Iminium ion-enamine activation

Figure 42.2 Iminium ion-enamine activation sequence compatibility between the nucleophile (Nu) and the electrophile (E) is required.

Almost simultaneously, MacMillan and colleagues developed a similar MCR based on the iminium ion-enamine activation of enals (Scheme 42.11) [33]. They used the chiral imidazolidinone catalyst 41 to combine the enantioselective conjugate additions of a large number of diverse carbon-based nucleophiles with the a-chlorination of the resulting aldehyde intermediate 42, which proceeds under enamine catalysis [35]. The reaction sequence is accompanied by a high syn-selectivity and excellent enantioselectivities. 

Scheme 42.16 Asymmetric organocatalytic triple cascade by way of an enamine-iminium ion-enamine activation of aldehydes. Protocol point the minor diastereomer was determined as the 5-epimerof 59 all substrates added at the outset of the reaction.

Scheme 42.20 Changing the fate of a domino process by modulating the concentration of enal 58 (a) double domino reaction by means of an iminium ion-enamine activation sequence (b) quadruple...

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