LA REACTION DE WITTIG-HORNER EN MILIEU HETEROGENE IV: PERFORMANCES COMPAREES DE BASES FAIBLES TELLES QUE K₂CO₃ ET KHCO₃ DANS L'EAU OU DES SOLVANTS ANHYDRES

Abstract

The Wittig-Horner reaction has been explored with phosphonates , CO[sbnd]R², CN) with K₂CO₃ or KHCO₃ as bases in water or anhydrous solvents such as THF, toluene and CH₂Cl₂, with or without phase-transfer catalysis. The scope and limitations of these procedures, which can give excellent yields (75–100%), have been compared. Olefins are formed with E geometry for A = COOEt, CO[sbnd]R² (R′ [dbnd] H) and as mixtures of E/Z compounds for A [dbnd] CN. Side reactions (i.e. crotonization, isomerization, saponification, Knoevenagel and Cannizzaro reactions) can be eliminated using reaction conditions modified for each case. Optimum times and temperatures of the reactions have been determined for improved yields. The use of a two phase liquid-liquid system in water without solvent often gives excellent yields (A [dbnd] COOEt, COR², CN). However, benzaldehyde gives almost quantitative yields (A [dbnd] COOEt) in a solid-liquid heterogenous medium in boiling toluene using solid K₂CO₃ or KHCO₃, with or without phase-transfer catalysis to accelerate the reaction. This last procedure, which should simplify the further work-up of the reaction, is not attractive with aliphatic linear aldehydes and requires our further attention.