Synthesis of 2,4,6-Triazidopyridine and Its 3,5-Diiodo Derivative

Abstract

2,4,6-Trifluoropyridine was diiodinated with a mixture of potassium iodide and periodic acid in sulfuric acid at 55 °C to give 2,4,6-trifluoro-3,5-diiodopyridine in 85% yield. Both the starting trifluoropyridine and its 3,5-diiodo derivative readily react with excess sodium azide in dimethyl sulfoxide at room temperature to afford 2,4,6-triazidopyridine and 2,4,6-triazido-3,5-diiodopyridine in high yields. In the 15 N NMR spectra of the triazides, the N α atoms of the α-and γ-azido groups show very differing chemical shifts, which indicates the different reactivity of these groups in 1,3-dipolar cycloaddition, phosphorylation, reduction, thermolysis, and photolysis reactions.2,4,6-Triazidopyridines are widely used as starting compounds in organic synthesis 1 and for the photochemical preparation of high-spin nitrenes. 2 In addition, some triazides are of interest as primary explosive materials and as precursors of nitrogen-rich carbon nanomaterials. 3 2,4,6-Triazido-3,5-dibromopyridine (2a) was the first representative of this class of compounds, obtained by triazidation of pentabromopyridine (1a) with sodium azide in dimethyl sulfoxide at room temperature in 86% yield. 4 Later, triazides 2b-h were synthesized by triazidation of the corresponding perhalogenated pyridines 1b-h, using similar protocols (Scheme 1). 5 Owing to the nonequivalence of the azido groups, such triazides underwent selective 1,3-dipolar cycloaddition, reduction, phosphorylation, thermolysis, and photolysis reactions to form, for example, compounds 3-6 (Scheme 2). 1 On the other hand, the photolysis of triazides 2b-d in cryogenic matrices gave the corresponding septet 2,4,6-trinitrenopyridines that were of considerable interest as models for organic molecular magnets. 2 Amongst the variations in substitution of pyridines 2a-j (Scheme 1), only triazides 2i and 2j remained unexplored. Both these triazides were considered as the most interesting model systems for photochemical studies.Triazides 2i and 2j were synthesized from commercially available 2,4,6-trifluoropyridine (7) (Scheme 3). It was reported that boiling pyridine 7 in a mixture of iodine and fuming nitric acid for 12 hours affords 3,5-diiodopyridine 8 in 55% yield. 6 However, the spectroscopic characteristics of compound 8 were not reported. Nowadays, iodination of strongly electron-deficient arenes is usually conducted using a mixture of potassium iodide, sulfuric acid, and a strong oxidative agent such as HIO 4 or H 5 IO 6 . 7 Thus, for example, diiodination of 1,3,5-trifluoro-2-nitrobenzene with mixture of potassium iodide, sulfuric acid, and periodic acid at 50 °C for 3.5 hours gave 1,3,5-trifluoro-4,6-diiodo-2-nitrobenzene in 89% yield. 8 Using a similar approach, we synthesized 3,5-diiodopyridine 8 from pyridine 7 in 85% yield. Compound 8 was obtained as a white solid with mp 79 °C. Its 13 C NMR spectrum displays characteristic signals at δ = 172.3, 163.0, and 60.6, corresponding to the carbon atoms in the α-, γ-, and β-positions of the pyridine ring, respectively. In the 19 F ...

15N NMR spectra and reactivity of 2,4,6‐triazidopyridines, 2,4,6‐triazidopyrimidine and 2,4,6‐triazido‐s‐triazine

“…The present 15 N NMR spectroscopic study confirmed that none of triazides 1–7 and 10 displays any signals between δ +50 and −90 ppm that can be assigned to isomeric tetrazoles. These data agree well with the results of previous 13 C NMR spectroscopic studies of triazides 1–7 and 10 …”

“…The compounds studied were prepared by triazidation of the corresponding chlorides or fluorides, according to the procedures described in the literature: triazides 1 , 2 , 3 , 4 , 5 , 6 , 7 and 10 …”

“…The compounds studied were prepared by triazidation of the corresponding chlorides or fluorides, according to the procedures described in the literature: triazides 1, [5] 2, [6] 3, [8] 4, [6] 5, [9] 6, [7] 7 [20] and 10. [19] NMR measurements 15 N NMR spectra were recorded at 294 K for~0.4-M solutions in CDCl 3 on a Bruker Avance III 500 spectrometer, equipped with a 5-mm BBO probehead with a working frequency of 50.6848 MHz for 15 N. The 1 H-decoupled 15 N NMR spectra were obtained by averaging 2000-3000 signal accumulations with a delay of 30 s (90º pulse width for 15 N, 15.5 μs).…”

“…When aromatic polyazides have two or more nonequivalent azido groups, these groups can selectively react with dipolarophiles, electrophiles, nucleophiles and reductants or undergo selective thermolysis and photolysis . Recently, we have reported the synthesis and some chemical transformations of triazides 1–6 (Scheme ) . It was found that, upon UV irradiation, triazides 2 and 3 undergo selective photolysis of the α ‐azido groups to form the corresponding quintet 2,6‐dinitrenopyridines .…”

“…[3,4] Recently, we have reported the synthesis and some chemical transformations of triazides 1-6 (Scheme 1). [5][6][7][8][9][10][11][12][13][14] It was found that, upon UV irradiation, triazides 2 and 3 undergo selective photolysis of the α-azido groups to form the corresponding quintet 2,6-dinitrenopyridines. [10][11][12] Triazides 3 and 5 added electron-rich dipolarophiles and phosphines selectively on the γ-azido group, while cycloadditions of electron-poor dipolarophiles occurred selectively on the α-azido groups of these triazides.…”