The Ugi reaction is one of the most famous multicomponent couplings, and its efficiency is still explained by the original mechanism suggested by Ugi in the 60s. This article aims to present a thorough theoretical study of this reaction. It describes how the imine is activated and how the new stereogenic center is formed. Our calculations strongly suggest alternatives to some commonly accepted features, such as the reversibility of the intermediate steps, and temper the nature of the driving force of the reaction.

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The mechanism of boron-to-nickel transmetalation, the key step of the nickel-catalyzed Suzuki-Miyaura (S-M) coupling, was examined both experimentally and theoretically. Dinuclear μ-hydroxo-bridged complexes formed by reaction of trans-[ArNi­(PR3)2X] with hydroxide are not directly involved in transmetalation, but they rather act as a resting state for the catalyst. The base/boronic acid ratio is the crucial parameter, as it modulates the extent of formation of these dinuclear species and thus tunes the catalytic activity. These findings explain some limitations encountered in practical applications of nickel-catalyzed S-M couplings and suggest how to tailor the experimental conditions in order to overcome these difficulties.