Bis([1,2,5]thiadiazolo)[3,4-f:3′,4′-h]quinoxaline-8,9-dicarbonitrile

Abstract

Compounds containing electron-withdrawing dicyanopyrazine and 1,2,5-chalcogenadiazole fragments are promising for the design of magnetic and optoelectronic materials. In this paper, bis([1,2,5]thiadiazolo)[3,4-f:3′,4′-h]quinoxaline-8,9-dicarbonitrile was prepared via Körner–Hinsberg condensation of benzo[1,2-c:3,4-c′]bis([1,2,5]thiadiazole)-4,5-dione with 2,3-diaminomaleonitrile in the presence of catalytic amounts of TsOH in refluxing ethanol. The structure of the newly synthesized compound was established via elemental analysis, mass spectrometry, ¹³C NMR, and IR spectroscopy.

1. Introduction

Fused 2,3-dicyanopyrazines have been actively studied. Among these compounds, 6,9-alkoxydithieno[2,3-f:3′,2′-h]quinoxaline-2,3-dicarbonitriles have been used as photocatalysts to enable the photoredox chemodivergent reduction in nitroaromatics to nitroso, bis-(N,O-diacetyl)-N-arylhydroxylamine, azoxy, azo and amino derivatives [1,2]. 13,14-Dihydroindolo[2,3-a]pyrazino[2,3-c]carbazole-6,7-dicarbonitrile was proposed as a colorimetric sensor for the visual detection of fluoride anion [3]. 1,2,5-Chalcogenadiazoles fused with benzene and various heterocycles constitute an important class of heterocyclic compounds owing to their broad applications in science and technology [4,5]. Also of great interest are compounds containing two electron-withdrawing fragments in the molecule: dicyanopyrazine and 1,2,5-chalcogenadiazole. 1,2,5-Selenadiazolo-[3,4-b]pyrazine-5,6-dicarbonitrile was used for the design and synthesis of anionic complexes with halide anions featuring Se–X chalcogen bonding [6] and radical anionic homospin [Na(18-crown-6)]⁺ salt, which revealed weak antiferromagnetic exchange interactions [7]. Macrocyclic complexes of tetrapyrazinoporphyrazines were prepared by template cyclotetramerization of 1,2,5-thiadiazolo-[3,4-b]pyrazine-5,6-dicarbonitrile in the presence of Mg butoxide and indium(III) chloride [8]. Herein, we report the synthesis of bis([1,2,5]thiadiazolo)[3,4-f:3′,4′-h]quinoxaline-8,9-dicarbonitrile 1 as a new small molecule containing two electron-withdrawing dicyanopyrazine and 1,2,5-thiadiazole fragments that may serve as a promising precursor for the design of new magnetic and optoelectronic materials [9,10]. For example, polycyclic dicyanopyrazines such as dibenzo[f,h]quinoxaline-2,3-dicarbonitrile and pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (Figure 1) have previously been successfully employed as organic components in TADF OLEDs [11,12,13], as well as in NIR TADF OLEDs [14,15].

2. Results and Discussion

To synthesize the target bis([1,2,5]thiadiazolo)[3,4-f:3′,4′-h]quinoxaline-8,9-dicarbonitrile 1, various Körner–Hinsberg condensation conditions of benzo[1,2-c:3,4-c′]bis([1,2,5]thiadiazole)-4,5-dione 2 [9] with 2,3-diaminomaleonitrile were investigated (

Table 1. Reaction of benzo[1,2-c:3,4-c′]bis([1,2,5]thiadiazole)-4,5-dione 2 with 2,3-diaminomaleonitrile.

Entry	Solvent	Catalyst (Equiv.)	T, °C	Time, h	Yield of 1, %
1	AcOH	-	118	1.5	46
2	EtOH	-	78	4	0
3	EtOH	conc. HCl (0.05)	78	1.5	25
4	EtOH	TsOH (0.05)	78	1.5	78
5	EtOH	TsOH (0.2)	78	1.5	72
6	EtOH	TsOH (0.05)	78	4	64

, Scheme 1). The reaction proceeded only under acidic conditions, and when refluxing in acetic acid, despite complete conversion of the starting diketone 2, the yield of the product is low (46%, entry 1). Hydrochloric acid as a catalyst also afforded a low yield of the product (25%, entry 3), while the addition of TsOH resulted in a substantial increase in the yield of the target product 1. Increasing the catalytic excess of the acid (entry 5) or the reaction time (entry 6) did not significantly improve the yield. Thus, refluxing in ethanol for 1.5 h in the presence of a catalytic amount of TsOH (0.05 equiv.) afforded compound 1 in a high yield of 78% (entry 4).

The structure of bis([1,2,5]thiadiazolo)[3,4-f:3′,4′-h]quinoxaline-8,9-dicarbonitrile 1 was established via elemental analysis, mass spectrometry, ¹³C NMR, and IR spectroscopy. Elemental analysis and mass spectrometry confirm the molecular formula of compound 1. The IR spectrum showed the absence of amino and keto groups and the presence of a cyano group at 2240 cm⁻¹.

In conclusion, bis([1,2,5]thiadiazolo)[3,4-f:3′,4′-h]quinoxaline-8,9-dicarbonitrile 1 was synthesized via the reaction of benzo[1,2-c:3,4-c′]bis([1,2,5]thiadiazole)-4,5-dione 2 and 2,3-diaminomaleonitrile in the presence of catalytic amounts of TsOH in ethanol. The resulting compound is a promising precursor for the design of new magnetic and optoelectronic materials.

3. Materials and Methods

Benzo[1,2-c:3,4-c′]bis([1,2,5]thiadiazole)-4,5-dione [16] was prepared according to the published method and validated by spectral data. 2,3-Diaminomaleonitrile and the other reagents and solvents were purchased from commercial sources and used as received. Elemental analysis was performed on a Perkin Elmer 2400 Elemental Analyser (Perkin Elmer-Inc., Waltham, MA, USA). The melting point was determined on a Kofler hot-stage apparatus and is uncorrected. ¹H and ¹³C NMR spectra were recorded on a Bruker AM-300 spectrometer (Bruker AXS Handheld Inc., Kennewick, WA, USA) (at frequencies of 300.1 and 75.5 MHz, respectively) in DMSO-d₆ solution, with the residual solvent signal used as the internal standard. The mass spectrum (EI, 70 eV) was obtained with a Finnigan MAT INCOS 50 instrument (Hazlet, NJ, USA). The IR spectrum was recorded with a Bruker “Alpha-T” instrument (Bruker Corporation, Billerica, MA, USA) in KBr pellet.

Experimental Procedure for the Synthesis of Compound 1

A mixture of benzo[1,2-c:3,4-c′]bis([1,2,5]thiadiazole)-4,5-dione (0.892 mmol, 200 mg), 2,3-diaminomaleonitrile (0.892 mmol, 96 mg), and p-toluenesulfonic acid (0.045 mmol, 9 mg) in ethanol (10 mL) was stirred for 1.5 h at reflux. The reaction mixture was then cooled to 0 °C and held for 30–60 min. The resulting precipitate was filtered off under vacuum, washed with ice-cold ethanol (2 × 3 mL), and air-dried. The crude product was dissolved in a minimal volume (5 mL) of boiling chloroform. The hot solution was filtered, and methanol was added to the filtrate. The mixture was cooled to 0 °C, and the resulting precipitate was filtered off, washed with cold methanol (2 × 2 mL), and air-dried to constant weight. Yield: 206 mg (78%), beige solid, m.p. > 300 °C (decomp.), R_f = 0.2 (ethanol). ¹H NMR (300 MHz, DMSO-d₆): no signals observed. ¹³C NMR (75 MHz, DMSO-d₆): δ 152.4, 150.1, 139.7, 133.0, 114.2. IR (ν, cm⁻¹): 2240, 2214, 1555, 1440, 1340, 1289, 1195, 1156, 1091, 826. LRMS, m/z (%): 296 [M]⁺ (100), 244 (6), 192 (8), 116 (12), 108 (15), 84 (21), 64 (26), 46 (30), 32 (65). Anal. Calcd. for C₁₀N₈S₂: C 40.54; N, 37.82; S, 21.64. Found: C, 40.35; N, 37.65; S, 21.45.