Halogen-azide exchange

Mechanistically most of these transformations correspond to 5N2-type substitutions chiral substrates react with inversion. In certain cases, however, azides may also be obtained under 5n1 condi-tions." " " Some di- and tri-arylmethanols for instance (Scheme 32) react with HN3 in the presence of trichloroacetic acid via the corresponding carbenium ions. Sulfuric acid seems to be inferior for these transformations." " Under highly acidic conditions the intermediate (20) obviously tends to decompose with the elimination of nitrogen (c/. Schmidt reaction "). SnI substitution is also highly probable in the reaction of a-halo ethers and sulfides with azide ions." " In some cases even SRNl-type substitution was observed for the halogen/azide exchange." ... 

Searching for other 6-membered "diazido malonyl N-heterocycles" we have selected the pyridazine derivative 25 and diazido barbituric acids 32 as model systems, since they are available easily and in large quantities. Compound 25 is obtained in the usual way by chlorination of 23 with sulfuryl chloride and exchange of the halogen atoms with sodium azide. 

Anions derived from halogenated imidazoles are frequently utilized in the formation of (7-heteroatom bonds. Bromolithium exchange of 961 (Scheme 233) followed by azidation 962 and reduction leads to 2-aminoimidazole 963 (PMB = -methoxybenzyl) <2003H(60)583>. The Mg-imidazolide intermediate from I/Mg exchange of 964, PBB = -bromobenzyl) reacts with sulfur dioxide for the synthesis of sulfonamide 965 <2003TL6509>. 

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