This year represents the 100th anniversary of the discovery
of
the Passerini three-component reaction. The related Ugi four-compound
reaction was discovered 37 years after the Passerini reaction. Undoubtedly,
both reactions are very important multicomponent reactions but the
Ugi reactions outperform the Passerini reactions in terms of combinatorial
space according to the equationxy[xis the number of building blocks per component, andyis the order of the multicomponent reaction (for Passerini,y= 3; for Ugi,y= 4)]. In this work,
a historical but contemporary perspective of the discoveries and innovations
of the two reactions is given. From a bird’s eye view and in
a more general sense, the discovery of novel reactions is discussed
and how it relates to inventions and innovations.