7.06 Oxidation Adjacent to C[dbnd]X Bonds by Dehydrogenation

Abstract

α,β-Unsaturated carbonyl compounds are versatile intermediates in the synthesis of pharmaceuticals and biologically active compounds. This chapter summarizes different oxidation methods available for dehydrogenation adjacent to carbonyl groups to access α,β-unsaturated carbonyl compounds. Historically important stoichiometric methods include sequential halogenation/dehydrohalogenation, elimination reactions that use sulfur and selenium reagents, and dichlorodicyanoquinone (DDQ)-mediated dehydrogenation. The use of hypervalent iodine reagents, such as 2-iodoxybenzoic acid (IBX), in α,β-dehydrogenation reactions has grown significantly, as have catalytic dehydrogenation methods, such as Pd-catalyzed methods capable of O2 or other desirable stoichiometric oxidants. An overview of each of these methods is presented, together with selected synthetic applications. The relative merits of the individual methods are also considered.