1.9.5.3 Formation of Conjugated Double Bonds

DDQ is used for dehydrogenation of organic compound for extending conjugation (Scheme 8).  For example, 1,2-diphenylehane can be converted into trans-stilbene in high yield. In a similar way, ketones can be transformed into a,b-unsaturated carbonyl compounds, which have been considerably employed in steroid chemistry. The products are generally obtained in high yield and the substituents commonly encountered are not affected.

Scheme 8

1.9.5.4 Allylic Oxidation

The oxidation of benzylic C-H bonds can be carried with DDQ to afford carbonyl compounds. The reactions in aqueous acetic acid proceeds via an intermediate benzylic acetate, which is hydrolyzed under the reaction conditions (Scheme 9).  In some cases, the benzylic acetate can be isolated (Scheme 10).

Scheme 9

Scheme 10

1.9.5.5 Oxidative Cyclization

DDQ has been extensively employed for the cyclodehydrogenation reactions of phenolic and carboxylic acids. These processes afford effective route for the synthesis of oxygen heterocycles