Organic Chemistry of Explosives

Adamantanes 79

The search for energetic compounds with high crystal densities has focused attention on the

polynitro derivatives of 1,3-bishomopentaprismane. However, the synthesis and incorporation

of this compact core into explosives is complex and synthetically challenging. In general, com-

plex caged structures require multiple, nontrivial synthetic steps, often with one or more of

these using a photoinitiated cyclization or cycloaddition step. The 1,3-bishomopentaprismane

core is no exception. The 2,6-dinitro isomer (93) requires the synthesis of [4]-peristylane-

2,6-dione (90), which is prepared in no fewer than seven steps from the cycloadduct (89).^25

Incorporation of the two nitro groups into the [4]-peristylane core uses standard robust chem-

istry, thegem-bromonitro intermediate (92) being formed from the bromination-oxidation of

the dioxime (91). The 1,3-bishomopentaprismane core is formed from the reaction of (92) with

tributyltin hydride in a radical induced C–C bond formation.^26

94

HON NOH

NO 2 NO 2

H H

96, 15 %

NO 2

H

O

O

m-CPBA, urea,

MeCN, Na 2 HPO 4

95, 23 %

(mixture of isomers)

+

K 3 Fe(CN) 6 , NaOH,

NaNO 2 , MeOH (aq)

99, 16 %

NO 2 NO 2

O 2 N NO 2

97, 33 %

NO 2 NO 2

NO 2

H

O 2 N

98, 18 %

NO 2

H NO 2

reflux

Figure 2.20

Paquette and co-workers^27 synthesized the 5,11-dinitro isomer of 1,3-bishomopentapris-

mane (95) by treating the dioxime (94) with a buffered solution ofm-CPBA in refluxing

acetonitrile. A significant amount of lactone by-product (96) is formed during this step and

may account for the low isolated yield of (95). Oxidative nitration of (95) with sodium nitrite

and potassium ferricyanide in alkaline solution yields a mixture of isomeric trinitro derivatives,

(97) and (98), in addition to the expected 5,5,11,11-tetranitro derivative (99), albeit in low yield.

Incomplete reactant to product conversion in this reaction may result from the low solubility of

either (97) or (98) in the reaction medium, and hence, incomplete formation of the intermediate

nitronate anions.

2.7 Adamantanes

The highly rigid skeleton of adamantane results in much higher crystal densities compared

to its open chain counterparts, and hence, higher performance for its nitro derivatives. The

adamantane core shows little to almost no strain and so some of its polynitro derivatives

show exceptionally high thermal stability. Research has focused on placing nitro groups on

the tertiary carbon bridgehead positions of adamantane, and forminggem-dinitro derivatives

at the methylene carbon positions. Both tertiary nitro and internalgem-dinitro functionalities

show high chemical stability.