Oxidative Cyclization Protocol for the Preparation of Energetic 3

Letter pubs.acs.org/OrgLett

Cite This: Org. Lett. 2018, 20, 8039−8042

Oxidative Cyclization Protocol for the Preparation of Energetic 3‑Amino-5‑R‑1,2,4-oxadiazoles Yongxing Tang,† Gregory H. Imler,‡ Damon A. Parrish,‡ and Jean’ne M. Shreeve*,† †

Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343, United States Naval Research Laboratory, 4555 Overlook Avenue, Washington, D.C. 20375, United States

‡

Downloaded via UNIV OF SOUTH DAKOTA on December 21, 2018 at 12:08:37 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: An efficient method has been developed for the synthesis of energetic 3-amino-5-R-1,2,4-oxadiazoles via iodobenzene diacetate (IBD)mediated oxidative cyclization in high yields at ambient temperature. Compound 1c has a graphite-like structure, which has seldom been reported in bicyclic compounds. The reaction of 3-amino-5-R-1,2,4-oxadiazole derivatives with hydrazine monohydrate in THF gives products that are a function of the substituent. Energetic performance calculations show detonation properties superior to TNT with concomitant lower impact and friction sensitivities. he oxadiazole skeleton is an important five-membered nitrogen-containing heterocycle. Molecules bearing oxadiazole moieties are found in a wide range of applications including medicinal chemistry, material science, and organic synthesis.1 In the field of energetic materials, the oxadiazole structural motifs commonly occur as backbones in single,2 fused,3 and bicyclic rings.4 Among them, oxadiazoles bearing the amino group are valuable building blocks in developing various functionalized energetic compounds.5 With the goal of balancing energetic performance and sensitivities, molecular combinations of amino oxadiazoles and various nitrogen-rich heterocyclic rings have been investigated. Various energetic derivatives that contain (a) 4-amino-1,2,5oxadiazole;5c,6 (b) 2-amino-1,3,4-oxadiazole;7 and (c) 5amino-1,2,4-oxadiazole (Figure 1)8 have been reported. Such

T

N-carbamimidoyl-substituted furazan/furoxan (1b, 2b, and 3b) (Scheme 1). Scheme 1. Synthesis of Furazan-Substituted 3-Amino-1,2,4oxadiazole Derivatives and Their Reactions with Hydrazine Monohydrate, G·HCl (Guanidine Hydrochloride), and IBD (Iodobenzene Diacetate)

Reaction of a carboxylic ester with hydrazine hydrate gives a hydrazide in high yield.7 It was expected that treatment of the carboxylic ester with guanidine would give N-carbamimidoylsubstituted products (1b, 2b, and 3b). The required guanidine solution in ethanol was easily prepared by reaction of equal molar amounts of sodium ethoxide and guanidinium hydrochloride. Then, at room temperature, the solution of guanidine in ethanol was treated with either the esters 1a9 or 3a10 or compound 2a11 to generate 1b, 2b, or 3b, which were isolated easily by filtration (Scheme 1). Next, we began the study of the oxidative cyclization of 1b with iodobenzene diacetate (IBD) as an oxidant. When 1b was treated with 1.5 equiv of IBD in DMF at room temperature for 24 h, 1c with a 3-amino-1,2,4oxadiazole ring was prepared in moderate yield. Based on this

Figure 1. Structures of amino-substituted oxadiazoles: (a) 4-amino1,2,5-oxadiazole, (b) 2-amino-1,3,4-oxadiazole, (c) 5-amino-1,2,4oxadiazole, and (d) 3-amino-1,2,4-oxadiazole.

combinations possess fine-tuned properties dictated by the constituent heterocycles due to their high heats of formation and thermal stabilities as well as chemical stabilities. Although molecular combinations offer seemingly limitless possibilities for structural diversity with desired structural or functional properties, the development of novel molecules remains to be expanded. Nitrogen-rich heterocyclic ringsubstituted 3-amino-1,2,4-oxadiazole derivatives [Figure 1(d)], which are potential energetic compounds, have not been reported. Because of our continuing interest in energetic materials, we now report the syntheses of several furazansubstituted 3-amino-1,2,4-oxadiazole derivatives formed via iodobenzene diacetate (IBD)-mediated oxidative cyclization of © 2018 American Chemical Society

Received: November 14, 2018 Published: December 10, 2018 8039

DOI: 10.1021/acs.orglett.8b03639 Org. Lett. 2018, 20, 8039−8042

Letter

Organic Letters promising result, two additional N-carbamimidoyl-substituted compounds with different oxadiazole rings (2b and 3b) were found to give 2c and 3c by using this IBD-oxidative cyclization protocol. Previously, the reactions of various 1,2,4-oxadiazoles with an excess of hydrazine monohydrate were reported to give 3amino-1,2,4-triazoles through a reductive ANRORC pathway.12 With 1c in hand, when we examined its chemical reactivity with hydrazine monohydrate in THF at room temperature for 24 h, 1d was isolated in high yield. The NMR data agree with literature values.4b In addition, the structure of 1d was confirmed by single crystal X-ray diffraction (Figure. 2a). However, regardless of the solvent (DMF or THF), the

Figure 3. (a) Single-crystal X-ray structure of 1c. (b) Threedimensional graphite-like layered packing diagram of 1c.

Compound 2c crystallizes from a mixture of acetone and methanol in the monoclinic space group P21/n with four molecules per unit cell (Z = 4). In comparison with 1c, it esd expected to give a crystal density of 1.795 g cm−3 at 293 K. The molecular structure is shown in Figure 4. All the atoms in

Figure 2. Single-crystal X-ray structure of (a) 1d and (b) 3d. Figure 4. Single-crystal X-ray structure of 2c.

attempted reaction of 2c with hydrazine monohydrate failed to give the corresponding product 2d, leaving the unreacted starting material (2c). Interestingly, treatment of 3c with hydrazine monohydrate in THF resulted in the formation of 3d where both the oxadiazole ring and the azo bridge were reduced. The molecular structure is shown in Figure 2b. In addition, many attempts to oxidize or nitrate 1c led to unknown mixtures or decomposed products only. Compound 1c crystallizes in the orthorhombic space group Pnma and contains four formula moieties in the unit cell. The crystal density is 1.685 g cm−3 at 296 K. The molecular structure is shown in Figure 3a. The 1,2,5-oxadiazole and 1,2,4oxadiazole rings, as well as the two amino groups, are planar. Both of the torsion angles of C2−C6−N7−N12 and N1−C2− C6−C7 are 0°. In addition, the torsion angle of N11−C10− N12−C7 is 180°. Such a completely coplanar structure with C−C bonded rings is rarely reported. The intermolecular hydrogen bonding helps to form a 2D planar layer structure (viewed along a axis and c axis). The layer structures were further packed by π−π interactions along b axis to construct a graphite-like stacking structure (Figure 3b). The distance between the layers is 3.189 Å, which is a little larger than 3.013 Å in TATB.13 The details for hydrogen bonding are given in the Supporting Information.

the molecule are essentially in the same plane with the torsion angle N(2)−C(7)−C(8)−O(9) of 177.48(13)°. Due to the molecular planarity, the bond lengths in the furoxan and the oxadiazole rings are all between the length of the formal C−N and C−C single and double bonds (C−N, 1.47 and 1.22 Å; C−C, 1.54 and 1.34 Å) (Supporting Information). As donors, the nitrogen atoms (N6 and N12) play important roles in forming hydrogen bonds thus enhancing the stability. Compound 3c (3c·2DMF) crystallizes as a DMF adduct in the triclinic space group P1. The crystal density is 1.447 g·cm−3 at 293 K due to the formation of the DMF adduct, while the gas pycnometer gives 1.712 g cm−3 (in the absence of the DMF molecule of crystallization) at room temperature. The molecular structure is shown in Figure 5. It is planar with the azo bridge in the typical trans configuration. The bond length of the azo bond N12−N12′ is 1.253(3) Å, which is comparable to azo-bridged molecules in the literature.5d,f Only two kinds of hydrogen bonds (N1−H1A···O13 2.813 Å and N1−H1B···N6 3.066 Å) are observed; the donors are from the nitrogen atom (N1) of the amino group, while the acceptors are the oxygen atoms in the DMF solvent and the nitrogen atom (N6) in the 1,2,4-oxadiazole ring. 8040

DOI: 10.1021/acs.orglett.8b03639 Org. Lett. 2018, 20, 8039−8042

Organic Letters

■

Letter

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.8b03639. Synthesis, calculation details, crystal refinements, NMR spectra, and DSC curves (PDF)

Figure 5. Single-crystal X-ray structure of 3c·2DMF.

Accession Codes

The properties of 1c, 2c, 3c, and 1d are summarized in Table 1. The measured density of 2c is 1.788 g cm−3, which is

CCDC 1862576−1862580 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

Table 1. Physicochemical and Energetic Properties of 1c, 2c, 3c, and 1d compds

ρa (g cm−3)

1c 2c 3c 1d TNT TATB

1.680 1.788 1.652 1.716 1.654 1.930

Dvb Pc (m s−1) (GPa) 7495 8193 7547 7798 6881 8179

20.4 26.8 21.6 21.5 19.5 30.5

ΔHfd (kJ g−1)

Tdece (°C)

ISf (J)

FSg (N)

1.11 1.01 2.35 1.73 −0.26 −0.54

249 219 213 245 300 350

>40 >40 >40 >40 15 50

>360 >360 >360 >360 353 >360

■

AUTHOR INFORMATION

Corresponding Author

*Fax: (+1) 208-885-9146. E-mail: [email protected]. ORCID

Yongxing Tang: 0000-0002-9549-9195 Jean’ne M. Shreeve: 0000-0001-8622-4897

Density (measured with a gas pycnometer at 25 °C). bDetonation velocity calculated with EXPLO5 v6.01. cDetonation pressure calculated with EXPLO5 v6.01. dHeat of formation. eDecomposition temperature (onset temperature at a heating rate of 5 °C min−1). f Impact sensitivity. gFriction sensitivity. a

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Financial support of the Office of Naval Research (NOOO1412-1-0536) and the Defense Threat Reduction Agency (HDTRA 1-11-1-0034) are gratefully acknowledged. We are also grateful to the M. J. Murdock Charitable Trust, Reference No. 2014120:MNL:11/20/2014 for funds supporting the purchase of a 500 MHz NMR spectrometer.

the largest among these four compounds. All have positive heats of formation and high thermal stabilities (>200 °C). With the measured densities and heats of formation in hand, the detonation performances were calculated using EXPLO5 v6.01.14 All of these compounds have detonation properties superior to TNT. Among them, 2c shows the highest detonation velocity (8193 m s−1), which is equivalent to TATB. However, the detonation pressure of 2c is 26.8 GPa, which is inferior to TATB. The sensitivities toward impact and friction were also determined based on standard BAM methods.15 The results show that all compounds were insensitive. The impact sensitivities are more than 40 J, and the friction sensitivities are higher than 360 N. In conclusion, a practical methodology for the synthesis of furazan-substituted 3-amino-1,2,4-oxadiazole derivatives from readily accessible N-carbamimidoyl-substituted substrates via an IBD-mediated oxidative cyclization reaction was developed. These 3-amino-1,2,4-oxadiazole derivatives have different chemical reactivities when they were treated with hydrazine monohydrate. The isolated products were fully characterized and confirmed by single-crystal X-ray diffraction analyses. Compound 1c has a totally planar structure. All compounds exhibit good detonation performance, superior to that of TNT. The detonation velocity of 2c is comparable to TATB. Because of the two amino groups present in these structures, further functionalization may lead to other useful energetic compounds. Overall, the synthesis protocol provides a useful and efficient step in the synthesis of the 3-amino-1,2,4-oxadiazole scaffold and is expected to greatly assist in the development of energetic materials.

■

REFERENCES

(1) (a) Boström, J.; Hogner, A.; Llinàs, A.; Wellner, E.; Plowright, A. T. J. Med. Chem. 2012, 55, 1817−1830. (b) Modi, V.; Modi, P. J. J. Saudi Chem. Soc. 2012, 16, 327−332. (2) (a) Tang, Y.; Gao, H.; Mitchell, L. A.; Parrish, D. A.; Shreeve, J. M. Angew. Chem., Int. Ed. 2016, 55, 1147−1150. Angew. Chem. 2016, 128, 1159−1162. (b) Zhai, L.; Qu, X.; Wang, B.; Bi, F.; Chen, S.; Fan, X.; Xie, G.; Wei, Q.; Gao, S. ChemPlusChem 2016, 81, 1156−1159. (c) He, C.; Shreeve, J. M. Angew. Chem., Int. Ed. 2016, 55, 772−775. Angew. Chem., 2016 128, 782−785. (d) Hermann, T. S.; Klapötke, T. M.; Krumm, B.; Stierstorfer, J. Asian J. Org. Chem. 2018, 7, 739−750. (e) Fu, Z.; Su, R.; Wang, Y.; Wang, Y.; Zeng, W.; Xiao, N.; Wu, Y.; Zhou, Z.; Chen, J.; Chen, F. Chem. - Eur. J. 2012, 18, 1886−1889. (f) Yu, Q.; Yin, P.; Zhang, J.; He, C.; Imler, G. H.; Parrish, D. A.; Shreeve, J. M. J. Am. Chem. Soc. 2017, 139, 8816−8819. (3) (a) Zelenov, V. P.; Lobanova, A. A.; Sysolyatin, S. V.; Sevodina, N. V. Russ. J. Org. Chem. 2013, 49, 455−465. (b) Tang, Y.; He, C.; Shreeve, J. M. J. Mater. Chem. A 2017, 5, 4314−4319. (c) Li, W.; Qi, X.; Jin, Y.; Wang, B.; Zhang, Q. ChemistrySelect 2018, 3, 849−854. (4) (a) Tang, Y.; He, C.; Mitchell, L. A.; Parrish, D. A.; Shreeve, J. M. J. Mater. Chem. A 2015, 3, 23143−23148. (b) Shaposhnikov, S. D.; Korobov, N. V.; Sergievskii, A. V.; Pirogov, S. V.; Mel’nikova, S. F.; Tselinskii, I. V. Russ. J. Org. Chem. 2002, 38, 1351−1355. (c) Tian, J.; Xiong, H.; Lin, Q.; Cheng, G.; Yang, H. New J. Chem. 2017, 41, 1918−1924. (d) Liang, L.; Wang, K.; Bian, C.; Ling, L.; Zhou, Z. Chem. - Eur. J. 2013, 19, 14902−14910. (e) Kettner, M. A.; Klapötke, T. M. Chem. Commun. 2014, 50, 2268−2270. (5) (a) Tang, Y.; Zhang, J.; Mitchell, L. A.; Parrish, D. A.; Shreeve, J. M. J. Am. Chem. Soc. 2015, 137, 15984−15987. (b) Stepanov, A. I.; Sannikov, V. S.; Dashko, D. V.; Roslyakov, A. G.; Astrat’ev, A. A.; 8041

DOI: 10.1021/acs.orglett.8b03639 Org. Lett. 2018, 20, 8039−8042

Letter

Organic Letters Stepanova, E. V. Chem. Heterocycl. Compd. 2015, 51, 350−360. (c) Zelenov, V. P.; Lobanova, A. A. Russ. Chem. Bull. 2011, 60, 334− 338. (d) Qu, Y.; Zeng, Q.; Wang, J.; Ma, Q.; Li, H.; Li, H.; Yang, G. Chem. - Eur. J. 2016, 22, 12527−12532. (e) He, C.; Gao, H.; Imler, G. H.; Parrish, D. A.; Shreeve, J. M. J. Mater. Chem. A 2018, 6, 9391− 9396. (f) Sun, Q.; Shen, C.; Li, X.; Lin, Q.; Lu, M. J. Mater. Chem. A 2017, 5, 11063−11070. (g) Zhang, W.; Zhang, J.; Deng, M.; Qi, X.; Nie, F.; Zhang, Q. Nat. Commun. 2017, 8, 181. (h) Hermann, T. S.; Karaghiosoff, K.; Klapötke, T. M.; Stierstorfer, J. Chem. - Eur. J. 2017, 23, 12087−12091. (i) Francois, E. G.; Chavez, D. E.; Sandstrom, M. M. Propellants, Explos., Pyrotech. 2010, 35, 529−534. (6) Klapötke, T. M.; Pflüger, C. Z. Z. Anorg. Allg. Chem. 2017, 643, 619−624. (7) Fershtat, L. L.; Kulikov, A. S.; Ananyev, I. V.; Struchkova, M. I.; Makhova, N. N. J. Heterocycl. Chem. 2016, 53, 102−108. (8) Hermann, T. S.; Klapötke, T. M.; Krumm, B.; Stierstorfer, J. J. Heterocycl. Chem. 2018, 55, 852−862. (9) (a) Willer, R. L.; Storey, R. F.; Deschamps, J. R.; Frisch, M. J. Heterocycl. Chem. 2013, 50, 949−954. (b) Willer, R. L.; Storey, R. F.; Jarrett, W. L.; Parrish, D. A. J. Heterocycl. Chem. 2012, 49, 705−709. (c) Willer, R. L.; Storey, R. F.; Frisch, M.; Deschamps, J. R. J. Heterocycl. Chem. 2012, 49, 227−231. (10) Xu, Z.; Cheng, G.; Yang, H.; Ju, X.; Yin, P.; Zhang, J.; Shreeve, J. M. Angew. Chem., Int. Ed. 2017, 56, 5877−5881. Angew. Chem. 2017, 129, 5971−5975. (11) Kulikov, A. S.; Ovchinnikov, I. V.; Molotov, S. I.; Makhova, N. N. Russ. Chem. Bull. 2003, 52, 1822−1828. (12) Palumbo Piccionello, A.; Guarcello, A.; Buscemi, S.; Vivona, N.; Pace, A. J. Org. Chem. 2010, 75, 8724−8727. (13) Wang, Y.; Liu, Y.; Song, S.; Yang, Z.; Qi, X.; Wang, K.; Liu, Y.; Zhang, Q.; Tian, Y. Nat. Commun. 2018, 9, 2444. (14) Sućeska, M. EXPLO5, version 6.01; Brodarski Institute: Zagreb, Croatia, 2013. (15) (a) Tests were conducted according to the UN Recommendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, 5th rev. ed.; United Nations Publication: New York, 2009. (b) 13.4.2 Test 3 (a)(ii) BAM Fallhammer, pp 75. (c) 13.5.1 Test 3 (b)(i) BAM friction apparatus, pp 104.

8042

DOI: 10.1021/acs.orglett.8b03639 Org. Lett. 2018, 20, 8039−8042