Innovations and Inventions: Why Was the Ugi Reaction Discovered Only 37 Years after the Passerini Reaction?

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 equation xy [x is the number of building blocks per component, and y is 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.