A series of 3-aryl-I -(tetrazoL5'-yI)triazenes was prepared by coupling tetrazole-5-diazonium ion with substituted anilines. The orientation of the ambident methylation reactions of the anion of these systems was investigated. ' 3C N.m.r. spectra of the mono-and di-methyl derivatives provided information on the preferred tautomeric structure of the parent triazenyltetrazole system.Triazene derivatives including heterocyclic triazenes have attracted recent attention because of their pharmacological properties including carcinogenic and anti-tumour activity. However, only a few tetrazol-5-yltriazene derivatives have been reported.'T6 These are mainly of the bis(substituted tetrazol-5-y1)triazene type formed in the diazotizations of some substituted aminotetrazole derivative^.^.^,^
Results and Discussion(a) Synthesis andAIkylation.--Herein a series of new 3-aryl-1-(tetrazol-5'-yl)triazenes (2) (Table 1) was prepared by coupling tetrazole-5-diazonium salts (1) with substituted anilines. Proton abstraction from the compounds (2) could occur at the triazene chain or the tetrazole ring giving the anions (3) or (4) and these could interchange via tautomerism (Scheme). Monoalkylation could occur at the 1-, 3-, l', or 2'-nitrogen atoms (Scheme). In the event mono-alkylations with methyl iodide occurred preferentially at positions 1' and 2' giving the products (6) and (5) respectively (Scheme). The dominant reaction occurred at the 1 '-position. The mono-anion (7) of the N(1')-methyl derivatives (6) is also an ambident system with five viable sites for attack, the 1-, 3-, 2'-, 3'-, and 4'-nitrogen atoms. Attack at the 3'-position would give a meso-ionic product. Introduction of a second methyl group to this anionic system with methyl iodide occurred on the exocyclic triazene chain giving the products (8) and (9) with the main reaction occurring at the 3-position (Scheme).The structure of the N-methyl isomers (5) and (6), and (8) and (9), were indicated from their 'H and 13C n.m.r. spectra (Table 2). The N-Me signals followed the patterns which we have previously established for N-alkylazoles where the N-Me group is less shielded in an N-N(Me)-N unit, structure (S), as compared with a C-N(Me)-N unit, structure (6), thereby allowing a distinction to be made between the two. The tetrazole C-5' shift which is known to be about 10 p.p.m. downfield in a 2,5-disubstituted tetrazole [structure (5)] relative to a 1,5disubstituted ring [structure (6)] also agreed with the assigned structure (Table 2). These assignments were confirmed for the series (6) through unequivocal syntheses by coupling of arene diazonium salts with 5-amino-1-methyltetrazole and for the series (5) by coupling diazotized 5-amino-2-methyltetrazole with p-substituted anilines. The structures of the dimethyl derivatives (8) and (9) were similarly established from 'H and 13C n.m.r. spectra and by unequivocal synthesis of the compound (8) from the corresponding N-methylaniline (Scheme) (Table 2). (b) Structure and Tautomerim.-The parent triazenes (2), with two tauto...
3-Aryl-1 -tetrazol-5-yltriazenes have been used as a bench-stable source of diazonium ions for the synthesis of substituted biaryls, aryl halides (iodides, bromides, and chlorides) and azo dyes. The dediazoniation process when induced by trihalogenoacetic acid or acetic acid did not involve free radicals.
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