Intramolecular 1,3-dipolar cycloaddition as a route to triazolobenzodiazepines and pyrrolobenzodiazepines

Intramolecular 1,3-dipolar cycloaddition between an alkyne and an azide leads to a series of 1,2,3-triazolo-fused 1,4-benzodiazepines, 1,2,5-benzothiadiazepines, pyrrolobenzodiazepines and pyrrolobenzothiadiazepines (8 examples). The products are privileged structures in medicinal chemistry. The precursor azido alkynes are obtained, usually as transient intermediates, by treatment of the corresponding aldehydes (derived from α-amino acids) with the Bestmann-Ohira reagent.