Science of Synthesis

Celik, I.; Hummel, S.; Kirsch, S. F., Science of Synthesis Knowledge Updates, (2019) 1, 1.

General Introduction

The merging of two modes of catalysis, for example of transition-metal catalysis with organocatalysis,[‌1‌–‌4‌] has become a key strategy to address problems in organic synthesis. The idea is simple: by using complementary activation modes of catalytic systems, reactivities may be feasible that are not possible with one catalytic system alone. The major challenge, however, is that two independent catalytic systems have a tendency to inactivate each other, as it is the case, for example, when a Lewis base catalyst is mixed with a Lewis acid catalyst. In this context, gold catalysis[‌5‌–‌7‌] has achieved a pivotal role because the unique carbophilicity of homogeneous gold catalysts makes it particularly attractive for mergers with other catalytic systems. Although gold catalysts have a Lewis acidic character, many examples have been reported where the gold complexes keep their catalytic activity for the activation of π-systems even in the presence of strong Lewis bases.[‌8‌,‌9‌] In general, gold catalysis can be combined with other modes of catalysis in two different ways: (1) The gold catalyst and the other catalyst are used in a one-pot system in consecutive order. In this case, the two catalysts have mostly independent duties, and the main achievement is to minimize the number of isolation steps. (2) The gold catalyst and the other catalyst are used in a one-pot system in a simultaneous fashion. Most reactions of this type are domino reactions, under so-called relay catalysis, where one catalyst transforms the substrate into a reactive intermediate and the other one takes over producing the final product. However, examples of dual catalysis are also known where both catalysts are required for the substrate activation in a synchronous way.

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