TheBucherer–Bergs reaction is thechemical reaction ofcarbonyl compounds (aldehydes orketones) orcyanohydrins withammonium carbonate andpotassium cyanide to givehydantoins.^[1][2][3][4] The reaction is named afterHans Theodor Bucherer.

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 thehydantoin product via anisocyanate intermediate.^{[citation needed]}

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 ofacetone andhydrocyanic 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 producehydantoins. Later, Bucherer and Lieb found that 50% alcohol was an effective solvent for the reaction. With this solvent,aldehydes reacted well, andketones 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.^[4]

One limitation of the Bucherer–Bergs reactions is that it only has one point of diversity. Only changes in the structure of the startingketone oraldehyde will lead to variations in the finalhydantoin.

One way to increase the number of points of diversity is by combining a reaction with 2-Methyleneaziridine with the Bucherer–Bergs reaction in aone-pot synthesis. First, the reaction of 2-Methyleneaziridine1 withGrignard reagent, catalytic Cu(I), and R²-X causes the 2-Methyleneaziridine to ring open and form aketimine2. The ketimine is then subjected to the Bucherer-Bergs reagents, resulting in a 5,5'- disubstituted hydantoin3. This reaction has three points of chemical diversity as the structure of theaziridine starting compound, the organometallic reagent, and theelectrophile can all be varied to synthesize a different hydantoin.^[5]

One improvement on the Bucherer–Bergs reaction has been the use of ultrasonication. More recently, many organic reactions have been accelerated by ultrasonic irradiation. In the past, the Bucherer–Bergs reaction has had problems with polymerization, long reaction time, and difficult work-up. 5,5-disubstituted hydantoins can be prepared using the Bucherer–Bergs reaction under ultrasonication. Compared with reports in the literature, this makes so the reaction can be carried out at a lower temperature, have a shorter reaction time, a higher yield, and a more simple work-up.^[6]

One variation of the Bucherer–Bergs reaction is the treatment of carbonyl compound withcarbon disulfide andammonium cyanide inmethanol solution to form 2,4-dithiohydantoins.^[7] In addition, the reaction of ketones with ammonium monothiocarbamate and sodium cyanide will yield 5,5-disubstituted 4-thiohydantoins.^[8]

In some cases, the carbonyl starting material can be sufficiently sterically biased so a singlestereoisomer is observed. However, in other cases, there is no selectivity at all, resulting in a 1:1 ratio of stereoisomers. An example taken from "Name Reactions: Heterocyclic Chemistry" by Jie Jack Li shows a case of stereospecificity in the Bucherer–Bergs reaction. While the end product of the Bucherer–Bergs reaction is ahydantoin, the hydantoin can undergohydrolysis to form an amino acid. This is what is assumed in the example below. For comparison, the amino acid product for theStrecker synthesis has also been included.^[9]

The hydantoins formed by the Bucherer–Bergs reaction have many useful applications. They:

• are useful in carbohydrate chemistry.
• are important heterocyclic scaffolds that induce biological effects.
• are useful precursors toamino acids, e. g.methionine.
• have pharmacological importance (ex. 5,5-diphenylhydantoin, also known asDilantin)

• Urech hydantoin synthesis
• Strecker amino acid synthesis

• Carbon-carbon bond forming reactions
• Condensation reactions
• Multiple component reactions
• Name reactions
• Nitrogen heterocycle forming reactions

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