Pd-Catalyzed TBHP-Mediated Selective Wacker-Type Oxidation and Oxo-acyloxylation of Olefins Using a 2-(1H-Indazol-1-yl)quinoline Ligand.

Abstract

Pd(II)-catalyzed oxidation of terminal olefins to methyl ketones has emerged as an attractive strategy for organic synthesis. Here we report the Pd(II)-catalyzed selective oxidation of olefins using tert-butyl hydroperoxide as the oxidant and 2-(1H-indazol-1-yl)quinoline as the ligand. A wide range of olefins were well tolerated in this reaction system to provide methyl ketones, whereas the presence of Ac2O initiated the oxo-acyloxylation to afford the α-acetoxyacetone products. Isotope labeling studies and active-intermediate-capture experiments were performed to elucidate the underlying selective reaction mechanism. Notably, the generation of α-acetoxyacetone products involves the palladium enolate intermediate while the methyl ketone products were generated through the most commonly proposed alkylperoxide intermediates, followed by 1,2-hydride migration.