1.3- triazenyl radicals

Also, the action of silyl radicals (or of organyl radicals) on silyl azides leads finally to amines and nitrogen (75). As reaction intermediates, triazenyl radicals—N—N—N—(e. g., MejSiN—N—NSiMc3) have been identified by ESR spectroscopy. 

Kim developed a new entry into A -heterocycles by radical cyclizations onto alkyl azides. Iodides, bromides and thionocarbonates (Scheme 28, Eq. 28.1) are suitable radical precursors. 5-Exo cyclizations afford 3,3-triazenyl radicals that lose N2 to furnish an aminyl radical [79]. Following this work, Kilburn has applied this strategy to the formation of spiro-heterocycles from methylenecyclopropanes [80]. Finally, this reaction was applied as a key step in a very elegant cascade synthesis of aspi-dospermidine developed by Murphy (Scheme 28, Eq. 28.2) [81]. 

Kim reported efficient radical cyclizations involving azides as radical traps (Scheme 8.33)7 This intramolecular amination process is efficient and proceeds via a 3,3-triazenyl radical that readily eliminates nitrogen to afford an aminyl radical. The use of (TMSlsSiH gives better results than BusSnH since azides are relatively inert toward tris(trimethylsilyl) silyl radicals. However, tin hydride can be used with alkyl iodides since the iodine atom abstraction by the stannyl radical is faster than its addition to the azide. 

Diazenyl radicals have also been detected in related systems. The rapid rearrangement of 1,3,5-triarylpentazadienes [equation (47)] involves intermediate triazenyl-diazenyl radical pairs, as indicated by the appearance in emission of the n.m.r. transitions of the -methyl protons of the starting material when Ar = Ar =j -CHg.C6H4 (Hol-laender and Neumann, 1970). The weak emission of benzene which accompanies a much more intense emission due to toluene when the 1,3-diaryltetrazene 6 decomposes in acetone at 50° has been interpreted... 

The adducts of azodicarboxylate with EtsSi or PhsSi radicals [79], have been identified as hydrazyl radicals (Reaction 5.41). The addition of RsSi radical to alkyl azides takes place at the terminal nitrogen (Reaction 5.42) affording the triazenyl o-type radical in which the SOMO is in the NNN plane (only one canonical structure is shown) [80,81]. 

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