Synthesis of Substituted Phenyl Ketones via Pd-Catalysed hydrodechlorination of Their Polychlorinated Derivatives

The following compounds, 2- and 3-methylacetophenones, 2- and 3-methylbenzophenones, and 2,2’-, 2,3’- and 3,3’-dimethylbenzophenones have been synthesized through a Pd-catalysed hydrodechlorination of the corresponding dichlorinated derivatives. The reaction has been carried out under multiphase conditions at 30-50°C, by bubbling H₂ at atmospheric pressure into a biphasic system constituted by an organic substrate solution (isooctane solvent) and an aqueous alkaline solution (50% aq KOH), in the presence of Pd/C (5% wt) and Aliquat 336 (triaprylylmethylammonium chloride). Likewise, fluorinated aceto- and benzophenones (4-fluoro-3-methylacetophenone and 4-fluoro-3-methylbenzo-, 4-fluoro-2’,3-dimethylbenzo-, 4-fluoro-3,3’-dimethylbenzophenones) have been prepared starting from the corresponding chlorinated methylfluoro- and dimethylfluoro ketones. Under such conditions, the presence of the onium salt allows the reaction to proceed with a high chemoselectivity: chlorine is removed while both the reduction of the carbonyl group and/or fluorine removal are prevented.

Synthesis of substituted phenones through a multiphase chemoselective hydrodechlorination