Search results
Results From The WOW.Com Content Network
The main limitation of the traditional Wittig reaction is that the reaction proceeds mainly via the erythro betaine intermediate, which leads to the Z-alkene. The erythro betaine can be converted to the threo betaine using phenyllithium at low temperature. [18] This modification affords the E-alkene. The Schlosser variant of the Wittig reaction
It is however less reactive than ylides lacking EWGs. For example they usually fail to react with ketones, necessitating the use of the Horner–Wadsworth–Emmons reaction as an alternative. Such stabilized ylides usually give rise to an E-alkene product when they react, rather than the more usual Z-alkene. A "stabilized" Wittig reagent.
The Horner–Wadsworth–Emmons (HWE) reaction is a chemical reaction used in organic chemistry of stabilized phosphonate carbanions with aldehydes (or ketones) to produce predominantly E-alkenes. [1] The Horner–Wadsworth–Emmons reaction. In 1958, Leopold Horner published a modified Wittig reaction using phosphonate-stabilized carbanions.
The [2,3]-Wittig rearrangement is the transformation of an allylic ether into a homoallylic alcohol via a concerted, pericyclic process.Because the reaction is concerted, it exhibits a high degree of stereocontrol, and can be employed early in a synthetic route to establish stereochemistry.
A 1,2-Wittig rearrangement is a categorization of chemical reactions in organic chemistry, and consists of a 1,2-rearrangement of an ether with an alkyllithium compound. [1] The reaction is named for Nobel Prize winning chemist Georg Wittig. [2] [3] The intermediate is an alkoxy lithium salt, and the final product an alcohol.
The compounds are isomeric, defined by the presence of a carbon-carbon double bond, and undergo similar reactions; thus, reactions involving alkylidene groups are typically described using the broader class of alkenes, even those which directly introduce a R 2 C= substituent (e.g. the Wittig reaction).
The Wittig reaction involves reaction of an aldehyde or ketone with a Wittig reagent (or phosphorane) of the type Ph 3 P=CHR to produce an alkene and Ph 3 P=O. The Wittig reagent is itself prepared easily from triphenylphosphine and an alkyl halide. [29] A typical example of the Wittig reaction. Related to the Wittig reaction is the Peterson ...
A common method for methylenation involves the Wittig reaction using methylenetriphenylphosphorane with an aldehyde (Ph = phenyl, C 6 H 5): [4] + = = + A related reaction can be accomplished with Tebbe's reagent, which is sufficiently versatile to allow methylenation of esters: [5]