New Unions of the U-4CR and Further Chemical Reaction

Recently, many new types of chemical products have been described that were produced by one-pot MCRs of by-functional educts [6], Since then, further progress has been made. In particular, those MCRs will be mentioned here which are unions of the U-4CR and related chemical reactions, and that have been developed recently by several chemical companies. 

Depending on the reaction conditions, a-iminodicarboxylic acid derivatives or 2,6-di-piperazinediones [120] are formed from a-amino acids, oxocompounds and isocyanides. The isomeric 2,4-piperazinediones can thus also be formed by some of the U-4CR of vicinal diamines, isocyanides, oxocompounds and glyoxylic monoesters [121,122],The libraries of highly substituted 2-piperazones were produced by the chemists of Merck Inc. from N-monosubstituted ethylenediamines, carboxylic acids, isocyanides and chloroacetalde-hyde. 

Chloroacetaldehyde combined with a-amino acids and isocyanides, then arizidine derivatives can thus be formed [123]. 

Instead of the U-4CR, a 3CR takes the place of its secondary reaction when 2-amino-pyridine or pyrazine, oxocompounds and isocyanides form their products, so that its carbonic acid components do not enter this product [124, 125]. In all probability, the intermediate protonated Schiff base reacts with its isocyanides so that, ultimately, the bicyclic 3-aminoimidazole [1,2a] pyridine is cyclized. Some further diversifications can proceed, if secondary amines can be acylized. No other simple way of producing a comparable collection of such a great variety of complex heterocycles can be accomplished [126]. 

Similar reactions of a-amino acids, as well those of a-amino amines are conceivable [128]. 

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