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Wittig reaction affords an important and useful method for the synthesis of alkenes by the treatment of aldehydes or ketones with alkyldinetripheylphosphorate (Ph3P =- CR2) or simply known as phosphorane.
The Wittig reagent, alkylidenetriphenylphosphorane, is prepared by treating trialkyl or triarylphosphine usually the latter with an alkyl halide in ether solution. The resulting phosphonium salt is treated with a strong base (such as C65Li, BuLi, NaNH2, NaH, C2H5ONa, etc.
The reaction probably proceeds by the nucleophilic attack of the ylide on the carbonyl carbon. The dipolar complex (betain) so formed decomposes to olefin and triphenyphosphine oxide via a four centred transition state.
The mechanism is supported by the fact that an optically active phosphonium salt reacts to produce a phosphine oxide with retention of configuration.
Phosphorous yields react in the same manner with the C = O groups of ketones and isocyanates as also with the N = O and C = N groups of nitroso and imine compounds respectively.
List of Name Reaction of Organic Chemistry consist of detail Reaction Mechanism of all name reactions of Organic Chemistry.