Since 1995 the new chemistry of multicomponent reactions and their libraries, including their heterocyclic chemistry

A growing number of products, including many heterocycles, can be prepared by the one-pot MultiComponent Reactions (MCRs) just by mixing three or more educts, and in many cases practically quantitative yields of pure products can be obtained. The 3CR by alpha-aminoalkylations of nucleophiles began i n the middle of the last century, and the syntheses of heterocycles by MCRs of three and four components were introduced by Hantzsch in the 1880s. The MCRs of the isocyanides with four and more educts began in 1959, and their compound libraries were mentioned since 1961. However, only since 1995 the often automated one-pot chemistry of the MCR of the isocyanides is used ex tensively. If a chemical compound can be prepared by a sequence of two comp onent reactions or a suitable MCR, the latter is always a superior procedur e. The U-4CR can be combined with other chemical reactions and MCRs as one- pot reactions of n > 4 components, and such unions even have a much greater variety of structurally and stereochemically different products. The educt s and products of Ugi-type MCRs are more variable than those of all previou s chemical reactions and other MCRs. Due to the progress in screening and a utomation processes in the last few years, many new compounds have been for med and investigated more rapidly than ever before. The search for new desi rable products can be accomplished more than 10,000 times faster than by th e older conventional methods. The now popular chemistry of the MCRs of the isocyanides fills the since long empty part of organic chemistry.