Eschenmoser fragmentation

The Eschenmoser fragmentation (also called the Eschenmoser-Tanabe fragmentation) is the chemical reaction of α,β-epoxyketones (1) with aryl sulfonylhydrazines (2) to give alkynes (3) and carbonyl compounds (4). This reaction is named after Albert Eschenmoser, a Swiss chemist.



Several examples exist in the literature.

Reaction mechanism
The mechanism of the Eschenmoser fragmentation begins with reaction of the α,β-epoxyketone (1) with aryl sulfonylhydrazine (2) to give the intermediate hydrazone (3). Proton transfer leads to intermediate 4, which undergoes the key fragmentation to the alkyne (6) and the carbonyl compound (7).



The proton transfers from hydrazone (3) to intermediate (4) can be catalyzed by pyridine, sodium bicarbonate, sodium carbonate, or silica gel.