Wacker Oxidation of Trisubstituted Alkenes: Pd(II)‐Catalyzed Oxidative Ring Expansion of Exocyclic <i>α,β</i>‐Unsaturated Carbonyl to 2‐Fluoro‐1,3‐Dicarbonyl Compounds

Abstract

AbstractThe 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.