Reactions Catalysed by a Combination of Metals and Organocatalysts

Abstract

This chapter includes all the major progress in the field of enantioselective tandem reactions promoted by the combination of metals and organocatalysts. It is divided into three sections dealing successively with the mode of catalysis followed, such as cooperative catalysis, relay catalysis, and sequential catalysis. Indeed, the two catalysts used in a tandem reaction can interact in a cooperative, relay or sequential manner. In cooperative catalysis, both the two catalysts are present at the onset of the reaction, and share the same catalytic cycle, activating two different functional groups cooperatively to achieve the bond-formation steps. On the other hand, in relay or sequential catalysis, the substrate first reacts with one catalyst to give an intermediate through a first catalytic cycle. Then, this former intermediate reacts with the second catalyst to provide, through a second catalytic cycle, the final product or an intermediate for subsequent transformations. The difference between relay and sequential catalysis consists of the presence or not of the two catalysts at the onset of the reaction. Thus, relay as well as sequential catalysis involves a set of reactions independently catalysed by two catalysts in a consecutive manner but, while in relay catalysis the two compatible catalysts are both present from onset, in sequential catalysis the addition of the second catalyst during the course of the reaction is necessary to avoid compatibility issues. This chapter well demonstrates that the combination of organocatalysts with transition metal catalysts has evolved as a new strategy to carry out enantioselective transformations that could not be performed in a traditional way by simply employing one of the two catalysts.