WittigReaktion

The Wittig reaction is a chemical reaction used to convert aldehydes or ketones into alkenes. It involves the reaction of a phosphorus ylide with a carbonyl compound. Phosphorus ylides, also known as Wittig reagents, are prepared by treating an alkyl halide with triphenylphosphine, followed by deprotonation with a strong base. The ylide then undergoes a cycloaddition reaction with the carbonyl compound, forming a four-membered ring intermediate called an oxaphosphetane. This intermediate subsequently decomposes to yield the desired alkene and triphenylphosphine oxide, a stable byproduct.

The stereochemistry of the alkene product can often be controlled depending on the structure of the ylide and the reaction conditions. Stabilized ylides, which have electron-withdrawing groups adjacent to the carbanion, tend to produce predominantly (E)-alkenes. Conversely, unstabilized ylides, lacking such stabilizing groups, often favor the formation of (Z)-alkenes. The Wittig reaction is a versatile and widely used method in organic synthesis for constructing carbon-carbon double bonds, finding application in the synthesis of natural products, pharmaceuticals, and materials. Its reliability and the ability to introduce specific alkene geometries make it a cornerstone of modern organic chemistry.