Preparative conversion of chloralamides to 2,5-diaryl-3a,6a-dihydro-[1,3] thiazolo[4,5-d ]-[1,3]thiazoles with the Lawesson reagent

Article abstract of DOI:10.1002/hc.20493

Based on readily available chloralamides, a preparative method for the synthesis of hitherto unknown 2,5-diaryl-3a,6a-dihydro[1,3]-thiazolo[4,5-d][1,3] thiazoles with the Lawesson reagent has been elaborated.

Full text of DOI:10.1002/hc.20493

Heteroatom Chemistry
Volume 19, Number 7, 2008
Preparative Conversion of Chloralamides to
2,5-Diaryl-3a,6a-dihydro-[1,3]thiazolo[4,5-d]-
[1,3]thiazoles with the Lawesson Reagent
Bogdan A. Demydchuk, Vladimir S. Brovarets, Alexander N.
Vasilenko, and Boris S. Drach
Institute of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine,
Murmanska str.1, 02660 Kyiv-94, Ukraine
Received 6 May 2008
containing amidals 4a–g have been obtained, which
ABSTRACT: Based on readily available chlo-
controllably react with the Lawesson reagent to give,
ralamides, a preparative method for the synthesis
in moderate to high yields, bicyclic heterocycles
of hitherto unknown 2,5-diaryl-3a,6a-dihydro[1,3]-
7a–g consisting of two [d]-annelated 2-thiazoline
thiazolo[4,5-d][1,3]thiazoles with the Lawesson
rings.
ꢀ
C
reagent has been elaborated. 2008 Wiley Periodicals,
The assigned structure of compounds 7a–g is
consistent with the IR and H NMR spectral data,
Inc. Heteroatom Chem 19:677–681, 2008; Published on-
line in Wiley InterScience (www.interscience.wiley.com).
which suggest that the cyclization involves the
DOI 10.1002/hc.20493
1
dichloromethyl and two acylamino groups. In addi-
tion, significant structural information was provided
by two-dimensional HMBC, HMQS, NOESY, and
INTRODUCTION
COSY experiments for compound 7b; they allowed
a complete assignment of 1H and 13C resonances
(Fig. 1), and the establishment of many correlations
between them (Table 1). The bicyclic structure of
molecule 7b was supported by the cross peaks aris-
ing from the interaction of the protons H6a (6.30
ppm) and H3a (7.70 ppm) with the carbon atoms C2
and C5. Signal assignment was also assisted by the
cross peaks of the coupled H2b,6b (7.68 ppm) and C2
(165.60 ppm) resonances as well as H2c,6c (7.78 ppm)
and C5 (165.71 ppm).
Chloral adducts of carboxamides, so-called chlo-
ralamides, have already found wide application
in the azole and azine synthesis, as reported, for
example, in the relevant monograph [1] and the
most recent publications [2–5]. Here we propose
an original method to convert readily available
chloralamides 1a–c to 2,5-disubstituted derivatives
of 3a,6a-dihydro[1,3]thiazolo[4,5-d][1,3]thiazole, a
novel heterocyclic system (Scheme 1).
Judging by the magnitude of the spin–spin cou-
pling constant 3 JH3aH6a = 8.8 Hz and taking into ac-
count the NOESY cross peaks of the H3a and H6a
signals, one can assume the cis configuration of the
mentioned hydrogen atoms in the bicyclic structure.
All this evidence implies the bicyclic structure
not only for compound 7b but for its analogues
7a,c–g as well. It is seen from Scheme 1 that
formation of these compounds probably involves in-
RESULTS AND DISCUSSION
After taking advantage of the previously found con-
versions 1 → 2 → 3, we have treated compounds
3a–c with benzoyl chloride or its analogues in the
presence of triethylamine. As a result, chlorine-
Correspondence to: Boris S. Drach; e-mail: drach@bpci.kiev.ua.
2008 Wiley Periodicals, Inc.
1
c
ꢀ
termediates 5 and 6. As corroborated by H NMR
677

678 Demydchuk et al.
OH
NH2
Cl
H
N
H
N
H
N
NH3
Zn, MeC(O)OH
R1
Cl
Cl
R1
R1
Cl Cl
Cl
Cl
O
O
O
1a–c
2a–c
3a–c
R2C(O)Cl, Et3N
H
H
R2
R1
N
N
LR
LR
O
O
Cl
Cl
4a–g
R1
R2
H
H
N
N
LR
LR
N
N
S
S
R2
R1
Cl
Cl
S
S
5
6
N
S
N
S
R2
R1
7a–g
(59-75%)
R2
R1
H
N
H
N
MnO2
N
N
S
S
R1
R2
S
S
N
S
N
S
8b
9
R2
R1
10 a,c,g
S
P
S
S
-MeOC H
P
S
C H OMe-
4
6 4
LR =
4
6
4
a
b
c
d
e
f
g
1–4,7,8,10
R1
Ph
4-MeC6H4
4-MeC6H4
4-ClC6H4
4-ClC6H4
Ph
Ph
Ph
4-MeC6H4
R2
Ph
4-MeC6H4
117.72
4-ClC6H4
thien-2-yl
thien-2-yl
SCHEME 1
128.98
132.35
165.71
130.25
7.70
165.60
H
129.72
143.08
128.98
132.91
132.91
7.56
N
N
21.75
2.33
H
4
3
3a
6a
H
5
2
b
c
1
6
S
H
S
H
H
H
H
H
6.30
H
7.49
7.78
60.09
7.68
7.29
FIGURE 1 The main correlations indicated by arrows and signal assignments, with chemical shifts given in ppm, for the 1H
and 13C NMR spectra of compound 7b.
Heteroatom Chemistry DOI 10.1002/hc

Preparative Conversion of Chloralamides to 2,5-Diaryl-3a,6a-dihydro-[1,3]thiazolo[4,5-d][1,3]thiazoles 679
TABLE 1 1H and 13C NMR Signal Assignments and Correlations in the COSY, NOESY, HMQC, and HMBC Spectra for
Compounds 7b
1H, δ
13C, δ
HMBC
143.08 (C4b), 130.25 (C3b, C5b
1H, δ
COSY
NOESY
HMQC
2.33 (Me)
–
7.68
7.29
6.30
7.70
7.29
7.68, 2.33
7.29
21.75
130.25
128.98
117.72
60.09
128.98
129.72
132.91
)
7.29 (C3bH, C5bH)
7.68 (C2bH, C6bH)
7.70 (C3aH)
21.75 (Me), 132.91 (C1b), 130.25 (C3b, C5b
)
128.98 (C2b, C6b), 143.08 (C4b), 132.91 (C1b), 165.60 (C2)
165.60 (C2), 165.71 (C5)
6.30
7.70
7.49
6.30 (C6aH)
165.60 (C2), 165.71 (C5), 117.72 (C3a
)
7.78 (C2cH)
7.49
128.98 (C2c, C6c), 132.35 (C1c), 165.71 (C5)
129.72 (C3c, C5c), 132.35 (C1c
128.98 (C2c, C6c
7.49 (C3cH, C5cH)
7.56 (C4cH)
7.78, 7.56
7.49
7.78, 7.56
7.49
)
)
spectra, the action of the Lawesson reagent on sub-
stituted thiazolines 5 and 6 can afford, in addition to
bicycles 7, the 4-amino-1,3-thiazole derivatives 8 and
9 as by-products. We managed to isolate one of such
compounds, 8b (R1 = R2 = 4-MeC6H4), in a moder-
ately low yield from the reaction mixture formed
on the treatment of amidal 4b with the Lawesson
reagent.
To conclude, the successive conversions 1 →→
4 →→ 7 yield a novel bicyclic system, 3a,6a-
dihydro[1,3]thiazolo[4,5-d][1,3]thiazole, and the ap-
plicational aspect of this finding calls for further
study. The synthetic approach proposed here is
of particular significance in view of the fact that
nonaromatic compounds 7a,c,g are readily oxidized
with manganese dioxide to furnish the correspond-
ing bicyclic heteroaromatics 10a,c,g, containing two
[d]-annelated thiazole rings (Scheme 1).
sponding acyl chloride (10 mmol) were added. The
mixture was allowed to stand at room temperature
for 2 h, and dioxane was removed in vacuo. For crys-
tallization, the residue was treated with H2O, filtered
off, and recrystallized from an appropriate solvent.
N-(1-Benzoylamino-2,2-dichloroethyl)benzamide
(4a). Compound 4a was prepared by a literature
procedure [7].
N-[1-(4-Methylbenzoylamino)-2,2-dichloroethyl]-
4-methylbenzamide (4b). Compound 4b was
prepared by a literature procedure [7].
N-[1-(4-Chlorobenzoylamino)-2,2-dichloroethyl]-
4-chlorobenzamide (4c). Compound 4c was
prepared by a literature procedure [7].
N-[1-(Benzoylamino)-2,2-dichloroethyl]-4-methyl-
benzamide (4d). Compound 4d was prepared fol-
lowing the general procedure from 3a (2.33 g) and
4-methylbenzoyl chloride (1.55 g). The product was
purified by recrystallization from dioxane; yield:
2.56 g (73%); colorless crystals; mp 213–215◦C; IR
(KBr): 1660 cm−1 (broad band, 2C O), 3050–3350
cm−1 (NH, assoc); 1H NMR (DMSO-d6/TMS) δ = 2.39
(s, 3H, CH3), 6.26 (m, 1H, CH), 6.41 (d, 1H, J = 6.0,
CHCl2), 7.27–7.87 (m, 9H, C6H5, C6H4), 8.66 (d, 1H,
J = 8.1, NH), 8.75 (d, 1H, J = 8.1, NH). Anal. Calcd
for C17H16Cl2N2O2: C, 58.13; H, 4.59; Cl, 20.19; N,
7.98. Found: C, 58.24; H, 4.63; Cl, 20.08; N, 7.80.
EXPERIMENTAL
Melting points were measured on en Fisher–Johns
melting point apparatus and are uncorrected. 1H and
13C NMR spectra for compound 7b were recorded on
a Varian Mercury-400 spectrometer at 400 and 100
MHz, respectively, and 1H NMR spectra for the other
compounds were recorded on a Varian Gemini-300
instrument at 300 MHz; all NMR measurements
were performed with TMS as internal standard and
DMSO-d6 as solvent. IR spectra were measured on
a UR-20 spectrophotometer in KBr disks. APCI MS
data for compound 7d were obtained on an Agilent
1100/DAD/MSD VL G1965a instrument.
N-[1-(Benzoylamino)-2,2-dichloroethyl]-4-chloro-
benzamide (4e). Compound 4e was prepared fol-
lowing the general procedure from 3a (2.33 g) and
4-chlorobenzoyl chloride (1.75 g). The product was
purified by recrystallization from dioxane; yield:
3.31 g (89%); colorless crystals; mp 191–192◦C; IR
(KBr): 1660 cm−1 (broad band, 2C O), 3050–3350
cm−1 (NH, assoc); 1H NMR (DMSO-d6/TMS) δ = 6.20
General Procedure for the Synthesis of N-(1-Acyl-
amino-2,2-dichloroethyl)carboxamides (4a–g)
To a solution of compound 3a–c (10 mmol) obtained
by the known procedure [6] in anhydrous dioxane
(50 mL), Et3N (1.4 mL, 10 mmol) and the corre-
Heteroatom Chemistry DOI 10.1002/hc

680 Demydchuk et al.
(m, 1H, CH), 6.44 (d, 1H, J = 5.7, CHCl2), 7.46–7.90
(m, 9H, C6H5, C6H4), 8.80 (d, 1H, J = 8.1, NH), 8.92
(d, 1H, J = 8.1, NH). Anal. Calcd for C16H13ClN2O2:
C, 51.71; H, 3.52; Cl, 28.62; N, 7.54. Found: C, 51.58;
H, 3.48; Cl, 28.45; N, 7.49.
(DMSO-d6/TMS) δ = 6.27 (d, 1H, J = 8.7, CH), 7.68
(d, 1H, J = 8.7, CH), 7.44–7.81 (m, 10H, 2C6H5).
Anal. Calcd for C16H12N2S2: C, 64.83; H, 4.08; N,
9.45; S, 21.63. Found: C, 64.68; H, 3.96; N, 9.31; S,
21.85.
N-[1-(Benzoylamino)-2,2-dichloroethyl]thiophene-
2-carboxamide (4f). Compound 4f was prepared
following the general procedure from 3a (2.33 g) and
thiophene-2-carbonyl chloride (1.47 g). The product
was purified by recrystallization from EtOH; yield:
3.26 g (95%); colorless crystals; mp 193–195◦C; IR
(KBr): 1660 cm−1 (broad band, 2C O), 3050–3350
cm−1 (NH, assoc); 1H NMR (DMSO-d6/TMS) δ = 6.15
(m, 1H, CH), 6.43 (d, 1H, J = 5.9, CHCl2), 7.14–7.88
(m, 8H, C6H5, thien-2-yl), 8.84 (m, 2H, 2NH). Anal.
Calcd for C14H12Cl2N2O2S: C, 48.99; H, 3.52; Cl,
20.66; N, 8.16; S, 9.34. Found: C, 48.87; H, 3.54; Cl,
20.38; N, 7.87; S, 9.41.
2,5-Bis(4-methylphenyl)-3a,6a-dihydro[1,3]thia-
zolo[4,5-d][1,3]thiazole (7b) and 2-(4-Methyl-
phenyl)-4-[4-methyl(thiobenzoyl)amino]-1,3-thiazole
(8b). Compound 7b was prepared following the
general procedure from 4b (1.09 g). The product
was purified by recrystallization from EtOH; yield:
0.69 g (71%); colorless crystals; mp 173–174◦C; IR
spectra (KBr): 1620–1700 and 3050–3600 cm−1 (no
bands were observed); 1H NMR (DMSO-d6/TMS)
δ = 2.38 (s, 6H, 2CH3), 6.24 (d, 1H, J = 8.8, CH), 7.62
(d, 1H, J = 8.8, CH), 7.26–7.69 (m, 8H, 2C6H4). Anal.
Calcd for C18H16N2S2: C, 66.63; H, 4.97; N, 8.63; S,
19.76. Found: C, 66.53; H, 4.82; N, 8.35; S, 19.56.
After isolating compound 7b, the alcoholic fil-
trate was evaporated to dryness and the residue
was recrystallized thrice from CH3CN to afford 8b;
yield: 0.15 g (15%); yellow crystals; mp 154–155◦C;
IR (KBr): 3100–3250 (NH, assoc); 1H NMR (DMSO-
d6/TMS) δ = 2.36 (s, 6H, 2CH3), 7.24–7.88 (m, 8H,
2C6H4), 8.81 (s, 1H, C5-thiaz.), 12.60 (s, 1H, NH).
Anal. Calcd for C18H16N2S2: C, 66.63; H, 4.97; N, 8.63;
S, 19.76. Found: C, 66.49; H, 4.81; N, 8.56; S, 20.08.
N-{2,2-Dichloro-1-[(4-methylbenzoyl)amino]-
ethyl}thiophene-2-carboxamide
(4g). Compound
4g was prepared following the general procedure
from 3b (2.47 g) and thiophene-2-carbonyl chloride
(1.47 g). The product was purified by recrystalliza-
tion from dioxane; yield: 3.43 g (96%); colorless
crystals; mp 189–190◦C; IR (KBr): 1660 cm−1 (broad
band, 2C O), 3050–3375 cm−1 (NH, assoc); 1H NMR
(DMSO-d6/TMS) δ = 2.39 (s, 3H, CH3), 6.13 (m, 1H,
CH), 6.42 (d, 1H, J = 6.0, CHCl2), 7.13–7.79 (m, 7H,
C6H4, thien-2-yl), 8.75 (d, 1H, J = 8.4, NH), 8.82 (d,
1H, J = 8.1, NH). Anal. Calcd for C15H14Cl2N2O2S:
C, 50.43; H, 3.95; Cl, 19.85; N, 7.84; S, 8.97. Found:
C, 50.28; H, 3.87; Cl, 19.80; N, 7.73; S, 9.02.
2,5-Bis(4-chlorophenyl)-3a,6a-dihydro[1,3]thia-
zolo[4,5-d][1,3]thiazole (7c). Compound 7c was
prepared following the general procedure from 4c
(1.22 g). The product was purified by recrystalliza-
tion from CH3CN; yield: 0.69 g (63%); colorless
crystals; mp 225–227◦C; IR spectra (KBr): 1620–
1700 and 3050–3600 cm−1 (no bands were observed);
1H NMR (DMSO-d6/TMS) δ = 6.34 (d, 1H, J = 8.7,
CH), 7.66 (d, 1H, J = 8.7, CH), 7.53–7.78 (m, 8H,
2C6H4). Anal. Calcd for C16H10Cl2N2S2: C, 52.61; H,
2.76; Cl, 19.41; N, 7.67; S, 17.55. Found: C, 52.54; H,
2.69; Cl, 19.11; N, 7.50; S, 17.50.
General Procedure for the Synthesis of 2,5-
Diaryl-3a,6a-dihydro[1,3]thiazolo[4,5-d][1,3]-
thiazoles (7a–e) and 2-Aryl-5-thien-2-yl-3a,6a-
dihydro[1,3]thiazolo[4,5-d][1,3]thiazoles (7f,g)
To a solution of compound 4a–g (3 mmol) in diox-
ane (30 mL), the Lawesson reagent (3.0 g, 7.5 mmol)
was added. The mixture was refluxed for 8–10 h, and
dioxane was removed in vacuo. For crystallization,
the residue was treated with 10% aqueous NaOH
(100 mL), filtered off, and recrystallized from an ap-
propriate solvent.
2-(4-Methylphenyl)-5-phenyl-3a,6a-dihydro[1,3]-
thiazolo[4,5-d][1,3]thiazole (7d). Compound 7d
was prepared following the general procedure
from 4d (1.05 g). The product was purified by
recrystallization from EtOH; yield: 0.53 g (57%);
colorless crystals; mp 151–153◦C; IR spectra (KBr):
1620–1700 and 3050–3600 cm−1 (no bands were
observed); 1H NMR (DMSO-d6/TMS) δ = 2.38 (s,
3H, CH3), 6.25 (d, 1H, J = 8.7, CH), 7.67 (d, 1H,
J = 8.7, CH), 7.26–7.80 (m, 9H, C6H5, C6H4); MS
for compound 7d: m/z = 311 [MH]+. Anal. Calcd
for C17H14N2S2: C, 65.77; H, 4.54; N, 9.02; S, 20.66.
Found: C, 65.83; H, 4.80; N, 8.89; S, 20.71.
2,5-Diphenyl-3a,6a-dihydro[1,3]thiazolo[4,5-d]-
[1,3]thiazole (7a). Compound 7a was prepared
following the general procedure from 4a (1.01 g).
The product was purified by recrystallization from
EtOH; yield: 0.67 g (75%); colorless crystals; mp
203–205◦C; IR spectra (KBr): 1620–1700 and 3050–
3600 cm−1 (no bands were observed); 1H NMR
Heteroatom Chemistry DOI 10.1002/hc

Preparative Conversion of Chloralamides to 2,5-Diaryl-3a,6a-dihydro-[1,3]thiazolo[4,5-d][1,3]thiazoles 681
2-(4-Chlorophenyl)-5-phenyl-3a,6a-dihydro[1,3]-
general procedure from 7a (0.30 g); yield: 0.18 g
(62%); colorless crystals; mp 214–215◦C; IR spectra
(KBr): 1620–1700 and 3050–3600 cm−1 (no bands
thiazolo[4,5-d][1,3]thiazole (7e). Compound 7e
was prepared following the general procedure
from 4e (1.11 g). The product was purified by
recrystallization from CH3CN; yield: 0.64 g (64%);
colorless crystals; mp 218–220◦C; IR spectra (KBr):
1620–1700 and 3050–3600 cm−1 (no bands were
observed); 1H NMR (DMSO-d6/TMS) δ = 6.30 (d, 1H,
J = 8.7, CH), 7.67 (d, 1H, J = 8.7, CH), 7.43–7.82 (m,
9H, C6H5, C6H4). Anal. Calcd for C16H11ClN2S2: C,
58.08; H, 3.35; Cl, 10.72; N, 8.47; S, 19.38. Found: C,
57.96; H, 3.28; Cl, 10.65; N, 8.50; S, 19.43.
1
were observed); H NMR (DMSO-d6/TMS) δ = 7.54–
8.05 (m, 10H, 2C6H5). Anal. Calcd for C16H10N2S2: C,
65.28; H, 3.42; N, 9.52; S, 21.78. Found: C, 65.36; H,
3.28; N, 9.38; S, 21.61.
2,5-Bis(4-chlorophenyl)[1,3]thiazolo[4,5-d][1,3]-
thiazole (10c). Compound 10c was prepared fol-
lowing the general procedure from 7c (0.36 g); yield:
0.15 g (42%); colorless crystals; mp >260◦C; IR
spectra (KBr): 1620–1700 and 3050–3600 cm−1 (no
bands were observed); 1H NMR (DMSO-d6/TMS)
δ = 7.61–8.04 (m, 8H, 2C6H4). Anal. Calcd for
C16H8Cl2N2S2: C, 52.90; H, 2.22; N, 7.71; S, 17.65;
Cl, 19.52. Found: C, 52.60; H, 2.15; N, 7.63; S, 17.89;
Cl, 19.47.
2-Phenyl-5-thien-2-yl-3a,6a-dihydro[1,3]thiazolo-
[4,5-d][1,3]thiazole (7f). Compound 7f was pre-
pared following the general procedure from 4f (1.03
g). The product was purified by recrystallization
from propan-2-ol; yield: 0.5 g (55%); colorless crys-
tals; mp 165–167◦C; IR spectra (KBr): 1620–1700
1
and 3050–3600 cm−1 (no bands were observed); H
2-(4-Methylphenyl)-5-thien-2-yl[1,3]thiazolo[4,5-
d][1,3]thiazole (10g). To a solution of compound
7g (0.31g, 1 mmol) in dioxane (20 mL), MnO2
(1.74 g, 20 mmol) was added. The mixture was
refluxed for 10 h and filtered, followed by the
removal of dioxane in vacuo and recrystallization
of the residue from dioxane; yield: 0.16 g (52%);
colorless crystals; mp 213–214◦C; IR spectra (KBr):
1620–1700 and 3050–3600 cm−1 (no bands were
observed); 1H NMR (DMSO-d6/TMS) δ = 2.39 (s,
3H, CH3), 7.23–7.91 (m, 7H, C6H4, thien-2-yl). Anal.
Calcd for C15H10N2S3: C, 57.29; H, 3.20; N, 8.91; S,
30.59. Found: C, 57.43; H, 3.06; N, 8.73; S, 30.50.
NMR (DMSO-d6/TMS) δ = 6.31 (d, 1H, J = 8.4, CH),
7.59 (d, 1H, J = 8.4, CH), 7.13–7.80 (m, 8H, C6H5,
thien-2-yl). Anal. Calcd for C14H10N2S3: C, 55.60; H,
3.33; N, 9.26; S, 31.80. Found: C, 55.64; H, 3.39; N,
9.18; S, 31.58.
2-(4-Methylphenyl)-5-thien-2-yl-3a,6a-dihydro-
[1,3]thiazolo[4,5-d][1,3]thiazole (7g). Compound
7g was prepared following the general procedure
from 4g (1.07 g). The product was purified by
recrystallization from propan-2-ol; yield: 0.56 g
(59%); colorless crystals; mp 160–161◦C; IR spectra
(KBr): 1620–1700 and 3050–3600 cm−1 (no bands
1
were observed); H NMR (DMSO-d6/TMS) δ = 2.38
REFERENCES
(s, 3H, CH3), 6.27 (d, 1H, J = 8.7, CH), 7.56 (d, 1H,
J = 8.7, CH), 7.12–7.79 (m, 7H, C6H4, thien-2-yl).
Anal. Calcd for C15H12N2S3: C, 56.93; H, 3.82; N,
8.85; S, 30.40. Found: C, 57.03; H, 3.90; N, 8.69; S,
30.48.
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General Procedure for the Synthesis of 2,5-
Diaryl[1,3]thiazolo[4,5-d][1,3]thiazoles (10a,c)
To a solution of compound 7a,c (1 mmol) in diox-
ane (20 mL), MnO2 (1.74 g, 20 mmol) was added.
The mixture was refluxed for 10–12 h and filtered,
followed by the removal of dioxane in vacuo and re-
crystallization of the residue from dioxane.
2,5-Diphenyl[1,3]thiazolo[4,5-d][1,3]thiazole
(10a). Compound 10a was prepared following the
Heteroatom Chemistry DOI 10.1002/hc