Tetrazole ring

Action of HSO3CI on 2-substituted thiazoles affords the 5-chlorosulfonyl derivatives (337, 338). Addition of 6-phenylthiazolo[2,3-e]tetra2ole to oleum opens the tetrazole ring to form 2-azido-4-phenyI-thiazolyl-5-sulfonic acid, isolated as its salt (339). 5-Chloro-sulphonyl derivative is obtained similarly by action of HSO,Cl. 

Compounds containing a fused quinoline-tetrazole ring system (90 Z = N) behave similarly to compounds containing the simple tetrazole ring and give salts of type 91 (Z =... 

Valence tautomerism of heterocyclic systems containing tetrazole rings has received much attention [76AHC(S1), p. 498 84CHEC-I(5)791 96CHEC-1I(4)621], The latest contributions to this area are considered in Section IV,C, which is concerned with the topic of azido-tetrazole tautomerism. 

Naphtho analogues, naphtho[2,l-e]tetrazolo[l,5-6][l,2,4]triazine, naph-tho[l,2-e]tetrazolo[l,5-b][l,2,4]triazine, and naphtho[2,3-e]tetrazolo[l,5-Zj][1, 2,4]triazine, were prepared (82JOC3168 84JOC3199) by cyclization of the respective hydrazine with sodium nitrite in acetic acid or by azide displacement of a leaving group. Elucidation of the site of annulation of the tetrazole ring was accomplished by X-ray analysis and l3C-NMR spectroscopy (Scheme 189). 

Figure 4. contour plots in the plane of the tetrazole ring. Dimensions and contour interval as in Figure 3. (a) Experimental (minimum contour -80 kcal/mol), (b) theoretical (minimum contour -60 kcal/mol). 

The thermolysis of l-([l,3,4]thiadiazol-2-yl)tetrazoles 133 gives rise to the loss of dinitrogen from the tetrazole ring and the formation of 2,6-diaryl[l,2,4]triazolo[5,l+][l,3,4]thiadiazoles 71 (Equation 39) <1985IJB908, 1990FA953>. (For another synthesis of compounds 71, see Section 11.07.8.1.5.)... 

Ring synthesis involving formation of the tetrazole ring via azide-tetrazole equilibrium 656... 

Ring synthesis including formation of the tetrazole ring by intramolecular 1,3-dipolar... 

Scheme 22 illustrates a special application of the azide-tetrazole ring closure described by Ponticelli et al. <2004JHC761>. The diazido compound 84 exists as an azide valence bond isomer. When this compound, however, is subjected to reduction by molybdenum hexacarbonyl, one azido group undergoes reduction selectively to an... 

Ring opening of the five-membered tetrazole ring has also been observed in several cases. The most trivial conversion is the equilibrium between the fused tetrazole and azidodiazine which, in principle, could take place with every fused tetrazole compound described in this chapter, and, therefore, no special comment on this type of ring opening needs to be discussed. 

The high nitrogen content and the endothermic nature of the tetrazole ring lends itself to the synthesis of energetic materials. Compounds such as -H tetrazole and 5-aminotetrazole can be used as nucleophiles to incorporate the tetrazole ring into other molecules. 5-Aminotetrazole is synthesized from the reaction of dicyandiamide with sodium azide in hydrochloric acid. 

Cefonicid Cefonicid, 7-D-mandelamido-3-[[(l-sulfomethyl]-l/f-tetrazol-5-yl]thio] methyl]-8-oxo-5-thia-l-azabicyclo[4.2.0]oct-2-en-2-carboxylic acid (32.1.2.26), is structurally similar to cefamandole and differs in the presence of a sulfonic acid group in the methyl substituent of the tetrazol ring. It is synthesized by a method analogous to that of the synthesis of cefamandole [120-123],... 

Fully conjugated aromatic tetrazole rings have structures (1) or (2) and are numbered as shown. These are discussed in Section 4.17.5. Dihydrotetrazoles are dealt with as nonconjugated systems in Section 4.17.6. The most common forms of these are the structures (3) and (4). The A -tetrazolines (3) may give diaziridines when heated or if aromatic substituents are present at C-5 cycloreversion to azides and imines may occur <87BSF525, 88CB1213>. The 1,4-dihydrotetrazoline structure (4) is common for Y = S, O, NR and CR2. 

The tetrazole ring exhibits only weak end absorptions at 200-220 nm in the ultraviolet and only tetrazoles with conjugated auxochromic groups give normal ultraviolet spectra. Absorption maxima are controlled by the conjugation which is usually more extensive in 2,5-disubstituted derivatives relative to the 1,5-disubstituted isomers. Thus 2,5-disubstituted tetrazoles have higher as seen from the following examples 1-Me,5-Ph, 232 nm, 2-Me,5-Ph, A ax 240 nm 1-Ph,5-H, A ax 236... 

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