol) dissolved in
5 cm3 toluene was added dropwise to the mixture of appropriate
3-amino-1-arylimino-1H-isoindole (1a–1c) (0.2mmol) and
0.43 cm3 N-ethyl-N,N-diisopropylamine (0.25 mmol) in tolu-
ene. The resulting suspension was stirred for 2 h at ambient
temperature and then the solid was filtered, thoroughly washed
with n-hexane. The yellow powder of product was purified by
recrystallization from 60% aqueous ethanol and dried on air.
rac-4-(4-Bromophenyl)-6-[(2,4-dimethylphenyl)imino]-3,4-
dihydro[1,3,5]triazino[2,1-a]isoindol-2(6H)-one
(3d, C24H19BrN4O)
rac-6-[(4-Methylphenyl)imino]-4-phenyl-3,4-dihydro[1,3,5]-
triazino[2,1-a]isoindol-2(6H)-one (3a, C23H18N4O)
From 1a (0.47 g, 2 mmol) and 2a (0.34 g, 2 mmol). Yield
1
0.59g (81%); mp 207–208ꢀC; H NMR: ꢀ ¼ 2.34 (s, CH3),
From 1b (0.50 g, 2 mmol) and 2c (0.49 g, 2 mmol). Yield
1
6.49 (d, 1H, J ¼ 2 Hz), 6.64 (d, 2H, J ¼ 7.6 Hz), 6.75 (d, 1H,
J ¼ 7.2 Hz), 7.14 (d, 2H, J ¼ 7.6 Hz), 7.38 (br, s, Ph), 7.49 (t,
1H, J ¼ 7.2 Hz), 7.70 (t, 1H, J ¼ 7.2 Hz), 8.00 (d, 1H, J ¼
7.2 Hz), 8.45 (d, 1H, J ¼ 2 Hz, NH) ppm; 13C NMR: ꢀ ¼ 20.65
0.72g (78%); mp 210–211ꢀC; H NMR: ꢀ ¼ 1.62 (s, CH3),
2.30 (s, CH3), 6.50 (d, 1H, J ¼ 1.8 Hz), 6.57 (d, 1H, J ¼
7.2 Hz), 6.64 (d, 1H, J ¼ 7.2 Hz), 6.95 (d, 1H, J ¼ 7.2 Hz),
7.00 (s, 1H), 7.34 (d, 2H, J ¼ 7.6 Hz), 7.49 (t, 1H, J ¼

4-Aryl-3,4-dihydro-1,3,5-triazino[2,1-a]isoindol-2-ones
943
7.2 Hz), 7.52 (d, 2H, J ¼ 7.6Hz), 7.70 (t, 1H, J ¼ 7.2 Hz), 8.02
(d, 1H, J ¼ 7.2 Hz), 8.45 (d, J ¼ 1.8 Hz, NH) ppm; 13C NMR:
ꢀ ¼ 17.81 (CH3), 20.32 (CH3), 65.28, 123.84, 125.13, 125.47,
126.52, 127.54, 128.47, 128.91, 129.15, 130.32, 130.75,
131.39, 131.63, 132.37, 136.39, 137.17, 152.31, 152.43,
156.39, 159.15 ppm; MS: m=z ¼ 459.0 [MH]þ.
as a riding-model approximation with Uiso ¼ nUeq of the car-
rier atom (n ¼ 1.5 for methyl and n ¼ 1.2 for the remaining
hydrogen atoms). Full-matrix least-squares refinement against
F2 in anisotropic approximation using 2319 reflections was
converged to wR2 ¼ 0.204 (R1 ¼ 0.069 for 1442 reflections
with F>4ꢆ(F), S ¼ 1.008). Atomic coordinates and crystallo-
graphic parameters have been deposited to the Cambridge
Crystallographic Data Centre (CCDC 658687). These data
can be obtained from the CCDC via www.ccdc.cam.ac.uk=
data_request=cif.
rac-4-(4-Chlorophenyl)-6-[(2,6-dimethylphenyl)imino]-
3,4-dihydro[1,3,5]triazino[2,1-a]isoindol-2(6H)-one
(3e, C24H19ClN4O)
From 1c (0.50 g, 2 mmol) and 2b (0.40 g, 2 mmol). Yield
1
0.68g (82%); mp 240–241ꢀC; H NMR: ꢀ ¼ 1.30 (s, CH3),
References
2.01 (s, CH3), 6.44 (d, 1H, J ¼ 7.6 Hz), 6.60 (d, 1H, J ¼ 2 Hz),
6.95–7.01 (m, 2H), 7.05 (d, 1H, J ¼ 7.2 Hz), 7.40 (d, 2H,
J ¼ 8 Hz), 7.42 (d, 2H, J ¼ 8 Hz), 7.48 (t, 1H, J ¼ 7.2 Hz),
7.72 (t, 1H, J ¼ 7.2Hz), 8.02 (d, 1H, J ¼ 7.6 Hz), 8.48 (d,
J ¼ 2 Hz, NH) ppm; 13C NMR: ꢀ ¼ 17.23 (CH3), 18.04 (CH3),
65.98, 123.97, 124.05, 124.07, 126.20, 126.41, 128.49,
128.80, 128.86, 129.11, 129.76, 131.58, 133.07, 133.39,
133.76, 134.74, 140.21, 145.37, 148.37, 155.10, 159.98 ppm;
MS: m=z ¼ 415.0 [MH]þ.
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6-[(2,6-Dimethylphenyl)imino]-4,4-diphenyl-3,4-dihydro-
[1,3,5]triazino[2,1-a]isoindol-2(6H)-one (3f, C30H24N4O)
The mixture of 0.50g 1c (2mmol) and 0.49g 2d (2mmol)
in 10 cm3 CH2Cl2 was refluxed for 3 h. After cooling the
formed solid was filtered and thoroughly washed with aqueous
ammonia solution. The yellow powder was recrystallized from
60% aqueous ethanol and dried on air. Yield 0.79 g (86%);
mp 235–236ꢀC; 1H NMR: ꢀ ¼ 1.55 (s, 2ꢄCH3), 6.35 (d, 1H,
J ¼ 7.6 Hz), 6.86–6.93 (m, 3H), 7.37 (br, s, 6H, m-, and p-
Ph), 7.44 (t, 1H, J ¼ 7.6 Hz), 7.59 (d, 4H, J ¼ 7.2 Hz, o-Ph),
7.71 (t, 1H, J ¼ 7.6 Hz), 8.04 (d, 1H, J ¼ 7.6 Hz), 8.80 (s, NH)
ppm; 13C NMR: ꢀ ¼ 18.04 (2ꢄCH3), 78.43, 123.98, 124.01,
125.83, 128.19, 128.50, 128.54, 128.82, 132.60, 133.46,
134.90, 140.84, 145.49, 149.11, 154.95, 159.85 ppm; MS:
m=z ¼ 457.2 [MH]þ.
14. Bu¨rgi HB, Dunitz DJ (1994) Structure Correlation, Vol 2.
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X-Ray crystal structure determination
The crystals of C16H15N3 are monoclinic. At 293 K a ¼
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16. Hordiyenko OV, Biitseva AV, Kornilov MYu, Brosse N,
ꢀ
˚
9.073(3), b ¼ 11.193(4), c ¼ 13.631(4) A, ꢂ ¼ 130.71(3) ,
3
˚
´
V ¼ 1344.8(8) A , Mr ¼ 249.3, Z ¼ 4, space group P21=n,
Hocquet A, Jamart-Gregoire B, Shishkin OV, Zubatyuk
dcalc ¼ 1.231 g=cm3, ꢃ(MoKꢄ) ¼ 0.08mmꢂ1, F(000) ¼ 528.
Intensity of 2473 reflections (2319 independent, Rint ¼ 0.04)
was measured on a Siemens P3=PC diffractometer with graph-
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˚
ite-monochromated Mo-Kꢄ radiation (l ¼ 0.71073 A) 2ꢅ-
scans, 2ꢅmax ¼ 50ꢀ. The structure was solved by direct method
and refined by full-matrix least-squares techniques on all F2
data using the SHELX-97 package [20]. All non-hydrogen
atoms were refined with anisotropic thermal parameters.
Positions of hydrogen atoms were located from difference
maps of the electron density and included in the refinement