Wittig Reaction

In the early 1950s, chemists Georg Wittig and Georg Geissler reported the reaction of methylenetriphenylphosphorane and benzophenone to form 1,1-diphenylethene and triphenylphosphine oxide in quantitative yield. Wittig recognized the importance of this reaction and carried out a comprehensive series of experiments in which several phosphoranes were reacted with various aldehydes and ketones to obtain the corresponding olefins. The reaction between carbonyl compounds and phosphoranes to generate carbon–carbon double bonds has subsequently become known as the Wittig reaction. Since its discovery, the Wittig reaction has become one of the most widely used synthetic techniques for the formation of alkenes.

The Wittig reaction has several important variants. One of the most notable is the Horner–Wittig reaction, which occurs when the phosphorus ylides are based on phosphine oxides rather than triarylphosphines. When stabilized alkyl phosphonate carbanions are used to create (E)-alpha, beta-unsaturated esters, the reaction is known as the Horner–Wadsworth–Emmons reaction. Another variant, the Schlosser modification, generates pure E-alkenes when two equivalents of a lithium halide salt is present during the ylide addition step.

The total synthesis of the alkaloid natural product buflavin utilized the Horner–Wittig reaction between a biaryl aldehyde and a metalated carbamate.