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The reactions of [3, 2-b] pyridino [4, 5] benzo-1, 3a, 6, 6a-tetraazapentalene [I] and its nitro- or halogeno-derivatives with some electrophiles and nucleophiles are described. The directive influence of the tetraazapentalene nucleus on electrophilic and nucleophilic substitution reactions at the pyridine and the benzene rings is discussed.

Explosives are employed extensively not only in military areas but also in civilian applications. There are many researchers working on the discovery of explosives. In recent years, synthetic and theoretical studies on polycyclic aromatic explosives have received significant interest. The present short review concentrates on the synthesis and some of the physico-chemical characteristics of energetic materials of the classes of tetraazapentalene, naphthalene, di- and tetraaza-naphthalene, pyrazolo-pyrazole, benzofuroxan, tetrazine and tetrazene derivatives as well as theoretical studies. A brief comment is also made on the emerging explosive concepts such as velocity of detonation, detonation pressure etc. The compounds in the review have the potential for subsequent applications in the area of energetic materials. Therefore, an endeavor is made to assemble the important contributions made by the various scientists in the area of energetic materials in this review.

Thermolysis of 7-azido-8-(2H-1,2,3-triazol-2-y1)-1,2,3,4-benzotetrazine 1,3-dioxide and 7-azido-8-(l H-1,2,3-triazol-l-yl)-1,2,3,4-benzotetrazine 1,3-dioxide afford new heterocyclic systems, viz., 7,11-dehydro-7H, 11H [1,2,3]triazolo[l′,2′:2,3][1,2,3]triazolo[4,5-f]-[1,2,3,4]benzotetrazine 1,3-dioxide and 7,9-dehydro-7 H, 9H [1,2,3]triazolo[2′,1′:2,3]-[1,2,3]triazolo[4,5-f][1,2,3,4]benzotetrazine 1,3-dioxide, respectively, and their thermal stability has been studied.

Thermolysis of 7-azido-6-(2H-1,2,3-triazol-2-yl)-1,2,3,4-benzotetrazine 1,3-dioxide and 7-azido-6-(1H-1,2,3-triazol-1-yl)-1,2,3,4-benzotetrazine 1,3-dioxide gives rise to the new heterocyclic systems: 6,10-dehydro-6H,10H-[1,2,3]triazolo[1′,2′:2,3][1,2,3]triazolo[4,5-g]-[1,2,3,4]benzotetrazine 2,4-dioxide and 6,8-dehydro-6H,8H-[1,2,3]triazolo[1′,2′:1,2][1,2,3]-triazolo[4,5-g][1,2,3,4]benzotetrazine 2,4-dioxide, respectively, their thermal stability and spectral properties have been studied.

A series of 1-substituted 4,5-diformyl-[1,2,3]triazole derivatives were prepared by 1,3-dipolar cyclo-addition of aryl azides with acetylene dicarboxaldehyde mono-diethylacetal. The triazoles were readily converted into 1-substituted [1,2,3]triazolo[4,5-d]pyridazines in good yields. The 1-(2-nitrophenyl)-[1,2,3]triazolo[4,5-d]pyridazine was found to be a useful intermediate for the generation of the novel 5H-benzo[1,2,3]triazolo[1′,2′:1,2]triazolo[4,5-d]pyridazin-6-ium inner salt ring system.

A density functional procedure has been used to compute gas phase heats of formation for a group of high-nitrogen molecules, primarily tetraazapentalene derivatives. Optimized structures and relative energies were computed for the key molecular framework and several isomeric forms. It is speculated that the unexpected tetraazapentalene stability observed experimentally is related to the relatively positive character of the triply-coordinated nitrogens.

New azacrown and azathiacrown ethers ( 5a-c and 7 ), incorporating two thiourea moieties, were synthesized from the hypervalent sulfur-containing tetraazapentalene ( 1 ) and diisothiocyanate derivatives of oligoethylene glycols and from 1 and 3,6,9-trithia-1,11-undecanediisothiocyanate, respectively, by cyclization and then desulfurization.

2,3-Bis[(p-isothiocyanatomethylphenyl)methyl]-6,7-dihydro-5H-2a-thia(2a-SIV)-2,3,4a,7a-tetraazacyclopent[cd]indene-1,4(2H,3H)-dithione, prepared from 2,3-dialkyl substituted tetraazapentalene derivatives and p-xylylene diisothiocyanate, reacted with N,N′-dialkyl substituted diamines to give macrocyclic compounds by ring closure in good yields. These macrocyclic compounds were converted into desulfurized macrocyclic compounds by treatment with NaBH4 and CF3COOH.

12π-Tetraazapentalenes, 2,3-disisubstituted 6,7-dihydro-5H-2a-thia(2a-S IV )--2,3,4a,7a-tetraazacyclopent-[cd]indene-1,4(2H,3H)-dithiones, 1 and 7, reacted with excess alkyl or aryl isothiocyanates and isocyanates to afford mono- and di-aryl or aryl substituted tetraazapentalene derivatives which have the thiocarbonyl and carbonyl groups

The 10-S-3 type tetraazapentalene derivatives in acidic conditions were converted to the ring-opeining products, 1,3-disubstituted perhydropyrimidin-2-ones, in high yields with the release of a hypervalent sulfur.

The novel 1-substituted 4,5,7,8-tetrahydro-3H-6,8 b-dithia(8a-S IV )-1,2a,5 a-triaza-8a-azoniadicyclo a, cd indene-2(1H)-thione bromides, the corresponding 8b-selena(8b-Se IV ) derivatives, and 1-substituted 4,5,8,9-tetrahydro-3H,7H-6,9 b-dithia(9b-S IV )-1,2a, 5a-triaza-9a-azoniacyclopenta [jk] fluorene-2(1H)-thione bromide and the corresponding 9b-selena(9b-Se IV ) derivatives were synthesized by the reaction of tetraazapentalene derivatives 1a,b and 2a,b with 2-bromoethyl and 3-bromopropyl isothiocyanates, respectively, in good yields

New azacrown and azathiacrown ethers ( 5a-c and 7 ), incorporating two thiourea moieties, were synthesized from the hypervalent sulfur-containing tetraazapentalene ( 1 ) and diisothiocyanate derivatives of oligoethylene glycols and from 1 and 3,6,9-trithia-1,11-undecanediisothiocyanate, respectively, by cyclization and then desulfurization.

2,3-Bis[(p-isothiocyanatomethylphenyl)methyl]-6,7-dihydro-5H-2a-thia(2a-SIV)-2,3,4a,7a-tetraazacyclopent[cd]indene-1,4(2H,3H)-dithione, prepared from 2,3-dialkyl substituted tetraazapentalene derivatives and p-xylylene diisothiocyanate, reacted with N,N′-dialkyl substituted diamines to give macrocyclic compounds by ring closure in good yields. These macrocyclic compounds were converted into desulfurized macrocyclic compounds by treatment with NaBH4 and CF3COOH.

A series of 1-substituted 4,5-diformyl-[1,2,3]triazole derivatives were prepared by 1,3-dipolar cyclo-addition of aryl azides with acetylene dicarboxaldehyde mono-diethylacetal. The triazoles were readily converted into 1-substituted [1,2,3]triazolo[4,5-d]pyridazines in good yields. The 1-(2-nitrophenyl)-[1,2,3]triazolo[4,5-d]pyridazine was found to be a useful intermediate for the generation of the novel 5H-benzo[1,2,3]triazolo[1′,2′:1,2]triazolo[4,5-d]pyridazin-6-ium inner salt ring system.

Thermolysis of regioisomeric 7-azido-8-triazolylbenzotetrazine dioxides (V) and (VII) affords new heterocyclic systems, viz.

Tetraazapentalene derivatives having fused cyclic systems reacted with the I2/NH4OH reagent to give 1,2,4-thiadiazolo[4,3-a]pyrimidine derivatives with the release of the hypervalent sulfur. The molecular structure of the product was determined by the X-ray crystallographic analysis.

12π-Tetraazapentalenes, 2,3-disisubstituted 6,7-dihydro-5H-2a-thia(2a-S IV )--2,3,4a,7a-tetraazacyclopent-[cd]indene-1,4(2H,3H)-dithiones, 1 and 7, reacted with excess alkyl or aryl isothiocyanates and isocyanates to afford mono- and di-aryl or aryl substituted tetraazapentalene derivatives which have the thiocarbonyl and carbonyl groups

The novel 1-substituted 4,5,7,8-tetrahydro-3H-6,8 b-dithia(8a-S IV )-1,2a,5 a-triaza-8a-azoniadicyclo a, cd indene-2(1H)-thione bromides, the corresponding 8b-selena(8b-Se IV ) derivatives, and 1-substituted 4,5,8,9-tetrahydro-3H,7H-6,9 b-dithia(9b-S IV )-1,2a, 5a-triaza-9a-azoniacyclopenta [jk] fluorene-2(1H)-thione bromide and the corresponding 9b-selena(9b-Se IV ) derivatives were synthesized by the reaction of tetraazapentalene derivatives 1a,b and 2a,b with 2-bromoethyl and 3-bromopropyl isothiocyanates, respectively, in good yields

The 10-S-3 type tetraazapentalene derivatives in acidic conditions were converted to the ring-opeining products, 1,3-disubstituted perhydropyrimidin-2-ones, in high yields with the release of a hypervalent sulfur.

An improved nitration procedure has been developed for the synthesis of y-Tacot (3). The synthesis of y-DBBD (8) has been completed in three steps from 3 in 37% yield. y-DBBD (8) was found to be thermally stable up to 274 °C (decomposed) and insensitive to impact (hammer blow). Nitration of z-BDDB (6) and y-DBBD (8) gave carbonyl derivatives resulting from in situ hydroysis/oxidation of the corresponding tetranitro derivatives z-TBBD (7) and y-TBBD (9), respectively.

Tetraazapentalene derivatives (R = CH3, CH2=CHCH2) reacted with ω-halogenoalkyl isothiocyanates to give novel tetraazapentalene derivatives with fused cyclic systems in good yields.

Dipyrido[1,2- a 2′,1′- f ]-1,3,4,6-tetraazapentalene ( 1a ) undergoes an [ α 8 + α [2] cycloaddition reaction with dimethyl acetylenedicarboxylate to give, upon CN bond cleavage, a substituted 1-azacycl[3.2.2]azine ( 2a ).

Tetraazapentalene derivatives ( 1 : R=CH 3 , CH 2 =CHCH 2 ) reacted with various α-haloketones to give N-substituted oxazoline-2-thione derivatives ( 2 , 4 , 5 , and 6 ).

Tetraazapentalenes (R = CH3 and CH2=CHCH2) reacted with isocyanates to give new types of tetraazapentalenes, (2) and (3). The compounds, 2 and 3 were also obtained by the reaction of isocyanates with thiadiazolopyrimidines.

An oxidative cyclization method is described for synthesizing molecules containing the 1,3,4,6-tetraazapentalene ring system.

Oxidation of 1 - phenylcarbamoylidazolidine - 2 - thione gives 2,3,5,6 - tetrahydro - 2 - phenylimidazo [1,2-d]- (1,2,4) - thiadiazole - 3 - one which undergoes addition reactions with heterocumulenes leading to various heteropentalenes. Oxidation of 1 - phenylthiocarbamoylimidazlidine- 2 - thione yields 1- (benzothiazol - 2- yl) - imidazolidine - 2 - thione, also obtained by acid catalysed decomposition of 3,4 - ethano - 2,3,4,5 - tetrahydro - 2, 5 - bisphenylimino - 1,6,6aS IV - trithia - 3,4 - diazapentalene. A similar acid catalysed decomposition to a benzothiazole occurs with 2,3,4,5 - tetrahydro - 1,6 - diphenyl - 3,4 - propano - 6aS IV - thia - 1,3,4,6 - tetraazapentalene -2, 5- dithione.

Tetraazapentalene derivatives (R = CH3, CH2=CHCH2) reacted with ω-halogenoalkyl isothiocyanates to give novel tetraazapentalene derivatives with fused cyclic systems in good yields.

The synthesis of unsymmetrical tetraazapentalene derivatives was achieved by the reaction of thiadiazole derivatives (2) with various isothiocyanates. Compounds 2 were easily derived from symmetrical tetraazapentalene derivatives.

The title compound (I) was oxidized to give 3-benzoyl-1-p-chlorophenyl-4-p-chlorophenylazo-5-phenylpyrazole (II) and 3-benzoyl-1-p-chlorophenyl-4-p-chlorophenylazoxy-5-phenylpyrazole (III), both of which underwent trans to cis isomerization on irradiation with ultraviolet light.

Tetraazapentalenes (R = CH3 and CH2=CHCH2) reacted with isocyanates to give new types of tetraazapentalenes, (2) and (3). The compounds, 2 and 3 were also obtained by the reaction of isocyanates with thiadiazolopyrimidines.