Synthesis of Nitro-Functionalized Polynitrogen Tricycles Bearing a Central 1,2,3-Triazolium Ylide

Abstract

This paper describes the synthesis of unprecedented fused nitroazaheterocyclic ring systems. Nitro tricycles with a central 1,2,3-triazole ring were obtained via a nitrene-mediated reaction of azidonitrobis(hetaryl) derivatives under thermolysis. The cyclization proceeded with complete chemoselectivity for the desired N-N bond formation. The key azidonitro bicycles were synthesized through an aromatic nucleophilic substitution from nitroazoles and 3-azido-2-chloropyrazine.

Key words

cyclizations - nitrene - heterocycles - nucleophilic aromatic substitution - energetic material

References and Notes

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6

Procedure of Aromatic Nucleophilic Substitution
A suspension of pyrazole (4.4 mmol, 1.1 equiv), 3-azido-2-chlorohetaryle (4 mmol, 1 equiv), and base (4.4 mmol, 1.1 equiv) in anhyd MeCN (16 mL) was stirred under reflux for 18 h. The resultant mixture was diluted in H₂O-EtOAc (1:1, 80 mL), after which the aqueous phase was extracted with EtOAc (2 × 15 mL). The organic layers were washed with H₂O (2 × 15 mL), dried over MgSO₄, filtered, and concentrated.
3-Azido-2-(1 H -pyrazol-1-yl)pyridine (2) The title compound was isolated as a colorless oil in 12% yield. IR: ν = 3055, 2104, 1469, 1408, 1305, 1265, 751, 727 cm^-¹. ^¹H NMR (200 MHz, CD₂Cl₂): δ = 6.50 (br s, 1 H), 7.35 (dd, J = 4.6, 8.0 Hz, 1 H), 7.66 (dd, J = 1.4, 8.0 Hz, 1 H), 7.84 (br s, 1 H), 8.23-8.34 (m, 2 H). ^¹³C NMR (50 MHz, CD₂Cl₂): δ = 107.4, 123.4, 129.0, 129.3, 130.6, 142.1, 142.7, 144.6. MS (IC⁺): m/z = 187 [MH⁺], 159 [MH⁺ - N₂]. HRMS (IC⁺, CH₄): m/z calcd for C₈H₇N₄ [MH⁺ - N₂]: 159.0671; found: 159.0658.

7

Cyclization Procedure Although no problems were encountered with these compounds, they should be considered as energetic compounds and be manipulated with appropriate safety precautions.
A suspension of the bicyclic compounds 6-11 (1 mmol) in dichlorobenzene (unless otherwise stated; 10 mL) was stirred at 165 ˚C for 150 min under an inert atmosphere. The resultant mixture was cooled which led to a substantial amount of tricycle precipitating. The solid product was collected by filtration, and more of the product could be collected after concentration of the filtrate under vacuum using a Kügelrohr apparatus.
Compound 3 (thermolysis in decalin as solvent) is described in ref. 3.

10

Procedure for the aromatic nucleophilic substitution, see ref. 6.
2-Azido-3-(3-nitro-1 H -1,2,4-triazol-1-yl)pyrazine (10) The title compound was isolated as a white solid in 93% yield; mp 185 ˚C. IR: ν = 3091, 1527, 1488, 1412, 1317, 1296, 1029, 938, 835, 807, 659 cm^-¹. ^¹H NMR (200 MHz, DMSO-d ₆): δ = 8.49 (d, J = 4.6 Hz, 1 H), 9.67 (d, J = 4.6 Hz, 1 H), 10.06 (s, 1 H). ^¹³C NMR (50 MHz, DMSO-d ₆): δ = 121.1, 131.4, 139.1, 139.3, 148.0, 163.5. MS (IC⁺): m/z = 263 [M + C₂H₅ ⁺], 234 [MH⁺], 206 [MH⁺ - N₂]. HRMS (IC⁺, NH₃): m/z calcd for C₆H₄N₉O₂ [MH⁺]: 234.0488; found: 234.0504.

11

Cyclization procedure, see ref. 7.
7-Nitro[1.2,4]triazolo[1′,2′:1,2][1,2,3] Triazolo[4,5- b ]pyrazinin-6-ium Ylide (16) The title compound was isolated as a dichlorobenzene-solvated black solid in 79% yield (NMR yield); mp 214 ˚C (dec., DSC). IR: ν = 2973, 2860, 1560, 1508, 1400, 1371, 1300, 1054, 1033, 1016, 834 cm^-¹. ^¹H NMR (200 MHz, DMSO-d ₆): δ = 8.66 (d, J = 2.4 Hz, 1 H), 8.98 (d, J = 2.4 Hz, 1 H), 9.81 (s, 1 H). ^¹³C NMR (50 MHz, DMSO-d ₆): δ = 124.3, 128.0, 138.6, 146.3, 146.7, 151.7. MS (IC⁺): m/z = 234 [M + C₂H₅ ⁺], 206 [MH⁺]. HRMS (IC⁺, CH₄): m/z calcd for C₆H₄N₇O₂ [MH⁺]: 206.0426; found: 206.0423.