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Methyl 2-Amino-4-[1-(tert-butoxycarbonyl)azetidin-3-yl]-1,3-selenazole-5-carboxylate
Short Note


N.D. Zelinsky Institute of Organic Chemistry Russian Academy of Sciences, 47 Leninsky Prospekt, 119991 Moscow, Russia
Nanotechnology Education and Research Center, South Ural State University, 76 Lenina Avenue, 454080 Chelyabinsk, Russia
Author to whom correspondence should be addressed.
Academic Editor: Fawaz Aldabbagh
Molbank 2021, 2021(2), M1229;
Received: 25 May 2021 / Revised: 2 June 2021 / Accepted: 3 June 2021 / Published: 5 June 2021
(This article belongs to the Special Issue Heteroatom Rich Organic Heterocycles)


New heterocyclic systems containing 1,2,5-chalcogenadiazoles are of great interest for the creation of organic photovoltaic materials and biologically active compounds. In this communication, 3,6-dibromopyridazine-4,5-diamine was investigated in reaction with selenium dioxide in order to obtain 4,7-dibromo-[1,2,5]selenadiazolo[3,4-d]pyridazine. We found that 7-bromo-[1,2,5]selenadiazolo[3,4-d]pyridazin-4(5H)-one, the first representative of the new heterocyclic system, was isolated as a hydrolysis product of the corresponding 4,7-dibromoderivative. The structure of the newly synthesized compound was established by means of elemental analysis, high-resolution mass spectrometry, 1H, 13C NMR, IR and UV spectroscopy, and mass spectrometry.
Keywords: [1,2,5]selenadiazolo[3,4-d]pyridazines; selenium dioxide; 3,6-dibromopyridazine-4,5-diamine; ring closure [1,2,5]selenadiazolo[3,4-d]pyridazines; selenium dioxide; 3,6-dibromopyridazine-4,5-diamine; ring closure

1. Introduction

Ortho-Diamine moiety in benzene or heterocyclic rings is often used for the construction of fused 1,2,5-chalcogena (thia, selena, tellura) diazoles [1,2,3,4], which are of great interest as various photovoltaic materials, i.e., organic solar cells (OSCs), organic light-emitting diodes (OLEDs), organic field effect transistors (OFETs), and others [5,6,7,8,9,10]. 4,7-Dibromo derivatives of these heterocyclic systems are the most convenient precursors for the synthesis of photoactive materials [11]. Recently, we synthesized one of the interesting precursors for fused 1,2,5-chalcogenadiazolopyridazines—3,6-dibromopyridazine-4,5-diamine 1 [12]. Herein, we report on the study of the reaction between 3,6-dibromopyridazine-4,5-diamine 1 and selenium dioxide and the synthesis of 7-bromo-[1,2,5]selenadiazolo[3,4-d]pyridazin-4(5H)-one 2, the first representative of a new heterocyclic system.

2. Results and Discussion

As a rule, cyclization of aromatic and heteroaromatic ortho-diamines was carried out with selenium dioxide in ethanol, less often in water, acetic acid, and MeCN [1]. It was found that the treatment of 3,6-dibromopyridazine-4,5-diamine 1 with SeO2 in EtOH under reflux after 1 h led to the formation of 7-bromo-[1,2,5]selenadiazolo[3,4-d]pyridazin-4(5H)-one 2 in good yield (Table 1, Entry 1). Apparently the isolation of this product is the result of hydrolysis of the initially formed 4,7-dibromo-[1,2,5]selenadiazolo[3,4-d]pyridazine 3 (Scheme 1). The ease of hydrolysis of 4,7-dibromo[1,2,5]chalcogenadiazolo[3,4-d]pyridazines into a monohydroxy derivative has been previously described for its closest analogue—thiadiazopyridazine [13]. Unfortunately, replacing ethanol with dry acetonitrile and using magnesium sulfate or molecular sieves as dehydrating agents did not change the result of the reaction; compound 2 was isolated in all cases with approximately the same yield (Table 1, Entries 2–4).
The structure of 7-bromo-[1,2,5]selenadiazolo[3,4-d]pyridazin-4(5H)-one 2 was confirmed by means of elemental analysis, high-resolution mass spectrometry, 1H, 13C NMR, UV and IR spectroscopy, and mass spectrometry. Compared with the starting amine 1, in the weak field of the 1H NMR spectrum of compound 2, one singlet (δH = 12.88 ppm) is observed, corresponding to the proton of the NH group of the pyridazine ring. This confirms both the fact of the closure of the selenadiazole ring from diamine 1 and the absence of the second bromine atom in the pyridazine ring. The 13C NMR spectrum shows a signal from the carbonyl amide group (δC = 157.6 ppm), as well as three signals from the carbons of the pyridazine ring with chemical shifts δC 126.6, 153.0, and 155.3 ppm.
In conclusion, it was shown that the reaction of 3,6-dibromopyridazine-4,5-diamine 1 with selenium dioxide gave 7-bromo-[1,2,5]selenadiazolo[3,4-d]pyridazin-4(5H)-one 2 apparently as a hydrolysis product of the intermediate 4,7-dibromo-[1,2,5]selenadiazolo[3,4-d]pyridazine 3. This result led to the formation of a new heterocyclic system and opened up possibilities to its further functionalization to obtain compounds with useful physical properties.

3. Materials and Methods

3,6-Dibromopyridazine-4,5-diamine 1 was prepared according to the published method [12]. The solvents and reagents were purchased from commercial sources and used as received. Elemental analysis was performed on a 2400 Elemental Analyzer (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 taken with a Bruker AM-300 machine (Bruker AXS Handheld Inc., Kennewick, WA, USA) (at frequencies of 300 and 75 MHz) in DMSO-d6 solution, with TMS as the standard. MS spectrum (EI, 70 eV) was obtained with a Finnigan MAT INCOS 50 instrument (Hazlet, NJ, USA). IR spectrum was measured with a Bruker “Alpha-T” instrument in KBr pellet. High-resolution MS spectrum was measured on a Bruker micrOTOF II instrument (Bruker Daltonik Gmbh, Bremen, Germany) using electrospray ionization (ESI). The measurement was performed in a positive ion mode (interface capillary voltage—4500 V) or in a negative ion mode (3200 V); the mass range was from m/z 50 to m/z 3000 Da; external or internal calibration was performed with Electrospray Calibrant Solution (Fluka). A syringe injection was used for solutions in acetonitrile, methanol, or water (flow rate 3 L/min). Nitrogen was applied as a dry gas; interface temperature was set at 180 °C. The interface temperature was set at 180 °C. Solution UV–visible absorption spectra were recorded using a OKB Spektr SF-2000 UV/Vis/NIR spectrophotometer controlled with SF-2000 software. All samples were measured in a 1 cm quartz cell at room temperature with 1 × 10−4 mol/mL concentration in DMSO.
Synthesis of 7-bromo-[1,2,5]selenadiazolo[3,4-d]pyridazin-4(5H)-one 2 (Supplementary Materials).
A mixture of 3,6-dibromopyridazine-4,5-diamine 1 (100 mg, 0.37 mmol) and SeO2 (49 mg, 0.45 mmol) in CH3CN (8.0 mL) was refluxed with stirring for 1 hour, cooled to room temperature. The CH3CN was evaporated under reduced pressure. The residue was purified by column chromatography on silica gel (Silica gel Merck 60, eluent: EtOAc–CH2Cl2, 1:5, v/v). Yield 79 mg (77%), yellow solid, mp = >250 °С, Rf = 0.3 (EtOAc–CH2Cl2, 1:10, v/v). 1H NMR (ppm): δ 12.88 (s, 1H, NH). 13C NMR (ppm): δ 157.6 (C=O), 155.3 (C(Br)-C=N), 153.0 (C-Br), 126.6 (C(O)-C=N). HRMS (ESI-TOF), m/z: calcd for C4H79BrN4OSe [M + Na]+, 302.8387, found, 302.8386. MS (EI, 70 eV), m/z (I, %): 283 ([M + 3]+,4), 282 ([M + 2]+, 35), 281 ([M + 1]+, 10), 280 ([M]+, 41), 279 ([M − 1]+, 6), 278 ([M − 2]+, 12), 277 ([M − 3]+, 5), 225 (8), 97 (30), 80 (50), 57 (80), 43 (100). IR spectrum, ν, cm–1: 3181, 3090, 2926, 2887 (NH), 1681 (C=O), 1495, 1386, 1364, 1342, 1284, 1146, 1040, 960, 771, 755, 706, 625, 548, 504, 444. UV–Vis spectrum (in DMSO), λmax: 254 nm (ε = 7426 M−1 cm−1), 301 nm (ε = 6185 M−1 cm−1), 360 nm (ε = 6209 M−1 cm−1). Anal. calcd. for C4HBrN4OSe (279.94): C, 17.16; H, 0.36; N, 20.01. Found: C, 17.28; H, 0.39; N, 19.83.

Supplementary Materials

The following are available online: copies of 1H, 13C-NMR, IR, UV and mass spectra for compound 2.

Author Contributions

Synthetic experiments, analysis of experimental results and NMR data, T.N.C.; conceptualization, writing—review and editing, supervision and project administration, O.A.R. All authors have read and agreed to the published version of the manuscript.


This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.


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Scheme 1. Synthesis of 7-bromo-[1,2,5]selenadiazolo[3,4-d]pyridazin-4(5H)-one 2.
Scheme 1. Synthesis of 7-bromo-[1,2,5]selenadiazolo[3,4-d]pyridazin-4(5H)-one 2.
Molbank 2021 m1229 sch001
Table 1. Reaction of 3,6-dibromopyridazine-4,5-diamine 1 with SeO2.
Table 1. Reaction of 3,6-dibromopyridazine-4,5-diamine 1 with SeO2.
EntrySolventDehydrating AgentTemperature, °CTime, hYield of 2, %
3MeСN MgSO481176
4MeСNMolecular sieves81175
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