Favorskii-Type Rearrangement of α,α′-Dihalo Ketones Induced by Enolates of (Diethoxyphosphinyl)acetic Esters and Its Application to the Synthesis of α,α′-Divinyl Ketones
A Favorskii-type rearrangement of 1,3-dihalo-3-methyl-2-butanone with enolate of ethyl (diethoxyphosphinyl)acetate or t-butyl (diethoxyphosphinyl)acetate gave ethyl 2-(diethoxyphosphinyl)-5-methyl-3-oxo-4-hexenoate (3a) or its t-butyl ester (3b). Compound 3b was applied to the preparation of (E)-5-methyl-1-(p-tolyl)-1,4-hexadien-3-one and diethyl (4-methyl-2-oxo-3-pentenyl)phosphonate, which are the important intermediates for natural product syntheses.
A new synthetic method of conjugated enones by the use of carbanion-induced Favorskii-typerearrangement is described. The reaction of α,α′-dihalo ketones R1R2(X)CC(O)CH2X with sodiomalonates Na+ −CR3(CO2R4)2 in THF at 0°C—room temperature gave conjugated enones R1R2C=CHC(O)CR3(CO2R4)2 in 42–66% yields. The reaction can be also adaptable to the enolates of ethyl cyanoacetate or malononitrile to give