Robinson ElcB reactions

The find stage is dehydration of the aldol and an ElcB reaction that involves the carbonyi group sa in a standard aldol reaction (Chapter 27). Another enolate must form In the same position as the last, the Robinson anneletlon mechanism—stage 3t the ElcB dehydration... 

The reaction is AdN2 addition to the polarized multiple bond (Adj, then p.t.). This reaction is easy to predict because the most stable product is formed under these equilibrium conditions. HSAB theory predicts that the combination of the two softest sites is favored. This conjugate addition is often called a Michael addition and forms the first step in the Robinson annotation diagramed in Figure 8.9. The later steps are an aldol addition (AdN2) to form the new ring followed by elimination by ElcB to give the bicyclic product. 

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