Eschenmoser fragmentation

The Eschenmoser fragmentation, first published in 1967, is the

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 hydrazone can either be protonated at the epoxide oxygen or deprotonated at the sulfonamide nitrogen to initiate the fragmentation, and thus the fragmentation is catalyzed by acids or bases. Most common reaction conditions, however, are treatment with acetic acid in dichloromethane. The proton transfer leads to intermediate (4), which undergoes the key fragmentation to alkyne (6) and the corresponding carbonyl compound (7).^[9] The driving force for the reaction is the formation of highly stable molecular nitrogen.

There is a

A closely related fragmentation has been reported, employing diazirine derivatives of cyclic α,β-epoxyketones.[11]

• Grob fragmentation
• Wharton reaction
• Shapiro reaction