Hellmann-Opitz 3-component reactions

In 1960 HeUmann and Opitz introduced their a-Aminoalkyliemng book, wherein they mentioned that the majority of the name reactions by MCRs belong together since they have in common their essential features. This collection of 3CRs can be considered as Hellmann-Opitz 3-component reactions, (HO-3CRs). They are either a-aminoalkylations of nucleophiles of MCR type I, or they form intermediate products that react with further bifunctional educts into heterocycles by 4CRs of type II. Their last step is always a ring closure that proceeds irreversibly. 

In 1960, Hellmann and Opitz l realized that the majority of the previously discussed named reactions and other related processes are all a-aminoalkylations of nucleophilic compounds of sufficiently weak acids, corresponding to MCRs of type I, or they have secondary reactions of type II that are followed by the formation of heterocycles [the Hell-mann-Opitz three-component reaction (HO-3CR),t Scheme 2]. In 1921, Passerinih 47] jjj. troduced his three-component reaction (P-3CR), which involves the reaction of a carboxylic acid 7, a carbonyl compound 1, and an isocyanide 10, to form (via rearrangement of the first-formed product 11) an a-carboxy-substituted alkanamide 12 (Scheme 2). This was the first example of a MCR of type II that involved an isocyanide. 

Most MCRs of type IA are 3CRs whose equilibrating products react with further educts by higher MCRs of type II. In 1960, Hellmann and Opitz published their a-Atni-noalkylierung book [7], which was a comprehensive list and discussion of all so-far-known MCRs. They realized, as did others previously, that the name reactions [2,5] S-3CR, the M-3CR [32] and many other 3CRs belong to the mechanistic family of a-aminoalkyla-tions of nucleophiles, which are usually the anions of deprotonated weak acids components. This collection of 3CRs is now also referred to as the HO-3CR [4],... 

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