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The Banert cascade is an organic reaction in which an NH-1,2,3-triazole is prepared from a propargyl halide or sulphate and sodium azide in a dioxane- water mixture at elevated temperatures. This cascade reaction is unusual because it consists of two consecutive rearrangement reactions.
Additional recommended knowledge
The starting material is prepared from propargyl chloride and an aldehyde or ketone such as acetaldehyde. In the first step an azido compound is formed in situ in a nucleophilic displacement of chloride by the azide ion. A (3,3)Sigmatropic reaction takes place between the azide and the alkyne to the allenyl azide. This allene rearranges to the triazafulvene in a 1,3-dipolar cycloaddition. The exocyclic alkene in this intermediate is very electrophilic because the triazole group has a dipole moment of 5 debye. The reaction sequence concludes with nucleophilic attack of a seconde azide ion on this alkene with more double bond rearrangements and proton abstraction from a proton source.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Banert_cascade". A list of authors is available in Wikipedia.|