Transition metal free functionalization of nitrogen heterocycles, triggered and driven by electrophilic acetylenes

The review covers the advances reached during the last five years in transition metal free functionalization and modification of nitrogen heterocycles with electrophilic acetylenes. The reactions are triggered and further driven by the initially formed 1,3(4)-dipole complexes (zwitterions), adducts of the nucleophilic attack of nitrogen heterocycles at the triple electrophilic carbon‑carbon bond of the acetylenes. The carbanionic sites of these zwitterions are usually captured by electrophiles such as second molecule of the acetylenes or other electrophilic CC and CO unsaturated compounds, as well as various CH, OH, NH, PH acids thereby raising molecular complexity (in the course of diverse cascade transformations) to a new higher level. The rich energy potential of the activated carbon‑carbon triple bond warrants mild reaction conditions and allows the functionalization to be performed without transition metal catalysts.