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a method of preparing olefins by reacting carbonyl-containing compounds—for example, aldehydes, ketones, formamides, isocyanates, and ketenes— with triphenylphosphine alkylidenes. An example is the formation of isobutene from triphenylphosphine methylene and acetone:
The starting triphenylphosphine methylene is prepared by the action of alkaline reagents on a triphenylmethyl phosphonium salt, which in turn is obtained from triphenylphosphine and an alkyl halide:
The alkaline reagents may be organolithium compounds, sodium amide, alkoxides, and so on.
The Wittig reaction is a very promising process of synthesis, which makes possible the preparation of various olefins, among them polynes (olefins with a large number of multiple bonds).
The synthesis of vitamin A is based on the Wittig reaction, which may also be used to prepare squalene (a precursor of cholesterol), lycopene, bixin esters, and so on.
The Wittig reaction was discovered by the German chemists G. Wittig and U. Schollkopf in 1954.