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Ylides, Wittig reaction

Keywords ketone, phosphorus ylide, Wittig reaction, microwave irradiation, ole-... [Pg.132]

The use of the phosphonate ester (Homer-Wadsworth-Emmons reaction) allows much easier separation of the product alkene, since the sodium phosphate byproduct is water soluble the byproduct of fhe Wiffig reaction, tri-phenylphosphine oxide, is not water soluble. In the Horner-Wadsworth-Emmons modification, a conjugated, or electron-withdrawing, substituent (such as a phenyl or carbonyl group) on the nucleophilic carbon is used to assist in the stabilization of the carbanion. This modification (Experiment [19B]) maybe used as an alternative to Experiment [19A] for the preparation of (E)-stilbene. The "instant-ylide" Wittig reaction yields predominantly the E isomer of... [Pg.298]

With "non-stabilized" ylides the Wittig Reaction gives predominantly Z-olefins. Seebach et al... [Pg.104]

The synthesis of vitamin Dj from a sensitive dienone was another etu-ly success of phosphorus ylide synthesis (H.H. Inhoffen, 1958 A). This Wittig reaction could be carried out without any isomerization of the diene. An excess of the ylide was needed presumably because the alkoxides formed from the hydroxy group in the educt removed some of the ylide. [Pg.31]

The phosphorus ylides of the Wittig reaction can be replaced by trimethylsilylmethyl-carbanions (Peterson reaction). These silylated carbanions add to carbonyl groups and can easily be eliminated with base to give olefins. The only by-products are volatile silanols. They are more easily removed than the phosphine oxides or phosphates of the more conventional Wittig or Homer reactions (D.J. Peterson, 1968). [Pg.33]

The Julia-Lythgoc olefination operates by addition of alkyl sulfone anions to carbonyl compounds and subsequent reductive deoxysulfonation (P. Kocienski, 1985). In comparison with the Wittig reaction, it has several advantages sulfones are often more readily available than phosphorus ylides, and it was often successful when the Wittig olefination failed. The elimination step yields exclusively or predominantly the more stable trans olefin stereoisomer. [Pg.34]

The Wittig reaction uses phosphorus ylides (called Wittig reagents) to convert aldehydes and ketones to alkenes... [Pg.730]

The sample solution to Problem 17 16(a) showed the prepara tion of 3 methyl 3 heptene by a Wittig reaction involving the ylide shown Write equations showing the formation of this ylide beginning with 2 bromobutane... [Pg.734]

The Wittig reaction (Sections 17 12-17 13) Reaction of a phosphorus ylide with aldehydes and ketones leads to the formation of an alkene A versa tile method for the regiospecific prepa ration of alkenes... [Pg.744]

The most attractive feature of the Wittig reaction is its regiospecificity. The location of the double bond is never in doubt. The double bond connects the carbon of the original C=0 group of the aldehyde or ketone and the negatively charged carbon of the ylide. [Pg.730]

To understand the mechanism of the Wittig reaction, we need to exanine the structure and properties of ylides. Ylides are neutral molecules that have two oppositely... [Pg.731]

Wittig reaction (Section 17.12) Method for the synthesis of alkenes by the reaction of an aldehyde or a ketone with a phosphorus ylide. [Pg.1297]

The Wittig reaction, for which George Wittig received the 1979 Nobel Prize in Chemistry, is an important synthetic procedure for converting aldehydes and ketones into alkenes. The active reagent is a phosphorous ylide which undergoes nucleophilic addition to the carbonyl carbon, e.g., for addition of triphenylphosphinemethylidene to acetone. [Pg.144]

Similar to phosphur ylides, sulfur ylides 1 and 2 possess the nucleophilic site at the carbon atom and the pendant leaving group at the heteroatom (sulfur). Different from the Wittig reaction, the Corey-Chaykovsky reaction does not lead to olefins. [Pg.3]

The reaction of an alkylidene phosphorane 1 (i.e. a phosphorus ylide) with an aldehyde or ketone 2 to yield an alkene 3 (i.e. an olefin) and a phosphine oxide 4, is called the Wittig reaction or Wittig olefination reaction. ... [Pg.293]

Treatment of dimethylsulfoxide (DMSO) with sodium hydride generates methylsulfinyl carbanion (dimsyl ion), which acts as an efficient base in the production of ylides. The Wittig reaction appears to proceed more readily in the DMSO solvent, and yields are generally improved over the reaction with -butyl lithium (i). Examples of this modification are given. [Pg.106]


See other pages where Ylides, Wittig reaction is mentioned: [Pg.332]    [Pg.340]    [Pg.340]    [Pg.504]    [Pg.112]    [Pg.319]    [Pg.799]    [Pg.738]    [Pg.340]    [Pg.319]    [Pg.801]    [Pg.821]    [Pg.738]    [Pg.319]    [Pg.801]    [Pg.675]    [Pg.332]    [Pg.340]    [Pg.340]    [Pg.504]    [Pg.112]    [Pg.319]    [Pg.799]    [Pg.738]    [Pg.340]    [Pg.319]    [Pg.801]    [Pg.821]    [Pg.738]    [Pg.319]    [Pg.801]    [Pg.675]    [Pg.431]    [Pg.31]    [Pg.732]    [Pg.302]    [Pg.732]    [Pg.62]    [Pg.295]    [Pg.30]    [Pg.377]   
See also in sourсe #XX -- [ Pg.456 ]

See also in sourсe #XX -- [ Pg.757 , Pg.758 , Pg.759 ]

See also in sourсe #XX -- [ Pg.757 , Pg.758 , Pg.759 ]

See also in sourсe #XX -- [ Pg.737 , Pg.738 , Pg.759 ]

See also in sourсe #XX -- [ Pg.456 ]

See also in sourсe #XX -- [ Pg.757 , Pg.758 , Pg.759 ]

See also in sourсe #XX -- [ Pg.738 , Pg.757 , Pg.759 ]




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