What is an unstable ylide

Captions English Add a one-line explanation of what this file represents. Summary [ edit ] Description Wittig reaction unstable ylide. Own work assumed based on copyright claims. Author No machine-readable author provided. Calvero assumed based on copyright claims. You cannot overwrite this file. The following other wikis use this file: Usage on ja. Structured data Items portrayed in this file depicts. Almost all of the final products are valuable families of compounds.

Keywords: dialkyl acetylenedicarboxylates , organophosphorus compounds , Protonation , Quinolines , Wittig reaction. Abstract: Stabilized phosphorus ylides, versatile intermediates in synthetic organic chemistry can be prepared by the novel reaction of dialkyl acetylenedicarboxylates DAAD , triphenylphosphine TPP and acids such as phenols, imides, amides, enols, oximes and alcohols.

Content Access Key:. Journal Name: Current Organic Chemistry. Volume 12 , Issue 1 , Journal Home. With unstabilized ylides: The Wittig reaction with unstabilized ylides yields Z-alkenes predominantly Z-selective.

This selectivity can be explained as follows:. The carbonyl compound and the ylide approach each other at right angles and form the puckered four membered oxaphosphetane ring in the transition state, in one step. The transition state is formed such that the large substituents are kept away from each other leading to the formation of a syn-oxaphosphetane which is less stable but formed very quickly than the corresponding anti diastereomer.

Hence finally the kinetically controlled Z-alkene is formed. With stabilized ylides: The Wittig reaction with stabilized ylides is E-selective. Since the ylide is stable and the formation of oxaphosphetane from the starting compounds is reversible, an equilibration is possible between relatively less stable syn form and more stable anti form of oxaphosphetane.

There is now much time for the syn oxaphosphetane to interconvert to more stable anti form before the decomposition occurs. Hence the E-alkene predominates. Thus the selectivity of the final product is thermodynamically controlled. The Schlosser modification : It is possible to get E-alkenes from non-stabilized ylides using this method Wittig-Schlosser reaction.

In Schlosser modification, the initially formed less stable syn betaine can be converted to anti form by treating with phenyllithium or n-butyllithium at very low temperatures o C.

This will furnish E-alkene finally upon protonation with an acid.