Experimental Observations and a Working Hypothesis

In sharp contrast to these results, we obtained a pair of E- and Z-a,/ -unsaturated ketones when the condensation of 28 was conducted under sufficiently mild conditions [32] such 

Formation of an a,fl-unsaturated (conjugated) dimer from a cyclic ketone is vital to the 

at a given concentration of add [37], a conjugated enone will be more extensively protonated than a ketone that lacks the extra a,/ -unsaturation (e.g., 7 H+/7 vs. TH+/1), it is mechanistically reasonable that the dimer — trimer step should be favorable for cyclic ketones that form a,/ -unsaturated (conjugated) dimers. On the other hand, / ,y-unsaturated al- 

To be useful, of course, a hypothesis must have predictive value. Can one predict in advance whether the aldol dimer from a particular ketone will be a,y -unsaturated or / , -unsaturated  

---