Wittig reagents

In organic chemistry, Wittig reagents are organophosphorus compounds of the formula R3P=CHR', where R is usually phenyl.

They are used to convert ketones and aldehydes to alkenes: Because they typically hydrolyze and oxidize readily, Wittig reagents are prepared using air-free techniques.

For stabilized Wittig reagents bearing conjugated electron-withdrawing groups, even relatively weak bases like aqueous sodium hydroxide or potassium carbonate can be employed.

Because phosphonium ylides are seldom isolated, the byproduct(s) generated upon deprotonation essentially plays the role of an additive in a Wittig reaction.

As a result, the choice of base has a strong influence on the efficiency and, when applicable, the stereochemical outcome of the Wittig reaction.

Wittig reagents are prepared by deprotonation of alkyl phosphonium salts, and this reaction can be reversed.