Wacker Oxidation of Trisubstituted Alkenes: Pd(II)-Catalyzed Oxidative Ring Expansion of Exocyclic α,β-Unsaturated Carbonyl to 2-Fluoro-1,3-Dicarbonyl Compounds.

The Wacker oxidation is a powerful synthetic method widely employed for the transformation of monosubstituted alkenes into methyl ketones. Its substrate scope has progressively expanded to include internal disubstituted and, more recently, gem-disubstituted alkenes. Herein, we report the first examples of Wacker-type oxidation of trisubstituted alkenes under Pd(II)/Pd(IV) catalysis. In the presence of Selectfluor (2.3 equiv) and a catalytic amount of Pd(MeCN)4(BF4)2 (10 mol%), exocyclic trisubstituted α,β-unsaturated carbonyl compounds undergo a fluorinative one-carbon ring expansion to deliver 2-fluoro-1,3-dicarbonyl compounds in good yields. The reaction displays broad functional group tolerance, including alkyl halide, aryl halide, alkyl tosylate, hydroxyl, carboxylic acid, ester, secondary amide, ketone, cyano, and N-phthalimide. While a semi-pinacol rearrangement of the Pd(IV) intermediate is a plausible mechanistic pathway given the excellent nucleofugality of the Pd(IV) atom, preliminary studies suggest that a 1,2-alkyl/Pd(IV) dyotropic rearrangement is operative in product formation.