Organic Chemistry of Explosives

Ring-opening nitration of nitrogen heterocycles 225

Good yields are attainable for some sterically hindered nitramines like di-iso-butylnitramine

(128) (Table 5.8, Entry 2). The synthesis ofN, N′-dinitrohexahydropyrimidine (117) from the

corresponding disilylamine (131) is of note (Table 5.8, Entry 4); this compound was previ-

ously synthesized^117 from the nitrative cleavage ofN, N′-dinitrosohexahydropyrimidine with

dinitrogen pentoxide–nitric acid in only 30 % yield (Table 5.7, Entry 3). Yields are lower for

compounds with silyl groups containing secondary and tertiary alkyl groups like TIPS and

TBDMS respectively. Secondary nitramides and nitroureas are also obtained in good yield

from the corresponding TMS derivatives (Table 5.8, Entries 5 and 6).

N

NO 2

H 3 C H 3 C

N

Si(CH 3 ) 3

H 3 C

N

NO 2

ONO 2 NO 2

O 2 NO

ONO 2

CH 3

+

137 HH 136

138

139

1 eq N 2 O 5 excess N 2 O 5

Figure 5.60

The reaction of the silylaziridine (136) with one equivalent of dinitrogen pentoxide in

methylene chloride yields theN-nitroaziridine (137), whereas with excess reagent a mixture

of theN, N-dinitramine-nitrate (138) and the dinitrate ester (139) is obtained; the former is a

high-energy compound and of some difficulty to prepare via other routes.^122

Nitrodesilylation with dinitrogen pentoxide is an important route to nitramine-based explo-

sives and may find future industrial use given its low environmental impact. Providing that anhy-

drous conditions are maintained (dinitrogen pentoxide prepared from the ozonolysis of dinitro-

gen tetroxide^123 ), reactions are suitable for the synthesis of products containing acid-sensitive

functionality. The trimethylsilyl precursors are readily prepared from chlorotrimethylsilane in

the presence of triethylamine for strong amine bases; weaker amine bases and amides/ureas

require lithiation with an alkyl lithium reagent before treatment with the chlorosilane.

5.8 Ring-opening nitration of strained nitrogen heterocycles

N

R''

140

R'R N

2 O 5 , CH 2 Cl 2

N 2 O 5 , CH 2 Cl 2

O 2 NO

N

NO 2

R

R'

R''

N

R'

R

O 2 NO N

NO 2

R

R'

141

(^142143)
Figure 5.61