More substituted nitrocubanes-

Pentanitrocubane(PNC) and Hexanitrocubane(HNC)

PNC

The literature was unsupportive of this optimistic view. Poor results were also obtained initially with nitrating agent such as NO₂BF₄, acetyl nitrate, amyl nitrate etc.

Tetranitrocubylsodium can be formed directly on treatment of TNC with sodium bis(trimethylsilyl) amide in THF at -75°C. It can react with electrophiles to provide a useful and convenient way to achieve further functionalization of cubane nucleus.

Base on the property of tetranitrocubylsodium, nitryl chloride(NO₂Cl) was used to further nitrate the cubane nucleus. Treatment of NO₂Cl with tetranitrocubylsodium in THF at -75°C works out 10-15% yield of pentanitrocubane(PNC). The yield increased to 30% when the solution was frozen to-180°C and allowed to warm slowly. This is called the interfacial nitration process. It is suggested that NO₂Cl oxidized tetranitrocubylsodium to a radical, which made the whole reaction worked.

Base on the property of NO₂Cl , N₂O₄ should be a better choice. The results showed that it is actually a better with 60:40 PNC to TNC ratio. The reaction is extremely clean.

PNC is colourless and highly crystalline. It is the first nitrated cubane to contain adjacent nitro groups. It behaves just TNC and other nitrocubanes, remarkly stable kinetically.

HNC

Although HNC can be prepared the same way as PNC, but the separation between PNC and HNC is extremely difficult.

However, if TIPS-substituted PNC( by N₂O₄ nitration from TIPS-sub TNC) react with potassium base (K(TMSN)₂and the nitration with N₂O₄ gave a mixture of (triisopropyl) HNC and PNC in 60:40 ratio. This step is important and crucial. The separation is now possible by column chromatography on silica gel. 30% isolated yield of PURE HNC could be obtained when further treated with SiO₂.