TheBanert cascade is anorganic reaction in which anNH-1,2,3-triazole is prepared from apropargylhalide orsulfate andsodium azide in adioxane- water mixture at elevated temperatures.[1] It is named after Klaus Banert, who first reported the process in 1989.[2] Thiscascade reaction is unusual because it consists of two consecutiverearrangement reactions.
The starting material is prepared frompropargyl chloride and analdehyde orketone such asacetaldehyde. In the first step anazido compound is formedin situ in anucleophilic displacement of chloride by theazide ion. A (3,3)Sigmatropic reaction takes place between theazide and thealkyne to the allenyl azide. Thisallene rearranges to the triazafulvene in a 6 pielectrocyclization. Theexocyclicalkene in this intermediate is very electrophilic because the triazole group has adipole moment of 5debye. The reaction sequence concludes withnucleophilic attack of a second azide ion on this alkene with more double bond rearrangements and proton abstraction from a proton source.