Bucherer-Berg multicomponent reactions

Scheme 1 The Strecker and Bucherer-Bergs Multicomponent Reactions 1...

Linear adducts would be produced from monofunctional inputs whatever the number of components employed [Figure 5.2, reaction (a)]. If one aimed at developing multicomponent syntheses of heterocycles, one simple solution would then be the use of polyfunctional substrates since these imply an intramolecular reaction at a certain stage of the sequence, leading eventually to heterocydes [Figure 5.2, reaction (b)[. Some very simple functional groups such as cyanide and carbonic acid are bifunctional in nature, as in the Bucherer-Bergs reaction. 

One may consider the Strecker reaction as the prototypical multicomponent reaction.15 Three reactants, an amine, a carbonyl compound, and a source of cyanide, come together in a single reaction vessel to afford a single product, an a-aminonitrile. Variations on this reaction process include the Bucherer-Bergs, Petasis, Ugi, and amidocarbonylation reactions. 

As many of the classical multicomponent reactions, the Strecker synthesis also takes advantage of the versatile chemistry of the initially formed imine. The formation of the amino nitrile, however, is reversible under the reaction conditions which usually results in lower yields. This problem was elegantly solved in the Bucherer-Bergs variation,3 4-376 where the initially formed aminonitrile is irreversibly trapped by formation of a hydantoin as depicted in Scheme 1.8 (entry b). 

Despite the wide scope and potential of the multicomponent (MC) Bucherer-Bergs reaction, this procedure exhibits a limitation since only changes in the structure of the corresponding ketones can be addressed, leading to variations in the skeleton of the final hydantoin [31]. However, with the aim in mind of increasing the utility and scope of... 

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