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.

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The preparation of a variety of structurally interesting oxygenated cage compounds involving atom-economic processes such as Claisen rearrangement, Diels–Alder reaction, [2+2] photocycloaddition, and ring-closing metathesis (RCM) as key steps is reported. For the first time, oxepane ring system is introduced in cage framework using olefin metathesis as a key step. These cage systems assembled here are difficult to prepare by traditional methods. The synthetic sequence described here opens up new routes to higher order polycycles containing heteroatoms without the involvement of protecting groups. Transannular cyclization observed during Grignard addition and the RCM protocol used here may be applicable to generate unknown oxygenated cage systems.

A new synthetic route to D-trishomocubanone and oxa- D-trishomocubane derivatives has been established by the rearrangement approach. A remotely located methyl substituent in the six-membered ring contributed to the acid-catalyzed rearrangement of the cage dione in an unusual fashion. This rearrangement approach provided an attractive route to extended D-trishomocubanes, which are not accessible by the conventional multistep synthetic sequence. For the first time, two phenyl groups were incorporated from the solvent into the strained trishomocubane skeleton in an unprecedented manner via carbocation-mediated rearrangement with the aid of BF·OEt. Interestingly, an oxa-bridged trishomocubane skeleton was also formed during acid-promoted rearrangement.

Rearranged cage ketones 6a and 6b are reported in eight linear synthetic steps from 2,5‐dimethoxybenzaldehyde 9 without the use of protecting groups. In this regard, Diels–Alder reaction, [2+2]photocycloaddition and Lewis acid promoted rearrangement with BF3·OEt2 were used as key steps. Surprisingly, during the ring expansion process with Lewis acid, solvent incorporation occurred. This rearrangement approach has provided difficult complex targets through non‐obvious synthetic routes. The rearrangement process demonstrated here opens up a new synthetic strategy to interesting and unusual cage molecules.