Bucherer–Bergs reaction

The Bucherer–Bergs reaction is the chemical reaction of carbonyl compounds (aldehydes or ketones) or cyanohydrins with ammonium carbonate and potassium cyanide to give hydantoins. The reaction is named after Hans Theodor Bucherer.

Overall Reaction

Following condensation of the carbonyl with the ammonium, the formed imine is attacked by the isocyanide to form the aminonitrile. Nucleophilic addition of aminonitrile to CO₂ leads to cyano-carbamic acid, which undergoes an intramolecular ring closing to 5-imino-oxazolidin-2-one. The 5-imino-oxazolidin-2-one rearranges to form the hydantoin product via an isocyanate intermediate.

Reactions similar to the Bucherer–Bergs reaction were first seen in 1905 and 1914 by Ciamician and Silber, who obtained 5,5-dimethylhydantoin from a mixture of acetone and hydrocyanic acid after it had been exposed to sunlight for five to seven months. In 1929, Bergs issued a patent that described his own synthesis of a number of 5-substituted hydantoins. Bucherer improved on Bergs’ method, finding that lower temperatures and pressures for the reaction were permissible. Bucherer and Steiner also found that cyanohydrins would react just as well as carbonyl compounds to produce hydantoins. Later, Bucherer and Lieb found that 50% alcohol was an effective solvent for the reaction. With this solvent, aldehydes reacted well, and ketones gave excellent yields. In 1934 Bucherer and Steiner proposed a mechanism for the reaction. While there were some issues with the mechanism, it was mostly accurate.

One limitation of the Bucherer–Bergs reactions is that it only has one point of diversity. Only changes in the structure of the starting ketone or aldehyde will lead to variations in the final hydantoin.

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