ꢀ ꢁ
A. Rasovic et al. / Tetrahedron 69 (2013) 10849e10857
10856
spectra were recorded on a PerkineElmer FTIR 1725X spectro-
photometer and are reported as wavenumbers (cmꢀ1). For IR
measurements the solid samples were prepared as KBr disks and
the liquid ones as capillary films. The NMR spectra were obtained
using a Varian Gemini 2000 instrument (1H at 200 MHz, 13C at
50.3 MHz). Chemical shifts are reported in parts per million (ppm)
51.40; H, 4.31; N, 9.99]; Rf (toluene/ethyl acetate, 3:2) 0.63; IR (KBr):
nmax 3182, 3128, 3055, 2927,1594,1522,1493, 1437, 1387,1291,1210,
1179, 826, 762, 696 cmꢀ1 1H NMR (DMSO-d6):
; d 1.28 (3H, t,
J¼7.5 Hz, CH3), 2.94 (2H, q, J¼7.5 Hz, CH2), 7.23 (1H, d, J¼7.6 Hz, p-
Ph), 7.42 (2H, t, J¼8.0 Hz, m-Ph), 7.46 (1H, s, ]CH), 7.62 (2H, d,
J¼7.8 Hz, o-Ph), 11.21 (1H, s, NH); 13C NMR (DMSO-d6):
d 13.2 (CH3),
on the
d
scale from TMS as an internal standard in the solvents
30.8 (CH2), 114.5 (]CH), 122.0 (o-Ph), 125.6 (p-Ph), 129.2 (m-Ph),
139.8 (CipsoePh), 180.5 (NeCeS), 182.7 (N]CeS), 190.8 (C]S); MS
(CI): m/z 281 (Mþ1)þ; UV (DMSO): lmax (ε) 356 nm (4070) and
435 nm (6090).
specified. Low-resolution mass spectra were recorded using a Fin-
nigan MAT 8230 BE spectrometer at 70 eV (EI). Isobutane was used
as the ionizing gas for the chemical ionization (CI) mass spectra.
The UV spectra were measured on a Beckman DU-50 spectropho-
tometer. Analytical thin-layer chromatography (TLC) was carried
out on Kieselgel G nach Stahl, and the spots were visualized by
iodine. Column chromatography was carried out on SiO2 (silica gel
4.2.3. Ethyl 3-(3-(2-(phenylamino)-2-thioxoethylidene)-3H-1,2,4-
dithiazol-5-yl)propanoate (7c). From 6c (100 mg, 0.32 mmol) and
LR (130 mg, 0.32 mmol) in dry toluene (6 mL) after column chro-
60 A, 12e26, ICN Biomedicals). Elemental analyses were performed
matography (toluene/EtOAc 10:0 to 5:1) the 3,3al
4,4-trithia-1-
ꢂ
at the microanalysis laboratory at the Department of Chemistry,
University of Belgrade. HRMS of 2,20-(4,40-thiobis(thiazole-4,2-
diyl))bis(N-phenylethanethioamide) 9a and diethyl 2,20-(4,40-thi-
obis(thiazole-4,2-diyl))diacetate 15 was carried out on 6210 TOF
LC/MS coupled with HPLC 1200 Series Agilent Technologies.
azapentalene 7c was isolated (60 mg, 55%) as yellowish solid; mp
162 ꢂC; [Found: C, 50.72; H, 4.50; N, 7.89; S, 27.00 C15H16N2O2S3
requires C, 51.11; H, 4.58; N, 7.95; S, 27.29]; Rf (toluene/ethyl acetate,
3:2) 0.65; IR (KBr): nmax 3184, 1715, 1526, 1493, 1460, 1436, 1372,
1290, 1232, 1214, 1182, 810, 762, 699 cmꢀ1 1H NMR (DMSO-d6):
;
d
1.18 (3H, t, J¼7.2 Hz, CH3), 2.80 (2H, t, J¼6.7 Hz, CH2CO), 3.18 (2H, t,
4.2. General procedure for the preparation of 3,3a
l
4,4-trithia-
J¼6.7 Hz, CH2CS), 4.08 (2H, q, J¼7.2 Hz, CH2O), 7.18e7.26 (1H, m, p-
Ph), 7.38e7.46 (2H, m, m-Ph), 7.45 (1H, s, ]CH), 7.61 (2H, d, J¼8.0 Hz,
1-azapentalenes 7aed
o-Ph), 11.23 (1H, s, NH); 13C NMR (DMSO-d6):
d 14.3 (CH3), 31.9
A colourless solution of (Z)-2-alkylidene-4-oxothiazolidines
6aed (0.164 mmol) and LR (0.164 mmol) in dry toluene (3 mL)
was heated in an oil bath at 105e110 ꢂC. Caution: All reactions in-
volving Lawesson’s reagent, due to the unpleasant odour, should be
carried out in a well-ventilated hood. The mixture was stirred at this
temperature for an additional 3e6 h when TLC indicated the
complete consumption of substrates 6aed. After cooling to room
temperature, the solvent was evaporated in vacuum. The residue
was chromatographed (toluene/ethyl acetate, 10:0/3:2, v/v)
affording yellow solid trithiaazapentalenes 7aed in small to mod-
erate yields (20e55%). The structural assignments of all isolated
products were made on the basis of spectroscopic data (IR, 1H and
13C NMR, MS, UV) and elemental analysis. The assignments are
(CH2CO), 32.6 (CH2CS), 60.3 (CH2O),114.7 (]CH),121.9 (o-Ph),125.6
(p-Ph),129.3 (m-Ph),139.8 (CipsoePh),171.8 (COester),180.3 (NeCeS),
182.3 (N]CeS),188.3 (C]S); MS (CI): m/z 353 (Mþ1)þ; UV (DMSO):
lmax (ε) 349 nm (9948), 416 nm (16,230) and 457 nm (9948).
4.2.4. Ethyl 3-(3-(2-(phenethylamino)-2-thioxoethylidene)-3H-1,2,4-
dithiazol-5-yl)propanoate (7d). From 6d (50 mg, 0.14 mmol) and LR
(60 mg, 0.14 mmol) in dry toluene (4 mL) after column chroma-
tography (toluene/EtOAc 10:0 to 5:1) the 3,3al
4,4-trithia-1-
azapentalene 7d was isolated (11 mg, 20%) as yellowish-orange
solid; mp 106e107 ꢂC; [Found: C, 53.46; H, 5.28; N, 7.34; S, 25.07
C
17H20N2O2S3 requires C, 53.66; H, 5.30; N, 7.36; S, 25.27]; Rf (tol-
uene/ethyl acetate, 3:2) 0.68; IR (KBr): nmax 3321, 1712, 1552, 1490,
1407, 1378, 1267, 1200, 1145, 1019, 814, 743, 691 cmꢀ1 1H NMR
(DMSO-d6):
based on the highly delocalized 3,3a
l
4,4-trithia-1-azapentalene
;
structures 4,7 with emphasis on an increased contribution of the
1,2-dithiole form (and on a decreased contribution of the 1,2,4-
dithiazole form) in the hybrid structure 4 in comparison with this
of 7.
d
1.17 (3H, t, J¼7.2 Hz, CH3), 2.77 (2H, t, J¼6.8 Hz,
CH2CO), 2.90 (2H, t, J¼7.3 Hz, CH2Ph), 3.11 (2H, t, J¼6.8 Hz, CH2CS),
3.57e3.67 (2H, m, CH2NH), 4.07 (2H, q, J¼7.2 Hz, CH2O), 7.16 (1H, s,
]CH), 7.22e7.35 (5H, m, Ph), 9.68 (1H, t, J¼5.3 Hz, NH); 13C NMR
(DMSO-d6):
d 14.3 (CH3), 31.8 (CH2CO), 31.9 (CH2Ph), 33.8 (CH2CS),
4.2.1. 2-(5-Methyl-3H-1,2,4-dithiazol-3-ylidene)-N-phenylethaneth-
ioamide (7a). From 6a (50 mg, 0.21 mmol) and LR (90 mg,
0.22 mmol) in toluene (4 mL) after column chromatography (tol-
46.8 (CH2NH), 60.3 (CH2O), 113.4 (]CH), 126.5 (p-Ph), 128.7 (o-Ph),
128.9 (m-Ph), 139.1 (CipsoePh), 171.9 (COester), 177.7 (NeCeS), 185.4
(N]CeS), 186.1 (C]S); MS (CI): m/z 381 (Mþ1)þ; UV (DMSO): lmax
(ε) 326 (5120), 414 nm (6800) and 436 nm (6050).
uene/EtOAc 10:0 to 8:2) the 3,3al
4,4-trithia-1-azapentalene 7a was
isolated (23 mg, 41%) as yellowish solid; mp 217 ꢂC; [Found: C,
49.64; H, 3.80; N, 10.46; S, 36.07 C11H10N2S3 requires C, 49.60; H,
3.78; N, 10.52; S, 36.10]; Rf (toluene/ethyl acetate, 3:2) 0.69; IR
(KBr): nmax 3182, 3128, 2959, 1598, 1542, 1486, 1440, 1421, 1385,
4.3. General procedure for the preparation of thiazoles 9a,15
A colourless solution of (Z)-2-alkylidene-4-oxothiazolidines
6a,12 (0.164 mmol) and LR (0.164 mmol) in dry toluene (3 mL)
was heated in an oil bath at 106e110 ꢂC. Caution: All reactions in-
volving Lawesson’s reagent, due to the unpleasant odour, should be
carried out in a well-ventilated hood. The mixture was stirred at this
temperature for additional 5e6 h when TLC indicated the complete
consumption of substrates 6a,12. After cooling to room tempera-
ture, the solvent was evaporated in vacuum. The residue was
chromatographed (toluene/ethyl acetate, 10:0/4:1, v/v) affording
brown oily thiazoles 9a,15 in a moderate yields (22e70%). The
structural assignments of all isolated products were made on the
basis of spectroscopic data (IR, 1H and 13C NMR, HRMS).
1292, 1215, 1184, 815, 766, 693 cmꢀ1 1H NMR (DMSO-d6):
; d 2.66
(3H, s, CH3), 7.21 (1H, t, J¼7.3 Hz, p-Ph), 7.42 (2H, t, J¼8.5 Hz, m-Ph),
7.48 (1H, s, ]CH), 7.62 (2H, d, J¼8.0 Hz, o-Ph), 11.24 (1H, s, NH); 13
C
NMR (DMSO-d6):
d 23.9 (CH3), 114.5 (]CH), 121.9 (o-Ph), 125.6 (p-
Ph), 129.2 (m-Ph), 139.9 (CipsoePh), 180.5 (NeCeS), 182.7 (N]CeS),
184.9 (C]S); MS (EI): m/z (rel. intensity): 266 (Mþ, 47), 233 (13),
208 (3), 174 (37), 160 (5), 143 (16), 132 (8), 118 (10), 101 (8), 77 (16),
59 (100); UV (DMSO): lmax (ε) 346 nm (7500) and 435 nm (11,200).
4.2.2. 2-(5-Ethyl-3H-1,2,4-dithiazol-3-ylidene)-N-phenyl-
ethanethioamide (7b). From 6b (50 mg, 0.20 mmol) and LR (80 mg,
0.20 mmol) in dry toluene (4 mL) after column chromatography
(toluene/EtOAc 10:0 to 6:1) the 3,3a
l
4,4-trithia-1-azapentalene 7b
4.3.1. 2,20-(4,40-Thiobis(thiazole-4,2-diyl))bis(N-phenyl-
ethanethioamide) (9a). From 6a (100 mg, 0.42 mmol) and LR
(170 mg, 0.42 mmol) in dry toluene (8 mL) after column
was isolated (11 mg, 20%) as dark yellowish-orange solid; mp
164 ꢂC; [Found: C, 51.80; H, 4.62; N, 9.60 C12H12N2S3 requires C,