Synthesis for the last two nitro cubanes- heptanitrocubane and octanitrocubane

HpNC

Interfacial nitration is not sufficient to further nitration for heptanitrocubane. Al though it is very good in deed, we need to find something which can successfully convert heptanitrocubane (HpNC).

In this procedure TNC was treated with at least 4 equivalents of the base NaN(TMS)₂ (where TMS = trimethylsilyl) at ±78 C in 1:1 THF/MeTHF. After the mono sodium salt had formed, the solution was cooled to between ±125 and ±130°C giving a clear, but very viscous fluid. This was stirred vigorously as excess N₂O₄ in cold isopentane was added. After one minute, the base was quenched, and the whole mixture was added to water. This resulted reproducibly in almost complete conversion of TNC (1 g scale) to HpNC (95% by NMR), isolated crystalline in 74% yield!

ONC

However, even in the presence of excess nitrating agent (N₂O₄ or many others) no indication
of any formation of ONC was ever seen. It is suspected that anion nitration with N₂O₄ proceeds by oxidation of the carbanion to the corresponding radical.Perhaps the anion of HpNC is too stabilized for this to occur. (HpNC is significantly ionized in neutral methanol.) This concept led to the use of the more powerful oxidant nitrosyl chloride. Addition of excess NOCl to a solution of the lithium salt of HpNC in dichloromethane at 78° C followed by ozonation at 78° C gave the long-sought ONC in 45±55% isolated yield on millimole scale. The intermediate product prior to oxidation is thought to be nitrosoheptanitrocubane.

Finally, the magic molecule, the so called the impossible molecule, octanitrocubane was synthesised. But, how good are they and how useful are they? Let us discuss about it in the following section.