Dehydration of p-hydroxyketones

Cerium chloride (CeCl3 7H20) in the presence of Nal catalyzes the diastereoselective dehydration of P hydroxyketones and esters such as 4.8 to the corresponding a, (3-unsaturated compound 4.9. 

Dehydration of p-hydroxyketones is both a common reaction (we will see in Chapters 17 and 20 why these molecules are easy to prepare) and a very straightforward one. The product obtained is invariably the conjugated one, whatever the mechanism. Acid-catalyzed reactions are common they are usually El with tertiary alcohols and E2 with primary alcohols. Secondary alcohols such as 10.18 may react by either or both mechanisms. 

Dehydration of p-hydroxyketones can also occur under basic conditions (Figure 10.33), the molecule forms a good carbanion (because of the inductive and resonance effect of the carbonyl group), and the leaving group, hydroxyl ion, is poor. 

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