Mechanism Stork enamine reaction

The Stork enamine reaction and the intramolecular aldol reaction can be carried out in sequence to allow the synthesis of cyclohexenones. For example, reaction of the pyrrolidine enamine of cyclohexanone with 3-buten-2-one. followed by enamine hydrolysis and base treatment, yields the product indicated. Write each step, and show the mechanism of each. 

The reactions that you have learned in this chapter are not just of academic interest they are critical tools that make possible the syntheses of powerful pharmaceuticals and bioactive molecules, some even on ton soale These reactions are significant because they constitute highly powerful methods for forming C—C bonds. Of the reactions you have seen thus far, though, perhaps the most versatile is the Stork enamine reaction. This general transformation was inspired by trying to copy mechanisms that nature uses for forming such C—C bonds. Since its initial discovery over half a century ago, the Stork enamine reaction has found countless applications. Here, we will mention four. 

The reaction of a,/3-unsaturated carbonyl compounds with enamines also leads to dihydropyrans, although it is not always possible to isolate these since they react further to give either ring-opened by-products or bicyclic derivatives arising from a Stork annelation. There has been considerable discussion on the mechanism of this reaction, although the initial nucleophilic attack of the enamine on the /3-carbon of the diene is not in doubt (63JA207). It is possible that a zwitterionic species is involved, either as an intermediate or merely in equilibrium with the dihydropyran (67JCS(C)226). 

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