Studies on Trifluoromethyl Ketones. VII. Ene Reaction of Trifluroacetaldehyde and Its Application for Synthesis of Trifluoromethyl Compounds.

Abstract

As an extension of our studies on the ene reaction of trifluoromethyl ketones, the ene reaction of trifluoroacetaldehyde was examined. The aldehyde reacted with various ene compounds as a good enophile in the presence of Lewis acids, among which methylaluminum dichloride workded best, though polymerization of the aldehyde caused by the Lewis acid among which methylaluminum dichloride worked best, though polymerization of the aldehyde caused by the Lewis acid often lowered the isolation yields of the ene reaction. The ene reaction products were successfully oxidized to trifluoromethyl β, γ-unsaturated ketones with Dess Martin reagent. Reduction of the ene reaction products followed by oxidation with Jones reagent gave saturated trifluoromethyl ketones. The β, γ-unsaturated ketone rearranged on thermolysis to an α, β-unsaturated ketone. These ketones obtained were converted to otehr types of trifluoromethyl compounds. Thus, the ene reaction of trifluoroacetaldehyde provides a versatile method for synthesis of many types of trifluoromethyl compounds. During this derivatization, a trifluoromethyl group was found to behave as a much larger substituent than a decyl group.