Unions of MCRs and Related Reactions

The even more sophisticated stereospecific formation of the chiral alkaloid 63 by Stevens and Lee [49], and the previous synthesis of 58 and related procedures have in common their essential ring-closing steps corresponding to unions of M-3CRs.The a-amino-alkylating MCRs of type I [4,7] correspond to collections of equilibrating subreactions. Such positive formation of polyheterocyclic products correspond to almost irreversible cyclocondensations. These elegant syntheses correspond to an area of preparative chemistry whose products can be formed successfully, and where unions of reversible MCRs can have virtually irreversible final steps. 

14 MCRs of More than Four Functional Groups 

In 1993 it was realized that one-pot MCRs of five and more educts can take place as unions of the U-4CR and other reactions or MCRs. A great variety of their educts and products can participate, if the irreversible U-4CR can be combined with a great variety of further types of participating chemical compounds. 

Usually, the higher MCRs are unions of the U-4CR and further chemical reactions or MCRs. However, these procedures are the rare exceptions. The majority of MCR unions proceeds only well if at least one of its participating MCRs belongs to type II. In these exceptional cases, an irreversible final step of MCR unions takes place, although all of the participating subreactions of MCRs are reversible. 

When the U-4CR was introduced, some 5CRs were also introduced. Instead of the usual carboxylic acids 3A of the U-4CR, the methoxycarboxylic acids were also used. Since the acid components of this reaction equilibrate with methanol 4a and C02 8, as well as with the ions 63 and 6c [8,13b, 112], five different educts can participate as the first unior of an U-4CR and the reaction of 4a and C028. 

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