Helvetica Chimica Acta – Vol. 98 (2015)
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toluene) indicated the complete consumption of 12, the mixture was evaporated, and the crude product
purified by column chromatography (CC; SiO2, 5 Â 7 cm); AcOEt/toluene gradient from 1:5 to 1:10.
Yield: 94.4 mg (87%). Colorless solid. M.p. 1768. 1H-NMR (CDCl3): 1.25 (t, J ¼ 7.0, 4 Me); 4.29 (q, J ¼ 7.0,
4 CH2O); 4.80 (s, HÀC(4), HÀC(9)); 7.23 (s, HÀC(5), HÀC(10)). 13C-NMR (CDCl3): 13.9 (Me); 63.1
(CH2O); 67.4 (C(4), C(9)); 85.0 (C(2), C(7)); 126.0 (C(5), C(10)); 129.6, 135.1 (C(4a), C(5a), C(9a),
C(10a)); 166.3 (CO). EI-MS: 514 (100, Mþ), 441 (82), 395 (76), 267 (70). Anal. calc. for C22H26O10S2
(514.57): C 51.35, H 5.09; found: C 51.39, H 5.15.
In the first period of the reaction – in particular, when only a very small excess of dienophile 14 was
applied – the intermediate monoadduct 15 could be established by its NMR data (Table).
1
Diethyl 4,7-Dihydrothieto[2,3-g][3,1]benzoxathiine-2,2-dicarboxylate (15). H-NMR (CDCl3): 1.23
(t, J ¼ 7.0, 2 Me); 4.24 (q, J ¼ 7.0, 2 CH2O); 4.25 (s, HÀC(5)); 4.73 (s, HÀC(12)); 6.89, 6.97 (2s, HÀC(2),
HÀC(7)). 13C-NMR (CDCl3): 13.9 (Me); 36.3 (C(5)); 62.9 (CH2O); 68.4 (C(12)); 85.0 (C(10)); 119.6,
123.2 (C(2), C(7)); 126.4, 137.3, 139.7, 142.1 (C(1), C(3), C(6), C(8)); 166.6 (CO).
Tetraethyl 1,10-Dihydrobenzo[1,2-d:4,3-d’]bis[1,3]oxathiine-3,3,8,8-tetracarboxylate (22). A soln. of
benzobisthiete 18 (35 mg, 0.21 mmol) and 14 (87 mg, 0.50 mmol) was heated to reflux in 50 ml of dry
toluene. As soon as the TLC (SiO2; toluene) indicated the complete consumption of 18, the mixture was
evaporated and the crude product purified by CC (SiO2 (40 Â 4 cm); petroleum ether (40 – 708; PE)/
AcOEt, gradient 5 :1 to 3 :1. Alternatively, two consecutive column chromatographies with the solvent
mixtures ratio 5 :1 and then 3 :1 can be performed. Yield: 26 mg (24%). Colorless oil. 1H-NMR (CDCl3):
1.24 (t, J ¼ 7.0, 4 Me); 4.25 (q, J ¼ 7.0, 4 CH2O); 4.88 (s, HÀC(4), HÀC(5)); 7.28 (s, HÀC(9), HÀ(10)).
13C-NMR (CDCl3): 13.9 (Me); 63.1 (CH2O); 63.5 (C(4), C(5)); 84.7 (C(2) C(7)); 128.3 (C(9), C(10));
129.8, 131.7 (C(4a), C(4b), C(8a), C(10a)); 166.2 (CO). HR-ESI-MS: 514.0977 (Mþ, C22H26O10S2þ ; calc.
514.0967).
Dimethyl 2,3-Bis[(dimethylcarbamothioyl)oxy]benzene-1,4-dicarboxylate (25). 2,3-Dihydroxyben-
zene-1,4-dicarboxylic acid dimethylester (23; [22], 20.0 g, 88.0 mmol), dimethylthiocarbamoylchlorid
(24; 65.51 g, 0.53 mol) and DABCO (59.46 g, 0.53 mol) were stirred under Ar in 250 ml of dry DMFat r.t.
The clear, pale yellow soln. became soon turbid. After stirring overnight, the suspension was poured on
1000 ml of an ice-water mixture. The crude product was collected, washed with H2O and carefully dried
at 1058. The obtained pale yellow product (31.87 g, 90%) melted at 1468 and was analytically pure.
1H-NMR (CDCl3): 3.31, 3.42 (2s, Me2N); 3.83 (s, MeO); 7.92 (s, HÀC(5), HÀC(6)). 13C-NMR (CDCl3):
39.0, 43.3 (Me2N); 52.4 (MeO); 127.8 (C(5), C(6)); 128.6 (C(1), C(4)); 146.9 (C(2), C(3)); 163.5 (CO);
186.1 (CS). FD-MS: 400 (Mþ, 100). Anal. calc. for C16H20N2O6S2 (400.47): C 47.99, H 5.03, N 7.00, S 16.01;
found: C 48 48.01, H 5.09, N 6.89, S 15.93.
Dimethyl 2,3-Bis[(dimethylcarbamoyl)sulfanyl]benzene-1,4-dicarboxylate (26). Ester 25 (12.0 g,
30 mmol) was heated in 180 ml of diphenylether to 2058. TLC control (SiO2; PE/AcOEt 1:1) revealed
complete consumption of 25 after approximately 45 min. The diphenylether was distilled off at 0.1 kPa
and the residue purified by column filtration (SiO2; 12 Â 10 cm; PE/AcOEt 1:2). Yield: 7.54 g (63%).
M.p. 968. 1H-NMR (CDCl3): 2.98, 3.04 (2s, Me2N); 3.81 (s, MeO); 7.77 (s, HÀC(5), HÀC(6)). 13C-NMR
(CDCl3): 31.9 (Me2N); 47.3 (MeO); 124.8 (C(5), C(6)); 131.3, 134.9 (C(1), C(2), C(3), C(4)); 160.0,
161.6 (CO). FD-MS: (400, Mþ). Anal. calc. for C16H20N2O6S2 (400.47): C 47.99, H 5.03, N 7.00, S 16.01;
found: C 48.04, H 5.07, N 6.98, S 16.03.
(2,3-Disulfanylbenzene-1,4-diyl)dimethanol (27). Ester 26 (4.0 g, 10.0 mmol) suspended in 50 ml of
dry THF was dropped at 08 under Ar to LiAlH4 (1.90 g, 50.0 mmol) in 250 ml of dry THF. After the
addition was completed, the mixture was heated to reflux. TLC control (SiO2; PE/AcOEt) indicated the
end of the reaction after 1 h reflux. AcOEt (20 ml) and H2O (20 ml) were slowly added to the mixture at
08. After addition of 200 ml of 2m H2SO4 and vigorous stirring, the mixture was extracted four times with
AcOEt, 30 ml each. The combined solns. were washed with H2O, which contained NaCl, dried (MgSO4),
and evaporated at 0.1 kPa. A yellow solid (2.0 g, 99%) remained, which melted at 1158 and was
analytically pure. 1H-NMR (CDCl3): 4.66 (s, CH2); 7.26 (s, HÀC(5), HÀC(6)). 13C-NMR ((D6)acetone):
64.6 (CH2); 126.0 (C(5), C(6)); 131.7 (C(2), C(3)); 140.6 (C(1), C(4)). EI-MS (70 eV): 202 (5, Mþ), 166
(100, [M À 2 H2O]þ). Anal. calc. for C8H10O2S2: C 47.50, H 4.98, S 31.7; found: C 47.43, H 4.89, S 31.71.
2,2,9,9-Tetramethyl-4,7-dihydrobenzo[1,2-d:6,5-d’]bis[1,3]oxathiine (29). Diol 27 (400 mg, 2.0 mmol)
was stirred in 50 ml of dry acetone (28) at r.t. in the presence of 50 mg of DOWEX 50Wꢁ, an acidic ion