Phase-Transfer Catalysis Reaction with Strong Bases

Mechanism and kinetics of Horner–Wadsworth–Emmons reaction in liquid–liquid phase-transfer catalytic system

“…Namely, in these systems, because the deprotonation of "weakly acidic" phosphonate (pK a > 23) hardly occurred or had a low rate, the yield of product was relatively low. It had been found that PTC system also could provide a relatively strong alkaline agent, which could quickly deprotonate the "weakly acidic" substrate and initiate the bond-forming reaction [16], for example liquid-liquid PTC (LL-PTC) system for isomerization of allylbenzene [17] and dehydrobromination of (2-bromoethyl) benzene [18]. However, HWE reaction of "weakly acidic" phosphonate under PTC conditions had rarely been reported [19,20].…”

Vinylogous and Arylogous Stereoselective Base-Promoted Phase-Transfer Catalysis

“…Such a developmental delay is quite surprising if one takes into account the unique benefits of PTC. A very important aspect, for instance, is the exceptional efficacy of base-initiated PTC in activating very weakly acidic pronucleophiles (pK a up to 23) despite non anhydrous conditions [36], matching or even exceeding the performances of homogeneous organic superbases. The presence of solid or highly concentrated aqueous alkali bases, makes it possible to generate strongly basic carbanions in non-hydrated form into the organic phase.…”

Third-Liquid Phase Transfer Catalysis for Horner–Wadsworth–Emmons Reactions of “Moderately Acidic” and “Weakly Acidic” Phosphonates

“…Hydroxide-initiated phase-transfer catalysis (HI-PTC) which facilitates the use of inexpensive hydroxide base and obviates the need for dipolar aprotic solvent is one of the most synthetically useful PTC techniques, and has been applied successfully in a large number of reactions, such as alkylation of phenols, dichlorocarbene addition, carbon-alkylation and carbon-arylation of phenylacetonitrile derivates, Knoevenagel condensation reaction, Witting reaction, and Horner-Wadsworth-Emmons (HWE) reaction. − The liquid–liquid PTC (LL-PTC) system, solid–liquid PTC system, third-liquid PTC (TLPTC) system, and solid–liquid–liquid system were always used to conduct the HI-PTC reaction. − Among these PTC systems, TLPTC has been demonstrated as a powerful method against biphasic PTC in a number of commercially hydroxide-initiated reactions. The advantages of TLPTC include high reaction rate and selectivity, easy separation of the catalyst and the product, mild reaction conditions, and steady reuse of the catalyst. , Although these properties make the TLPTC system a promising class of new heterogeneous catalysis systems, it is generally acknowledged that the full potential of the new synthetic technique has not been identified, especially for the hydroxide-initiated reaction.…”