Intramolecular cyclization of S-alkyl derivatives of aminomercaptoimidazoles and -benzimidazoles as a method for the annulation of the thiadiazine ring

Article abstract of DOI:10.1007/s11172-012-0157-8

A method was developed for the annulation of the tetrahydrothiadiazine moiety to the imidazole and benzimidazole rings through intramolecular cyclization of S-alkyl derivatives of aminomercaptoimidazoles and -benzimidazoles. The factors controlling the stereoselectivity of the formation of the tetrahydrothiadiazine ring were revealed.

Full text of DOI:10.1007/s11172-012-0157-8

Russian Chemical Bulletin, International Edition, Vol. 61, No. 6, pp. 1154—1160, June, 2012
1154
Intramolecular cyclization of
Sꢀalkyl derivatives of aminomercaptoimidazoles and ꢀbenzimidazoles
as a method for the annulation of the thiadiazine ring
N. I. Gaponenko,a A. A. Kolodina,b A. V. Lesin,a and S. V. Kurbatova
aDepartment of Chemistry, Southern Federal University,
7 ul. Zorge, 344090 RostovꢀonꢀDon, Russian Federation.
Eꢀmail: gaponenkoꢀnataly@mail.ru
bSouthern Scientific Center of Russian Academy of Sciences,
41 ul. Chekhova, 344006 RostovꢀonꢀDon, Russian Federation.
Eꢀmail: lexandra@inbox.ru
A method was developed for the annulation of the tetrahydrothiadiazine moiety to the
imidazole and benzimidazole rings through intramolecular cyclization of Sꢀalkyl derivatives of
aminomercaptoimidazoles and ꢀbenzimidazoles. The factors controlling the stereoselectivity of
the formation of the tetrahydrothiadiazine ring were revealed.
Key words: [1,3,4]thiadiazino[3,2ꢀa]benzimidazole, imidazo[2,1ꢀb][1,3,4]thiadiazine, tetraꢀ
hydrothiadiazine, annulation, Xꢀray diffraction study.
Previously, we have reported on the new stereoselecꢀ
tive method for the annulation of the tetrahydrothiadiꢀ
azine ring as applied to the synthesis of 6,7ꢀdihydroꢀ5Hꢀ
1,2,4ꢀtriazolo[3,4ꢀb][1,3,4]thiadiazines,1 3,4ꢀdihydroꢀ
2Hꢀimidazo[2,1ꢀb][1,3,4]thiadiazines,2 and spirocyclic
1,2,4ꢀtriazolo[3,4ꢀb][1,3,4]thiadiazines and [1,3,4]thiadiꢀ
azino[3,2ꢀa]benzimidazoles.3
To extend the scope and show the versatility of this
approach to the synthesis of thiadiazine derivatives and
to study the structural features and the behavior of
the reaction products, we investigated the intramolecular
cyclization with the participation of Sꢀmethyleneꢀsubstiꢀ
tuted 1ꢀaminoꢀ2ꢀmercaptoimidazoles and ꢀbenzimidꢀ
azoles.
In contrast to aminomercaptotriazole derivatives, the
synthesis and biological activity of which were reported in
several reviews,4—6 polycyclic systems bearing the Nꢀamiꢀ
noꢀ2ꢀmercaptoimidazole moiety are poorly studied, alꢀ
though it is known that the structures containing this group
exhibit a broad range of antiviral activity.7 For example,
compounds A and B are inhibitors of human immunodefiꢀ
ciency virus (HIV) replication.7,8
Scarce data on the methods for the synthesis of fused
imidazothiadiazines refer to either the annulation of the
imidazole ring to the thiadiazaheterocycle9 or to the reacꢀ
tion of Nꢀaminoꢀ2ꢀmercaptoimidazole with ꢀhalo keꢀ
tones9—11 (Scheme 1). In both cases, the biheterocycle is
assembled through the carbon—heteroatom (nitrogen, sulꢀ
fur) bond formation. The approach developed in our works
is based on the diastereoselective formation of the carꢀ
bon—carbon bond in the final step of the cyclization.
The reactions of 1ꢀaminoꢀ1Hꢀbenzimidazoleꢀ2ꢀthiꢀ
ol (1) and 1ꢀaminoꢀ1Hꢀimidazoleꢀ2ꢀthiol (2) with pꢀnitroꢀ
benzyl bromide afforded 1ꢀaminoꢀ2ꢀ[(4ꢀnitrobenzyl)thio]ꢀ
1Hꢀbenzimidazole (3) and 1ꢀaminoꢀ2ꢀ[(4ꢀnitrobenzyl)ꢀ
thio]ꢀ1Hꢀimidazole (4), respectively. These reaction prodꢀ
ucts undergo condensation with substituted benzaldehydes
Scheme 1
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1144—1149, June, 2012.
1066ꢀ5285/12/6106ꢀ1154 © 2012 Springer Science+Business Media, Inc.

Tetrahydrothiadiazine ring annulation
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 6, June, 2012
1155
Scheme 2
R = H (2, 4, 6a,b),
(1, 3, 5a,b);
Ar = 4ꢀNO2C6H4 (3, 4, 5a—c, 6a,b);
Ar´ = 4ꢀClC6H4 (5a, 6a), Ph (5b), 4ꢀBrC6H4 (5c), 3ꢀClC6H4 (6b)
followed by the cyclization under basic catalysis condiꢀ
tions to form the corresponding [1,3,4]thiadiazino[3,2ꢀa]ꢀ
benzimidazoles 5a—c and imidazo[2,1ꢀb][1,3,4]thiaꢀ
diazines 6a,b (Scheme 2).
Thiadiazines 5 were also prepared by the independent
synthesis through the alkylation of the corresponding
Nꢀbenzimidazolylimines 7 with pꢀnitrobenzyl bromide
(Scheme 3) giving acyclic Nꢀ(Rꢀbenzylidene)ꢀ2ꢀ[(4ꢀ
nitrobenzyl)thio]ꢀ1Hꢀbenzimidazoleꢀ1ꢀamines 9 followed
by the cyclization of the latter in the presence of a strong
base to yield target compounds 5. Hence, it is evident that
in both cases, the cyclization is preceded by the formation
of the corresponding acyclic benzylthio derivative of imidꢀ
azolylimine followed by the ionization of the Sꢀmethylene
unit by the action of NaOH and the nucleophilic attack of
the resulting carbanion on the azomethine nitrogen atom
to form the C(2)—C(3) bond of the thiadiazine ring.
1
The H NMR spectra of 3,4ꢀdihydroꢀ2Hꢀ[1,3,4]thiaꢀ
diazino[3,2ꢀa]benzimidazoles 5 and imidazo[2,1ꢀb][1,3,4]ꢀ
thiadiazines 6 show three oneꢀproton peaks: doublets of
the NH and C(2)H groups and a doublet of doublets of the
C(3)H group at H 7.5—7.7, 5.25, and 5.0, respectively.
The intensity and multiplicity of the signals, as well as
the spinꢀspin coupling between H(2) and H(3) (~10 Hz),
Scheme 3
R = H (8, 12a,b),
(5a—d, 7a—d, 9a—d, 10a—c, 11a—g)
Comꢀ
pound
5a
5b
5c
5d
7a
7b
7c
Ar´
R´
Comꢀ
pound
8
9a
9b
9c
9d
10a
10b
10c
Ar´
R´
Comꢀ
pound
11a
11b
11c
11d
11e
11f
Ar´
R´
4ꢀClC6H4
Ph
4ꢀBrC6H4
4ꢀMeC6H4
4ꢀClC6H4
Ph
4ꢀNO2C6H4
4ꢀNO2C6H4
4ꢀNO2C6H4
4ꢀNO2C6H4
4ꢀBrC6H4
4ꢀClC6H4
Ph
4ꢀBrC6H4
4ꢀMeC6H4
4ꢀBrC6H4
4ꢀBrC6H4
4ꢀClC6H4
—
4ꢀBrC6H4
4ꢀBrC6H4
4ꢀClC6H4
4ꢀBrC6H4
4ꢀMeC6H4
Ph
Ph
4ꢀBrC6H4
4ꢀBrC6H4
C(O)C6H4Brꢀ4
C(O)C6H4NO2ꢀ4
C(O)C6H4Clꢀ4
C(O)C6H4OMeꢀ4
C(O)C6H4Brꢀ4
C(O)C6H4Clꢀ4
C(O)C6H4NO2ꢀ4
C(O)Ph
4ꢀNO2C6H4
4ꢀNO2C6H4
4ꢀNO2C6H4
4ꢀNO2C6H4
C(O)C6H4Brꢀ4
C(O)C6H4NO2ꢀ4
C(O)C6H4Clꢀ4
—
—
—
—
4ꢀBrC6H4
4ꢀMeC6H4
11g
12a
12b
7d
C(O)C6H4Brꢀ4

1156
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 6, June, 2012
Gaponenko et al.
Scheme 4
indicate that the substituents at the chiral carbon atoms
C(2) and C(3) of the thiadiazine ring in imidazothiadiꢀ
azines 5 and 6 are in trans positions. Previously, we have
observed12 a similar arrangement of the substituents in
triazolothiadiazines, whose structures were established by
Xꢀray diffraction. This suggests the transꢀdiastereoselecꢀ
tivity of the annulation of the hydrogenated thiadiazine
ring to aminomercaptoazole derivatives, which is apparꢀ
ently attributed to steric interactions between the bulky
aryl moieties.
The treatment of Nꢀbenzimidazolylimines 7 with phenꢀ
acyl bromides gives Sꢀsubstituted compounds 10, which
are transformed into the corresponding thiadiazines 11 in
the presence of sodium methoxide. The oneꢀpot synthesis
of compounds 11 without the isolation of acyclic precurꢀ
sors 10 involves the reaction of imines 7 with phenacyl
bromide in the presence of 2 equivalents of sodium methꢀ
oxide (see Scheme 3).
However, as opposed to the spectra of compounds 5
and 6, which do not show even weak signals of the minor
diastereomers, all signals in the 1H NMR spectra
of 3,4ꢀdihydroꢀ2Hꢀ[1,3,4]thiadiazino[3,2ꢀa]benzimidꢀ
azoles 11 are doubled in a ratio of 60 : 40, which can be
attributed to the formation of a mixture of diastereomers.
The alkylation of aldimine 8 with phenacyl halides
affords imidazothiadiazines 12a,b (see Scheme 3). In the
1H NMR spectra of these compounds, like in the spectra
of compounds 11, all signals are doubled in a ratio of
68 : 32 (for 12a) and 83 : 17 (for 12b). In this case, the
doubling of the signals can also be attributed to the formaꢀ
tion of a mixture of diastereomers. The vicinal spinꢀspin
coupling constants of the protons H(2) and H(3) of the
thiadiazine ring of compounds 11 and 12 are in the range
of 2.2—5.6 Hz, which indicates that these protons are
either simultaneously in pseudoequatorial positions or in
pseudoaxial and pseudoequatorial positions.
In our opinion, the rational explanation for this strikꢀ
ing difference in the diastereoselectivity of the cyclization
of the superficially similar benzyl and phenacyl derivatives
is as follows. The H atom in position 2 of compounds 11
and 12 is adjacent to the S atom and the aroyl group.
This makes possible the enolization (Scheme 4) resulting
in the inversion of the configuration at the C(2) atom
and, consequently, in the formation of a mixture of diaꢀ
stereomers.
The virtually coplanar arrangement of the atoms of the
imidazothiadiazine system is distorted by the deviation of
the C(3) atom from the plane of the imidazole ring by
0.73 Å; the C(1) and N(4) atoms deviate from this plane
by 0.07 and 0.04 Å, respectively. The C(1)—H(1A) and
Br(18)
C(15)
C(16)
C(17)
C(14)
C(13)
C(12)
O(11)
C(10)
H(1A)
S(1)
C(1)
C(9)
H(3A)
C(3)
N(8)
C(24)
C(7)
C(6)
N(5)
N(4)
C(19)
C(20)
C(21)
C(23)
C(22)
According to the results of the Xꢀray diffraction study,
compound 12b crystallizes as a racemate (space group
P21/n) formed by two enantiomers (R, S and S, R) (Fig. 1).
The predominance of one of the two pairs of enantiomers
can be attributed to the presence of the intramolecular
N(4)—H(4N)...O(11) hydrogen bond (N...O, 2.801(4) Å;
N—H—O, 135(1)) stabilizing this structure.*
Br(25)
Fig. 1. Molecular structure of compound 12b (S,Rꢀenantiomer)
with displacement ellipsoids (p = 50%). The asymmetric carbon
atoms C(1) and C(3) have the S and R configurations, resꢀ
pectively, according to the Cahn—Ingold—Prelog notational
system.
* The Xꢀray diffraction structure was described using the crystalꢀ
lographic atomꢀnumbering scheme (see Fig. 1).

Tetrahydrothiadiazine ring annulation
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 6, June, 2012
1157
3ꢀ(4ꢀChlorophenyl)ꢀ2ꢀ(4ꢀnitrophenyl)ꢀ3,4ꢀdihydroꢀ2Hꢀ[1,3,4]ꢀ
thiadiazino[3,2ꢀa]benzimidazole (5a). Yield 16% (A), 38% (B),
m.p. 203—206 C. Found (%): C, 59.82; H, 3.64; N, 13.41.
C21H15ClN4O2S. Calculated (%): C, 59.64; H, 3.58; N, 13.25.
1H NMR (DMSOꢀd6), : 5.03 (dd, 1 H, H(3), J = 9.5 Hz,
J = 10.5 Hz); 5.34 (d, 1 H, H(2), J = 9.5 Hz); 7.13—7.24 (m, 2 H,
benzimidazole); 7.26—7.47 (m, 6 H, NH, C6H4Clꢀ4, benzimidꢀ
azole); 7.48—7.59 (m, 1 H, benzimidazole); 7.74 and 8.12 (both d,
2 H each, C6H4NO2ꢀ4, J = 8.4 Hz). 13C NMR (DMSOꢀd6),
: 48.3, 63.3, 80.1, 109.7, 118.5, 122.3, 122.8, 124.6, 129.5, 130.6,
131.3, 133.7, 135.4, 136.9, 140.9, 143.6, 145.7, 148.0.
2ꢀ(4ꢀNitrophenyl)ꢀ3ꢀphenylꢀ3,4ꢀdihydroꢀ2Hꢀ[1,3,4]thiadiꢀ
azino[3,2ꢀa]benzimidazole (5b). Yield 31% (A), 25% (B), m.p.
212—215 C. Found (%): C, 65.12; H, 4.24; N, 14.60.
C21H16N4O2S. Calculated (%): C, 64.93; H, 4.15; N, 14.42.
1H NMR (DMSOꢀd6), : 4.96 (dd, 1 H, H(3), J = 9.5 Hz,
J = 10.7 Hz); 5.35 (d, 1 H, H(2), J = 9.5 Hz); 7.14—7.33 (m, 6 H,
NH, Ph, benzimidazole); 7.35—7.44 (m, 3 H, Ph, benzimidꢀ
azole); 7.46—7.58 (m, 1 H, benzimidazole); 7.72 and 8.09 (both d,
2 H each, C6H4NO2ꢀ4, J = 8.8 Hz).
Fig. 2. Newman projection along the C(3)—C(1) bond of
molecule 12b.
C(3)—H(3A) bonds are in pseudoequatorial positions (the
H(1A)—C(1)—C(3)—H(3A) torsion angle is 63), whereꢀ
as the C(1)—C(10) and C(3)—C(19) bonds are in pseudoꢀ
axial positions. Therefore, the aryl substituents are in the
trans orientation with respect to the thiadiazine ring (the
C(10)—C(1)—C(3)—C(19) and C(10)—C(1)—C(3)—
H(3A) torsion angles are 173.7(2) and 57, respectively)
(Fig. 2). The dihedral angle between the planes of two
pꢀBrC6H4 groups is 8.6(2).
Therefore, the general method, which we have develꢀ
oped earlier for the synthesis of 1,3,4ꢀthiadiazines fused
with azoles, was applied for the first time to the preparaꢀ
tion of new [1,3,4]thiadiazino[3,2ꢀa]benzimidazoles.
The annulation of the tetrahydrothiadiazine ring occurs
through the formation of the C—C bond in the final step
of heterocyclization and is diastereoselective.
3ꢀ(4ꢀBromophenyl)ꢀ2ꢀ(4ꢀnitrophenyl)ꢀ3,4ꢀdihydroꢀ2Hꢀ[1,3,4]ꢀ
thiadiazino[3,2ꢀa]benzimidazole (5c). Yield 48% (A), 11.4% (B),
m.p. 225—228 C. Found (%): C, 53.85; H, 3.18; N, 11.87.
C21H15BrN4O2S. Calculated (%): C, 53.97; H, 3.24; N, 11.99.
1H NMR (DMSOꢀd6), : 4.99 (dd, 1 H, H(3), J = 9.8 Hz,
J = 10.7 Hz); 5.29 (d, 1 H, H(2), J = 9.8 Hz); 7.10—7.19 (m, 2 H,
benzimidazole); 7.25 (d, 1 H, NH, J = 10.7 Hz); 7.3 (d, 2 H,
C6H4Brꢀ4, J = 8.5 Hz); 7.33—7.38 (m, 1 H, benzimidazole);
7.42—7.53 (m, 3 H, C6H4Brꢀ4, benzimidazole); 7.69 and 8.08
(both d, 2 H each, C6H4NO2ꢀ4, J = 8.8 Hz).
Experimental
3ꢀ(4ꢀMethylphenyl)ꢀ2ꢀ(4ꢀnitrophenyl)ꢀ3,4ꢀdihydroꢀ2Hꢀ
[1,3,4]thiadiazino[3,2ꢀa]benzimidazole (5d). Yield 35% (B), m.p.
162—165 C. Found (%): C, 65.49; H, 4.60; N, 13.83.
C22H18N4O2S. Calculated (%): C, 65.65; H, 4.51; N, 13.92.
1H NMR (DMSOꢀd6), : 2.21 (s, 3 H, Me); 4.92 (dd, 1 H, H(3),
J = 9.8 Hz, J = 10.5 Hz); 5.33 (d, 1 H, H(2), J = 9.8 Hz); 7.07
(d, 2 H, C6H4Meꢀ4, J = 8.1 Hz); 7.13—7.24 (m, 3 H, benzimidꢀ
azole, NH); 7.26 (d, 2 H, C6H4Meꢀ4, J = 8.1 Hz); 7.34—7.42
(m, 1 H, benzimidazole); 7.48—7.54 (m, 1 H, benzimidazole);
7.71 and 8.10 (both d, 2 H each, C6H4NO2ꢀ4, J = 8.8 Hz). MS,
m/z (Irel (%)): 402 [M]+ (42), 284 (48), 266 (32), 253 (74), 236
(50), 192 (30), 178 (100), 165 (48), 152 (22), 134 (26), 118 (65),
108 (60), 91 (64).
3ꢀ(4ꢀChlorophenyl)ꢀ2ꢀ(4ꢀnitrophenyl)ꢀ3,4ꢀdihydroꢀ2Hꢀimidꢀ
azo[2,1ꢀb][1,3,4]thiadiazine (6a). A catalytic amount of NaOH
(0.5 mmol) was added to a solution of Sꢀbenzyl ester 4 (0.5 g,
2 mmol) and pꢀchlorobenzaldehyde (0.3 g, 2 mmol) in ethanol
(10 mL). The reaction mixture was refluxed for 1 h, cooled,
diluted with water (30 mL), and neutralized with dilute hydroꢀ
chloric acid. The precipitate that formed was filtered off,
recrystallized from CHCl3, and washed with CCl4. Yield 48%,
m.p. 133—135 C. Found (%): C, 54.91; H, 3.56; N, 14.87.
C17H13ClN4O2S. Calculated (%): C, 54.77; H, 3.51; N, 15.03.
1H NMR (DMSOꢀd6), : 4.86 (dd, 1 H, H(3), J = 10.2 Hz,
J = 9.8 Hz); 5.17 (d, 1 H, H(2), J = 9.8 Hz); 6.89 and 7.29 (both d,
1 H each, imidazole, J = 1.4 Hz); 7.33 (m, 5 H, NH, HAr);
7.66 and 8.09 (both d, 2 H each, HAr, J = 8.8 Hz). 13C NMR
(DMSOꢀd6), : 48.1, 63.3, 121.0, 124.2, 125.6, 129.1, 130.3,
131.0, 132.7, 133.3, 136.6, 145.7, 147.5. MS, m/z (Irel (%)): 372
[M]+ (27), 273 (73), 234 (100), 259 (25), 202 (32), 186 (62), 178
(90), 165 (30), 152 (43), 138 (34), 129 (20), 102 (34), 89 (33).
1
The H NMR spectra were recorded on a Bruker DPXꢀ250
instrument at 25 C in CDCl3 and DMSOꢀd6 using Me4Si as the
internal standard. The electron impact mass spectra were obꢀ
tained on a Finnigan MAT INCOS 50 mass spectrometer (ionꢀ
ization energy was 70 eV). The melting points were measured in
glass capillaries using a PTP (M) instrument and are uncorrected.
1ꢀAminoꢀ1Hꢀbenzimidazoleꢀ2ꢀthiols 1 (m.p. 201—204 C),13
1ꢀaminoꢀ1Hꢀimidazoleꢀ2ꢀthiol hydrochloride
2
(m.p.
167—168 C),14 1ꢀaminoꢀ2ꢀ[(4ꢀnitrobenzyl)thio]ꢀ1Hꢀbenzimidꢀ
azole 3 (m.p. 140—143 C),3 1ꢀaminoꢀ2ꢀ(4ꢀnitrobenzylthio)ꢀ
imidazole 4 (m.p. 155 C),2 1ꢀ[(Rꢀbenzylidene)amino]ꢀ1Hꢀ
benzimidazoleꢀ2ꢀthiols 7a, 7b, 7c, and 7d (m.p. 217, 220, 210,
and 203 C, respectively),13 and 1ꢀ[(4ꢀbromophenyl)methylꢀ
ideneamino]ꢀ1Hꢀimidazoleꢀ2ꢀthiol 8 (m.p. 237 C)2 were synꢀ
thesized according to procedures described previously. All reꢀ
agents were commercial products (Sigma—Aldrich). The solꢀ
vents were purified according to standard procedures.15
Compounds 5 (general procedure). Method A. A catalytic
amount of NaOH (0.5 mmol) was added to a solution of Sꢀbenzyl
ester 3 (1 mmol) and aromatic aldehyde (1 mmol) in ethanol
(10 mL). The reaction mixture was refluxed for 2 h, cooled,
diluted with water (30 mL), and neutralized with dilute hydroꢀ
chloric acid. The precipitate that formed was filtered off and
recrystallized from MeCN.
Method B. Nꢀ(RꢀBenzylidene)ꢀ2ꢀ[(4ꢀnitrobenzyl)thio]ꢀ1Hꢀ
benzimidazoleꢀ1ꢀamine 9a—d (1 mmol) was added to a solution
of MeONa (1 mmol) in methanol (3 mL). The reaction mixture
was heated for 5 min, cooled, and diluted with water (20 mL).
The precipitate that formed was filtered off and recrystallized
from MeCN.

1158
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 6, June, 2012
Gaponenko et al.
3ꢀ(3ꢀChlorophenyl)ꢀ2ꢀ(4ꢀnitrophenyl)ꢀ3,4ꢀdihydroꢀ2Hꢀimidꢀ
azo[2,1ꢀb][1,3,4]thiadiazine (6b) was synthesized by analogy
with compound 6a from equimolar amounts of compound 4 and
mꢀchlorobenzaldehyde. Yield 42%, m.p. 119—121 C. Found (%):
C, 54.86; H, 3.57; N, 15.12. C17H13ClN4O2S. Calculated (%):
C, 54.77; H, 3.51; N, 15.03. 1H NMR (CDCl3), : 4.42 (dd,
1 H, H(3), J = 8.8 Hz, J = 9.5 Hz); 4.85 (d, 1 H, H(2), J = 8.8 Hz);
5.21 (d, 1 H, NH, J = 9.5 Hz); 6.97 (m, 1 H, HAr); 7.00 and 7.08
(both d, 1 H each, imidazole, J = 1.26 Hz); 7.16—7.22 (m, 2 H,
HAr); 7.39 (m, 3 H, HAr); 8.11 (d, 2 H, C6H4NO2ꢀ4, J = 8.8 Hz).
Compounds 9 (general procedure). 1ꢀ[(RꢀBenzylidene)ꢀ
amino]ꢀ1Hꢀbenzimidazoleꢀ2ꢀthiol 7a—d (1 mmol) was added to
a solution of NaOH (1 mmol) in methanol (3 mL). After the
complete dissolution of 7a—d, pꢀnitrobenzyl bromide (1 mmol)
was added. The reaction mixture was stirred for 10 min and
diluted with water (20 mL). The precipitate that formed was
filtered off and recrystallized from ethanol.
Nꢀ(4ꢀChlorobenzylidene)ꢀ2ꢀ[(4ꢀnitrobenzyl)thio]ꢀ1Hꢀbenzꢀ
imidazoleꢀ1ꢀamine (9a). Yield 65%, m.p. 231—233 C. Found (%):
C, 59.82; H, 3.65; N, 13.43. C21H15ClN4O2S. Calculated (%):
C, 59.64; H, 3.58; N, 13.25. 1H NMR (DMSOꢀd6), : 4.73
(s, 2 H, CH2); 7.24—7.35 (m, 2 H, benzimidazole); 7.57—7.70
(m, 3 H, C6H4Clꢀ4, benzimidazole); 7.82 (d, 2 H, C6H4NO2ꢀ4,
J = 8.8 Hz); 7.99 (d, 2 H, C6H4Clꢀ4, J = 8.9 Hz); 8.06—8.13
(m, 1 H, benzimidazole); 8.20 (d, 2 H, C6H4NO2ꢀ4, J = 8.8 Hz);
9.2 (s, 1 H, N=CH).
NꢀBenzylideneꢀ2ꢀ[(4ꢀnitrobenzyl)thio]ꢀ1Hꢀbenzimidazoleꢀ1ꢀ
amine (9b). Yield 72%, m.p. 115—118 C. Found (%): C, 65.08;
H, 4.21; N, 14.57. C21H16N4O2S. Calculated (%): C, 64.93;
H, 4.15; N, 14.42. 1H NMR (DMSOꢀd6), : 4.73 (s, 2 H, CH2);
7.22—7.35 (m, 2 H, benzimidazole); 7.48—7.59 (m, 3 H, Ph);
7.61—7.70 (m, 1 H, benzimidazole); 7.83 (d, 2 H, C6H4NO2ꢀ4,
J = 8.8 Hz); 7.91—8.02 (m, 2 H, Ph); 8.03—8.11 (m, 1 H,
benzimidazole); 8.22 (d, 2 H, C6H4NO2ꢀ4, J = 8.8 Hz); 9.19
(s, 1 H, N=CH).
Nꢀ(4ꢀBromobenzylidene)ꢀ2ꢀ[(4ꢀnitrobenzyl)thio]ꢀ1Hꢀbenzꢀ
imidazoleꢀ1ꢀamine (9c). Yield 69%, m.p. 180—185 C. Found (%):
C, 53.85; H, 3.18; N, 11.87. C21H15BrN4O2S. Calculated (%):
C, 53.97; H, 3.24; N, 11.99. 1H NMR (DMSOꢀd6), : 4.71
(s, 2 H, CH2); 7.23—7.38 (m, 2 H, benzimidazole); 7.50—7.85
(m, 8 H, benzimidazole, C6H4NO2ꢀ4, C6H4Brꢀ4); 8.20 (d, 2 H,
C6H4NO2ꢀ4, J = 8.8 Hz); 8.87 (s, 1 H, N=CH).
Nꢀ(4ꢀMethylbenzylidene)ꢀ2ꢀ[(4ꢀnitrobenzyl)thio]ꢀ1Hꢀbenzꢀ
imidazoleꢀ1ꢀamine (9d). Yield 62.3%, m.p.148—152 C. Found (%):
C, 65.54; H, 4.42; N, 13.80. C22H18N4O2S. Calculated (%):
C, 65.65; H, 4.51; N, 13.92. 1H NMR (DMSOꢀd6), : 2.34 (s, 3 H,
Me); 4.68 (s, 2 H, CH2); 7.19—7.27 (m, 2 H, benzimidazole);
7.33 (d, 2 H, C6H4Meꢀ4, J = 8.1 Hz); 7.56—7.64 (m, 1 H,
benzimidazole); 7.79 (d, 2 H, C6H4NO2ꢀ4, J = 8.8 Hz); 7.83
(d, 2 H, C6H4Meꢀ4, J = 8.1 Hz); 7.96—8.06 (m, 1 H, benzimidꢀ
azole); 8.16 (d, 2 H, C6H4NO2ꢀ4, J = 8.8); 9.11 (s, 1 H, N=CH).
MS, m/z (Irel (%)): 402 [M]+ (30), 284 (32), 266 (34), 253 (50),
233 (28), 207 (45), 192 (12), 180 (20), 150 (56), 132 (32), 122 (24),
103 (38), 90 (70), 78 (100).
Compounds 10 were synthesized by analogy with compounds
9 from equimolar amounts of compounds 7 and the correspondꢀ
ing phenacyl bromides and recrystallized from ethanol.
2ꢀ({1ꢀ[(4ꢀBromobenzylidene)amino]ꢀ1Hꢀbenzimidazolꢀ2ꢀ
yl}thio)ꢀ1ꢀ(4ꢀbromophenyl)ethanone (10a). Yield 14.4%,
m.p. 190—193 C. Found (%): C, 49.84; H, 2.80; N, 7.83.
C22H15Br2N3OS. Calculated (%): C, 49.93; H, 2.86; N, 7.94.
1H NMR (DMSOꢀd6), : 5.01 (s, 2 H, CH2); 7.16—7.29 (m, 2 H,
benzimidazole); 7.43—7.53 (m, 1 H, benzimidazole); 7.71—7.83
(m, 4 H, C6H4Brꢀ4); 7.92 and 8.00 (both d, 2 H each, C6H4Brꢀ4,
J = 8.5 Hz); 8.06—8.13 (m, 1 H, benzimidazole); 9.18 (s, 1 H,
N=CH). MS, m/z (Irel (%)): 529 [M]+ (2), 380 (2), 346 (9), 331
(3), 299 (2), 198 (10), 183 (65), 174 (12), 163 (17), 150 (100), 118
(15), 89 (50), 76 (48).
2ꢀ({1ꢀ[(4ꢀBromobenzylidene)amino]ꢀ1Hꢀbenzimidazolꢀ2ꢀyl}ꢀ
thio)ꢀ1ꢀ(4ꢀnitrophenyl)ethanone (10b). Yield 69%, m.p. 189—193 C.
Found (%): C, 53.22; H, 3.00; N, 11.19. C22H15BrN4O3S. Calcuꢀ
lated (%): C, 53.34; H, 3.05; N, 11.31. 1H NMR (DMSOꢀd6), :
5.12 (s, 2 H, CH2); 7.20—7.36 (m, 2 H, benzimidazole); 7.45—7.58
(m, 1 H, benzimidazole); 7.80 and 7.98 (both d, 2 H each,
C6H4Brꢀ4, J = 8.4 Hz); 8.10—8.18 (m, 1 H, benzimidazole);
8.34 and 8.42 (both d, 2 H each, C6H4NO2ꢀ4, J = 9.1 Hz); 9.23
(s, 1 H, N=CH).
2ꢀ({1ꢀ[(4ꢀChlorobenzylidene)amino]ꢀ1Hꢀbenzimidazoleꢀ2ꢀ
yl}thio)ꢀ1ꢀ(4ꢀchlorophenyl)ethanone (10c). Yield 20%, m.p.
195—198 C. Found (%): C, 60.20; H, 3.50; N, 9.73.
C22H15Cl2N3OS. Calculated (%): C, 60.01; H, 3.43; N, 9.54.
1H NMR (DMSOꢀd6), : 5.05 (s, 2 H, CH2); 7.19—7.34 (m, 2 H,
benzimidazole); 7.45—7.56 (m, 1 H, benzimidazole); 7.62—7.72
(m, 4 H, C6H4Clꢀ4); 8.04 (d, 2 H, C6H4Clꢀ4, J = 8.7 Hz);
8.07—8.15 (m, 3 H, C6H4Clꢀ4, benzimidazole); 9.23 (s, 1 H,
N=CH).
Compounds 11 (general procedure). Method A. 2ꢀ({1ꢀ[(4ꢀRꢀ
Benzylidene)amino]ꢀ1Hꢀbenzimidazolꢀ2ꢀyl}thio)ꢀ1ꢀ(4ꢀR´ꢀ
phenyl)ethanone 10a—c (1 mmol) was added to a solution of
MeONa (1 mmol) in methanol (3 mL). The reaction mixture
was heated for 5 min, cooled, and diluted with water (20 mL).
The precipitate that formed was filtered off and recrystallized
from acetonitrile.
Method B. 1ꢀ[(RꢀBenzylidene)amino]ꢀ1Hꢀbenzimidazoleꢀ
2ꢀthiols 7a—d (1 mmol) was added to a solution of MeONa
(1 mmol) in methanol (3 mL). After their complete dissolution,
the corresponding phenacyl bromide (1 mmol) was added. The
reaction mixture was stirred for 10 min, and a solution of MeOH
(1 mmol) in methanol (3 mL) was added. The reaction mixture
was heated for 5 min, cooled, diluted with water (20 mL), and
neutralized with dilute hydrochloric acid. The precipitate that
formed was filtered off and recrystallized from acetonitrile.
2ꢀ(4ꢀBromobenzoyl)ꢀ3ꢀ(4ꢀbromophenyl)ꢀ3,4ꢀdihydroꢀ2Hꢀ
[1,3,4]thiadiazino[3,2ꢀa]benzimidazole (11a). Yield 40% (A),
21% (B), m.p. 176—178 C. Found (%): C, 50.12; H, 2.93;
N, 8.11. C22H15Br2N3OS. Calculated (%): C, 49.93; H, 2.86;
N, 7.94. 1H NMR (DMSOꢀd6), : 5.20 (dd, 1 H, H(3), J = 4.7 Hz,
J = 5.8 Hz); 5.86 (d, 1 H, H(2), J = 4.7 Hz); 7.12—7.25 (m, 3 H,
benzimidazole); 7.45 (d, 2 H, C6H4Brꢀ4, J = 6.9 Hz); 7.48—7.56
(m, 4 H, NH, C6H4Brꢀ4, benzimidazole); 7.83 and 8.03 (both d,
2 H each, C6H4Brꢀ4, J = 8.7 Hz). MS, m/z (Irel (%)): 529 [M]+
(2), 380 (3), 366 (3), 346 (21), 287 (11), 206 (10), 183 (100), 163
(37), 156 (58), 150 (78), 134 (23), 102 (53), 90 (38), 76 (80).
3ꢀ(4ꢀBromophenyl)ꢀ2ꢀ(4ꢀnitrobenzoyl)ꢀ3,4ꢀdihydroꢀ2Hꢀ
[1,3,4]thiadiazino[3,2ꢀa]benzimidazole (11b). Yield 32% (A),
13.6% (B), m.p. 124—128 C. Found (%): C, 53.51; H, 3.10;
N, 11.49. C22H15BrN4O3S. Calculated (%): C, 53.34; H, 3.05;
N, 11.31. 1H NMR (CDCl3), : 5.27 (dd, 1 H, H(3), J = 4.2 Hz,
J = 3.2 Hz); 5.93 (d, 1 H, H(2), J = 4.2 Hz); 7.10—7.34 (m, 3 H,
NH, benzimidazole); 7.40—7.57 (m, 6 H, C6H4Brꢀ4, benzꢀ
imidazole); 8.32 and 8.39 (both d, 2 H each, C6H4NO2ꢀ4,
J = 8.8 Hz).

Tetrahydrothiadiazine ring annulation
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 6, June, 2012
1159
2ꢀ(4ꢀChlorobenzoyl)ꢀ3ꢀ(4ꢀchlorophenyl)ꢀ3,4ꢀdihydroꢀ2Hꢀ
[1,3,4]thiadiazino[3,2ꢀa]benzimidazole (11c). Yield 13% (A),
20% (B), m.p. 170—172 C. Found (%): C, 60.17; H, 3.50;
N, 9.70. C22H15Cl2N3OS. Calculated (%): C, 60.01; H, 3.43;
N, 9.54. 1H NMR (DMSOꢀd6), : 5.21 (dd, 1 H, H(3), J = 4.6 Hz,
J = 5.4 Hz); 5.87 (d, 1 H, H(2), J = 4.6 Hz); 7.09—7.28 (m, 3 H,
benzimidazole); 7.38 (d, 2 H, C6H4Clꢀ4, J = 8.7 Hz); 7.43—7.53
(m, 2 H, NH, benzimidazole); 7.58 and 7.69 (both d, 2 H each,
C6H4Clꢀ4, J = 8.5 Hz); 8.11 (d, 2 H, C6H4Clꢀ4, J = 8.7 Hz).
3ꢀ(4ꢀBromophenyl)ꢀ2ꢀ(4ꢀmethoxybenzoyl)ꢀ3,4ꢀdihydroꢀ2Hꢀ
[1,3,4]thiadiazino[3,2ꢀa]benzimidazole (11d). Yield 27% (B),
m.p. 101—103 C. Found (%): C, 57.38; H, 3.70; N, 8.64.
C23H18BrN3O2S. Calculated (%): C, 57.51; H, 3.78; N, 8.75.
1H NMR (DMSOꢀd6), : 3.82 (s, 3 H, OMe); 5.05 (m, 1 H,
H(3)); 5.81 (d, 1 H, H(2), J = 5.6 Hz); 7.00 (d, 1 H, benzimidꢀ
azole, J = 8.7 Hz); 7.07 (d, 1 H, NH, J = 9.1 Hz); 7.13—7.22
(m, 3 H, C6H4OMeꢀ4, benzimidazole); 7.26—7.35 (m, 1 H, benzꢀ
imidazole); 7.38—7.55 (m, 5 H, C6H4OMeꢀ4, C6H4Brꢀ4, benzꢀ
imidazole); 8.02 (d, 2 H, C6H4Brꢀ4, J = 8.8 Hz).
Ph); 7.96 (d, 2 H, HAr, J = 8.8 Hz). MS, m/z (Irel (%)): 401 [M]+
(3), 399 [M]+ (3), 296 (18), 294 (7), 182 (3), 157 (4), 134 (10),
133 (22), 105 (77), 77 (100), 51 (42).
2ꢀ(4ꢀBromobenzoyl)ꢀ3ꢀ(4ꢀbromophenyl)ꢀ3,4ꢀdihydroꢀ2Hꢀ
imidazo[2,1ꢀb][1,3,4]thiadiazine (12b) was synthesized by analꢀ
ogy with compound 12a from equimolar amounts of compound 8
and pꢀbromophenacyl bromide. The compound was recrystalꢀ
lized from acetonitrile. Yield 60%, m.p. 192 C. Found (%):
C, 45.19; H, 2.76; N, 8.91. C18H13Br2N3OS. Calculated (%):
C, 45.12; H, 2.73; N, 8.77. 1H NMR (DMSOꢀd6), : 5.03 (dd, 1 H,
H(3), J = 2.8 Hz, J = 10.3 Hz); 5.83 (d, 1 H, H(2), J = 2.8 Hz);
6.91 (d, 1 H, H(7), J = 1.2 Hz); 7.23 (d, 2 H, HAr, J = 8.5 Hz);
7.27 (d, 1 H, H(6), J = 1.2 Hz); 7.29 (d, 1 H, NH, J = 10.3 Hz);
7.45 (d, 2 H, HAr, J = 8.5 Hz); 7.72 and 7.81 (both d, 2 H each,
HAr, J = 8.7 Hz). 13C NMR (DMSOꢀd6), : 45.3, 58.2, 121.6,
122.0, 126.3, 129.2, 130.6, 131.2, 131.6, 132.2, 132.9, 134.4,
138.1, 195.1. MS, m/z (Irel (%)): 296 (21), 294 (21), 183 (87),
178 (11), 155 (80), 134 (16), 113 (64), 102 (70), 89 (46), 76 (100),
50 (66).
2ꢀ(4ꢀBromobenzoyl)ꢀ3ꢀ(4ꢀmethylphenyl)ꢀ3,4ꢀdihydroꢀ2Hꢀ
[1,3,4]thiadiazino[3,2ꢀa]benzimidazole (11e). Yield 15% (B),
m.p. 190—192 C. Found (%): C, 59.35; H, 3.86; N, 8.91.
C23H18BrN3OS. Calculated (%): C, 59.49; H, 3.91; N, 9.05.
1H NMR (DMSOꢀd6), : 2.19 (s, 3 H, Me); 5.03 (dd, 1 H, H(3),
J = 5.3 Hz, J = 6.0 Hz); 5.86 (d, 1 H, H(2), J = 5.3 Hz);
7.02—7.19 (m, 5 H, C6H4Meꢀ4, benzimidazole); 7.35—7.51
(m, 4 H, NH, benzimidazole); 7.77 and 7.97 (both d, 2 H each,
C6H4Brꢀ4, J = 8.4 Hz).
Xꢀray diffraction study of compound 12b. Crystals are monoꢀ
clinic, at 293 K a = 8.981(4) Å, b = 10.934(5) Å, c = 17.954(9) Å,
 = 92.190(12), V = 1761.9(14) Å3, dcalc = 1.806 g cm–1, space
group P21/n, Z = 4. The intensities of 10344 reflections were
measured on a Smart 1000 CCD automated diffractometer at
293 K (MoꢀK radiation, graphite monochromator, ꢀscanning
technique, 2
= 55), and 4018 independent reflections
max
(Rint = 0.0332) were used in subsequent calculations. The strucꢀ
ture was solved by direct methods and refined by the fullꢀmatrix
leastꢀsquares method with anisotropic displacement parameters
based on F2hkl. The hydrogen atom of the NH group was located
in difference electron density maps. The H(C) atoms were posiꢀ
tioned geometrically. All hydrogen atoms were refined isotropiꢀ
cally using a riding model. The final R factors were wR2 = 0.0976,
GOF = 1.001 based on all independent reflections (R1 = 0.0358,
calculated for 2729 observed reflections with I > 2(I)). All calꢀ
culations were carried out with the use of the SHELXTL PLUS
program package.16
2ꢀ(4ꢀChlorobenzoyl)ꢀ3ꢀphenylꢀ3,4ꢀdihydroꢀ2Hꢀ[1,3,4]thiadiꢀ
azino[3,2ꢀa]benzimidazole (11f). Yield 25% (B), m.p. 183—187 C.
Found (%): C, 65.27; H, 4.05; N, 10.44. C22H16ClN3OS. Calcuꢀ
1
lated (%): C, 65.10; H, 3.97; N, 10.35. H NMR (DMSOꢀd6),
: 5.08 (dd, 1 H, H(3), J = 5.3 Hz, J = 6.0 Hz); 5.85 (d, 1 H, H(2),
J = 5.3 Hz); 7.11—7.33 (m, 6 H, Ph, NH, benzimidazole);
7.38—7.56 (m, 4 H, Ph, benzimidazole); 7.62 and 8.05 (both d,
2 H each, C6H4Clꢀ4, J = 8.4 Hz). 13C NMR (DMSOꢀd6), : 45.2,
58.1, 109.9, 118.5, 122.4, 122.9, 128.1, 128.8, 129.4, 130.1, 131.7,
134.3, 135.3, 138.3, 140.1, 140.6, 141.9, 195.3.
The complete crystallographic data were deposited with the
Cambridge Crystallographic Data Centre (CCDC 822147).
2ꢀ(4ꢀNitrobenzoyl)ꢀ3ꢀphenylꢀ3,4ꢀdihydroꢀ2Hꢀ[1,3,4]thiadiꢀ
azino[3,2ꢀa]benzimidazole (11g). Yield 16.8% (B), m.p. 185—190 C.
Found (%): C, 63.63; H, 3.96; N, 13.64. C22H16N4O3S. Calcuꢀ
We thank Yu. V. Nelyubina (A. N. Nesmeyanov Instiꢀ
tute of Organoelement Compounds of the Russian Acadeꢀ
my of Sciences, Moscow) for performing the Xꢀray difꢀ
fraction study.
This work was financially supported by the Council on
Grants at the President of the Russian Federation (Proꢀ
gram for State Support of Leading Scientific Schools of
the Russian Federation, Grant NShꢀ927.2012.3) and
the Russian Foundation for Basic Research (Project
Nos 09ꢀ03ꢀ00726ꢀa and 11ꢀ03ꢀ00145ꢀa).
1
lated (%): C, 63.45; H, 3.87; N, 13.45. H NMR (DMSOꢀd6),
: 5.23 (dd, 1 H, H(3), J = 4.6 Hz, J = 5.8 Hz); 5.98 (d, 1 H, H(2),
J = 4.6 Hz); 7.11—7.42 (m, 6 H, Ph, NH, benzimidazole);
7.44—7.63 (m, 4 H, Ph, benzimidazole); 8.33 and 8.41 (both d,
2 H each, C6H4NO2ꢀ4, J = 9.1 Hz). 13C NMR (DMSOꢀd6),
: 45.9, 57.5, 109.9, 118.5, 122.4, 122.9, 127.9, 128.0, 128.8,
129.4, 130.8, 131.2, 135.3, 138.2, 140.5, 140.6, 141.5, 195.4.
2ꢀBenzoylꢀ3ꢀ(4ꢀbromophenyl)ꢀ3,4ꢀdihydroꢀ2Hꢀimidazo[2,1ꢀb]ꢀ
[1,3,4]thiadiazine (12a). Methylideneaminoꢀ1Hꢀimidazoleꢀ2ꢀ
thiol 8 (0.28 g, 1 mmol) was added to a solution of NaOH (0.04 g,
1 mmol) in methanol (3 mL). After the complete dissolution,
phenacyl bromide (0.2 g, 1 mmol) was added. The reaction mixꢀ
ture was stirred for 5 min and diluted with water (20 mL). The
precipitate that formed was filtered off and recrystallized from
acetonitrile. Yield 57%, m.p. 190 C. Found (%): C, 54.14;
H, 3.61; N, 10.65. C18H14BrN3OS. Calculated (%): C, 54.01;
H, 3.53; N, 10.50. 1H NMR (acetoneꢀd6), : 5.01—5.05 (m, 1 H,
H(3)); 5.74 (d, 1 H, H(2), J = 2.6 Hz); 6.91 (d, 1 H, H(7),
J = 1.3 Hz); 7.03 (d, 1 H, NH, J = 11.4 Hz); 7.24 (d, 1 H, H(6),
J = 1.3 Hz); 7.48 (d, 2 H, HAr, J = 8.8 Hz); 7.53—7.56 (m, 5 H,
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Received April 25, 2011;
in revised form March 5, 2012