Azides other multiple bonds

The history of cycloaddition chemistry using aliphatic diazo compounds began in the 1890s when Buchner (1) and von Pechmann (2) reported that ethyl diazoacetate and diazomethane underwent cycloaddition across carbon-carbon multiple bonds. Ever since that time, diazo compounds have occupied a major place in [3 +2]-cycloaddition chemistry (3,4). For a long time, diazo compounds, as well as organic azides, have been one of the more synthetically useful classes of 1,3-dipoles. No doubt this was because many different mono- and disubstituted diazo compounds could be prepared (Scheme 8.1) and isolated in pure form, in contrast to other 1,3-dipoles that are typically generated as transient species. 

For the above reasons nitrogen forms many compounds of types not formed by other elements of this group, and for this reason we deal separately with the stereochemistry of this element. For example, the only compounds of N and P which are structurally similar are the molecules in which the elements are 3-covalent and the phosphonium and ammonium ions. There are no nitrogen analogues of the phosphorus pentahalides, and there is little resemblance between the oxygen compounds of the two elements. Monatomic ions of nitrogen and phosphorus are known only in the solid state, in the salt-like nitrides and phosphides of the more electropositive elements. The multiple-bonded azide ion, N3, is peculiar to nitrogen. 

The reactivity of heteroatom-substituted stannenes has not been fully reported so far. On the other hand, those of tetraarylstannenes 26 and 27 and transient stannenes 33 and 34 have been widely investigated (Scheme 2.9.10). These compounds readily undergo 1,2-addition with various protic reagents and iodomethane. Their reactions with multiple-bond compounds such as ketones, butadienes, and azides result in the formation of the corresponding [2- -n]-cycloadducts (n = 2, 3,4). 

Cycloaddition. TMSA, like other alkyl azides, reacts with alkynes and C-hetero multiple bonds to give [3 + 2] cycloaddition products, triazoles and tetrazoles. For example, the reaction of TMSA with 2-butyne gives 4,5-dimethyl-2-trimethyl-silyl-1,2,3-triazole in 78-87% yields (eq 9), and TMSA and cyanoferrocene react to give 5-ferrocenyl-2-trimethylsilyltetra-zole in 75% yield (eq 10). ... 

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