Enamine catalysis combined approaches

The main focus in this chapter will be on combined approaches using enamine catalysis and iminium catalysis especially in one-pot cascade reactions. As discussed in the following examples, the combined use of these two activation modes has led to the development of some of the most impressive and efficient organocatalytic natural product syntheses conducted so far (301-305). 

It has been shown in this chapter that combined iminium-enamine catalyzed approaches offer the potential to achieve complex (multistep) transformations in a single operational step, thus giving access to high structural complexity combined with excellent effectivity. In addition, it was pointed out also that organocatalysis can be used successfully when combined with metal catalysis e.g. metathesis). Although these complex approaches have been pursued only for the last few years, the results obtained so far are very promising and thus this methodology should be applied more widely in the future (Table 3). 

Later, MacMillan s group described a cascade with a combination of iminium ion, enamine, and Rh catalysis [21], This chemistry allowed quick generation of the intermediates 159, starting from alkene-tethered ketone 155, crotonaldehyde 72, and Mukaiyama reagent 156 (Scheme 9.51), which is difficult to obtain by a traditional and routine approach. 

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