Lewis Acid Mediated Reactions of Zirconacyclopentenes with Aldehydes Affording Homoallyl Ketones via Oppenauer-Type Oxidation

Three different components involving alkynes, ethylene, and aldehydes were selectively integrated in a one-pot procedure to afford homoallyl ketones in good yields, via an effective combination of zirconocene-mediated C-C bond forming reactions and Lewis acid mediated organic transformation. Mechanistic studies revealed that a formal Oppenauer oxidation of seven-membered oxazirconacycles, generated in situ from the reactions of zirconacyclopentenes and aldehydes, was promoted by Lewis acid-aldehyde adducts. As a whole, the first aldehyde was incorporated into the product and the second aldehyde was reduced to an alcohol. Multiply deuterated homoallyl ketones could be readily prepared in high yields with more than 98% deuterium incorporation by using this method.