Eschenmoser fragmentation

The Eschenmoser fragmentation, first published in 1967, is the chemical reaction of α,β-epoxyketones (1) with aryl sulfonylhydrazines (2) to give alkynes (3) and carbonyl compounds (4).

[1][2][3] The reaction is named after the Swiss chemist Albert Eschenmoser, who devised it in collaboration with an industrial research group of Günther Ohloff, and applied it to the production of muscone and related macrocyclic musks.

[5][6] The general formula of the fragmentation using p-toluenesulfonylhydrazide is:[3] Several examples exist in the literature,[7][8] and the reaction is also carried out on industrial scale.

The mechanism of the Eschenmoser fragmentation begins with the condensation of an α,β-epoxyketone (1) with an aryl sulfonylhydrazine (2) to afford the intermediate hydrazone (3).

This Fehr–Ohloff–Büchi variant of the Eschenmoser–Ohloff fragramentation in which an epoxidation step is avoided is suited to sterically-demanding substrates where low yields typically result from classical Eschenmoser fragmentation.