Direct Regioselective Dehydrogenation of alpha-Substituted Cyclic Ketones

We disclose a highly regioselective, catalytic one-step dehydrogenation of alpha-substituted cyclic ketones in the presence of 2,3-dichlorobenzo-5,6-dicyano-1,4-benzoquinone (DDQ). The high regioselectivity originates from a phosphoric acid-catalyzed enolization, selectively affording the thermodynamically preferred enol, followed by the subsequent oxidation event. Our method provides reliable access to several alpha-aryl and alpha-alkyl substituted alpha,beta-unsaturated ketones.