Synthesis of stilbene, 1,4-distyrylbenzene and 4,4′-distyrylbiphenyl via Horner–Wadsworth–Emmons reaction in phase-transfer catalysis system

• Stilbene, 1,4-distyrylbenzene and 4,4′-distyrylbiphenyl were synthesized in liquid–liquid and solid–liquid PTC systems.
• HWE reaction under PTC conditions showed high activity and geometric selectivity at relatively low temperatures.
• The basicity of the available OH‾ had a significant influence on the activity and mechanism of HWE reaction in PTC system.
• The region where the Cannizzaro intermediate was generated in the side reaction was varied with the reactivity of aldehyde.
• The third phase and the reusability of the aqueous phase enhanced convenience and operability of PTC system.

Stilbenes, 1,4-distyrylbenzenes and 4,4′-distyrylbiphenyls were synthesized via Horner–Wadsworth–Emmons (HWE) reaction in liquid–liquid (LL) and solid–liquid (SL) phase transfer catalysis (PTC) systems. The effect of the side reaction, reactants and the third phase on the activity of HWE reaction were investigated. For aldehydes bearing electron-donating substitute, the yields were more than 90% and the products were all (E)-isomers in both PTC systems. The SL-PTC system was milder than LL-PTC system for HWE reaction due to the different mechanisms. The side reaction of aldehyde was similar to Cannizzaro reaction, whereas the molar ratio of benzoic acid to benzyl alcohol as the products was not 1:1. The limited third phase was discovered to exist in LL-PTC system. In SL-PTC system, the third phase could increase substantially the reaction rate. Moreover, the aqueous phase in LL-PTC system could be reused four times without sacrifice of the yield and reaction rate.

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