Phosphorus ylides alkylation

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. 

Phosphorus ylides are prepared from alkyl halides by a two step sequence The first step is a nucleophilic substitution of the 8 2 type by triphenylphosphme on an alkyl halide to give an alkyltriphenylphosphonium salt... 

Phosphorus ylides like 1 can be prepared by various routes. The most common route is the reaction of triphenylphosphine 5 with an alkyl halide 6 to give a triphenylphosphonium salt 7, and treatment of that salt with a base to give the corresponding ylide 1 ... 

The reactivity of the phosphorus ylide 1 strongly depends on substituents R R. For preparative use R often is a phenyl group. When R or R is an electron-withdrawing group, the negative charge can be delocalized over several centers, and the reactivity at the ylide carbon is reduced. The reactivity of the carbonyl compound towards addition of the ylide increases with the electrophilic character of the C=0 group. R R are often both alkyl, or alkyl and aryl. 

An aldehyde or ketone reacts with a phosphorus ylide to yield an alkene in which the oxygen atom of the carbonyl reactant is replaced by the =0 2 of the ylide. Preparation of the phosphorus ylide itself usually involves reaction of a primary alkyl halide with triphenylphosphine, so the ylide is typically primary, RCH = P Ph)3-This means that the disubstituted alkene carbon in the product comes from the carbonyl reactant, while the monosubstituted alkene carbon comes from the ylicle. 

It would be expected that a few straightforward steps could accomplish the transformation of alkyl bromide 14 into phosphorus ylide 12 (Scheme 2b). On the other hand, the evolution of 14 from substituted aromatic furan ring 15 may not be obvious. It is, in fact, conceivable that the action of ethylene glycol on substituted furan... 

The first silicon-organophosphorus betaine with a thiolate center (15a) was synthesized by the reaction of stable silanethione (14) with trimethyl-methylenephosphorane (Scheme 8) and characterized by multinuclear NMR spectroscopy.14 Compound 15a is formed under kinetic control and is transformed, under the thermodynamically controlled conditions, into the silaacenaphthene salt (16). The processes presented in this scheme reflect the competition of the basicity and nucleophilicity of phosphorus ylides. Betaine 15b prepared from less nucleophilic and less basic ylide with phenyl substituents at the phosphorus atom is much less resistant toward retro-decomposition compared to the alkyl analog. Its equilibrium concentration does not exceed 6%. 

Non-heteroatom-substituted carbene complexes can also be generated by treatment of electrophilic transition metal complexes with ylides (e.g. diazoalkanes, phosphorus ylides, nucleophilic carbene complexes, etc. Section 3.1.3). Alkyl complexes with a leaving group in the a-position are formed as intermediates. These alkyl complexes can undergo spontaneous release of the leaving group to yield a carbene complex (Figure 3.2). 

Phosphorus ylides are usually prepared by deprotonation of phosphonium salts. The phosphonium salts most often used are alkyltriphenylphosphonium halides, which can be prepared by the reaction of triphenylphosphine and an alkyl halide ... 

Alkyl halide reacts with triphenylphospine to give a phosphonium salt, which is an important intermediate for the preparation of phosphorus ylide (see Section 5.3.2). 

Preparation of phosphorus ylide Phosphorus ylides are produced from the reaction of triphenylphosphine and alkyl hahdes. Phosphorus ylide is a... 

Preparation of alkenes Ketone reacts with phosphorus ylide to give alkene. By dividing a target molecule at the double bond, one can decide which of the two components should best come from the carbonyl, and which from the ylide. In general, the ylide should come from an unhindered alkyl halide since triphenyl phosphine is bulky. 

Although the phosphorus ylide shown has three R groups on the phosphorus atom, other phosphorus ylides are known where other atoms, e.g., oxygen, replace one or more of these R groups. When the three groups are all alkyl or aryl, the phosphorus ylide is also called a phosphorane. 

In the Wittig reaction an aldehyde or ketone is treated with a phosphorus ylide (also called aphosphorane) to give an olefin.638 Phosphorus ylides are usually prepared by treatment of a phosphonium salt with a base,639 and phosphonium salts are usually prepared from the phosphine and an alkyl halide (0-43) ... 

Wittig reactions can also be performed with support-bound phosphorus ylides. Polystyrene-bound alkylphosphonium salts have been prepared from the corresponding alkyl mesylates or halides and trialkyl- or triarylphosphines (Figure 5.8 [60,80]). Because polystyrene is a hydrophobic support, salt formation does not proceed smoothly and quaternization of phosphines generally requires forcing conditions. The... 

Exercise 16-13 a. Phosphorus ylides can be prepared by heating triphenyl phosphine, (C6H5)3P, with a primary alkyl halide, RCH2X, in a solvent such as benzene. The initial product then is mixed with an equivalent quantity of a very strong base, such as phenyllithium in ether. Write equations for the reactions and probable mechanisms involved, using ethyl bromide as the alkyl halide. 

Reviews have featured epoxidation, cyclopropanation, aziridination, olefination, and rearrangement reactions of asymmetric ylides 66 non-phosphorus stabilized carbanions in alkene synthesis 67 phosphorus ylides and related compounds 68 the Wittig reaction 69,70 and [2,3]-Wittig rearrangement of a-phosphonylated sulfonium and ammonium ylides.71 Reactions of carbanions with electrophilic reagents, including alkylation and Wittig-Homer olefination reactions, have been discussed with reference to Hammett per correlations.72... 

The reaction of aldehydes or ketones with phosphorus ylides produces alkenes of unambiguous double-bond locations. Phosphorous ylides are prepared by reacting a phosphine with an alkyl halide, followed by treatment with a base. Ylides have positive and negative charges on adjacent atoms. 

The phosphorus-stabilized carbanion is an ylide (pronounced ilL-id )—a molecule that bears no overall charge but has a negatively charged carbon atom bonded to a positively charged heteroatom. Phosphorus ylides are prepared from tri-phenylphosphine and alkyl halides in a two-step process. The first step is nucleophilic attack by triphenylphosphine on an unhindered (usually primary) alkyl halide. The product is an alkyltriphenylphosphonium salt. The phosphonium salt is treated with a strong base (usually butyllithium) to abstract a proton from the carbon atom bonded to phosphorus. 

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