Direct Umpolung Morita-Baylis-Hillman Like Alpha-Functionalization Of Enones Via Enolonium Species

Herein we report on the umpolung of Morita-Baylis-Hillman type intermediates and application to the alpha-functionalization of enone C-H bonds. This reaction gives direct access to alpha-chloro-enones, 1,2-diketones and alpha-tosyloxy-enones. The latter are important intermediates for cross-coupling reaction and, to the best of our knowledge, cannot be made in a single step from enones in any other way. The proposed mechanism is supported by spectroscopic studies. The key initial step involves conjugate attack of an amine (DABCO or pyridine), likely assisted by hypervalent iodine acting as a Lewis acid leading to formation of an electrophilic beta-ammonium-enolonium species. Nucleophilic attack by acetate, tosylate, or chloride anion is followed by base induced elimination of the ammonium species to give the noted products. Hydrolysis of alpha-acetoxy-enones lead to formation of 1,2-diketones. The alpha-tosyl-enones participate in Negishi coupling reactions under standard conditions.