5 - tetrazolide anion

The tetrazole-catalysed alcoholysis of simple dialkylphosphoramidates (267) in THE to yield trialkylphosphites (268) occurs via nucleophilic catalysis (Scheme 29). The proposed mechanism sees tetrazole acting first as an acid catalyst to give the protonated intermediate (269), which then reacts with tetrazolide anion to yield the tetrazolylphosphite (270) alcoholysis of the latter (270) then yields the final product, the trialkylphosphite (268). ... 

The scope of the rearrangement reaction whereby azido-l,2,3-triazolide ion (66) is converted to the (diazomethyl)tetrazolide ion (68) has been studied. Where R = H, substituted phenyl, Me, and C02Me the reaction proceeds at a rate which is largely independent of substituent extensive decomposition is observed where R = COMe, COAr, and CN. PM3 calculations used to explore the energy profile of the reaction pathway indicate that the order of anion stability is (67) < (66) < (68) and that the rearrangement is of the type (66) (67) (68) for which 2 and k i ki. 

Unsubstituted tetrazole behaves as an organic acid with acidity close to that of acetic acid. In general, depending on the substituent in position 5, tetrazole ionization occurs in the range from —0.8 unit of the Hq scale to 7 unit of the pH scale. Proton elimination from 1H- and 277-tetrazoles 24 and 106 results in formation of the tetrazolate anion (tetrazolide) 7 (Scheme 5) characterized by high aromaticity and good Jt-electron delocalization. 

The change in the nature of the tetrazole substrate on going from tetrazolide 7 to contact ion pairs, solvent-separated ion pairs with a metal cation, to complexes of 231 and 232 type, etc., can result in deviations from the canonical mechanisms like those described above (Schemes 22 and 23). Also, the possibility cannot be excluded that the ion pairs formed by anion 7 react with the electrophile concurrently by several alternative pathways. We believe that just this versatility of reaction routes explains the difference between the predicted rate and selectivity of the electrophilic attack under ideal conditions and the experimental result. In the light of these comments, new data on the application of ion pairs formed by anions of type 7 to the synthesis of N-substituted tetrazoles are discussed. As far as possible, attention is given to conclusions with respect to the regioselectivity of electrophile attack. 

Tetrazoles exhibit qualities of acids, bases, acceptors of hydrogen bonds (cf. Section 6.07.4.5), and polydentate ligands (cf. Section 6.07.5.3.4). NH-LJnsubstituted tetrazoles behave both as substrates and intermediates in transacylation processes (cf. Section 6.07.5.4), etc. Tetrazolate anions (tetrazolides) possess high aromaticity and reactivity toward electrophilic reagents (cf. Sections 6.07.4.1 and 6.07.5.3.2). The thermal and photochemical decomposition of tetrazoles involves formation of nitrenes and other intermediates of high reactivity (cf. Sections 6.07.5.2 and 6.07.5.7) These properties provide a possibility of use tetrazoles as catalysts in chemical and biochemical reactions. 

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