Greening Wittig Reactions: Solvent-Free Synthesis of Ethyl trans-Cinnamate and trans-3- (9-Anthryl)-2-Propenoic Acid Ethyl Ester

The two reactions presented here are solvent-free alternatives to published procedures of Wittig reactions. The first example is a reaction between a solid phosphorane and liquid aldehyde while the second reaction takes place in a melt. Both reactions are fast, proceed with high yield and excellent stereoselectivity, and their product isolation is simple. The simplicity of the experiments allows students to perform them simultaneously and to construct a small NMR data set. The spectral data provide a basis for an inquiry-based discussion of (i) the factors influencing the chemical shifts of alkenyl proton, (ii) the analysis of NMR spectrum containing a mixture, and (iii) the role of strong dipole–dipole interactions in dictating the stereochemical outcome of the Wittig reaction.