Stereoselective synthesis of analogs of natural isoprenoids based on the reaction of alkyl 4-dialkoxyphosphoryl-3-methylbut-2-enoates with aldehydes in ionic liquids and in an imidazolium salt—benzene system

Condensation of alkyl 4-dialkoxyphosphoryl-3-methylbut-2-enoates with a number of aldehydes under the Horner—Emmons reaction conditions in 1-butyl-3-methylimidazolium hexafluorophosphate and tetrafluoroborate and in 1-butyl-3-methylimidazolium bromide—benzene and 1-butyl-2,3-dimethylimidazolium hexafluorophosphate—benzene systems was studied. The E/Z-stereoisomer ratio of the olefination products for the reaction carried out in ionic liquids was 3 : 1, which corresponds to the values attained previously in the KOH—benzene—Bu₄ ⁿNBr (cat.) system. Quantum-chemical calculations were used to determine the averaged radii (r ₀) of the Bu₄ ⁿN] and substituted imidazolium cations by means of the Gaussian 98 program package. The stereoselectivity of olefination in the KOH—PhH—phase-transfer catalyst system decreases with a decrease in the r ₀ value for the catalyst cation. The possibility of recovery and reuse of ionic liquids is demonstrated.