An enhanced stereoselective synthesis of α,β-unsaturated esters through the Horner-Wadsworth-Emmons reaction in deep eutectic solvents

A new scalable synthesis of (E)-α,β-unsaturated esters has been developed using protic, non-toxic, and biodegradable deep eutectic solvents through the Horner-Wadsworth-Emmons reaction between triethyl phosphonates and (hetero)aromatic carbonyl compounds, encompassing electron-withdrawing and electron-donating groups. Stereoselective preparation of disubstituted or trisubstituted ethyl cinnamate derivatives is achieved in the presence of LiOH, K2CO3, or DBU as bases, at room temperature and under air. Demonstrated with the synthesis of (E)-ethyl 3-(4-bromophenyl)acrylate, the same eutectic mixture (choline chloride/urea) proved to be reusable for three consecutive runs. Gram-scale reactions (10 mmol) can be carried out without the formation of side products, thereby ensuring high atom economy and an EcoScale score of 71.

Practical Synthesis of Terminal Vinyl Fluorides

The synthesis of di- and trisubstituted vinyl fluorides with high isomeric purity remains a challenge for organic synthesis. While many methods exist to access these compounds, the separation of the desired isomer from the minor isomer and/or starting materials often is difficult. Herein, we report a practical method to access di- and trisubstituted vinyl fluorides via a selective Horner-Wadsworth-Emmons olefination/hydrolysis, which provides crystalline 2-fluoroacrylic acids in high (>98%) E-isomeric purity. A subsequent silver-catalyzed stereoretentive decarboxylation provides the title substances with high isomeric purity and without the need for tedious chromatography to remove the minor isomer. The process was amenable to a variety of aldehydes and ketones and provided a diverse array of di- and trisubstituted vinyl fluorides. The sequence was applied to the synthesis of antibacterial and anti-inflammatory compounds.

One-Pot O2-Oxidation and the Horner-Wadsworth-Emmons Reaction of Primary Alcohols for the Synthesis of (Z)-α,β-Unsaturated Esters

We developed one-pot oxidation/olefination procedures of primary alcohols giving Z-α,β-unsaturated esters 3. TEMPO-(CuCl or CuBr₂)-(2,2'-bipyridine) (1:1:1) catalyzed O₂ oxidation of primary alcohols in the presence of Z-selective Horner-Wadsworth-Emmons reagent 1b and K₃PO₄ or NaH gave 3 with Z/E = 84:16 to 96:4 in high yields. A stepwise reaction was also developed. After TEMPO-CuBr₂-(2,2'-bipyridine)-K₃PO₄ (1:1:1:1) catalyzed O₂ oxidation of alcohols in MeCN, the resulting mixture was treated with a THF solution of 1b and t-BuOK at -78 °C to 0 °C, giving 3 with higher selectivity (Z/E = 91:9 to 99:1).