Büchner–Curtius–Schlotterbeck reaction

[3] Two German chemists also preceded Schlotterbeck in discovery of the reaction, Hans von Pechmann in 1895 and Viktor Meyer in 1905.

The epoxide product is formed by an intramolecular addition reaction in which a lone pair from the oxygen attacks the carbocation (6).

[9] The reaction has since been modified to proceed in the presence of Lewis acids and common organic solvents such as THF and dichloromethane.

Reactions generally run at room temperature for about an hour, and the yield ranges from 70%-80% based on the choice of Lewis acid and solvent.

[10] Steric effects of the alkyl substituents on the carbonyl reactant have been shown to affect both the rates and yields of Büchner–Curtius–Schlotterbeck reaction.

[7] The observed decrease in rate and increase in epoxide yield as the size of the alkyl group becomes larger indicates a steric effect.

In addition to accelerating the reaction, electron-withdrawing substituents typically increase the amount of epoxide produced (Table 2).

The opposite influence has also been observed in the reaction of piperonal with diazomethane, which exhibits increased carbonyl yield in the presence of methanol.

In general, the R-group most capable of stabilizing the partial positive charge formed during the rearrangement migrates preferentially.

[11][12] As shown below, if the reaction of piperanol (IV) with diazomethane is carried out in the absence of methanol, the ketone obtained though a hydride shift is the major product (V).

[11][12] The diazoalkane employed can also determine relative yields of products by influencing migratory preferences, as conveyed by the reactions of o-nitropiperonal with diazomethane and diazoethane.

For example, an acyl-diazomethane can react with an aldehyde in the presence of a DBU catalyst to form isolable α-diazo-β-hydroxy esters (shown below).