Design and Synthesis of Nitro Cage Heterocycles as Energetic Materials Derived from Pentacycloundecane (PCUD) Systems

Abstract

A variety of pentacycloundecane (PCUD) based cage compounds containing nitro groups were synthesized via a simple synthetic method starting with cage diones. Eight PCUDs were used for nitro functionalization. These cage diones were prepared starting with easily accessible starting materials such as 2,3-dimethylhydroquinone, 1,4-dihydroxybenzene, and cyclopentadiene. Here, we have used Diels-Alder (DA) reaction, [2 + 2] photocycloaddition, and Henry reaction as key steps. Transannular cyclization plays an important role to generate a nitro substituted cage heterocycles via base promoted reaction using nitromethane as a reagent. Some of these oxa-cage structures have been further supported by single-crystal X-ray diffraction studies. Energetic performance of the title compounds was evaluated using DFT based calculations. These bis(nitromethyl)octahydro-1H-1,3,4,6(epiethane-[1,1,2,2]tetrayl)-pentaleno[1,6-bc]furan analogues (11 b-18 b) owned the densities in the range of 1.37-1.60 g/cm 3 . All the studied compounds possess high positive enthalpy of formation (33.68-230.48 kJ/mol, except compound with dimethyl groups (16 b, À 11.38 kJ/mol) and very good thermal (T m = 99-147 °C) and kinetic stabilities. Ammonium perchlorate based various propulsion formulations suggests that these compounds could be excellent candidates in the solid rocket propulsion.

Construction of Three Novel Oxygen-Containing Cagelike Frameworks and Synthesis of their Energetic Derivatives

“…1 H NMR (500 MHz,Chloroformd) δ 5.60 (t, J = 6.11 Hz, 1H), 4.81 (d, J = 4.66 Hz, 1H), 4.71 (t, J = 5.09 Hz, 1H), 4.58 (d, J = 3.65 Hz, 1H), 4.40 (t, J = 4.31 Hz, 1H), 4.23 (d, J = 8.37 Hz, 1H), 2.44 (d, J = 12.54 Hz, 1H), 2.37 (ddd, J = 6.27, 4.22, 1.90 Hz, 2H), 1.77 (dt, J = 12.65, 4.38 Hz, 1H). 13 C NMR ( 126MHz, Chloroform-d) δ 80. 1, 74.6, 74.4, 73.9, 72.9, 69.2, 33.8, 30.1. IR (thin film, υ cm -1 ): 2982,2896,1636,1281,1270,1067,1042,994,931,842,809,752,689,639,617,444 White solid; yield: 241 mg, (92%).…”

“…1 H NMR (500 MHz, Chloroformd) δ 5.51 (q, J = 4.95 Hz, 2H), 4.25 (t, J = 3.10 Hz, 2H), 4.12 (t, J = 4.14 Hz, 2H), 2.27 (t, J = 3.80 Hz, 4H). 13 C NMR (126 MHz, Chloroform-d) δ 75.0, 69.3, 68.0, 30.5. IR (thin film, υ cm -1 ): 2978, 1632, 1621, 1324, 1269, 1224, 1061, 1031.57.…”

“…1 H NMR (500 MHz, Chloroformd) δ 5.15 (t, J = 3.71 Hz, 2H), 4.07 (t, J = 4.31 Hz, 2H), 2.30 (d, J = 4.83 Hz, 2H), 2.14 (dd, J = 13.94, 3.96 Hz, 2H), 2.09 -2.02 (m, 2H), 1.91 (d, J = 3.48 Hz, 2H). 13 C NMR (126 MHz, Chloroform-d) δ 79.8, 66.3, 30.9, 28.6, 24.8. IR (thin film, υ cm -1 ): 2964,2949,884,1633,1614,1270,1027,974,860,842,831,753,694.…”

“…1 H NMR (500 MHz, δ 5.01 (t, J = 3.39 Hz, 1H), 4.73 (d, J = 6.21 Hz, 1H), 4.46 (d, J = 8.53 Hz, 1H), 4.40 (d, J = 3.98 Hz, 1H), 2.90 (dd, J = 18.05, 8.54 Hz, 1H), 2.80 (d, J = 17.96 Hz, 1H), 2.60 (d, J = 12.98 Hz, 1H), 2.37 (ddd, J = 13.12, 6.27, 2.85 Hz, 1H). 13 C NMR (126 MHz, Chloroform-d) δ 202. 0, 200.8, 82.7, 81.6, 79.0, 78.3, 40.8, 40.6.…”

“…Column chromatography was performed using either aluminum oxide gel (spherical, neutral, 200-300 mesh) or silica gel (200-300 mesh). 1 H and 13 C nuclear magnetic resonance (NMR) spectra were obtained at frequencies of 500 MHz and 126 MHz, respectively. The solvents used for NMR measurements were chloroform-d, methanol-d4, DMSO-d6 and acetone-d6, with tetramethylsilane (TMS) serving as the internal standard.…”