Mild and Convenient Synthesis of Benzodithiazoles by Oxidative Cyclization of Bis(thiobenzanilides)

Zahid Hassan; Peter Langer

doi:10.1055/s-0032-1317510

Synlett, Inhaltsverzeichnis

Synlett 2012; 23(19): 2811-2813
DOI: 10.1055/s-0032-1317510

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Mild and Convenient Synthesis of Benzodithiazoles by Oxidative Cyclization of Bis(thiobenzanilides)

Zahid Hassan

^aInstitut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany Fax: +49(381)4986412 eMail: peter.langer@uni-rostock.de

,

Peter Langer*

^aInstitut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany Fax: +49(381)4986412 eMail: peter.langer@uni-rostock.de

^bLeibniz-Institut für Katalyse an der Universität Rostock e.V., Albert-Einstein-Str. 29a, 18059 Rostock, Germany

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Abstract

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Abstract

Benzodithiazoles were prepared by oxidative cyclization of bis(thiobenzanilides). The reactions were performed at room temperature under mild conditions and rely on the use of N-benzyl-DABCO tribromide.

Key words

benzodithiazoles - thioamides - organic ammonium tribromides - cyclization - C–S bond formation

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Referenzen

References and Notes

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14 General Procedure A for the Synthesis of 6a–f To a cold suspension of 1,3-benzenediamine 4 (1.0 equiv, 18.5 mmol) and Et₃N (5.1 mL, 37 mmol, 2.0 equiv) in dry CH₂Cl₂ (50 mL), a CH₂Cl₂ solution (10 mL) of benzoyl chloride 5a–g (2.0 equiv) was added dropwise. The reaction mixture was stirred at 20 °C for 12 h and subsequently poured into 100 mL of H₂O. The organic layer was separated, washed with an aq solution of NaHCO₃ and with H₂O (30 mL), and dried by Mg₂SO₄. The solution was filtered and concentrated under reduced pressure.
15 N,N′-(1,3-Phenylene)bis(4-methylbenzamide) (6a) Starting with 4 (2.00 g, 18.5 mmol, 1.0 equiv), Et₃N (5.1 mL, 37 mmol, 2.0 equiv), 4-methylbenzoyl chloride (4.8 mg, 37 mmol, 2.0 equiv), CH₂Cl₂ (25 mL), following General Procedure A, 6a was isolated (3.5 g, 55%); mp 257–259 °C. ¹H NMR (300 MHz, DMSO-d ₆): δ = 3.37 (s, 6 H, CH₃), 7.29–7.37 (m, 5 H), 7.51 (dd, J = 7.9, 1.8 Hz, 2 H), 7.92 (d, J = 8.2 Hz, 4 H), 8.34 (t, J = 3.2 Hz, 1 H), 10.2 (s, 2 H, NH). ¹³C NMR (75.5 MHz, DMSO-d ₆): δ = 20.7 (2-CH₃), 112.9, 115.9, 127.7, 128.4, 128.8 (CH), 132.0, 139.3, 141.5 (C), 165.3 (CO). GC–MS (EI, 70 eV): m/z (%) = 344 (67) [M⁺], 119 (99), 91 (44), 65 (13). HRMS (EI, 70 eV): m/z calcd for C₂₂H₂₀N₂O₂ [M]⁺: 344.1519; found: 344.1522.
16 General Procedure B for the Synthesis of 7a–f The amide starting material (0.5 mmol) and Lawesson’s reagent (0.5 mmol) were refluxed in toluene (30 mL) for 1 h. Upon cooling, the solvent was evaporated using a rotary evaporator. The crude mixture was purified by column chromatography (silica gel, CH₂Cl₂–hexane = 1:1) to obtain the deep yellow colored compounds 7a–f in high yields (76–82%).
17 N,N′-(1,3-Phenylene)bis(4-methylbenzothioamide) (7a) Starting with 6a (1.00 g, 1.0 equiv), Lawesson’s reagent (0.80 g, 1.0 equiv), toluene (25 mL), following General Procedure B, 7a was isolated (1.34 g, 92%). ¹H NMR (300 MHz, DMSO-d ₆): δ = 2.39 (s, 6 H, CH₃), 7.29 (d, J = 8.1 Hz, 4 H), 7.49 (t, 3 H), 7.69 (d, J = 7.6 Hz, 4 H), 8.35 (s, 1 H), 11.74 (s, 2 H, NH). ¹³C NMR (75.5 MHz, DMSO-d ₆): δ = 20.8 (2-CH₃), 120.1, 122.2, 127.5, 128.3, 128.5 (CH), 139.4, 140.1, 140.9 (C), 197.4 (CS). GC–MS (EI, 70 eV): m/z (%) = 377 (76) [M⁺], 343 (67), 240 (43), 226 (93), 135 (70); HRMS (EI, 70 eV): m/z calcd for C₂₂H₂₀N₂S₂ [M]⁺: 377.1140; found: 377.1138.
18 General Procedure C for the Oxidative Cyclization of Thiobenzanilides To a stirred solution of thiobenzanilide 7a–f (1.0 equiv) in CH₂Cl₂–CCl₄ (1:1, 10 mL), N-benzyl-DABCO tribromide (2.0 equiv) was added. The reaction mixture was stirred for 30–90 min at 20 °C (TLC control). The solvent was removed under reduced pressure, and the residue was subjected to column chromatography (CH₂Cl₂–hexane, 1:1) to obtain products 8a–f.
19 1,4-Bis[4-methylphenyl]benzo[1,2-d:4,5-d]bisdithiazole (8a) Starting with 7a (200 mg, 1.0 equiv), N-benzyl-DABCO tribromide (450 mg, 2.0 equiv), CH₂Cl₂–CCl₄ (1:1, 10 mL), following General Procedure C, 8a was isolated as a yellow solid (138 mg, 70%); mp 221–223 °C. ¹H NMR (300 MHz, DMSO-d ₆): δ = 2.38 (s, 6 H, CH₃), 7.31 (d, J = 8.1 Hz, 4 H), 7.98 (d, J = 8.4 Hz, 5 H), 8.03 (s, 1 H). ¹³C NMR (75.5 MHz, DMSO-d ₆): δ = 26.3 (CH₃), 124.8, 125.1, 132.2, 134.8 (CH), 135.3, 141.4, 146.6, 158.6, 172.2 (C). GC–MS (EI, 70 eV): m/z (%) = 372 (100) [M⁺], 186 (16), 138 (43). HRMS (EI, 70 eV): m/z calcd for C₂₂H₁₆N₂S₂ [M]⁺: 372.0749; found: 372.0751.