Wacker-Type Heck-Matsuda Arylations of Alkyl and Silyl Alkenyl Ethers to Access Carbonyl Compounds

The Wacker-type oxidation in Heck-Matsuda reactions consists in the migration of a palladium hydride intermediate through successive migratory insertions along the carbon chain, followed by a terminal oxidation process, usually leading an alcohol to the corresponding aldehyde or ketone. In our hands, alkyl and silyl-protected alcohols also underwent efficient Wacker-type reactions. These new redox arylations demonstrate that the presence of a free hydroxyl group is not a sine qua non condition for an effective Wacker-type oxidation as previously thought. Deuterium labelled alkenyl ethers permitted to track the putative carbinolic palladation step in the conversion of the starting free alcohols, silyl, and methyl ethers into the corresponding methyl ketone with >98% deuterium retention at the β position. The isolation of R3SiOMe and R3SiF as by-products suggests that the alkenyl silyl ethers, and presumably methyl ethers, undergo a nucleophilic-assisted Wacker -type oxidation process, which has been supported by DFT calculations.