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, K 2 CO 3 , 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.