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Synlett 2003(15): 2389-2391  
DOI: 10.1055/s-2003-42095
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Unsymmetrical Pyrrolo[3,2-b]pyrrole-2,5-diones

Peter Langer*, Falko Helmholz, Rita Schroeder
Institut für Chemie und Biochemie der Ernst-Moritz-Arndt-Universität Greifswald, Soldmannstr. 16, 17487 Greifswald, Germany
e-Mail: Peter.langer@uni-greifswald.de;
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Publication History

Received 14 July 2003
Publication Date:
15 October 2003 (online)

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Abstract

The first unsymmetrical oxalic acid-bis(imidoyl)dichlorides were prepared and applied to the one-pot synthesis of the first unsymmetrical pyrrolo[3,2-b]pyrrole-2,5-diones and 2,2′-bis-quinazolin-4-ones.

Key words

one-pot synthesis - unsymmetrical pyrrolo[3,2-b]pyrrole-2,5-diones - dilactams of pulvinic acid

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General Procedure for the Synthesis of Unsymmetrical Oxalic Acid-bis(imidoyl) dichlorides ( 4). Oxalic acid N -phenyl- N ′-(2,4-dimethylphenyl)-bis(imidoyl) dichloride ( 4e): A toluene solution (60 mL) of 3e (2.68 g, 10.0 mmol) and of PCl5 (4.16 g, 20.0 mmol) was refluxed for 1 h. The mixture was concentrated to 30 mL and stored at -20 °C to give a yellow precipitate. The later was isolated by filtration and recrystallized from n-heptane to give 4e as yellow crystals (2.00 g, 65%), mp 148 °C. IR (KBr): 826 (m), 1443 (w), 1521 (m), 1666 (s), 3282 (s)cm-1. 1H NMR (200 MHz, CDCl3): δ = 2.23 (s, 3 H, CH3), 2.34 (s, 3 H,CH3), 6.94-7.66 (m, 8 H, Ar). 13C NMR (50 Hz, CDCl3): δ = 17.83, 21.03, 118.65, 120.12, 120.35, 126.51, 126.73, 128.95, 129.74, 131.27, 136.47, 136.60, 142.01, 145.79. MS (EI, 70 eV):
m/z (%) = 305 (15) [M+], 269 (7), 166 (33), 138 (36), 77 (44), 28 (100). Anal. Calcd for C16H14Cl2N2 (305.06): C, 62.99; H, 4.58; N, 9.17. Found: C, 63.08; H, 4.96; N, 9.09. All new compounds gave satisfactory spectroscopic and analytical and/or high resolution mass data.

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General Procedure for the Synthesis of Unsymmetrical Pyrrolo[3,2- b ]pyrrole-2,5-diones ( 6). A THF solution of LDA was prepared by addition of n-BuLi (5.15 mL, 7.92 mmol, solution in n-hexane) to a THF solution (6.1 mL) of diisopropylamine (1.22 mL, 8.71 mmol) at 0 °C. After stirring for 30 min a THF solution (33 mL) of ethyl 4-tolylacetate (1.18 mL, 6.60 mmol) was added. The solution was stirred for 1 h at 0 °C. The mixture was cooled to -78 °C and a THF solution (18 mL) of 4c (967 mg, 3.00 mmol) was slowly added. The solution was warmed to 20 °C during 14 h and was stirred for 36 h at 20 °C. The mixture was poured into an aqueous solution of ammonium chloride (300 mL, 5 M). The addition of Et2O (200 mL) resulted in the formation of a precipitate, which was washed with Et2O, dried in vacuo and recrystallized from DMF. For some products DMSO was used. The product 6e was obtained as an orange solid (538 mg, 35%), mp 344 °C. IR (KBr): 977 (m), 1168 (m), 1252 (m), 1301 (w), 1415 (m), 1514 (s), 1612 (m), 1653 (s), 1735 (s), 3437 (m)cm-1. UV-Vis: 361 (4.33). 1H NMR (200 MHz, CDCl3): δ = 2.27 (s, 6 H, CH3), 2.33 (s, 3 H, CH3), 3.79 (s, 3 H, OCH3), 6.77-7.09 (m, 16 H, Ar). 13C NMR (50 Hz, CDCl3): δ = 21.12, 21.33 (CH3), 55.57 (OCH3), 104.72, 104.78 (C), 113.97 (CH), 125.23, 125.28 (C), 125.91 (CH), 126.83 (C), 127.42, 128.24, 128.32, 129.23, 129.69, 129.75 (CH), 131.28, 137.17, 137.18, 137.96, 137.97, 144.80, 145.06, 158.67 (C), 170.91, 171.05 (CO). MS (EI, 70 eV): m/z (%) = 512 (100) [M+], 497 (11), 496 (10), 236 (10), 102 (36). Anal. Calcd for C34H28O3N2 (512.6): C, 79.66; H, 5.51; N, 5.46. Found: C, 79.19; H, 5.86; N, 5.37.