Banert cascade

The Banert cascade is an organic reaction in which an NH-1,2,3-triazole is prepared from a propargyl halide or sulfate and sodium azide in a dioxane- water mixture at elevated temperatures.

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.

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 second azide ion on this alkene with more double bond rearrangements and proton abstraction from a proton source.